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1
Harish, J. "Computational Modelling Of Heat Transfer In Reheat Furnaces." Thesis, Indian Institute of Science, 2000. http://hdl.handle.net/2005/234.
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Furnaces that heat metal parts (blooms) prior to hot-working processes such as rolling or forging are called pre-forming reheat furnaces. In these furnaces, the fundamental idea is to heat the blooms to a prescribed temperature without very large temperature gradients in them. This is to ensure correct performance of the metal parts subsequent to reheating. Due to the elevated temperature in the furnace chamber, radiation is the dominant mode of heat transfer from the furnace to the bloom. In addition, there is convection heat transfer from the hot gases to the bloom. The heat transfer within the bloom is by conduction. In order to design a new furnace or to improve the performance of existing ones, the heat transfer analysis has to be done accurately. Given the complex geometry and large number of parameters encountered in the furnace, an analytical solution is difficult, and hence numerical modeling has to be resorted to.
In the present work, a numerical technique for modelling the steady-state and transient heat transfer in a reheat furnace is developed. The work mainly involves the development of a radiation heat transfer analysis code for a reheat furnace, since a major part of the heat transfer in the furnace chamber is due to radiation from the roof and combustion gases. The code is modified from an existing finite volume method (FVM) based radiation heat transfer solver, The existing solver is a general purpose radiation heat transfer solver for enclosures and incorporates the following features: surface-to-surface radiation, gray absorbing-emitting medium in the enclosure, multiple reflections off the bounding walls, shadowing effects due to obstructions in the enclosure, diffuse reflection and enclosures with irregular geometry.
As a part of the present work, it has now been extended to include the following features that characterise radiation heat transfer in the furnace chamber
· Combination of specular and diffuse reflection as is the case with most real surfaces
· Participating non-gray media, as the combustion gases in the furnace chamber exhibit highly spectral radiative characteristics
Transient 2D conduction heat transfer within the metal part is then modelled using a FVM-based code. Radiation heat flux from the radiation model and convection heat flux calculated using existing correlations act as boundary conditions for the conduction model. A global iteration involving the radiation model and the conduction model is carried out for the overall solution.
For the study, two types of reheat furnaces were chosen; the pusher-type furnace and the walking beam furnace. The difference in the heating process of the two furnaces implies that they have to be modelled differently. In the pusher-type furnace, the heating of the blooms is only from the hot roof and the gas. In the walking beam furnace, the heating is also from the hearth and the blooms adjacent to any given bloom.
The model can predict the bloom residence time for any particular combination of furnace conditions and load dimensions. The effects of variations of emissivities of the load, thickness of the load and the residence time of billet in the furnaces were studied.
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Zu, Yingqing. "Computational modelling of complex flow and heat transfer." Thesis, University of Nottingham, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.537819.
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Huzayyin, Omar A. "Computational Modeling of Convective Heat Transfer in Compact and Enhanced Heat Exchangers." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1313754781.
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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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Iyer, Kaushik A. "Quantitative characterization of thermophysical properties in computational heat transfer." Full text open access at:, 1993. http://content.ohsu.edu/u?/etd,273.
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Reichrath, Sven. "Convective heat and mass transfer in glasshouses." Thesis, University of Exeter, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391213.
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Soria, Guerrero Manel. "Parallel multigrid algorithms for computational fluid dynamics and heat transfer." Doctoral thesis, Universitat Politècnica de Catalunya, 2000. http://hdl.handle.net/10803/6678.
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The main purpose of the dissertation is to contribute to the development of numerical techniques for computational heat transfer and fluid flow, suitable for low cost (loosely coupled) parallel computers. It is focused on implicit integration schemes, using finite control volumes with multigrid (MG) algorithms.Natural convection in closed cavities is used as a problem model to introduce different aspects related with the integration of the incompressible Navier-Stokes equations, such as the solution of the pressure correction (or similar) equations that is the bottleneck of the algorithms for parallel computers. The main goal of the dissertation has been to develop new algorithms to advance in the solution of this problem rather than to implement a complete parallel CFD code.
An overview of different sequential multigrid algorithms is presented, pointing out the difference between geometric and algebraic multigrid. A detailed description of segregated ACM is given. The direct simulation of a turbulent natural convection flow is presented as an application example. A short description of the coupled ACM variant is given.
Background information of parallel computing technology is provided and the the key aspects for its efficient use in CFD are discussed. The limitations of low cost, loosely coupled cost parallel computers (high latency and low bandwidth) are introduced. An overview of different control-volume based PCFD and linear equation solvers is done. As an example, a code to solve reactive flows using Schwartz Alternating Method that runs particularly well on Beowulf clusters is given.
Different alternatives for latency-tolerant parallel multigrid are examined, mainly the DDV cycle proposed by Brandt and Diskin in a theoretical paper. One of its main features is that, supressing pre-smoothing, it allows to reduce the each-to-neighbours communications to one per MG iteration. In the dissertation, the cycle is extended to two-dimensional domain decompositions. The effect of each of its features is separately analyzed, concluding that the use of a direct solver for the coarsest level and the overlapping areas are important aspects. The conclusion is not so clear respect to the suppression of the pre-smoothing iterations.
A very efficient direct method to solve the coarser MG level is needed for efficient parallel MG. In this work, variant of the Schur complement algorithm, specific for relatively small, constant matrices has been developed. It is based on the implicit solution of the interfaces of the processors subdomains. In the implementation proposed in this work, a parallel evaluation and storage of the inverse of the interface matrix is used. The inner nodes of each domain are also solved with a direct algorithm. The resulting algorithm, after a pre-processing stage, allows a very efficient solution of pressure correction equations of incompressible flows in loosely coupled parallel computers.
Finally, all the elements presented in the work are combined in the DDACM algorithm, an algebraic MG equivalent to the DDV cycle, that is as a combination of a parallel ACM algorithm with BILU smoothing and a specific version of the Schur complement direct solver. It can be treated as a black-box linear solver and tailored to different parallel architectures.
The parallel algorithms analysed (different variants of V cycle and DDV) and developed in the work (a specific version of the Schur complement algorithm and the DDACM multigrid algorithm) are benchmarked using a cluster of 16 PCs with a switched 100 Mbits/s network.
The general conclusion is that the algorithms developed are suitable options to solve the pressure correction equation, that is the main bottleneck for the solution of implicit flows on loosely coupled parallel computers.
8
Leathard, Matthew James. "Computational modelling of coolant heat transfer in internal combustion engines." Thesis, University of Bath, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248102.
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Vila, Verde A. S. A. "Computational study of defects and heat transfer in gold nanostructures." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1373500/.
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Gold nanoparticles are promising tools for cancer therapy and cell imaging due to their non-toxicity, high heat conduction and tunable optical properties for the infraredvisible region. Nanoparticles production often involves thermal annealing, a process that changes the structure of the nanoparticle by mechanisms that are not yet well understood. For any of the biomedical applications, the nanoparticles are organically-coated to allow targeting and efficient uptake by cancer cells. Once the nanoparticles are inside the cell, their optical tunability allows the use of specific wavelengths strongly absorbed or scattered by the particles but poorly interacting with the medium to induce hyperthermia or obtain an image of the cell. In any case, the nanoparticle is expected to heat up. Although the propagation of heat is well understood at the macroscale, the details of the heat transfer at the nanoscale are still poorly understood. In this work, we use classical, equilibrium molecular dynamics simulations to create nanoparticles and investigate how their crystalline structure and the number and type of defects evolves as a function of annealing conditions. We use both analytical methods and classical non-equilibrium molecular dynamics simulations to investigate the effects of the particle size and the type of interface on the heat transfer properties of bare and organic-coated gold nanoparticles embedded in water. Water was chosen to mimic the cellular medium because it is the most abundant cellular component. Our simulations with a slab system of water and gold suggest that the material present at the interface between the gold and the water affects the heat transfer in the system. Moreover, our analytical calculations and computational results indicate that the heat transfer is dominated by the heat conduction in the medium for large nanoparticles, while for smaller nanoparticles the interface controls the overall heat propagation.
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Iverson, Jared M. "Computational fluid dynamics validation of buoyant turbulent flow heat transfer." Thesis, Utah State University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1550153.
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Computational fluid dynamics (CFD) is commonly implemented in industry to perform fluid-flow and heat-transfer analysis and design. Turbulence model studies in literature show that fluid flows influenced by buoyancy still pose a significant challenge to modeling. The Experimental Fluid Dynamics Laboratory at Utah State University constructed a rotatable buoyancy wind tunnel to perform particle image velocimetry experiments for the validation of CFD turbulence models pertaining to buoyant heat-transfer flows. This study validated RANS turbulence models implemented within the general purpose CFD software STAR-CCM+, including the k – ε models: realizable two-layer, standard two-layer, standard low-Re, v2 – f, the k- ω models from Wilcox and Menter, and the Reynolds stress transport and Spalart - Allmaras models. The turbulence models were validated against experimental heat flux and velocity data in mixed and forced convection flows at mixed convection ratios in the range of 0.1 ≤ Gr/Re2 ≤ 0.8. The k- εε standard low-Re turbulence model was found most capable overall of predicting the fluid velocity and heat flux of the mixed convection flows, while mixed results were obtained for forced convection.
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Iverson, Jared M. "Computational Fluid Dynamics Validation of Buoyant Turbulent Flow Heat Transfer." DigitalCommons@USU, 2013. https://digitalcommons.usu.edu/etd/2025.
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Computational fluid dynamics (CFD) is commonly used to visualize and understand complicated fluid flow and heat transfer in many industries. It is imperative to validate the CFD computer models in order to avoid costly design choices where experimentation cannot be used to ratify the predictions of computer models. Assessments of CFD computer models in the literature conclude that significant errors occur in computer model predictions of fluid flow influenced by buoyancy forces.
The Experimental Fluid Dynamics Laboratory at Utah State University constructed a wind tunnel with which to perform experiments on buoyancy induced fluid flow. The experiments measured the heat transfer and fluid velocity occurring in the buoyant flows to be used to validate computer models. Additional experimental measurements at the inlet and around the walls from each experiment allowed the computer models to simulate the fluid flow with realistic boundary conditions.For this study, four experiments were performed, including two cases where the buoy- ancy influence was significant, and two where it was not. For each set of two cases, one experiment was performed where the heat transfer occurred from a wall of the wind tunnel held at constant temperature and in the other experiment the wall temperature fluctuated axially.
This study used the experimental data to validate computer models available in the general purpose CFD software STAR-CCM+, including the k − ε models: realizable two- layer, standard two-layer, standard low-Re, v2 − f, the k − ω models from Wilcox and Menter, and the Reynolds stress transport and Spalart–Allmaras models. The k − ε stan- dard low-Re model was found most capable overall of predicting the fluid flow and heat transfer that occurred in the flows where the buoyancy influence was significant. For the experimental cases where the buoyancy influence was less significant, the validation results were inconsistent.
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Liu, Qingyun. "COUPLING HEAT TRANSFER AND FLUID FLOW SOLVERS FOR MULTI-DISCIPLINARY SIMULATIONS." MSSTATE, 2003. http://sun.library.msstate.edu/ETD-db/theses/available/etd-11122003-165044/.
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The purpose of this study is to build, test, validate, and implement two heat transfer models, and couple them to an existing fluid flow solver, which can then be used for simulating multi-disciplinary problems. The first model is for heat conduction computations, the other one is a quasi-one-dimensional cooling channel model for water-cooled jacket structural analysis. The first model employs the integral, conservative form of the thermal energy equation, which is discretized by means of a finite-volume numerical scheme. A special algorithm is developed at the interface between the solid and fluid regions, in order to keep the heat flux consistent. The properties of the solid region materials can be temperature dependent, and different materials can be used in different parts of the domains, thanks to a multi-block gridding strategy. The cooling channel flow model is developed by using uasi-one-dimensional conservation laws of mass, momentum, and energy, taking into account the effects of heat transfer and friction. It is possible to have phase changes in the channel, and a mixture model is applied, which allows two phases to be present, as long as they move at the same bulk velocity and vapor quality does not exceed relatively small values. The coupling process of both models (with the fluid solver and with each other) is handled within the Loci system, and is detailed in this study. A hot-air nozzle wall problem is simulated, and the computed results are validated with available experimental data. Finally, a more complex case involving the water-cooled nozzle of a Rocket Based Combined Cycle(RBCC) gaseous oxygen/gaseous hydrogen thruster is simulated, which involves all three models, fully coupled. The calculated temperatures in the nozzle wall and at the cooling channel outlet compare favorably with experimental data.
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Nijemeisland, Michiel. "Verification Studies of Computational Fluid Dynamics in Fixed Bed Heat Transfer." Digital WPI, 2000. https://digitalcommons.wpi.edu/etd-theses/318.
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Computational Fluid Dynamics (CFD) is one of the fields that has strongly developed since the recent development of faster computers and numerical modeling. CFD is also finding its way into chemical engineering on several levels. We have used CFD for detailed modeling of heat and mass transfer in a packed bed. One of the major questions in CFD modeling is whether the computer model describes reality well enough to consider it a reasonable alternative to data collection. For this assumption a validation of CFD data against experimental data is desired. We have developed a low tube to particle, structured model for this purpose. Data was gathered both with an experimental setup and with an identical CFD model. These data sets were then compared to validate the CFD results. Several aspects in creating the model and acquiring the data were emphasized. The final result in the simulation is dependent on mesh density (model detail) and iteration parameters. The iteration parameters were kept constant so they would not influence the method of solution. The model detail was investigated and optimized, too much detail delays the simulation unnecessarily and too little detail will distort the solution. The amount of data produced by the CFD simulations is enormous and needs to be reduced for interpretation. The method of data reduction was largely influenced by the experimental method. Data from the CFD simulations was compared to experimental data through radial temperature profiles in the gas phase collected directly above the packed bed. It was found that the CFD data and the experimental data show quantitatively as well as qualitatively comparable temperature profiles, with the used model detail. With several systematic variances explained CFD has shown to be an ample modeling tool for heat and mass transfer in low tube to particle (N) packed beds.
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Betancourt, Arturo. "Computational study of the heat transfer and fluid structure of a shell and tube heat exchanger." Thesis, Florida Atlantic University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10172609.
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A common technique to improve the performance of shell and tube heat exchangers (STHE) is by redirecting the flow in the shell side with a series of baffles. A key aspect in this technique is to understand the interaction of the fluid dynamics and heat transfer. Computational fluid dynamics simulations and experiments were performed to analysis the 3-dimensional flow and heat transfer on the shell side of an STHE with and without baffles. Although, it was found that there was a small difference in the average exit temperature between the two cases, the heat transfer coefficient was locally enhanced in the baffled case due to flow structures. The flow in the unbaffled case was highly streamed, while for the baffled case the flow was a highly complex flow with vortex structures formed by the tip of the baffles, the tubes, and the interaction of flow with the shell wall.
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Schneider, Alex Joseph. "Computational Modeling of Total Temperature Probes." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/51550.
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A study is presented to explore the suitability of CFD as a tool in the design and analysis of total temperature probes. Simulations were completed using 2D axisymmetric and 3D geometry of stagnation total temperature probes using ANSYS Fluent. The geometric effects explored include comparisons of shielded and unshielded probes, the effect of leading edge curvature on near-field flow, and the influence of freestream Mach number and pressure on probe performance. Data were compared to experimental results from the literature, with freestream conditions of M=0.3-0.9, p_t=0.2-1 atm, T_t=300-1111.1 K.
It is shown that 2D axisymmetric geometry is ill-suited for analyses of unshielded probes with bare-wire thermocouples due to their dependence upon accurate geometric characterization of bare-wire thermocouples. It is also shown that shielded probes face additional challenges when modeled using 2D axisymmetric geometry, including vent area sizing inconsistencies.
Analysis of shielded probes using both 2D axisymmetric and 3D geometry were able to produce aerodynamic recovery correction values similar to the experimental results from the literature. 2D axisymmetric geometry is shown to be sensitive to changes in freestream Mach number and pressure based upon the sizing of vent geometry, described in this report. Aerodynamic recovery correction values generated by 3D geometry do not show this sensitivity and very nearly match the results from the literature.
A second study was completed of a cooled, shielded total temperature probe which was designed, manufactured, and tested at Virginia Tech to characterize conduction error. The probe was designed utilizing conventional total temperature design guidelines and modified with feedback from CFD analysis. This test case was used to validate the role of CFD in the design of total temperature probes and the fidelity of the solutions generated when compared to experimental results. A high level of agreement between CFD predictions and experimental results is shown, while simplified, low-order model results under predicted probe recovery.Master of Science
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Berger, Sandrine. "Implementation of a coupled computational chain to the combustion chamber's heat transfer." Phd thesis, Toulouse, INPT, 2016. http://oatao.univ-toulouse.fr/16636/1/Berger_Sandrine.pdf.
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The design of aeronautical engines is subject to many constraints that cover performance gain as well as increasingly sensitive environmental issues. These often contradicting objectives are currently being answered through an increase in the local and global temperature in the hot stages of the engine. As a result, the solid parts encounter very high temperature levels and gradients that are critical for the engine lifespan. Combustion chamber walls in particular are subject to large thermal constraints. It is thus essential for designers to characterize accurately the local thermal state of such devices. Today, wall temperature evaluation is obtained experimentally by complex thermocolor tests. To limit such expensive experiments, efforts are currently performed to provide high fidelity numerical tools able to predict the combustion chamber wall temperature. This specific thermal field however requires the consideration of all the modes of heat transfer (convection, conduction and radiation) and the heat production (through the chemical reaction) within the burner. The resolution of such a multi-physic problem can be done numerically through the use of several dedicated numerical and algorithmic approaches. In this manuscript, the methodology relies on a partitioned coupling approach, based on a Large Eddy Simulation (LES) solver to resolve the flow motion and the chemical reactions, a Discrete Ordinate Method (DOM) radiation solver and an unsteady solid conduction code. The various issues related to computer resources distribution as well as the coupling methodology employed to deal with disparity of time and space scales present in each mode of heat transfer are addressed in this manuscript. Coupled application high performance studies, carried out both on a toy model and an industrial burner configuration evidence parameters of importance as well as potential path of improvements. The thermal coupling approach is then considered from a physical point of view on two distinct configurations. First, one addresses the impact of the methodology and the thermal equilibrium state between a reacting fluid and a solid for a simple flame holder academic case. The effect of the flame holder wall temperature on the flame stabilization pattern is addressed through fluid-only predictions. These simulations highlight interestingly three different theoretical equilibrium states. The physical relevance of these three states is then assessed through the computation of several CHT simulations for different initial solutions and solid conductivities. It is shown that only two equilibrium states are physical and that bifurcation between the two possible physical states depends both on solid conductivity and initial condition.Furthermore, the coupling methodology is shown to have no impact on the solutions within the range of parameters tested. A similar methodology is then applied to a helicopter combustor for which radiative heat transfer is additionally considered. Different computations are presented to assess the role of each heat transfer process on the temperature field: a reference adiabatic fluid-only simulation, Conjugate Heat Transfer, RadiationFluid Thermal Interaction and fully coupled simulations are performed. It is shown that coupling LES with conduction in walls is feasible in an industrial context with acceptable CPU costs and gives good trends of temperature repartition. Then, for the combustor geometry and operating point studied, computations illustrate that radiation plays an important role in the wall temperature distribution. Comparisons with thermocolor tests are globally in a better agreement when the three solvers are coupled.
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Mitchell, Robert David. "A computational study of heat transfer on transonic flow over an aerofoil." Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238992.
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Lucente, Carlin Miller. "COMPUTATIONAL ANALYSES FOR FLUID FLOW AND HEAT TRANSFER IN DIFFERENT CURVED GEOMETRIES." Cleveland State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=csu1337176681.
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Gifford, Brandon T. "Analysis of Heat Transfer in a Thermoacoustic Stove using Computational Fluid Dynamics." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1338254016.
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Milburn, Catherine A. "A computational fluid dynamics study of heat loss from an offshore oil well." Thesis, University of Aberdeen, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364687.
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Computational Fluid Dynamics (CFD) is used in this study to assess the influence of temperature-dependent oil viscosity and density on the flow of oil up the well, and therefore the amount of insulation required. CFD is a difficult tool to apply to flows where the grid aspect ratio is as high as it needs to be to accommodate the full length of an oil well with a realistic number of grid points. Each model was therefore intensive in terms of computational effort and time. This study shows that by allowing oil viscosity and density to vary with temperature in a 2150 m vertical well with no insulation, the production output is significantly affected. The drop in production output is approximately 3% when oil viscosity varies with temperature, but when coupled with temperature-dependent density the loss in production increases to 22%. Ten CFD models, each with a different value of insulation heat transmission coefficient lying in the range 0.35 Wm-2K-1 to 16900 Wm-2K-1, are used to establish the temperature drop between riser inlet and outlet. The results obtained allow an operator to select an appropriate insulation based on the allowable temperature drop up the well, assuming all other properties are equal. The completion fluid region is situated outside the oil flow, tubing and insulation. The fluid is stationary which suggests that natural convection currents are present. Seven CFD models with annulus heights ranging from 1 m to 64 m are used to detect these currents, and assess the effectiveness of water as an insulating completion fluid. This thesis establishes that the natural convection currents do not split into multiple cells, but remain mono-cellular when the Grashof number is approximately 1x108 and the Prandtl number is 2.3. This work also shows that heat loss due to natural convection from the completion fluid is an important contributory factor to the overall heat loss from a well, dependent on the well height.
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Neu, Samuel Charles. "Experimental and Computational Investigation of Electrohydrodynamically –Enhanced Nucleate Boiling." Digital WPI, 2016. https://digitalcommons.wpi.edu/etd-dissertations/405.
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"The importance of two-phase heat transfer for thermal management of aerospace avionic systems has become increasingly important as these systems have become miniaturized. Embedded active cooling systems are used to remove heat from processors and other electronic components and transferring this heat to radiators or other heat exchangers. As the characteristic dimension of flow channels for two-phase flow becomes comparable to bubble size, the mini-channels (< 3 mm) used to direct the cooling fluid can complicate nucleate boiling heat transfer. Bubbles can encounter other heated walls, rapidly expanding and greatly reducing heat transfer as well as causing pressure oscillations and flow instabilities. The use of eletrohydrodynamic (EHD) effects, through the introduction of non-uniform electric fields, can help mitigate this problem by altering the behavior of nucleating bubbles. A combined experimental and computational study was undertaken using HFE-7100, an engineered fluid used in heat transfer applications, to investigate the potential for enhancement of nucleate boiling using EHD effects induced by applying a non-uniform electric field. In the experimental study, a minichannel was constructed consisting of an upper and lower copper electrode and glass side walls to allow visualization. The channel height and width were 3mm and 4.76 mm respectively, representative of the minichannel regime. The upper electrode was grounded while the lower electrode was heated and biased to high voltage. Optical imaging combined with post-processing and statistical analysis was used to quantify the effect of EHD on the bubble behavior. Bubbles were found to form preferentially on nucleation sites resulting from imperfections in the heated copper surface over artificially created nucleation sites. When a high voltage is applied across the electrodes, the electric field enhancement along the rim of the nucleation site is believed to influence the force balance on the forming bubble and thereby influence the bubble departure size and frequency. EHD forces also act on the bubble surface as a result of the variation in permittivity between the liquid and vapor phases, altering its shape as has been previously reported in the literature. Test results are presented that demonstrate that the application of EHD increases the nucleation site density on the heated surface and increase the bubble departure frequency from individual sites. In addition, test results are presented to show that EHD forces alter the shape of bubbles during growth and the vertical position of the detached bubbles as they are carried along in the cross flow. To better understand the underlying phenomena affecting the bubble shape and departure frequency, a numerical simulation of the bubble growth and departure was performed using COMSOL multiphysics software customized to incorporate a user-defined body force based on the Maxwell Stress Tensor. Tracking of the bubble surface, including coalescence and breakup was incorporated using the phase field variable method in which the Navier-Stokes and heat transfer equations are solved for each phase of the fluid. Results from the simulations confirmed the sensitivity of the bubble elongation and neck formation to the nucleation site geometry, specifically the angle along the rim where field enhancement occurs. The enhanced constriction of the bubble neck resulted in early detachment of bubbles when compared to simulations in which EHD was not applied. This finding provides some insight into the higher bubble departure frequency and nucleation site density observed in the experiment. The results from the combined experimental and numerical study suggest that EHD enhancement may provide a mechanism for extending the use of nucleate heat transfer to minichannels, thereby enabling additional options for cooling in compact, embedded systems. "
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Uapipatanakul, Sakchai. "Development of computational methods for conjugate heat transfer analysis in complex industrial applications." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/development-of-computational-methods-for-conjugate-heat-transfer-analysis-in-complex-industrial-applications(3910eec7-601d-4da1-8c08-854404bbba3a).html.
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Conjugate heat transfer is a crucial issue in a number of turbulent engineering fluidflow applications, particularly in nuclear engineering and heat exchanger equipment. Temperature fluctuations in the near-wall turbulent fluid lead to similar fluctuationsin the temperature of the solid wall, and these fluctuations in the solid cause thermalstress in the material which may lead to fatigue and finally damage. In the present study, the Reynolds Average Navier-Stokes (RANS) modelling approachhas been adopted, with four equation k−ε−θ2−εθ eddy viscosity based modelsemployed to account for the turbulence in the fluid region. Transport equations forthe mean temperature, temperature variance, θ2, and its dissipation rate, εθ, have beensimultaneously solved across the solid region, with suitable matching conditions forthe thermal fields at the fluid/solid interface. The study has started by examining the case of fully developed channel flow withheat transfer through a thick wall, for which Tiselj et al. [2001b] provide DNS dataat a range of thermal activity ratios (essentially a ratio of the fluid and solid thermalmaterial properties). Initial simulations were performed with the existing Hanjali´cet al. [1996] four-equation model, extended across the solid region as described above. However, this model was found not to produce the correct sensitivity to thermal activityratio of the near wall θ2 values in the fluid, or the decay rate of θ2 across the solid wall. Therefore, a number of model refinements are proposed in order to improve predictionsin both fluid and solid regions over a range of thermal activity ratios. These refinementsare based on elements from a three-equation non-linear EVM designed to bring aboutbetter profiles of the variables k, ε, θ2 and εθ near the wall , and their inclusion is shownto produce a good matching with the DNS data of Tiselj et al. [2001b].Thereafter, a further, more complex test case has been investigated, namely an opposedwall jet flow, in which a hot wall jet flows vertically downward into an ascendingcold flow. As in the channel flow case, the thermal field is also solved across the solidwalls. The modified model results are compared with results from the Hanjali´c modeland LES and experimental data of Addad et al. [2004] and He et al. [2002] respectively. In this test case, the modified model presents generally good agreement with the LESand experimental data in the dynamic flow field, particularly the penetration point ofthe jet flow. In the thermal field, the modified model also shows improvements in the θ2predictions, particularly in the decay of the θ2 across the wall, which is consistent withthe behaviour found in the simple channel flow case. Although the modified model hasshown significant improvements in the conjugate heat transfer predictions, in some instancesit was difficult to obtain fully-converged steady state numerical results. Thusthe particular investigation with the inlet jet location shows non-convergence numericalresults in this steady state assumption. Thus, unsteady flow calculations have beenperformed for this case. These show large scale unsteadiness in the jet penetration area. In the dynamic field, the total rms values of the modelled and mean fluctuations showgood agreement with the LES data. In the thermal field calculation, a range of the flowconditions and solid material properties have been considered, and the predicted conjugateheat transfer predicted performance is broadly in line with the behaviour shownin the channel flow.
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Subramaniam, Vishwanath. "Computational analysis of binary-fluid heat and mass transfer in falling films and droplets." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26485.
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Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Garimella, Srinivas; Committee Member: Fuller, Tom; Committee Member: Jeter, Sheldon; Committee Member: Lieuwen, Tim; Committee Member: Wepfer, William. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Reid, Terry Vincent. "A Computational Approach For Investigating Unsteady Turbine Heat Transfer Due To Shock Wave Impact." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/25983.
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The effects of shock wave impact on unsteady turbine heat transfer are investigated. A numerical approach is developed to simulate the flow physics present in a previously performed unsteady wind tunnel experiment.
The windtunnel experiment included unheated and heated flows over a cascade of highly loaded turbine blades. After the flow over the blades was established, a single shock with a pressure ratio of 1.1 was introduced into the wind tunnel test section. A single blade was equipped with pressure transducers and heat flux microsensors. As the shock wave strikes the blade, time resolved pressure, temperature, and heat transfer data were recorded.Ph. D.
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Malick, Zeshan. "Computational Modelling of Cavity Arrays with Heat Transfer using Implicit Large Eddy Simulations." Thesis, Cranfield University, 2010. http://hdl.handle.net/1826/4357.
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This PhD programme was sponsored by the United Kingdom Atomic Energy Authority (UKAEA). The aim of this study is to conduct advanced computational modelling of a cooling device used in the fusion process which recycles waste energy. The development of efficient, water cooled tiles, that can sustain heat loads of approximately 20 MW (in quasi-steady state conditions) is the motivation of the current work. The information presented here will contribute to thermal-mechanical analysis, to be conducted at the Joint European Torus (JET) in future years. The devices known as “Hypervapotrons” have been used successfully at JET to provide a ion dump that dissipates residual energy from the fusion process. A capability to model the flow structure and heat transfer, across a large number of geometric and material options is provided within. Differences in geometry, result in changes to the flow structure and heat transfer rates. The desire to optimise such designs relies upon the fundamental understanding of the flow field within the main section, where the geometry may be defined as a cavity array. The benchmark case of a lid driven cavity flow was used for the validation of the flow field solution. Solutions using high resolution methods in the formulation provided a good comparison with established experimental data. Therefore, validation of incompressible, Implicit Large Eddy Simulations (ILES) for a wall bounded, three dimensional, turbulent flow is provided within. The sensitivity of the high order reconstruction in conjunction with the characteristics based scheme (Drikakis & Rider, 2005), to resolve turbulent flow structure is provided here. The solution response to grid resolution and a regularised velocity profile at the upper lid surface is also detailed. The investigation provided insight and confidence in the turbulence modelling approach which is relatively recent. It was also demonstrated through the lid driven case (and later in the Hypervapotron cases) that high order reconstruction was a simulation prerequisite, based on grid resolutions used within. Additional validation was also provided against numerical and analytical solutions for the Conjugate Heat Transfer (CHT) and scalar temperature field. Where appropriate both unsteady and steady problems based on a composite, three layer medium are detailed to provide preliminary validation for the implementation of the temperature scalar and conjugate boundary conditions. Unfortunately, it was not feasible to solve the coupled problem with an explicit solver as used in this study. However, it is suggested that the initial stages of thermal boundary layer development may be observed leading to the locations of incipient boiling. Two different Reynolds numbers were considered for the Hypervapotron ”Standard” geometry, Re=12000 and Re=18000. The different flow structures show that the cavity aspect ratio of the Standard design promotes lower flow speeds at the cavity base, since two or three counter rotating vortices coexist inside the cavities depending on Reynolds number. A detailed analysis on the impact of the number of repeating units within the computational domain is also provided. Results are presented of ensemble averaged quantities based on the Reynolds decomposition. The temperature distribution present in the solid, fluid and its interface for the thermally developing case is achieved. In addition the total and decomposed heat fluxes are presented for the Hypervapotron (Standard design) which provides similar comparison with recent Reynolds Averaged Navier-Stokes (RANS) simulations.
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Bhave, Chittatosh C. "A Computational Study of the Heat Transfer Characteristics of Offset-Strip Fin Cores." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1504796130207434.
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Ichikawa, Yoshikazu. "Prediction of pore pressures, heat and moisture transfer leading to spalling of concrete during fire." Thesis, Imperial College London, 2000. http://hdl.handle.net/10044/1/8721.
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Reardon, Jonathan Paul. "Computational Modeling of Radiation Effects on Total Temperature Probes." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/64518.
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The requirement for accurate total temperature measurements in gaseous flows was first recognized many years ago by engineers working on the development of superchargers and combustion diagnostics. A standard temperature sensor for high temperature applications was and remains to be the thermocouple. However, this sensor is characterized by errors due to conduction heat transfer from the sensing element, as well as errors associated with the flow over it. In particular in high temperature flows, the sensing element of the thermocouple will be much hotter than its surroundings, leading to radiation heat losses. This in turn will lead to large errors in the temperature indicated by the thermocouple. Because the design and testing of thermocouple sensors can be time consuming and costly due to the many parameters that can be varied and because of the high level of detail attainable from computational studies, the use of advanced computational simulations is ideally suited to the study of thermocouple performance.
This work sought to investigate the errors associated with the use of total temperature thermocouple probes and to assess the ability to predict the performance of such probes using coupled fluid-heat transfer simulations. This was done for a wide range of flow temperatures and subsonic velocities. Simulations were undertaken for three total temperature thermocouple probe designs. The first two probes were legacy probes developed by Glawe, Simmons, and Stickney in the 1950's and were used as a validation case since these probes were extensively documented in a National Advisory Committee for Aeronautics (NACA) technical report. The third probe studied was developed at Virginia Tech which was used to investigate conduction errors experimentally. In all cases, the results of the computational simulations were compared to the experimental results to assess their applicability. In the case of the legacy NACA probes, it was shown that the predicted radiation correction compared well with the documented values. This served as a validation of the computational method. Next the procedure was extended to the conduction error case, where the recovery factor, a metric used to relate the total temperature of the flow to the total temperature indicated by the sensor, was compared. Good agreement between the experimental results was found. The effects of radiation were quantified and shown to be small. It was also demonstrated that computational simulations can be used to obtain quantities that are not easily measured experimentally. Specifically, the heat transfer coefficients and the flow through the vented shield were investigated. The heat transfer coefficients were tabulated as Nusselt numbers and were compared to a legacy correlation. It was found that although the legacy correlation under-predicted the Nusselt number, the predicted results did follow the same trend. A new correlation of the same functional form was therefore suggested. Finally, it was found that the mounting strut had a large effect on the internal flow patterns and therefore the heat transfer to the thermocouple. Overall, this work highlights the usefulness of computational simulations in the design and analysis of total temperature thermocouple sensors.Master of Science
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Higgins, K. "Comparison of engineering correlations for predicting heat transfer in zero-pressure-gradient compressible boundary layers with CFD and experimental data." Fishermans Bend, Victoria : Defence Science and Technology Organisation, 2008. http://hdl.handle.net/1947/9653.
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Walker, Patrick Gareth Chemical Engineering & Industrial Chemistry UNSW. "CFD modeling of heat exchange fouling." Awarded by:University of New South Wales. Chemical Engineering & Industrial Chemistry, 2005. http://handle.unsw.edu.au/1959.4/22385.
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Heat exchanger fouling is the deposition of material onto the heat transfer surface causing a reduction in thermal efficiency. A study using Computational Fluid Dynamics (CFD) was conducted to increase understanding of key aspects of fouling in desalination processes. Fouling is a complex phenomenon and therefore this numerical model was developed in stages. Each stage required a critical assessment of each fouling process in order to design physical models to describe the process???s intricate kinetic and thermodynamic behaviour. The completed physical models were incorporated into the simulations through employing extra transport equations, and coding additional subroutines depicting the behaviour of the aqueous phase involved in the fouling phenomena prominent in crystalline streams. The research objectives of creating a CFD model to predict fouling behaviour and assess the influence of key operating parameters were achieved. The completed model of the key crystallisation fouling processes monitors the temporal variation of the fouling resistance. The fouling rates predicted from these results revealed that the numerical model satisfactorily reproduced the phenomenon observed experimentally. Inspection of the CFD results at a local level indicated that the interface temperature was the most influential operating parameter. The research also examined the likelihood that the crystallisation and particulate fouling mechanisms coexist. It was found that the distribution of velocity increased the likelihood of the particulate phase forming within the boundary layer, thus emphasizing the importance of differentiating between behaviour within the bulk and the boundary layer. These numerical results also implied that the probability of this composite fouling was greater in turbulent flow. Finally, supersaturation was confirmed as the key parameter when precipitation occurred within the bulk/boundary layer. This investigation demonstrated the advantages of using CFD to assess heat exchanger fouling. It produced additional physical models which when incorporated into the CFD code adequately modeled key aspects of the crystallisation and particulate fouling mechanisms. These innovative modelling ideas should encourage extensive use of CFD in future fouling investigations. It is recommended that further work include detailed experimental data to assist in defining the key kinetic and thermodynamic parameters to extend the scope of the required physical models.
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Adamic, Raymond Matthew. "CFD and Heat Transfer Models of Baking Bread in a Tunnel Oven." Cleveland State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=csu1355521233.
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Varela, Ballesta Sylvana Verónica. "Computational and experimental modeling of fluid flow and heat transfer processes in complex geometries." Doctoral thesis, Universitat Rovira i Virgili, 2012. http://hdl.handle.net/10803/80717.
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El objetivo principal de este trabajo es el estudio numérico (caffa3d.MB) y experimental (PIV) de los campos de velocidad y de temperatura en dominios complejos como los encontrados en las computadoras u otros sistemas electrónicos refrigerados que contengan circuitos impresos (PCB, Printed Circuit Board). La refrigeración es uno de los principales desafíos que estos dispositivos se deben tratar. La disipación del calor de los dispositivos de circuitos electrónicos se ha convertido en una cuestión importante a tener en cuenta durante su diseño. Los PCB son circuitos electrónicos que generan calor por efecto Joule y necesitan ser enfriados. Son cada vez más pequeños y por lo tanto los problemas del calentamiento disminuyen su eficiencia y vida útil. El estudio de la velocidad y los campos de temperatura está estrechamente relacionada con el análisis de la evolución espacial y temporal de las estructuras de flujo que se encuentran en las cavidades cerradas que contiene PCB y con el entendimiento de la influencia de la geometría, la velocidad de entrada de fluido y temperatura de la placa en el proceso de enfriamiento del PCB.The main objective of this work is the numerical (caffa3d.MB) and experimental (PIV) study of the velocity and temperature fields in complex domains like those encountered in computers or other electronic refrigerated systems with printed circuit board (PCB). Cooling is one of the main challenges these devices have to deal with. Heat removal from the electronic circuit devices has become an important issue to take into account during their design. PCB's are electronic circuits that generate heat by Joule effect and need to be cooled down. They are becoming smaller and therefore some warming problems appear that lowers their efficiency and lifespan. The study of the velocity and temperature fields is closely connected with the analysis of the spatial and temporal evolution of the flow structures found in PCB enclosed cavities and with the understanding of the influence of the geometry, the inlet fluid velocity and plate temperature in the cooling process of the PCB.
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Au, Edwin C. F. "A computational scheme for calculating refrigerant properties & heat transfer in boiling tube flow /." Title page, contents and abstract only, 1998. http://web4.library.adelaide.edu.au/theses/09ENS/09ensa888.pdf.
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Maqableh, Ayman M. M. "Computational study of multi-phase air/oil heat transfer in aero-engine bearing chambers." Thesis, University of Nottingham, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417410.
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Zitzmann, Tobias. "Adaptive modelling of dynamic conjugate heat transfer and air movement using computational fluid dynamics." Thesis, De Montfort University, 2007. http://hdl.handle.net/2086/4287.
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Altea, Claudinei de Moura. "Computational determination of convective heat transfer and pressure drop coefficients of hydrogenerators ventilation system." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3150/tde-28092016-095253/.
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The objective of the present work is to determinate the pressure drop and the heat transfer coefficients, normally applied to analytical calculations of hydrogenerators thermal design, obtained by applying numerical calculation (Computational Fluid Dynamics - CFD) and validated by experimental results and field measurements. The object of study is limited to the most important region of the ventilation system (the cooling air ducts of stator core) to get numerical results of heat transfer and pressure drop coefficients, which are impacted mostly by the entrance of air ducts. The numerical calculations considered three-dimensional, steady-state, incompressible and turbulent flow; and were based on the Finite Volume methodology. The turbulent flow computations were carried out with procedures based on RANS equations by selecting k-omega SST (Shear-Stress Transport) as turbulence model. Grid quality metrics were monitored and the uncertainties due to discretization errors were evaluated by means of a grid independence study and application of an uncertainty estimation procedure based on Richardson extrapolation. The validation of numerical method developed by the present work (specifically to simulate the flow dynamics behavior and to obtain numerically the pressure drop coefficient of the airflow to enter and pass through the Stator Core Air Duct in a hydrogenerator) is performed by comparing the numerical results to experimental data published by Wustmann (2005). The reference experimental data were obtained by a model test. The comparison between numerical and experimental results shows that the difference of pressure drop for Reynolds numbers higher than 5000 is 2% at maximum, while for lower Reynolds numbers, the difference increases significantly and reaches 10%. It is presented that the most reasonable hypothesis for higher discrepancy at lower Reynolds numbers can be assigned to the experiment\'s non-steady-state condition. It is to conclude that the proposed numerical method is validated for the upper region of the analyzed range. Additionally to the model test validation, field measurements were executed in order to confirm numerical results. Measurements of pressure drop in the stator core of a real hydrogenerator were a challenge. Nevertheless, despite all the difficulties and considerable high field measuring uncertainties, trend curves behavior are similar to numerical results. Finally, series of numerical calculation, varying geometrical parameters of the air-duct inlet design and operational data, were done in order to obtain pressure drop coefficients trend curves to be directly applied to analytical calculation routines of whole hydrogenerator ventilation systems. Parallel to it, thermal numerical calculation was executed in the prototype simulation in order to define the convective heat transfer coefficient.O objetivo do presente trabalho é determinar os coeficientes de perda de carga e transferência de calor, normalmente aplicados nos cálculos analíticos de design térmico de hidrogeradores, obtido pela aplicação de cálculo numérico (Computacional Fluid Dynamics - CFD) e validado por resultados experimentais e medições de campo. O objeto de estudo é limitado à região mais importante do sistema de ventilação (os dutos de ar de arrefecimento do núcleo do estator) para obter resultados numéricos dos coeficientes de transferência de calor e de perda de carga, que são impactados principalmente pela entrada de dutos de ar. Os cálculos numéricos consideraram escoamentos tridimensionais, em regime permanente, incompressíveis e turbulentos; e foram baseados no método dos volumes finitos. Os cálculos de escoamento turbulento foram realizados com procedimentos baseados em equações médias (RANS), utilizando o modelo k-omega SST (Shear-Stress Transport) como modelo de turbulência. Métricas de qualidade de malha foram monitoradas e as incertezas devido à erros de discretização foram avaliadas por meio de um estudo de independência de malha e aplicação de um procedimento de estimativa de incertezas com base na extrapolação de Richardson. A validação do método numérico desenvolvido pelo presente trabalho (especificamente para simular o comportamento dinâmico do escoamento e obter numericamente o coeficiente de perda de carga do escoamento ao entrar no duto de ar e atravessar o núcleo do estator de um hidrogerador) é realizada comparando os resultados numéricos com dados experimentais publicados por Wustmann (2005). Os dados experimentais foram obtidos como referência por um teste de modelo. A comparação entre os resultados numéricos e experimentais mostra que a diferença da perda de carga para números de Reynolds mais elevados do que 5000 é no máximo de 2%, enquanto que para números de Reynolds inferiores, a diferença aumenta significativamente e atinge 10%. A hipótese mais razoável para a maior discrepância para número de Reynolds menores é a possível influência de instabilidades do escoamento no experimento, fazendo com que o regime seja não-permanente. Conclui-se que o método numérico proposto é validado para a região superior do intervalo analisado. Além da validação pelo ensaio de modelo, medições de campo foram executadas, a fim de confirmar os resultados numéricos. As medições de perda de carga no núcleo do estator de um hidrogerador real era um desafio. No entanto, apesar de todas as dificuldades e consideráveis incertezas da medição campo, o comportamento das curvas de tendência ficou alinhado com resultados numéricos. Finalmente, uma série de cálculos numéricos, variando parâmetros geométricos do design da entrada do duto de ar e dados operacionais, foram executados a fim de se obter curvas de tendência para coeficientes de perda de carga (resultados deste trabalho) a serem aplicadas diretamente à rotinas de cálculos analíticos de sistemas completos de ventilação de hidrogeradores. Paralelamente à isso, o cálculo térmico numérico foi executado na simulação do protótipo, a fim de se definir o coeficiente de transferência de calor por convecção.
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Lin, Kuan-Ting. "Experimental and Computational Study of Novel Plate-Fin-Surfaces for Enhancing Forced Convection Heat Transfer in Compact Heat Exchangers." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1623166309984355.
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Fourie, Lionel Fabian. "Computational modelling of a hot-wire chemical vapour deposition reactor chamber." University of Western Cape, 2020. http://hdl.handle.net/11394/7523.
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>Magister Scientiae - MScIn this thesis, I explore the subjects of fluid dynamics and the Hot-Wire Chemical Vapour Deposition (HWCVD) process. HWCVD, in its simplicity, is one of the more powerful and elegant deposition techniques available in thin film research which allows for both the growth and post deposition treatments of functional thin films. In the HWCVD process, the quality of the final films is determined by a fixed set of deposition parameters namely: temperature, pressure and the gas flow rate. Finding the optimal combination of these parameters is key to obtaining the desired film specifications during every deposition. Conducting multiple trial experiments to determine said parameters can be expensive and time consuming, this is where simulation methods come into play. One such simulation method is Computational Fluid Dynamics (CFD) modelling
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Surendran, Mahesh. "Computational Fluid Dynamic Modeling of Natural Convection in Vertically Heated Rods." DigitalCommons@USU, 2016. https://digitalcommons.usu.edu/etd/5168.
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Natural convection is a phenomenon that occurs in a wide range of applications such as cooling towers, air conditioners, and power plants. Natural convection may be used in decay heat removal systems such as spent fuel casks, where the higher reliability inherent of natural convection is more desirable than forced convection. Passive systems, such as natural convection, may provide better safety, and hence have received much attention recently. Cooling of spent fuel rods is conventionally done using water as the coolant. However, it involves contaminating the water with radiation from the fuel rods. Contamination becomes dangerous and difficult for humans to handle. Further, the recent nuclear tragedy in Fukushima, Japan has taught us the dangers of contamination of water with nuclear radiation. Natural convection can perhaps significantly reduce the risk since it is self-sufficient and does not rely on other secondary system such as a blower as in cases of forced convection.
The Utah State University Experimental Fluid Dynamics lab has recently designed an experiment that models natural convection using heated rod bundles enclosed in a rectangular cavity. The data available from this experiment provides and opportunity to study and validate computational fluid dynamics(CFD)models. The validated CFD models can be used to study multiple configurations, boundary conditions, and changes in physics(natural and/or forced convection). The results are to be validated using experimental data such as the velocity field from particle image velocimetry (PIV), pressure drops across various sections of the geometry, and temperature distributions along the vertically heated rods. This research work involves modeling natural convection using two-layer turbulence models such as k - ε and RST (Reynolds stress transport) using both shear driven (Wolfstein) and buoyancy driven (Xu) near-wall formulations. The interpolation scheme employed is second-order upwinding using the general purpose code STAR-CCM+. The pressure velocity coupling is done using the SIMPLE method. It is ascertained that turbulence models with two-layer formulations are well suited for modeling natural convection. Further it is established that k - ε and Reynolds stress turbulence models with the buoyancy driven (Xu)formulation are able to accurately predict the flow rate and temperature distribution.
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Davies, Gareth Frank. "Development of a predictive model of the performance of domestic gas ovens using computational fluid dynamics." Thesis, London South Bank University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263995.
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Kulkarni, Aditya Narayan. "Computational and Experimental Investigation of Internal Cooling Passages for Gas Turbine Applications." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1590591363859471.
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Deshpande, Samruddhi Aniruddha. "Numerical Investigation of Various Heat Transfer Performance Enhancement Configurations for Energy Harvesting Applications." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/72129.
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Conventional understanding of quality of energy suggests that heat is a low grade form of energy. Hence converting this energy into useful form of work was assumed difficult. However, this understanding was challenged by researchers over the last few decades. With advances in solar, thermal and geothermal energy harvesting, they believed that these sources of energy had great potential to operate as dependable avenues for electrical power. In recent times, waste heat from automobiles, oil and gas and manufacturing industries were employed to harness power. Statistics show that US alone has a potential of generating 120,000 GWh/year of electricity from oil , gas and manufacturing industries, while automobiles can contribute upto 15,900 GWh/year.
Thermoelectric generators (TEGs) can be employed to capture some of this otherwise wasted heat and to convert this heat into useful electrical energy. This field of research as compared to gas turbine industry has emerged recently over past 30 decades. Researchers have shown that efficiency of these TEGs modules can be improved by integrating heat transfer augmentation features on the hot side of these modules. Gas turbines employ advanced technologies for internal and external cooling. These technologies have applications over wide range of applications, one of which is thermoelectricity. Hence, making use of gas turbine technologies in thermoelectrics would surely improve the efficiency of existing TEGs.
This study makes an effort to develop innovative technologies for gas turbine as well as thermoelectric applications. The first part of the study analyzes heat transfer augmentation from four different configurations for low aspect ratio channels and the second part deal with characterizing improvement in efficiency of TEGs due to the heat transfer augmentation techniques.Master of Science
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Liu, Xuejun Bhavnani S. H. "Experimental and computational study of fluid flow and heat transfer in the lost foam casting process." Auburn, Ala., 2005. http://hdl.handle.net/10415/1270.
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Detaranto, Michael Francis. "CFD analysis of airflow patterns and heat transfer in small, medium, and large structures." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/50813.
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Designing buildings to use energy more efficiently can lead to lower energy costs, while
maintaining comfort for occupants. Computational fluid dynamics (CFD) can be utilized to
visualize and simulate expected flows in buildings and structures. CFD gives architects and
designers the ability to calculate the velocity, pressure, and heat transfer within a building.
Previous research has not modeled natural ventilation situations that challenge common design
rules of thumb used for cross-ventilation and single-sided ventilation. The current study uses a
commercial code (FLUENT) to simulate cross-ventilation in simple structures and analyzes the
flow patterns and heat transfer in the rooms. In the Casa Giuliana apartment and the Affleck house,
this study simulates passive cooling in spaces well-designed for natural ventilation. Heat loads,
human models, and electronics are included in the apartment to expand on prior research into
natural ventilation in a full-scale building. Two different cases were simulated. The first had a
volume flow rate similar to the ambient conditions, while the second had a much lower flow rate
that had an ACH of 5, near the minimum recommended value Passive cooling in the Affleck house
is simulated and has an unorthodox ventilation method; a window in the floor that opens to an
exterior basement is opened along with windows and doors of the main floor to create a pressure
difference. In the Affleck house, two different combinations of window and door openings are
simulated to model different scenarios. Temperature contours, flow patterns, and the air changes
per hour (ACH) are explored to analyze the ventilation of these structures.Master of Science
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Ozturk, Harun Kemal. "A computational study of flow and heat transfer in gas turbine axial compressor stator-wells." Thesis, University of Sussex, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388675.
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Krishnababu, Senthil Kumar. "A computational investigation of tip leakage flow and heat transfer in unshrouded axial flow turbines." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614265.
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Morris, Angela. "Experimental and Computational Study of Heat Transfer on a Turbine Blade Tip with a Shelf." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/76906.
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Cooling of turbine parts in a gas turbine engine is necessary for operation as the temperature of combustion gases is higher than the melting temperature of the turbine materials. The gap between rotating turbine blades and the stationary shroud provides an unintended flow path for hot gases. Gases that flow through the tip region cause pressure losses in the turbine section and high heat loads to the blade tip. This thesis studies the heat transfer on an innovative tip geometry intended to help reduce aerodynamic losses. The blade tip has a depression (shelf) on the tip surface along much of the pressure side of the blade and film-cooling holes along the depression. This research experimentally measured the effect of the shelf, coolant flow and tip gap on heat transfer on the blade tip.
Stationary experiments were performed in a low speed wind tunnel on a linear cascade with two different tip gaps and multiple coolant flow rates through the film-cooling holes. Tests showed that baseline Nusselt numbers on the tip surface were reduced with the shelf tip compared with a flat tip. Measurements indicated that film-cooling was more effective with a small tip gap than with a large tip gap. Experimental and computational results demonstrated a lack of coolant spreading that was detrimental to regions between the film-cooling holes. While the coolant was effective on the blade tip, the leading and trailing edge regions were found to have high heat transfer coefficients with little available cooling.Master of Science
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Li, Lifeng. "Numerical study of surface heat transfer enhancement in an impinging solar receiver." Thesis, Uppsala universitet, Fasta tillståndets fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-237365.
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During the impinging heat transfer, a jet of working fluid, either gas or liquid, will besprayed onto the heat transfer surface. Due to the high turbulence of the fluid, the heat transfer coefficient between the wall and the fluid will be largely enhanced. Previously, an impinging type solar receiver with a cylindrical cavity absorber was designed for solar dish system. However, non-uniform temperature distribution in the circumferential direction was found on absorber surface from the numerical model, which will greatly limit receiver's working temperature and finally affect receiver's efficiency. One of the possible alternatives to solve the problem is through modifying the roughness of the target wall surface. This thesis work aims to evaluate the possibility and is focusing on the study of heat transfer characteristics. The simulation results will be used for future experimental impinging solar receiver optimization work. Computational Fluid Dynamics (CFD) is used to model the conjugate heat transfer phenomenon of atypical air impinging system. The simulation is divided into two parts. The first simulation was conducted with one rib arranged on the target surface where heat transfer coefficient is relatively low to demonstrate the effects of rib shape (triangular,rectangular, and semi-circular) and rib height (2.5mm, 1.5mm, and 0.5mm). The circular rib with 1.5mm height is proved to be most effective among all to acquirerelatively uniform temperature distribution. In the second part, the amount of ribs is taken into consideration in order to reach more uniform surface heat flux. The target wall thickness is also varied to assess its influence.
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Chul, Chang Young. "Experimental, theoretical and computational modelling of airflow to investigate the themalhydraulic performance and ventilation efficiency in a clean room." Thesis, University of Bristol, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389239.
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Tran, Tri Van. "Coupled thermo-hydro-mechanical computational modeling of an end bearing heat exchanger pile." Thesis, Kansas State University, 2015. http://hdl.handle.net/2097/19070.
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Master of ScienceDepartment of Civil Engineering
Dunja Peric
Piles have been used for many years in civil infrastructure as foundations for buildings, bridges, and retaining walls. Energy piles are thermo-active foundation systems that use geothermal energy for heating and cooling of buildings. Ground source heat is a very attractive, economical, efficient and sustainable alternative to current heating practices. Unlike the air temperature, the temperature below the Earth’s surface remains relatively constant throughout the year, somewhere between 10oC to 15oC below a depth of 6 m to 9 m (Kelly, 2011). This provides an opportunity for construction of thermo-active foundation systems with embedded geothermal loops. The main purpose of such thermo-active system is to transfer deep ground heat to a building through the fluid circulating within the geothermal loop. It is because these thermo-active foundation systems enable heat exchange between the deep ground and the building that is called the heat exchanger pile (HEP). The thermal energy supplied by a HEP can then supplement air-pump-based heating/cooling system. Although heat exchanger piles have been successfully implemented in Europe and Asia, their usage in U.S. remains uncommon. One reason for this might be currently limited understanding of the associated soil-structure interaction, thus unfavorably affecting the design procedures. To this end, a study was undertaken to investigate the predictive capabilities of computational models and to gain a better understanding of the load-transfer mechanisms of energy piles. Thus, coupled thermo-hydro-mechanical computational modeling of a single actual end bearing HEP was carried out for different loading scenarios including thermal and mechanical loads by using the finite element code ABAQUS/Standard 6.13-2. The results of the analyses of the heat exchanger pile with two different types of layered soil profile are presented: isotropic and anisotropic. The computational model was validated and verified successfully against field test results for all considered loading scenarios. Additional analyses were performed to gain a deeper insight into the effects of soil layering and on the behavior of energy piles. It was found that changes in the soil stiffness affected primarily the head displacement and vertical stresses and strains in the pile.