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1
Webber, Helen. "Compact heat exchanger heat transfer coefficient enhancement." Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540881.
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Macbeth, Tyler James. "Conjugate Heat Transfer and Average Versus Variable Heat Transfer Coefficients." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/5801.
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An average heat transfer coefficient, h_bar, is often used to solve heat transfer problems. It should be understood that this is an approximation and may provide inaccurate results, especially when the temperature field is of interest. The proper method to solve heat transfer problems is with a conjugate approach. However, there seems to be a lack of clear explanations of conjugate heat transfer in literature. The objective of this work is to provide a clear explanation of conjugate heat transfer and to determine the discrepancy in the temperature field when the interface boundary condition is approximated using h_bar compared to a local, or variable, heat transfer coefficient, h(x). Simple one-dimensional problems are presented and solved analytically using both h(x) and h_bar. Due to the one-dimensional assumption, h(x) appears in the governing equation for which the common methods to solve the differential equations with an average coefficient are no longer valid. Two methods, the integral equation and generalized Bessel methods are presented to handle the variable coefficient. The generalized Bessel method has previously only been used with homogeneous governing equations. This work extends the use of the generalized Bessel method to non-homogeneous problems by developing a relation for the Wronskian of the general solution to the generalized Bessel equation. The solution methods are applied to three problems: an external flow past a flat plate, a conjugate interface between two solids and a conjugate interface between a fluid and a solid. The main parameter that is varied is a combination of the Biot number and a geometric aspect ratio, A_1^2 = Bi*L^2/d_1^2. The Biot number is assumed small since the problems are one-dimensional and thus variation in A_1^2 is mostly due to a change in the aspect ratio. A large A_1^2 represents a long and thin solid whereas a small A_1^2 represents a short and thick solid. It is found that a larger A_1^2 leads to less problem conjugation. This means that use of h_bar has a lesser effect on the temperature field for a long and thin solid. Also, use of ¯ over h(x) tends to generally under predict the solid temperature. In addition is was found that A_2^2, the A^2 value for the second subdomain, tends to have more effect on the shape of the temperature profile of solid 1 and A_1^2 has a greater effect on the magnitude of the difference in temperature profiles between the use of h(x) and h_bar. In general increasing the A^2 values reduced conjugation.
3
Hussein, Mohammed Sabah. "Coefficient identification problems in heat transfer." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/12291/.
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The aim of this thesis is to find the numerical solution for various coefficient identification problems in heat transfer and extend the possibility of simultaneous determination of several physical properties. In particular, the problems of coefficient identification in a fixed or moving domain for one and multiple unknowns are investigated. These inverse problems are solved subject to various types of overdetermination conditions such as non-local, heat flux, Cauchy data, mass/energy specification, general integral type overdetermination, time-average condition, time-average of heat flux, Stefan condition and heat momentum of the first and second order. The difficulty associated with these problems is that they are ill-posed, as their solutions are unstable to inclusion of random noise in input data, therefore traditional techniques fail to provide accurate and stable solutions. Throughout this thesis, the Crank-Nicolson finite-difference method (FDM) is mainly used as a direct solver except in Chapter 7 where a three-level scheme is employed in order to deal with the nonlinear heat equation. An explicit FDM scheme is also employed in Chapter 10 for the two-dimensional case. The inverse problems investigated are discretised using the FDM and recast as nonlinear least-squares minimization problems with simple bounds on the unknown coefficients. The resulting problem is efficiently solved using the \emph{fmincon} or \emph{lsqnonlin} routines from MATLAB optimization toolbox. The Tikhonov regularization method is included where necessary. The choice of the regularization parameter(s) is thoroughly discussed. The stability of the numerical solution is investigated by introducing Gaussian random noise into the input data. The numerical solutions are compared with their known analytical solution, where available, and with the corresponding direct problem numerical solution where no analytical solution is available.
4
Ammari, H. D. "The heat transfer coefficient on film cooled surfaces." Thesis, University of Nottingham, 1989. http://eprints.nottingham.ac.uk/12730/.
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A systematic investigation of the effects of coolant-to-mainstream density ratio and mainstream acceleration on the heat transfer following injection through a row of holes in a flat plate into a turbulent boundary layer is described. A mass transfer technique was employed which uses a swollen polymer surface and laser holographic interferometry. The constant concentration of the test surface simulated isothermal conditions. Density ratios in excess of unity, representative of gas turbine operating conditions, were obtained using foreign gas injection into mainstream air. The experimental technique was validated for such measurements. The cooling film heat transfer coefficient was measured for a range of blowing configurations and flow conditions; the holes were spaced at three diameter intervals and inclined at 35° or 90° to the mainstream, and the ranges of the other pertinent test parameters covered were, 0.5 5 blowing rate 5 2.0, 1.0 5 density ratio S 1.52, and 0.0 S acceleration parameter S 5x 10'. However, the tests with mainstream acceleration were performed with 35° injection only. The heat transfer coefficient was found to be increased by injection, and with the blowing rate for both 35° and 90° injection. Close to the injection site, normal blowing produced higher heat transfer coefficients than angled blowing, but gave lower coefficients far downstream. There were large differences in behaviour between the two injection angles with varying density ratio. For normal injection, the heat transfer coefficient at a fixed blowing rate was insensitive to the variation of density ratio, whereas for 35° injection strong dependence was observed, an increase in the density ratio leading to a decrease in the coefficient. Similar behaviour for the inclined injection case was also found in the presence of strong favourable pressure gradient. As mainstream acceleration acts to suppress injection induced turbulence, the heat transfer coefficient under the film with and without density ratio was found to decrease in the presence of mainstream acceleration relative to that in absence of acceleration. The heat transfer coefficient was observed to relate to the acceleration parameter in an approximately linear manner, an increase in the acceleration resulting in a decrease in the coefficient. For normal injection, good scaling of the heat transfer coefficient including density ratios was achieved with the blowing parameter. For 35° injection, the coolant to mainstream velocity ratio was seen to scale the data best. Correlations for the heat transfer data using these scaling parameters. With these correlations data obtained at density ratios not representative of gas turbine practice can be adapted for design calculations. The predictions of a computational fluid dynamics general purpose program called PHOENICS were tested against the present measurements and those of others. In general, the computed results of film cooling effectiveness agreed reasonably well with available experimental data. The ability to predict the heat transfer coefficient associated with film cooling was satisfactory for normal injection, but not as satisfactory for injection through 35° holes.
5
Haam, Seungjoo. "Local heat transfer in a mixing vessel using heat flux sensors." The Ohio State University, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=osu1102528786.
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Tothill, M. H. "Turbine blade heat transfer coefficient determination using optical pyrometry." Thesis, Cranfield University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.352954.
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Wells, Robert G. "Laminar flow with an axially varying heat transfer coefficient." Thesis, Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/101333.
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A theoretical study of convective heat transfer is presented for a laminar flow subjected to an axial variation in the external heat transfer coefficient (or dimensionless Biot number). Since conventional techniques fail for a variable boundary condition parameter, a variable eigenfunction approach is developed. An analysis is carried out for a periodic heat transfer coefficient, which serves as a model for heat transfer from a duct fitted with an array of evenly spaced fins. Three solution methods for the variable eigenfunction technique are examined: an Nth order approximation method, an iterative method and a stepwise periodic method. The stepwise periodic method provides the most convenient and accurate solution for a stepwise periodic Biot number. Graphical results match exactly to ones obtained by Charmchi and Sparrow from a finite-difference scheme. A connected region technique is also developed to provide limited exact results to test the validity of the three solution methods.
The study of a finned duct by a stepwise periodic Biot number is carried out via a parametric study, an average (constant) Biot number approximation and an assumed velocity profile analysis. Results for the parametric study show that external finning yields substantial heat transfer enhancement over an unfinned duct, especially when the Biot number of the unfinned regions is low. A decrease in the interfin spacing causes increased enhancement. Variations of the period of the Biot number causes relatively small changes in enhancement as long as the ratio of finned to unfinned surface remains unchanged. An average (constant) Biot number approximation for a specified finned tube is compared to the stepwise periodic Biot number solution. The results show that the constant Biot number approximation provides accurate results. Finally, the results for the influence of the assumed velocity profile demonstrate that a constant velocity flow provides increased heat transfer and more effective enhancement by external finning than a laminar fully developed flow, especially at high Biot numbers.
This study provides insight into heat transfer enhancement due to finning and also develops a solution methodology for problems involving variable boundary condition parameters.M.S.
8
Li, Ke. "Experimental Study of Heat Transfer Coefficient and Film Cooling Effectiveness." Thesis, KTH, Energiteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-249061.
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This thesis investigates the possibility to evaluate the film cooling thermal performance on flat plate using Thermochromic Liquid Crystal. After an introduction of the basic concept and background of gas turbine blades film cooling and Thermochromic Liquid Crystal, a thorough explanation of four methods is presented. Dimensional or similarity analysis is implemented to build relationship between real engine and laboratory model. Also, the Reynolds number and Blowing ratio are the fundamental of test object design and TLC selection. This study illustrated the layout of the test rig and corresponding setups, and the following part explains the data collection system and image processing MATLAB script which is vital for the success of data extraction. The least square method is applied to figure time-series optimal solution in solver. All the experiments are conducted at near room temperature as opposed to the extremely high gas turbine exhausted gas, including two calibration test and one heat transfer experiment. The heat transfer coefficient and film cooling effectiveness are the target objective through the entire project. By comparison with a similar experiment in a literature, the outcomes partially validated the film cooling performance under the pre-set flow and thermal condition and the Liquid Crystal thermography technique is proved to be a trustworthy method to mapping heat transfer surface.Denna avhandling undersöker möjligheten att utvärdera filmkylningens termiska prestanda på plan platta med användning av Termokromisk Flytande Kristall (TLC). Efter en introduktion av grundkonceptet och bakgrunden till gasturbinbladens filmkylning och termokromisk flytande kristall presenteras en grundlig förklaring av fyra metoder. Dimensionell eller likhetsanalys implementeras för att bygga upp förhållandet mellan verklig motor och laboratoriemodell. Reynoldstalet och blåsningsförhållandet (blowing ratio) är också grunden för testobjektdesign och TLC-val. Denna studie illustrerade provriggens layout och tillhörande inställningar. I följande del förklaras datainsamlingssystemet och bildbehandling, MATLABTM-skriptet som är avgörande för framgång med datautvärdering. Den minsta kvadratiska metoden tillämpas för att hitta tidsseriens optimala lösning i lösaren. Alla experiment utförs vid nära rumstemperatur i motsats till den höga temperature på gasturbingasen, inklusive två kalibreringstest och ett värmeöverföringsexperiment. Värmeöverföringskoefficienten och filmkylningseffektiviteten är målmålet genom hela projektet. Resultaten validerade partiellt filmkylningens prestanda under det förinställda flödet och det termiska tillståndet. Liquid Crystal-termografitekniken har visat sig vara en pålitlig metod för att kartlägga värmeöverföringsytan jämfört med ett liknande experiment i den öppna litteraturen.
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Skosana, Petrus Jabu. "Wall Heat Transfer Coefficient in a Molten Salt Bubble Column." Diss., University of Pretoria, 2014. http://hdl.handle.net/2263/46246.
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The Council for Scientific and Industrial Research (CSIR) is developing a novel process to
produce titanium metal at a lower cost than the current Kroll process used commercially. The
technology initiated by the CSIR will benefit South Africa in achieving the long-term goal of
establishing a competitive titanium metal industry.
A bubble column reactor is one of the suitable reactors that were considered for the
production of titanium metal. This reactor will be operated with a molten salt medium. Bubble
columns are widely used in various fields of process engineering, such as oxidation,
hydrogenation, fermentation, Fischer–Tropsch synthesis and waste water treatment. The
advantages of these reactors over other multiphase reactors are simple construction, good
mass and heat transfer, absence of moving parts and low operating costs.
High heat transfer is important in reactors when high thermal duties are required. An
appropriate measurement of the heat transfer coefficient is of primary importance for
designing reactors that are highly exothermic or endothermic.
An experimental test facility to measure wall heat transfer coefficients was constructed and
operated. The experimental setup was operated with tap water, heat transfer oil 32 and
lithium chloride–potassium chloride (LiCl–KCl) eutectic by bubbling argon gas through the
liquids. The column was operated at a temperature of 40 oC for the water experiments, at 75,
103 and 170 oC for the heat transfer oil experiments, and at 450 oC for the molten salt
experiments. All the experiments were run at superficial gas velocities in the range of 0.006
to 0.05 m/s. Three heating tapes, each connected to a corresponding variable AC voltage
controller, were used to heat the column media. Heat transfer coefficients were determined by inducing a known heat flux through the column
wall and measuring the temperature difference between the wall and the reactor contents. In
order to balance the system, heat was removed by cooling water flowing through a copper
tube on the inside of the column. Temperature differences between the column wall and the
liquid were measured at five axial locations.
A mechanistic model for estimating the kinematic turbulent viscosity and dispersion
coefficient was developed from a mechanism of momentum exchange between large
circulation cells. By analogy between heat and momentum transfer, these circulation cells
also transfer heat from the wall to the liquid.
There were some challenges when operating the bubble column with molten salt due to
leakages on the welds and aggressive corrosion of the column. The experimental results
were obtained when operating the column with water and heat transfer oil. It was found that
the heat transfer coefficient increases with superficial gas velocity. The values of the heat
transfer coefficient for the argon–water system were higher than those for the argon–heat
transfer oil system. The heat transfer coefficients were also found to increase with an
increase in temperature. Gas holdup increased with the superficial gas velocity. It was found
that the estimated axial dispersion coefficients are within the range of those reported in the
literature and the ratios of dispersion coefficients are in agreement with those in the
literature. The estimated kinematic turbulent viscosities were comparable with those in the
literature.Dissertation (MEng)--University of Pretoria, 2014.
tm2015
Chemical Engineering
MEng
Unrestricted
10
Jeong, Dahai. "Laboratory Measurements of the Moist Enthalpy Transfer Coefficient." Scholarly Repository, 2008. http://scholarlyrepository.miami.edu/oa_theses/145.
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The enthalpy (sensible and latent heat) exchange processes within the surface layers at an air-water interface have been examined in 15-m wind-wave tunnel at the University of Miami. Measurements yielded 72 mean values of fluxes and bulk variables in the wind speed (referred to 10 m) range form 0.6 to 39 m/s, covering a full range of aerodynamic conditions from smooth to fully rough. Meteorological variables and bulk enthalpy transfer coefficients, measured at 0.2-m height, were adjusted to neutral stratification and 10-m height following the Monin-Obukhov similarity approach. The ratio of the bulk coefficients of enthalpy and momentum was estimated to evaluate Emanuel's (1995) hypothesis. Indirect "Calorimetric" measurements gave reliable estimates of enthalpy flux from the air-water interface, but the moisture gained in the lower air from evaporation of spray over the rough water remained uncertain, stressing the need for flux measurements along with simultaneous spray data to quantify spray's contribution to the turbulent air-water enthalpy fluxes.
11
Samayamantula, Sri Prithvi Samrat. "Development of a Computer Program for Transient Heat Transfer Coefficient Studies." Wright State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=wright15581072805784.
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TICONA, EPIFANIO MAMANI. "EXPERIMENTAL DETERMINATION OF THE HEAT TRANSFER COEFFICIENT IN AN ICE SLURRY GENERATOR." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2003. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=3765@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOUm sistema térmico de armazenamento da energia com pasta de cristais de gelo foi desenvolvido para aplicações de condicionamento de ar e resfriamento de processos. O sistema usa um evaporador orbital de haste, um trocador de calor vertical do tipo tubo e carcaça com intensificação mecânica de transferência de calor. A pasta de gelo é produzida continuamente sem acumulação no evaporador e é compatível com unidades condensadoras convencionais, tanques de armazenamento e bombas. Soluções aquosas diluídas ou soluções inorgânicas de salmoura promovem a formação de cristais de gelo, e o gelo líquido resultante pode ser bombeado ou por gravidade alimentar um tanque de armazenamento. O circuito hidráulico de refrigeração (carga térmica) pode ser desacoplado da produção do gelo utilizando-se o tanque de armazenamento. O armazenamento de gelo líquido fornece temperaturas consistentemente baixas à medida que se derrete o gelo, que por sua forma pode ser derretido também muito rapidamente. Com suas altas temperaturas características de evaporação e elevados fluxos do calor, os sistemas de geração de gelo líquido apresentam potencial para reduzir significativamente os custos de capital inicial e operação, quando comparados com tecnologias de sistemas estáticos de gelo ou ice harvesting.
New ice crystal slurry thermal energy storage (TES) system has been developed for both HVAC and process cooling applications. The system uses an orbital rod evaporator (ORE), a vertical shell-and-tube heat exchanger with mechanical heat transfer augmentation, as a dynamic ice maker to generate liquid ice. Ice forms continuously without accumulation in the ORE and is compatible with conventional condensing units, storage tanks, and pumps. Dilute glycol or inorganic brine solutions promote formation of ice crystals, and the resulting liquid ice may be pumped or gravity fed to a storage tank. The cooling load circuit can be hydraulically decoupled from ice production at the storage tank. Stored liquid ice provides consistently low solution supply temperatures over significant portions of the ice melt period and may be melted very rapidly. With its characteristic high evaporator temperatures and high heat fluxes, ORE TES systems have the potential for significantly lower capital and operating costs than static ice or ice harvesting technologies.
13
Jahedi, Mohammad. "Computational study of multiple impinging jets on heat transfer." Thesis, Högskolan i Gävle, Avdelningen för bygg- energi- och miljöteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-13791.
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This numerical study presents investigation of impinging jets cooling effect on a hot flat plate. Different configuration of single jet, 5-cross and 9-square setups have been studied computationally in order to understand about their behaviour and differences behind their physics. Moreover, a specific confined wall was designed to increase two crucial parameters of the cooling effect of impinging jets; average heat transfer coefficient of impingement wall and average air temperature difference of outlet the domain and jet inlet. The 2-D simulation has been performed to design the confined wall to optimise the domain geometry to achieve project goals contains highest average heat transfer coefficient of hot plate in parallel to highest average air temperature difference of outlet. Different effective parameters were chosen after 2-D simulation study and literature review; Jet to wall distance H/D = 5, Radial distance from centre of plate R/D = 20, jet diameter D = 10 mm. The 3-D computational study was performed on single jet, 5-cross and 9-square configurations to investigate the differences of results and find best setup for the specific boundary condition in this project. Single jet geometry reveals high temperature level in the outlet, but very low average heat transfer coefficient due to performance of a single jet in a domain (Re= 17,232). In the other side, 5-cross setup has been studied for Reynolds number of 9,828, 11,466, 17,232 and 20,000 and it was found that range of 11,466 to 17,232 performs very well to achieve the purposes in this study. Moreover, turbulence models of , and have been used to verify the models (Re=17,232) with available experimental data for fully developed profile of the jets inlets and wall jet velocity and Reynolds stress components near the wall boundary condition. All three turbulence models predict well the velocity components for jets fully developed profile and for wall boundary condition of the target plate. But since model has been validated with the Reynolds stress components by experimental data, therefore is more reliable to continue the study with verified simulation. Finally 9-square configuration was investigated (Re=17,232) and the result compared with other setups. It was concluded that 5-cross multiple jets is best design for this project while 9-square multiple impinging jets also fulfils the project purpose, but for extended application in industry each setup is suitable for specific conditions. 5-cross multiple jets is good choice for large cooling area which can be used in number of packages to cover the area, while 9-square jets setup performs well where very high local heat transfer is needed in a limited area.
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Nguyen, Clayton Ma. "Heat transfer coefficients of particulate in tubular heat exchangers." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53960.
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This experimental study explores the heat transfer from heated bare and finned tubular surfaces to particulates in packed bed cross flow. The results from this experiment will be used to help select the type of particulates that will be used. Additionally, these results will assist in estimating heat transfer in prototype and commercial particle to fluid heat exchangers (PFHX).
This research is part of larger effort in the use of particulates in concentrating solar power technology. These solid particles are heated by concentrated sunlight to very high temperatures at which they are a suitable heat source for various thermal power and thermochemical cycles. Furthermore, one of the advantages of this concept is the ability to store thermal energy in the solid particles at relatively low cost. However, an important feature of any Particle Heat Receiver (PHR) system is the PFHX, which is the interface between the solar energy system and the thermal power or chemical system. In order to create this system material data is needed for the design and optimization of this PFHX.
The paper focuses on the heat transfer properties of particulates to solid surfaces under plug flow conditions. The particulates will be evaluated for three grain sizes of sand and two grain sizes of proppants. These two materials will be tested at one, five and ten millimeters per second in order to see how the various flow rates, which will be required for different loads, will affect the heat transfer coefficient. Finally the heat transfer coefficient will also be evaluated for both finned and non-finned heat exchangers to see the effect that changes in the surface geometry and surface area have on the heat transfer coefficient. The heat transfer coefficient will help determine the appropriate material that will be used in the PHR system.
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VINAGRE, HARRY T. MAIA. "EXPERIMENTAL DETERMINATION OF THE HEAT TRANSFER COEFFICIENT IN DUCTS OF ELLIPTICAL CROSS SECTION." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1987. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33283@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORDeterminou-se experimentalmente o coeficiente local de troca de calor, para o escoamento turbulento interno, em tubos de seção transversal elíptica. As condições de contorno impostas foram, temperatura constante na parede e entrada abrupta, com canto vivo, em uma placa plana. Foram obtidos resultados na região de entrada e na região desenvolvida, cobrindo a faixa de número de Reynolds de 7 000 a 60 000. Foram investigadas as razões de aspecto 0,12, 0,25 e 0,5 e os resultados, comparados com os encontrados na literatura para placa plana e tubo circular. Uma diferença máxima de 16 por cento, foi encontrada em relação aos resultados para tubo circular. Portanto, a utilização de tubos elípticos em trocadores de calor é, em geral, vantajosa do ponto de vista térmico.
Experiments were performed to determine local heat transfer coefficients for the turbulent flow in a duct with elliptical cross section. The boundary conditions imposed were isothermal wall and abrupt-contraction at the entrance built into a large wall. Both entrance-region and fully-developed results were obtained, whereas the Reynolds number was varied in the overall range 7,000-60,000. The aspect ratios 0.12, 0.25 and 0.5 were investigated and the results compared with the ones for parallel planes and for circular tubes, found in the open literature. The measured heat transfer coefficients displayed a maximum deviation of 16 percent relative to the results for the circular tube. Therefore, using elliptical ducts in heat exchangers is in general advisable as far as heat transfer is concerned.
16
Beale, James H. "Internal flow subjected to an axial variation of the external heat transfer coefficient." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/91162.
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A theoretical investigation of internal flow subjected to an axial variation of the external convection coefficient is presented. Since the variable boundary condition parameter causes the problem to become nonseparable, conventional techniques do not apply. Instead, the Green's function technique is used to convert the governing partial differential equations into a singular Volterra integral equation for the temperature of the fluid at the wall. The integral equation is resolved numerically by the trapezoid rule with the aid of a singularity subtraction procedure. The solution methodology is developed in terms of a fully turbulent flow which is shown to contain fully laminar and slug flow as special cases.
Before examining the results generated by numerical solution of the integral equation, a thorough study is made of each of the building blocks required in the solution procedure. A comparison of the respective dimensionless velocity profiles and dimensionless total diffusivities for each of the flow models is presented. Next, an analysis of the eigenvalue problem for each flow model is presented with consideration given to the normalized eigenfunctions and the eigenvalues themselves. Finally, the singular nature of the Green's function is examined showing the effect of the parameters Ho, Re and Pr.
The technique is applied to study the heat transfer from a finned tube. A parameter study is presented to examine the effects of the external finning and the flow model. The effect of external finning is examined through specific variations of the external convection coefficient, while the flow model is selected through the velocity profile and eddy diffusivity. In examining turbulent flow, the effects of the parameters, Re and Pr, are considered.M.S.
17
Wahlberg, Tobias. "Modeling of Heat Transfer." Thesis, Mälardalens högskola, Akademin för hållbar samhälls- och teknikutveckling, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-12217.
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Modeling of heat transfer using Dymola. In this report a evaporator, economizer and superheater where modeled. The report describes how the models where modeled and what input was most suitable for a accurate model.
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Steyn, Rowan Marthinus. "Local heat transfer coefficients in an annular passage with flow turbulation." Diss., University of Pretoria, 2020. http://hdl.handle.net/2263/73459.
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In this experimental and numerical investigation, the use of flow turbulation was considered as a method to increase local heat transfer coefficients in annular heat transfer passages. Experimental data was obtained for cases with and without inserted ring turbulators within a horizontal annular test section using water for average Reynolds numbers ranging from 2000 to 7500 and average Prandtl numbers ranging from 6.73 to 6.79. The test section was heated uniformly on the inner annular wall and had a hydraulic diameter of 14.8mm, a diameter ratio (inner wall diameter to outer wall diameter) of 0.648, and a length to hydraulic diameter ratio of approximately 74. A set of circular cross sectioned ring-type turbulators were used which had a thickness of 1mm, a ring diameter of 15.1mm and a pitch of 50mm. It was found that the presence of the flow turbulators increased the average Nusselt number by between 33.9% and 45.8%. The experimental tests were followed by numerical simulations to identify the response in the heat transfer coefficient by changing the geometry of the turbulators. For this, the turbulator diameters were ranged from 0.5 mm to 2 mm, and the gap size (between the inner wall and a turbulator ring) ranged from 0.125 mm to 4 mm at a pitch of 50 mm. The results showed that the use of turbulators increased the Nusselt numbers by a maximum of 34.8% and that the maximum can be achieved for a turbulator diameter of 2 mm and a gap size of 0.25 mm, for all the Reynolds numbers tested. From the numeric determined pressure drop values it was found that the smaller gap size had the lowest pressure drop and the smallest turbulators also produced the lowest pressure drop.Dissertation (MEng)--University of Pretoria 2020
South African Centre for High Performance Computing (CHPC)
Mechanical and Aeronautical Engineering
MEng
Unrestricted
19
Le, An. "THE EFFECT OF HEAT TRANSFER COEFFICIENT ON HIGH ASPECT RATIO CHANNEL ACCOMPANIED BY VARYING RIB ASPECT RATIO." Master's thesis, University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2233.
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Heat transfer and pressure data were performed and reported on two different rigs. The first rig has an aspect ratio of (19:1) with two different inlet conditions and the second rig is composed of two different aspect ratio channels, (1:8) and (1:4). Rib turbulators were used as a flow disruptor scheme to enhance the heat transfer and friction factor. Rib aspect ratios ranging from (1:1) to (1:5) rib-height-to-width ratio were used. The first channel rib-width-to-pitch (Wr/P) ratio was kept at 1/2 where flow was kept at relatively low Reynolds numbers, between 3000 and 13000. Results from the current tests showed that existing correlations could be used for high aspect ratio channels in predicting the effectiveness of the cooling scheme. Two different inlet conditions were tested; one was arranged so that the flow was hydrodynamically fully-developed at the entrance of the heated section, while the other uses an abrupt entrance from bleeding off mass flow from a horizontal channel. The heat transfer augmentation (compared to a well known and accepted correlation proposed by Dittus-Boelter) in these channels are extremely high with an average of 350% to 400%. However, this was accompanied by a substantial increase in the pressure drop, causing the overall thermal performance to increase between twenty to thirty percent. The second channel rib-width-to-pitch ratio (Wr/P) ranges from 0.1, 0.3, and 0.5; the flow conditions are tested from 20,000 to 40,000 Reynolds number. Correlations for heat transfer and friction augmentation of the test data was also given. The test shows large rib blockage ratio does not demonstrate the best thermal performance; however it does give a high heat transfer augmentation ranging from 200 to 300 percent for both aspect ratios depending on the width of the used ribs.M.S.M.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering MSME
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Playford, William. "Well-conditioned heat transfer measurements on engine scale gas turbine rigs." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274997.
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High combustion temperatures are required in gas-turbine engines to achieve high cycle efficiencies. With increasing temperature, however, the life span of the turbine components are reduced. The ability to accurately predict engine component temperature as a function of combustion temperature is required to strike this balance correctly. An experimental heat transfer measurement technique is developed in this thesis, which builds on a large body of existing literature. The technique enables a detailed quantification of turbine heat transfer on test rigs which closely represent gas-turbine engine configurations. Fundamental improvements are made to existing methods, in the definition of the ‘semi- infinite limit’ for transient measurement techniques, in Infra-red camera calibration, and in thermal effusivity measurement. The improvements were developed from first principles, verified experimentally, and have been used on a world leading heat transfer rig (the FACTOR combustor-turbine interaction rig, run on the NG-Turb facility at DLR Göttingen). It was found that optimisation of a number of measurement parameters was required to minimise the measurement uncertainty. It is shown that the optimum measurement parameters are dependant, and sensitive to the specific configuration of the test rig. An experimental procedure was developed and tested, which has been ‘tuned’ for measurements on the FACTOR test rig. Despite the challenging measurement environment on the FACTOR rig, it was found that state-of-the-art heat transfer measurement uncertainties of approximately 5%, could nevertheless still be achieved, by using the new methods. General principles and rules are established which can be used to guide the design of future heat transfer measurements, with the aim of minimising measurement uncertainty.
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Bandyopadhyay, Deep Becker Bryan R. "Determination of heat transfer coefficient and correlation of dimensionless number for freezing of foods." Diss., UMK access, 2004.
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Thesis (M.S.)--School of Computing and Engineering . University of Missouri--Kansas City, 2004."A thesis in mechanical engineering." Typescript. Advisor: Bryan R. Becker Vita. Title from "catalog record" of the print edition Description based on contents viewed Feb. 22, 2006. Includes bibliographical references (leaves 100-104). Online version of the print edition.
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Prausa, Jeffrey Nathaniel. "Heat Transfer Coefficient and Adiabatic Effectiveness Measurements for an Internal Turbine Vane Cooling Feature." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/76790.
Full textAbstract:
Aircraft engine manufacturers strive for greater performance and efficiency by continually increasing the turbine inlet temperature. High turbine inlet temperatures significantly degrade the lifetime of components in the turbine. Modern gas turbines operate with turbine inlet temperatures well above the melting temperature of key turbine components. Without active cooling schemes, modern turbines would fail catastrophically. This study will evaluate a novel cooling scheme for turbine airfoils, called microcircuit cooling, in which small cooling channels are located extremely close to the surface of a turbine airfoil. Coolant bled from the compressor passes through the microcircuits and exits through film cooling slots. On further cooling benefit is that the microcircuit passages are filled with irregular pin fin features that serve to increase convective cooling through the channels.
Results from this study indicate a strong interaction between the internal microcircuit features and the external film-cooling from the slot exit. Asymmetric cooling patterns downstream of the slot resulted from the asymmetric pin fin design within the microcircuit. Adiabatic effectiveness levels were found to be optimum for the slot design at a blowing ratio of 0.37. The pin fin arrangement along with the impingement cooling at the microcircuit entrance increased the area-averaged heat transfer by a factor of three, relative to an obstructed channel, over a Reynolds range of 5,000 to 15,000.Master of Science
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Crosser, Kara Elizabeth. "Heat Transfer Assessment of Aluminum Alloy Corrugated Naval Ship Deck Panels under VTOL Aircraft Thermal Loads." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/72947.
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The behavior of aluminum alloy ship deck panels under the thermal loads of Vertical Take-off-and Landing (VTOL) capable aircraft has become a question of interest with the introduction of new primarily aluminum alloy ships to the U.S. Naval Fleet. This study seeks to provide an initial investigation of this question by examining the transient transfer of heat through aluminum alloy ship deck panels under application of the local heat transfer similar to that of a VTOL aircraft exhaust plume core in typical operation.
In this study, a jet stream intended to replicate the key physics of the core of a VTOL aircraft plume was impinged onto the upper surface of aluminum alloy corrugated deck panel test specimen. Temperature measurements are taken via thermocouples on the face of the specimen opposite the impingement to evaluate heat transfer through the specimen. This data is used to assess the effects of variation in the geometry of the corrugation between specimen. Qualitative temperature distributions were also gathered on the impingement surface via thermal imaging. A quantitative assessment of the heat paths for transverse and vertical heat transfer was made based on a thermal resistance model, leading to a conceptual description of predominant heat flow paths in the specimen, specifically weld lines between the corrugation and the flat plate surfaces.
In support of this, thermal images indicated that the weld lines provided paths for heat to be pulled away from the center of heat application more rapidly than over the rest of the surface. Ultimately, heat transfer through the specimen was found to be more dependent on the flow conditions than the variations in geometry of the deck panels due to the low variation in thermal resistance across the plate. A recommendation is made based upon this observation to use the deck panels similarly to heat exchanges by adding a small amount of through-deck airflow in the areas of high heat load.Master of Science
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Edwards, Bronwyn K. "Effect of combined nanoparticle and polymeric dispersions on critical heat flux, nucleate boiling heat transfer coefficient, and coating adhesion." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53288.
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Thesis (S.M. and S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 123-126).
An experimental study was performed to determine thermal performance and adhesion effects of a combined nanoparticle and polymeric dispersion coating. The critical heat flux (CHF) values and nucleate boiling heat transfer coefficients (HTC) of nickel wires pre-coated using 1.0% alumina, 0.1% alumina, 500ppm polyallylamine hydrochloride (PAH), and 0.1% alumina combined with 500ppm PAH dispersions were determined using the pool-boiling method. The adhesion of 0.1% alumina and combined 0.1% alumina and 500ppm PAH coatings was evaluated using the tape and modified bend test methods. Results of the pool boiling experiments showed that the wire heaters pre-coated with combined 0.1% alumina and 500ppm PAH dispersion increase the CHF in water by -40% compared to bare wire heaters, compared to an enhancement of -37% with a 0.1% alumina coating. The combined 0.1% alumina and 500ppm PAH dispersion degrades the wire HTC by less than 1%, compared to a degradation of over 26% with a 0.1% alumina coating. Results from the tape test indicate qualitatively that the combined 0.1% alumina and 500ppm PAH dispersion coating adheres better than the 0.1% alumina nanoparticle coating. Results from the modified bend test showed that the combined 0.1% alumina and 500ppm PAH dispersion coating did not fail at the failure strain of the 0.1% alumina nanoparticle coating (8.108x 10-4). The addition of PAH to alumina nanofluid for creating a nanoparticle coating through boiling deposition was found to improve both coating thermal performance and adhesion over the pure alumina nanofluid.
by Bronwyn K. Edwards.
S.M.and S.B.
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Smith, Dwight E. "An Investigation of Heat Transfer Coefficient and Film Cooling Effectiveness in a Transonic Turbine Cascade." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/43913.
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This study is an investigation of the film cooling effectiveness and heat transfer coefficient of a two-dimensional turbine rotor blade in a linear transonic cascade. Experiments were performed in Virginia Tech's Transonic Cascade Wind Tunnel with an exit Mach number 0f 1.2 and an exit Reynolds numbers of 5x106 to simulate real engine flow conditions. The freestream and coolant flows were maintained at a total temperature ratio of 2(+,-)0.4 and a total pressure ratio of 1.04. The freestream turbulence was approximately 1%. There are six rows of staggered, discrete cooling holes on and near the leading edge of the blade in a showerhead configuration. Cooled air was used as the coolant. Experiments were performed with and without film cooling on the surface of the blade. The heat transfer coefficient was found to increase with the addition of film cooling an average of 14% overall and to a maximum of 26% at the first gauge location. The average film cooling effectiveness along the chord-wise direction of the blade is 25%. Trends were found in both the uncooled and the film-cooled experiments that suggest either a transition from a laminar to a turbulent film regime or the existence of three-dimensionality in the flow-field over the gauges.Master of Science
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Omer, Muhammad. "Impingement Cooling: Heat Transfer Measurement by Liquid Crystal Thermography." Thesis, Linköping University, Applied Thermodynamics and Fluid Mechanics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-52859.
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In modern gas turbines parts of combustion chamber and turbine section are under heavy heat load, for example, the rotor inlet temperature is far higher than the melting point of the rotor blade material. These high temperatures causes thermal stresses in the material, therefore it is very important to cool the components for safe operation and to achieve desired component life. But on the other hand the cooling reduces the turbine efficiency, for that reason it is vital to understand and optimize the cooling technique.
In this project Thermochromic Liquid Crystals (TLCs) are used to measure distribution of heat transfer coefficient over a scaled up combustor liner section. TLCs change their color with the variation of temperature in a particular temperature range. The color-temperature change relation of a TLC is sharp and precise; therefore TLCs are used to measure surface temperature by painting the TLC over a test surface. This method is called Liquid Crystal Thermography (LCT). LCT is getting popular in industry due to its high-resolution results, repeatability and ease of use.
Test model in present study consists of two plates, target plate and impingement plate. Cooling of the target plate is achieved by impingement of air coming through holes in the impingement plate. The downstream surface of the impingement plate is then cooled by cross flow and re-impingement of the coolant air.
Heat transfer on the target plate is not uniform; areas under the jet which are called stagnation points have high heat transfer as compare to the areas away from the center of jet. It is almost the same situation for the impingement plate but the location of stagnation point is different. A transient technique is used to measure this non-uniform heat transfer distribution. It is assumed that the plates are semi-infinitely thick and there is no lateral heat transfer in the plates. To fulfill the assumptions a calculated time limit is followed and the test plates are made of Plexiglas which has very low thermal conductivity.
The transient technique requires a step-change in the mainstream temperature of the test section. However, in practical a delayed increase in mainstream temperature is attained. This issue is dealt by applying Duhamel’s theorem on the step-change heat transfer equation. MATLAB is used to get the Hue data of the recorded video frames and calculate the time taken for each pixel to reach a predefined surface temperature. Having all temperatures and time values the heat transfer equation is iteratively solved to get the value of heat transfer coefficient of each and every pixel of the test surface.
In total fifteen tests are conducted with different Reynolds number and different jet-to-target plate distances. It is concluded that for both the target and impingement plates, a high Reynolds number provides better overall heat transfer and increase in jet-to-target distance
decreases the overall heat transfer.
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Virk, Akashdeep Singh. "Heat Transfer Characterization in Jet Flames Impinging on Flat Plates." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/52985.
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The experimental work involves calculation of radial distribution of heat transfer coefficient at the surface of a flat Aluminium plate being impinged by a turbulent flame jet. Heat transfer coefficient distribution at the surface is computed from the measured heat flux and temperature data using a reference method and a slope method. The heat transfer coefficient (h) has a nearly bell shaped radial distribution at the plate surface for H/d =3.3. The value of h drops by 37 % from r/d =0 to r/d= 2. Upon increasing the axial distance to H/d = 5, the stagnation point h decreased by 15%. Adiabatic surface temperature (AST) distribution at the plate surface was computed from the measured heat flux and temperature. AST values were found to be lower than the measured gas temperature values at the stagnation point. Radial distribution of gas temperature at the surface was estimated by least squares linear curve fitting through the convection dominated region of net heat flux data and was validated by experimental measurements with an aspirated thermocouple. For low axial distances (H/d =3.3), the gas temperature dropped by only 15 % from r/d = 0 to r/d = 2. Total heat flux distribution is separated into radiative and convective components with the use of calculated heat transfer coefficient and estimated gas temperatures. At H/d = 3.3, the radiation was found to be less than 25 % of the net heat flux for r/d ≤ 2.Master of Science
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Arenson, Mordechai. "Determination of convective heat transfer coefficients in turning." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ37256.pdf.
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Lu, Yuan. "A Study on Gas Quench Steel Hardenability." Digital WPI, 2015. https://digitalcommons.wpi.edu/etd-theses/125.
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Gas quench technology has been rapidly developed recently with the intent to replace water and oil quench for medium and high hardenability steel. One of the significant advantages is to reduce the distortion and stress, compared to water and oil quench. However, not like liquid quench, no gas quench steel hardenability test standard exists. The fundamental difference between liquid quench and gas quench is heat transfer coefficient. The workpiece with the same hardness after liquid and gas quench process may have different microstructure due to different cooling curves. The concept of equivalent gas quench heat transfer coefficient (HTC) is proposed to have the same cooling curve, microstructure and hardness when compared with liquid quench. Several influencing factors on steel hardenability have been discussed, such as austenizing temperature, heating rate, holding time, composition variation and grain size difference. The phase quantification by X-ray Diffraction and Rietveld Refinement method is developed to measure phase percentage for steel microstructure, including martensite, ferrite and carbides. The limitations and improvements of modified Jominy gas quench test are discussed. The fundamental limitation of Jominy gas quench test is that one gas quench condition cannot be used for both low hardenability steel and high hardenability steel at the same time. The same steel grade would have different hardenability curves under different gas quench conditions, which made it difficult to compare the hardenability among different steels. The critical HTC test based on Grossmann test is proposed to overcome the limitations. In the test, different gas quench HTC conditions are applied to the sample with the same geometry. After sectioning each bar at mid-length, the bar that has 50% martensite at its center is selected, and the applied gas quench HTC of this bar is designated as the critical HTC. This test has many advantages to take the place of modified Jominy gas quench test. Since one of the advantages of gas quench is greater process flexibility to vary cooling rates, gas marquenching technology is proposed to obtain martensite with less sever cooling rate and reduce the distortion and stress.
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Kaya, Ebubekir. "Effects Of Off-center Angle On The Heat Transfer Coefficient On Vertical Tier Of Multiple Spherical Surfaces." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12605714/index.pdf.
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EFFECTS OF OFF-CENTER ANGLE
ON THE HEAT TRANSFER COEFFICIENT ON VERTiCAL TIER OF MULTIPLE SPHERICAL SURFACES
Kaya, Ebubekir
M.S., Department of Mechanical Engineering
Supervisor: Assoc. Prof. Dr. Cemil Yamali
December 2004, 112 pages
The purpose of this study is to investigate the laminar film condensation phenomenon of steam on a vertical tier of multiple spherical surfaces by using both analytical and experimental methods. The analytical heat transfer results were obtained by following the Nusselt type of analysis and represented graphically. In addition, in order to observe the real behavior of the film condensation, an experimental setup was manufactured and experiments were done.
In analytical sectionmass flow rate, (mean) velocity, film thickness, local heat flux and local heat transfer coefficient values were obtained and plotted as depending on angular position. Moreover, mean heat flux and mean heat transfer coefficient variations were presented with respect to diameter of the sphere and sub-cooling. On the other hand, for the experimental section, heat flux and mean heat transfer coefficient values were obtained and expressed as depending on sub-cooling. To see the effects of off-center angle, setup was inclined for different angles and experiments were repeated for each inclination angle. At the end of the study, mean heat transfer coefficients belong to analytical and experimental studies were compared to each other as well as to the literature.
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Choi, Jungho. "An experimental investigation of turbine blade heat transfer and turbine blade trailing edge cooling." Texas A&M University, 2004. http://hdl.handle.net/1969.1/1377.
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This experimental study contains two points; part1 turbine blade heat transfer
under low Reynolds number flow conditions, and part 2 trailing edge cooling and
heat transfer. The effect of unsteady wake and free stream turbulence on heat transfer
and pressure coefficients of a turbine blade was investigated in low Reynolds number
flows. The experiments were performed on a five blade linear cascade in a low speed
wind tunnel. A spoked wheel type wake generator and two different turbulence grids
were employed to generate different levels of the Strouhal number and turbulence
intensity, respectively. The cascade inlet Reynolds number based on blade chord
length was varied from 15,700 to 105,000, and the Strouhal number was varied from 0
to 2.96 by changing the rotating wake passing frequency (rod speed) and cascade inlet
velocity. A thin foil thermocouple instrumented blade was used to determine the
surface heat transfer coefficient.
A liquid crystal technique based on hue value detection was used to measure
the heat transfer coefficient on a trailing edge film cooling model and internal model of
a gas turbine blade. It was also used to determine the film effectiveness on the trailing
edge. For the internal model, Reynolds numbers based on the hydraulic diameter of
the exit slot and exit velocity were 5,000, 10,000, 20,000, and 30,000 and
corresponding coolant to mainstream velocity ratios were 0.3, 0.6, 1.2, and 1.8 for
the external models, respectively. The experiments were performed at two different
designs and each design has several different models such as staggered / inline exit,
straight / tapered entrance, and smooth / rib entrance. The compressed air was used in
coolant air. A circular turbulence grid was employed to upstream in the wind tunnel
and square ribs were employed in the inlet chamber to generate turbulence intensity
externally and internally, respectively.
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Enico, Daniel. "External Heat Transfer Coefficient Predictions on a Transonic Turbine Nozzle Guide Vane Using Computational Fluid Dynamics." Thesis, Linköpings universitet, Mekanisk värmeteori och strömningslära, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-178173.
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The high turbine inlet temperature of modern gas turbines poses a challenge to the material used in the turbine blading of the primary stages. Mechanical failure mechanisms are more pronounced at these high temperatures, setting the lifetime of the blade. It is therefore crucial to obtain accurate local metal temperature predictions of the turbine blade. Accurately predicting the external heat transfer coefficient (HTC) distribution of the blade is therefore of uttermost importance. At present time, Siemens Energy uses the boundary layer code TEXSTAN for this purpose. The limitations coupled to such codes however make them less applicable for the complex flow physics involved in the hot gas path of turbine blading. The thesis therefore aims at introducing CFD for calculating the external HTC. This includes conducting an extensive literature study to find and validate a suitable methodology. The literature study was centered around RANS modeling, reviewing how the calculation of the HTC has evolved and the performance of some common turbulence and transition models. From the literature study, the SST k − ω model in conjunction with the γ − Reθ transition model, the v2 − f model and the Lag EB k − ε model were chosen for the investigation of a suitable methodology. The validation of the methodology was based on the extensively studied LS89 vane linear cascade of the von Karman Institute. In total 13 test cases of the cascade were chosen to represent a wide range of flow conditions. Both a periodic model and a model of the entire LS89 cascade were tested but there were great uncertainties whether or not the correct flow conditions were achieved with the model of the entire cascade. It was therefore abandoned and a periodic model was used instead. The decay of turbulence intensity is not known in the LS89 cascade. This made the case difficult to model since the turbulence boundary conditions then were incomplete. Two approaches were attempted to handle this deficiency, where one was ultimately found invalid. It was recognized that the Steelant-Dick postulation could be used in order to find a turbulent length scale which when specified at the inlet, lead to fairly good agreement with data of the HTC. The validation showed that the SST γ − Reθ model performs relatively well on the suction side and in transition onset predictions but worse on the pressure side for certain flow conditions. The v2 − f model performed better on the pressure side and on a small portion of the suction side. Literature emphasized the importance of obtaining proper turbulence characteristics around the vane for accurate HTC-predictions. It was found that the results of the validation step could be closely coupled to this statement and that further work is needed regarding this. Further research must also be done on the Steelant-Dick postulation to validate it as a reliable method in prescribing the inlet length scale.
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Yu, Haixuan. "An integrated systems approach to understanding distortion and residual stress during thermal processing: design for heat treating." Digital WPI, 2019. https://digitalcommons.wpi.edu/etd-dissertations/565.
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Heat treatment processes are used to develop the desired mechanical properties for steels. Unfortunately, heat treatment, especially quenching, can cause distortion. Failure to meet geometry specifications can result in extensive rework or rejection of the parts. A series of quenching simulations, using DANTE, have been conducted on an AISI 4140 steel Navy C-ring distortion coupon and a WPI designed plate with a hole to determine the effects of quenching process parameters including part geometry, agitation during quenching, and quench start temperatures on distortion. The heat transfer coefficients (HTC) of the quenchant with selected pump speeds were measured by CHTE quench probe system, which is the key input for heat treatment simulation. The maximum HTC of the quenching oil was increased from 2350 W/m2K to 2666 W/m2K with higher pump speed. Quenching experiments were also conducted. It was found that the experimental measured gap opening of the standard Navy C-rings increased from 0.307mm without agitation to 0.536mm at a high agitation. Quench start temperature does not have a significant effect on the gap opening. The experimental results showed good agreement with simulation results. The important processing parameter identification was conducted using design of experiments (DoE) coupled with analysis of variance (ANOVA). The effect of processing parameters in decreasing order of importance were determined to be: quenchant type, part geometry, agitation speed, quenching orientation, quenchant temperature, immersion rates, and quench starts temperature. Based on the simulation and experimental results, it was found that the two most import parameters are: 1. The part geometry and size (product design) 2. The temperature dependent heat transfer coefficients between the part and the quenchant (process design) The coupling of these product and process parameters is necessary to apply the systems analysis that must be accomplished to understand the interaction between the part design and process design parameters. This coupling can be accomplished by locally applying the well-known Biot number. Bi (T) = h(T) * L / k(T) Where h(T) = film coefficient or convective heat transfer coefficient [W/m2*K]. LC = characteristic length, which is generally described as the volume of the body divided by the surface area of the body [m]. k(T) = thermal conductivity of the body [W/m*k] The concept of a local Biot number is introduced to quantify the local variations of part size, geometry and heat transfer coefficient. First, a large Bi indicates large temperature gradients within the part. Second, large local (geometry dependent) variations in Bi number will lead to large lateral temperature gradients. Therefore, variations in local Bi can lead to large temperature gradients and therefore high stress during quenching and finally distortion. This local Bi concept can be used in a systems approach to designing a part and the quenching system. This systems approach can be designated as design for heat treating.
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Alhamdan, Abdullah M. "Experimental studies on natural and forced convection around spherical and mushroom shaped particles." The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1145369315.
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Domeij, Bäckryd Rebecka. "Simulation of Heat Transfer on a Gas Sensor Component." Thesis, Linköping University, Department of Mathematics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-131.
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Gas sensors are today used in many different application areas, and one growing future market is battery operated sensors. As many gas sensor components are heated, one major limit of the operation time is caused by the power dissipated as heat. AppliedSensor is a company that develops and produces gas sensor components, modules and solutions, among which battery operated gas sensors are one targeted market.
The aim of the diploma work has been to simulate the heat transfer on a hydrogen gas sensor component and its closest surroundings consisting of a carrier mounted on a printed circuit board. The component is heated in order to improve the performance of the gas sensing element.
Power dissipation occurs by all three modes of heat transfer; conduction from the component through bond wires and carrier to the printed circuit board as well as convection and radiation from all the surfaces. It is of interest to AppliedSensor to understand which factors influence the heat transfer. This knowledge will be used to improve different aspects of the gas sensor, such as the power consumption.
Modeling and simulation have been performed in FEMLAB, a tool for solving partial differential equations by the finite element method. The sensor system has been defined by the geometry and the material properties of the objects. The system of partial differential equations, consisting of the heat equation describing conduction and boundary conditions specifying convection and radiation, was solved and the solution was validated against experimental data.
The convection increases with the increase of hydrogen concentration. A great effort was made to finding a model for the convection. Two different approaches were taken, the first based on known theory from the area and the second on experimental data. When the first method was compared to experiments, it turned out that the theory was insufficient to describe this small system involving hydrogen, which was an unexpected but interesting result. The second method matched the experiments well. For the continuation of the project at the company, a better model of the convection would be a great improvement.
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Carlsson, Per. "Flow Through a Throttle Body : A Comparative Study of Heat Transfer, Wall Surface Roughness and Discharge Coefficient." Thesis, Linköping University, Department of Management and Engineering, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-8378.
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When designing a new fuel management system for a spark ignition engine the amount of air that is fed to the cylinders is highly important. A tool that is being used to improve the performance and reduce emission levels is engine modeling were a fuel management system can be tested and designed in a computer environment thus saving valuable setup time in an engine test cell. One important part of the modeling is the throttle which regulates the air. The current isentropic model has been investigated in this report. A throttle body and intake manifold has been simulated using Computational Fluid Dynamics (CFD) and the influence of surface heating and surface wall roughness has been calculated. A method to calculate the effective flow area has been constructed and tested by simulating at two different throttle plate angles and several pressure ratios across the throttle plate. The results show that both surface wall roughness and wall heating will reduce the mass flow rate compared to a smooth and adiabatic wall respectively. The reduction is both dependent on pressure ratio and throttle plate angle. The effective area has showed to follow the same behaviour as the mass flow rate for the larger simulated throttle plate angle 31 degrees, i.e. an increase as the pressure drop over the throttle plate becomes larger. At the smaller throttle plate angle 21 degrees, the behaviour is completely different and a reduction of the effective area can be seen for the highest pressure drop where a increase is expected.
När ett nytt bränslesystem ska designas till en bensinmotor är det viktigt att veta hur stor mängd luft som hamnar i cylindrarna. Ett verktyg som är på frammarsch för att förbättra prestanda och minska emissioner är modellbaserad simulering. Med hjälp av detta kan ett bränslesystem designas och testas i datormiljö och därigenom spara dyrbar tid som annars måste tillbringas i en motortestcell. En viktig del av denna modellering är spjället eller trotteln vilken reglerar luften. I denna rapport har studier gjort på den nuvarande isentropiska modellen. Ett spjällhus och insugsgrenrör har simulerats med hjälp av Computational Fluid Dynamics (CFD) och påverkan av värme samt ytjämnhet på väggen har beräknats. En metod att beräkna den effektiva genomströmmade arean har konstruerats och testats vid två olika spjällvinklar samt flertalet tryckkvoter över spjället. Resultaten visar att både en uppvärmd vägg och en vägg med skrovlighet kommer att minska massflödet jämfört med en adiabatisk respektive en slät vägg. Minskningen har både spjällvinkel samt tryckkvots beroende. Den effektiva genomströmmade arean har visats sig följa samma beteende som massflödet vid den större simulerade spjällvinkeln 31 grader, det vill säga öka med ökat tryckfall över spjället. Vid den mindre vinkeln 21 grader, är beteendet helt annorlunda jämfört med massflödet och en minskning av den effektiva arean kan ses vid det största tryckfallet där en ökning förväntades.
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Sørum, Mikkel. "Experimental investigation of the impact in the heat transfer coefficient and pressure drop during boiling flow instabilities." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-26581.
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High heat transfer rates at reasonably low temperature differences can be obtained by utilizing a boiling fluid. The use of boiling heat transfer is often limited by onset of a heat transfer crisis named the Critical Heat Flux (CHF). The CHF is accompanied by an inordinate increase in temperature with the most severe consequence being related to the physical burnout of the heated surface. Two-phase boiling flows in channels are sometimes prone to flow instabilities. Density Wave Oscillations (DWO) is the most common type of thermo-hydraulic instability. DWO are fluid waves of alternating higher and lower densities propagating across the system. It is characterized by large cyclic fluctuations in flow rate and pressure and has a period of about twice the heated channel transit time. The literature survey condenses previous results and identifies different approaches for obtaining them in experimental studies. The purpose of this study is to perform an experimental investigation on the effect of flow instabilities on the heat transfer coefficient and pressure drop characteristics of a 5 mm uniformly heated horizontal boiling in-tube system utilizing R134a as the working fluid. The experiments confirmed that the system stability is improved by opening the inlet restriction valve and omitting exit orifice. The influence of the pump system characteristics on DWO was also explored. Establishing an unconditional stable system configuration allowed for generation of reference data. DWO was found to occur when vapor quality becomes sufficiently high in a system operating with inlet and exit restrictions and some degree of inlet subcooling. Mimicking DWO by superimposing flow oscillations by cycling the pump drive was also a viable solution. It was found that the overall heat transfer decreased proportionally to the flow amplitude. Shifting the period of oscillation from its natural frequency to lower frequencies reduces the heat transfer. The saturated boiling heat transfer coefficient was highly dependent on heat flux, and almost independent of flow rate, indicating that nucleate boiling was the dominant heat transfer mechanism. Comparisons were made to saturated boiling correlations. Heat transfer scales generally well with pressure drop, except a sudden reduction when DWO commences. The local heat transfer coefficient in the test section outlet increased with heat flux until it suddenly dropped due to an abrupt increase in wall temperature, distinguished as the normal CHF. The onset of DWO was found to trigger premature CHF at heat fluxed of about 90% the normal CHF.
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Wang, Wei-Wen William. "Condensation and single-phase heat transfer coefficient and flow regime visualization in microchannel tubes for HFC-134A /." The Ohio State University, 1999. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488192119266647.
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Eferemo, Daniel. "Numerical investigation of the convective heat transfer coefficient of the human body using a representative cylindrical model." Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/26904.
Full textAbstract:
The principal objective of this study is to investigate, develop and verify a framework for determining the convective heat transfer co-efficient from a cylindrical model that can easily be adaptable to more complex geometry - more specifically the human body geometry. Analysis of the model under forced convection airflow conditions between the transition velocity of about 1m/s - calculated using the Reynolds number - up until 12m/s were carried out. The boundary condition, however, also included differences in turbulence intensities and cylinder orientation with respect to wind flow (seen as wind direction in some texts). A total of 90 Computational Fluid Dynamic (CFD) calculations from these variations were analysed for the model under forced convective flow. Similar analysis were carried out for the model under natural convection with air flow velocity of 0.1m/s. Here, the temperature difference between the model and its surrounding environments and the cylinder orientation with respect to wind flow were varied to allow for a total of 15 CFD analysis. From these analysis, for forced convection, strong dependence of the convective heat transfer coefficient on air velocity, cylinder orientation and turbulence intensity was confirmed. For natural convection, a dependence on the cylinder orientation and temperature difference between the model and its environment was confirmed. The results from the CFD simulations were then compared with those found in texts from literature. Formulas for the convective heat transfer coefficient for both forced and natural convection considering the respective dependent variables are also proposed. The resulting formulas and the step by step CFD process described in this thesis provides a framework for the computation of the convective heat transfer coefficient of the human body via computer aided simulations. This framework can easily be adaptable to the convective heat transfer coefficient calculations of the human body with some geometric modelling adjustments, thus resulting in similar representative equations for a human geometric model.
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Wasson, Rachel Ann. "Separation of the Heat Transfer Components for Diffusion Flames Impinging onto Ceilings." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/50588.
Full textAbstract:
Two series of experiments were performed to determine the flow characteristics and to quantify the heat transfer components from a propane diffusion flame impinging onto a ceiling. A 0.3 m square sand burner with propane as the fuel type provided a steady-state fire. In the first series of experiments, measurements of gas temperature and velocity were made at 76 mm vertical intervals above the burner up to the ceiling. Fire heat release rates (HRRs) of 50 kW and 90 kW with free flame length to ceiling height ratios, Lf/H, of 2, 1.5, 1, 0.8, 0.85 were used to determine their effects on the measured parameters. Gas temperatures within the continuous flaming region were relatively constant, and measured to be independent of ceiling height and HRR, while velocities increased with elevation and were independent of ceiling height yet weakly dependent on HRR. Within the intermittent region, gas temperature was weakly affected by the presence of the ceiling at various heights, while the effect on velocity was more pronounced. HRR had an effect on both temperature and velocity within the intermittent region of the fire plume. Comparisons with existing fire plume correlations showed that the unbounded correlations can be used to provide a good approximation of the gas temperature for the ceiling bounded case; while the correlations for the velocity can only be used for elevations up to approximately 60% of the ceiling height. Elevations above this cutoff were significantly affected by the presence of the ceiling.
The second series of experiments investigated HRRs of 50 kW and 90 kW with free flame length to ceiling height ratios, Lf/H, of 2, 1.5, and 1. Heat flux and gas temperature at the stagnation point of the ceiling were measured using hybrid heat flux gauges and an aspirated Type K thermocouple. Four methods of calculating the convective heat transfer coefficient, h, were developed and adapted; two reference methods and two slope methods. The components of heat transfer at the impingement point were separated using these calculated h values. The reference method 2, and both slope methods only required the use of the non-cooled hybrid gauge measurements and were in overall good agreement with one another. The reference method 1 differed significantly, being up to 15.8 times lower than the others. The trends in the two groups were contradictory, with the h calculated using the reference method 1 increasing with ceiling height while the others showed no strong trend with ceiling height. The disagreements between the methods greatly affected the components of heat transfer, particularly at the lowest ceiling heights. Convection calculated using the h from reference method 1 contributed only 2-5% of the total exposure heat flux at the lowest ceiling heights, whereas with the other methods convection contributed 20-50% of the total exposure heat flux. The limitations of each method are discussed. Further investigation is required for all methods to determine their applicability within the flaming region of a fire.Master of Science
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Babenko, Maksims. "A Study of Heat Transfer at the Cavity-Polymer Interface in Microinjection Moulding. The effects of processing conditions, cavity surface roughness and polymer physical properties on the heat transfer coefficient." Thesis, University of Bradford, 2015. http://hdl.handle.net/10454/14745.
Full textAbstract:
This thesis investigates the cooling behaviour of polymers during the microinjection moulding process. The work included bespoke experimental mould design and manufacturing, material characterisation, infra-red temperature measurements, cooling analysis and cooling prediction using commercial simulation software. To measure surface temperature of the polymers, compounding of polypropylene and polystyrene with carbon black masterbatch was performed to make materials opaque for the IR camera. The effects of addition of carbon black masterbatch were analysed using differential scanning calorimetry and Fourier transform infrared spectroscopy. Sapphire windows formed part of the mould wall and allowed thermal measurements using an IR camera. They were laser machined on their inside surfaces to generate a range of finishes and structures. Their topographies were analysed using laser confocal microscope. The surface energy of sapphire windows was measured and compared to typical mould steel, employing a contact angle measurement technique and calculated using Owens-Wendt theory. A heating chamber was designed and manufactured to study spreading of polymer melts on sapphire and steel substrates. A design of experiments approach was taken to investigate the influence of surface finish and the main processing parameters on polymer cooling during microinjection moulding. Cooling curves were obtained over an area of 1.92 by 1.92 mm of the sapphire window. These experiments were conducted on the Battenfeld Microsystem 50 microinjection moulding machine. A simulation study of polymer cooling during the microinjection moulding process was performed using Moldflow software. Particular interest was paid to the effect of the values of the interfacial heat transfer coefficient (HTC) on the simulated cooling predictions. Predicted temperature curves were compared to experimentally obtained temperature distributions, to obtain HTC values valid for the material and processing parameters.
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Reid, W. J. "Experimental investigation of circumferentially non-uniform heat flux on the heat transfer coefficient in a smooth horizontal tube with buoyancy driven secondary flow." Diss., University of Pretoria, 2005. http://hdl.handle.net/2263/66236.
Full textAbstract:
Most heat transfer tubes are designed for either fully uniform wall temperature or fully uniform wall
heat flux boundary conditions under forced convection. Several applications, including but not limited
to the solar collectors of renewable energy systems, do however operate with non-uniform boundary
conditions. Limited research has been conducted on non-uniform wall heat flux heat transfer
coefficients in circular tubes, especially for mixed convection conditions. Such works are normally
numerical in nature and little experimental work is available. In this experimental investigation the
effects of the circumferential heat flux distribution and heat flux intensity on the single phase (liquid)
internal heat transfer coefficient were considered for a horizontal circular tube. Focus was placed on
the laminar flow regime of water within a stainless steel tube with an inner diameter of 27.8 mm and
a length to diameter ratio of 72. Different outer wall heat flux conditions, including fully uniform and
partially uniform heat fluxes were studied for Reynolds numbers ranging from 650 to 2 600 and a
Prandtl number range of 4 to 7. The heat flux conditions included 360˚ (uniform) heating, lower 180˚
heating, upper 180˚ heating, 180˚ left and right hemispherical heating, lower 90˚ heating, upper 90˚
heating and slanted 180˚ heating. Depending on the angle span of the heating, local heat fluxes of 6
631 W/m2
, 4 421 W/m2
, 3 316 W/m2
, 2 210 W/m2
and 1 658 W/m2 were applied. Results indicate that
the local and average steady state Nusselt numbers are greatly influenced by the applied heat flux
position and intensity. Highest average heat transfer coefficients were achieved for case where the
applied heat flux was positioned on the lower half (in terms of gravity) of the tubes circumference,
while the lowest heat transfer coefficients were achieved when the heating was applied to the upper
half of the tube. Variations in the heat transfer coefficient were found to be due to the secondary
buoyancy induced flow effect. The relative thermal performance of the different heating scenarios
where characterised and described by means of newly developed heat transfer coefficient
correlations for fully uniform heating, lower 180° heating, and upper 180° heating.Dissertation (MEng)--University of Pretoria, 2018.
Mechanical and Aeronautical Engineering
MEng
Unrestricted
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Alsaiari, Abdulmohsen Omar. "Augmentation of Jet Impingement Heat Transfer on a Grooved Surface Under Wet and Dry Conditions." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/98502.
Full textAbstract:
Array jet impingement cooling experiments were performed on flat and grooved surfaces with the surface at a constant temperature. For the flat surface, power and temperature measurements were performed to obtain convection coefficients under a wide range of operating conditions such as jet speed, orifice to surface stand-of distance, and open area percentage. Cooling performance (CP) was calculated as the ratio between heat transfer and fan power. An empirical model was developed to predict jet impingement heat transfer taking into account the entrainment effects. Experimental results showed that jet impingement can provide high transfer rates with lower rates of cooling cost in comparison to contemporary conventional techniques in the industry. CP values over 279 were measured which are significantly higher than the standard values of 70 to 95 in current technology. The model enhanced prediction accuracy by taking into account the entrainment effects; an effect that is rarely considered in the literature. Experiments on the grooved surfaces were performed at dry and wet surface conditions. Under dry conditions, results showed 10%~55% improvement in heat transfer when compared to the flat surface. Improvement percentage tends to be higher at wider gaps between the array of orifices and the grooved surface. An improvement of 30%~40% was observed when increasing Re either by increasing orifice diameter or jet speed. Similar improvement was observed at higher flow open area percentages. No significant improvement in heat transfer resulted from decreasing the size of the grooves from 3.56mm to 2.54mm. Similarly, no noticeable change in heat transfer resulted from changing the relative position of the jets striking the surface at the top of the grooves to the bottom of the grooves. Deeper grooves with twice the depth gave statistically similar average heat transfer coefficients as shallower grooves. Under wet conditions, a hybrid cooling technique approach was proposed by using air jets impinging on a grooved surface with the grooves containing water. The approached is proposed and evaluated experimentally for its feasibility as an alternative for cooling towers of thermoelectric power plants. Convection heat and mass transfer coefficients were measured experimentally using the heat mass transfer analogy. Results showed that hybrid jet impingement provided high magnitudes of heat flux at low jet speeds and flow rates. High coefficients of performance CP > 3000, and heat fluxes > 8,000W/m2 were observed. Hybrid jet impingement showed 500% improvement as compared to jet impingement on a dry flat surface. CP values of hybrid jet impingement is 600% to 1,500% more as compared to performance of air-cooled condensers and wet cooling towers. Water use for hybrid jet impingement cooling is efficient since evaporation energy is absorbed from the surface directly instead of cooling air to near wet-bulb temperature.PHD
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Venter, Philip van Zyl. "A supercritical R-744 heat transfer simulation implementing various Nusselt number correlations / Philip van Zyl Venter." Thesis, North-West University, 2010. http://hdl.handle.net/10394/4234.
Full textAbstract:
During the past decade research has shown that global warming may have disastrous effects on our planet. In order to limit the damage that the human race seems to be causing, it was acknowledged that substances with a high global warming potential (GWP) should be phased out. In due time, R-134a with a GWP = 1300, may probably be phased out to make way for nature friendly refrigerants with a lower GWP. One of these contenders is carbon dioxide, R-744, with a GWP = 1.
Literature revealed that various Nusselt number (Nu) correlations have been developed to predict the convection heat transfer coefficients of supercritical R-744 in cooling. No proof could be found that any of the reported correlations accurately predict Nusselt numbers (Nus) and the subsequent convection heat transfer coefficients of supercritical R-744 in cooling.
Although there exist a number of Nu correlations that may be used for R-744, eight different correlations were chosen to be compared in a theoretical simulation program forming the first part of this study. A water-to-transcritical R-744 tube-in-tube heat exchanger was simulated. Although the results emphasise the importance of finding a more suitable Nu correlation for cooling supercritical R-744, no explicit conclusions could be made regarding the accuracy of any of the correlations used in this study.
For the second part of this study experimental data found in literature were used to evaluate the accuracy of the different correlations. Convection heat transfer coefficients, temperatures, pressures and tube diameter were employed for the calculation of experimental Nusselt numbers (Nuexp). The theoretical Nu and Nuexp were then plotted against the length of the heat exchanger for different pressures. It was observed that both Nuexp and Nu increase progressively to a maximal value and then decline as the tube length increases. From these results it were possible to group correlations according to the general patterns of their Nu variation over the tube length.
Graphs of Nuexp against Nus, calculated according to the Gnielinski correlation, generally followed a linear regression, with R2 > 0.9, when the temperature is equal or above the pseudocritical temperature. From this data a new correlation, Correlation I, based on average gradients and intersects, was formulated. Then a modification on the Haaland friction factor was used with the Gnielinski correlation to yield a second correlation, namely Correlation II. A third and more advanced correlation, Correlation III, was then formulated by employing graphs where gradients and y-intercepts were plotted against pressure. From this data a new parameter, namely the turning point pressure ratio of cooling supercritical R-744, was defined. It was concluded that the employed Nu correlations under predict Nu values (a minimum of 0.3% and a maximum of 81.6%). However, two of the correlations constantly over predicted Nus at greater tube lengths, i.e. below pseudocritical temperatures. It was also concluded that Correlation III proved to be more accurate than both Correlations I and II, as well as the existing correlations found in the literature and employed in this study. Correlation III Nus for cooling supercritical R-744 may only be valid for a diameter in the order of the experimental diameter of 7.73 mm, temperatures that are equal or above the pseudocritical temperature and at pressures ranging from 7.5 to 8.8 MPa.Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2010.
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La, Rosa Rivero Renzo Josue. "Effects on Heat Transfer Coefficient and Adiabatic Effectiveness in Combined Backside and Film Cooling with Short-Hole Geometry." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/97010.
Full textAbstract:
Heat transfer experiments were done on a flat plate to study the effect of internal counter-flow backside cooling on adiabatic film cooling effectiveness and heat transfer coefficient. In addition, the effects of density ratio (DR), blowing ratio (BR), diagonal length over diameter (L/D) ratio, and Reynolds number were studied using this new configuration. The results are compared to a conventional plenum fed case. Data were collected up to X/D =23 where X=0 at the holes, an S/D = 1.65 and L/D=1,2. Testing was done at low L/D ratios since short holes are normally found in double wall cooling applications in turbine components. A DR of 2 was used in order to simulate engine-like conditions and this was compared to a DR of 0.92 since relevant research is done at similar low DR. The BR range of 0.5 to 1.5 was chosen to simulate turbine conditions as well. In addition, previous research shows that peak effectiveness is found within this range. Infrared (IR) thermography was used to capture temperature contours on the surface of interest and the images were calibrated using a thermocouple and data analyzed through MATLAB software. A heated secondary fluid was used as 'coolant' in the present study. A steady state heat transfer model was used to perform the data reduction procedure. Results show that backside cooling configuration has a higher adiabatic film cooling effectiveness when compared to plenum fed configurations at the same conditions. In addition, the trend for effectiveness with varying BR is reversed when compared with traditional plenum fed cases. Yarn flow visualization tests show that flow exiting the holes in the backside cooling configuration is significantly different when compared to flow exiting the plenum fed holes. We hypothesize that backside cooling configuration has flow exiting the holes in various directions, including laterally, and behaving similar to slot film cooling, explaining the differences in trends. Increasing DR at constant BR shows an increase in adiabatic effectiveness and HTC in both backside cooling and plenum fed configurations due to the decreased momentum of the coolant, making film attachment to the surface more probable. The effects of L/D ratio in this study were negligible since both ratios used were small. This shows that the coolant flow is still underdeveloped at both L/D ratios. The study also showed that increasing turbulence through increasing Reynolds number decreased adiabatic effectiveness.MS
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Zareifard, Mohammad Reza. "Evaluation of fluid-to-particle heat transfer coefficient under tube-flow conditions involving particle motion with relevance to aseptic processing." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ55397.pdf.
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Hou, Longfeng. "Etude numérique sur le modèle de coefficient d’absorption corrélé en multi spectral." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0068.
Full textAbstract:
Le transfert radiatif dû aux gaz joue un rôle important dans les applications industrielles comme les chambres de combustion, les sciences atmosphériques, etc. Plusieurs modèles ont été proposées pour estimer les propriétés radiatives des gaz. Le plus précis est l'approche dite Raie Par Raie (RPR). Cependant, cette méthode implique un coût de calcul excessif qui la rend inappropriée pour la plupart des applications. Néanmoins, elle reste la méthode de référence que nous utiliserons pour l'évaluation d’autres modèles approchés. Le modèle de coefficient d’absorption corrélé (Ck) est généralement suffisant pour de nombreuses applications. Cette méthode est réputée précise lorsque petits gradients de température sont rencontrés au sein du gaz. Toutefois, si le milieu gazeux est soumis à d'importants gradients de température, la méthode Ck peut conduire à des erreurs qui peuvent atteindre 50% en termes de flux radiatifs par rapport à des simulations de RPR. Le but de cette thèse est de proposer une version améliorée de la méthode Ck, appelée l'approche de coefficient d’absorption corrélé en multi spectral (MSCk). La principale différence entre les modèles Ck et MSCk est que, dans l'approche Ck les intervalles spectraux sur lesquels les propriétés radiatives des gaz sont moyennées sont choisis contiguës alors que, dans l’approche MSCk, ces intervalles sont construits afin d'assurer que le coefficient d'absorption soit corrélé sur ces intervalles. Par conséquent, l'hypothèse de corrélation dans l’approche MSCk est mieux adaptée que dans l’approche Ck. La construction de ces intervalles spectraux (en utilisant la méthode de classification automatique de données fonctionnelles) est détaillée. Cette approche est évaluée par rapport à la référence RPR dans plusieurs cas test. Ces cas traitent de mélanges de gaz (H2O-N2 et H2O-CO2-N2) dans l’intervalle de température [300-3000K]. Les résultats montrent que la méthode MSCk permet d'obtenir de meilleures précisions que les méthodes Ck tout en restant acceptable en termes de coût de calculRadiative heat transfer of gas plays an important role in industrial applications such as in combustion chambers, atmospheric sciences, etc. Several models [11] have been proposed to estimate the radiative properties of gases. The most accurate one is the Line-By-Line (LBL) approach. However, this technique involves excessive computation cost which makes it inappropriate for most applications. Nevertheless, it remains the reference approach for the assessment of other approximate models. The Correlated k-distribution method (Ck) [11] was shown to be a relevant choice for many applications. This method performs usually well, when only small temperature gradients are involved [21]. However, if the gaseous medium is subject to large temperature gradients, it may lead to errors that can reach 50% in terms of radiative heat fluxes when compared to LBL simulations [21]. The aim of the present paper is to propose an enhanced version of the Ck method, called the Multi-Spectral Correlated k-distribution approach (MSCk). The main difference between Ck and MSCk models is that in the Ck approach spectral intervals over which the radiative properties of the gas are averaged are chosen contiguous whereas, in the MSCk technique, those intervals are built in order to ensure that the absorption coefficient are scaled over them [27]. Accordingly, the usual assumption of correlated spectrum used in k-distribution approaches for the treatment of non uniformities is more acceptable in the MSCk case than in the Ck one. The building of those spectral intervals (using Functional Data Clustering, [52]) is detailed and the approach is assessed against LBL reference data in several test cases. These cases involve H2O-N2 and H2O-CO2-N2 mixtures in the [300-3000K] temperature range. Results show that the MSCk method enables to achieve better accuracies than Ck methods while remaining acceptable in terms of computational cost
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Ahlman, Robert. "ASSESSMENT OF GOVERNING HEAT AND MASS TRANSFER COEFFICIENTS FOR CRYOGENIC NO-VENT TOP-OFF MODELING." Cleveland State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=csu1625819994533715.
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Kalinger, James Phillip. "Heat transfer coefficient and pressure drop gas cooling measurements for CO2/oil mixture in a micro channel tube." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2632.
Full textAbstract:
Thesis (M.S.) -- University of Maryland, College Park, 2005.Thesis research directed by: Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Karlsson, Fredrik, and Samuel Mani. "Beräkning och sammanställning av linjära köldbryggor : En jämförelse mellan HEAT2 och COMSOL Multiphysics." Thesis, KTH, Byggvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-174115.
Full textAbstract:
I dagens samhälle ligger stort fokus på att bygga miljövänliga och energieffektiva byggnader. För att möta de allt mer skärpta energikraven måste hela klimatskalet beaktas där köldbryggor utgör en betydande del. Examensarbetet går ut på att göra en sammanställning av linjära köldbryggor (ψ) för vanligt förekommande konstruktionsdetaljer där köldbryggor finns. Sammanställningen där olika isoleringsmaterial på fasadskiva och isolertjocklekar tabelleras, ska underlätta för framtida projektering. Två simuleringsprogram för beräkning av köldbryggor har jämförts och utvärderats med varandra. Utvärderingen har gjorts med avseende på vilket program som var mest lämpat för att lösa frågeställningen. De två simuleringsprogrammen som används vid detta arbete är HEAT2 och COMSOL Multiphysics. Arbetet har resulterat i en lathund som finns tillgänglig på ELU:s intranät. Lathunden innehåller U-värde och ψ-värde med illustrering av konstruktionsdetaljerna och i detta arbete redovisas tillvägagångssätt och utförandet. En utvärdering av det lämpligaste program för utförandet av uppgiften finns också redovisad.Currently there is a lot of focus on environmentally friendly and energy efficient buildings in our society. To face the more toughen energy requirements, the entire climate shell of the building has to be considered there thermal bridges constitute a significant part. This bachelor dissertation intends to create a compilation for Ψ-values of common construction details where thermal bridges are to be found. The compilation with a chart that includes insulating material and insulation thickness shall simplify in future projecting. Furthermore, two simulating programs for calculations of thermal bridges have been compared with each other. The two simulation programs that have been used in this dissertation are HEAT2 and COMSOL Multiphysics. This dissertation has resulted in a quick reference guide which is available at ELU`s internal network. This quick reference guide includes U-values and Ψ-values with an illustration of every construction detail and the procedure and execution is reported in this dissertation. An evaluation of which of the two programs that has been used was more appropriate for this purpose is presented as well.