Journal articles: 'Heat transfer coefficient U'

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Sablani, S. S., and H. S. Ramaswamy. "Note. End-over-end agitation processing of cans containing liquid particle mixtures. Influence of continuous versus oscillatory rotation / Nota. Agitación por volteo de latas con una mezcla de líquido y partículas en suspensión. Influencia de la agitación en continuo y oscilatoria." Food Science and Technology International 5, no. 5 (October 1999): 385–89. http://dx.doi.org/10.1177/108201329900500503.

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Convective heat transfer coefficients were evaluated during end-over-end rotation processing of cans filled with liquid and particle mixtures in a pilot-scale, overpressure water-immersion, rotary retort. Two modes of end-over-end agitation were employed, one involving a continuous and the other involving an oscillatory rotation of the cage containing cans. Nylon spheres of diameter 0.025 m were used as test particles and a high temperature bath oil was used as the test liquid. A lumped capacity approach was employed to determine the overall heat transfer coefficient, U, and an inverse heat transfer approach was used to determined the fluid to particle heat transfer coefficient, hfp. Effects of the two modes of rotation (continuous and oscillation) on the associated heat transfer coefficients were evaluated at three speeds (8, 16 and 24 rpm) and three radii of rotation (0,13 and 26 cm). An analysis of variance showed that the effects of rotation speed and mode of rotation on both U and htp were significant ( p < 0.05). However, the effect of radius of rotation was significant only with U. These factors also affected the calculated process times for achieving an accumulated lethality ( Fo) of 10 min at the particle center and in the can liquid in a similar fashion. In general, U and hfp values associated with continuous rotation were 10-40% higher than those associated with oscillatory rotation.

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Wang, Longfei, Songtao Wang, Xun Zhou, Fengbo Wen, and Zhongqi Wang. "Numerical Prediction of 45° Angled Ribs Effects on U-shaped Channels Heat Transfer and Flow under Multi Conditions." International Journal of Turbo & Jet-Engines 37, no. 1 (March 26, 2020): 41–59. http://dx.doi.org/10.1515/tjj-2017-0008.

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AbstractRibs effects on the heat transfer performance and cooling air flow characteristics in various aspect ratios (AR) U-shaped channels under different working conditions are numerically investigated. The ribs angle and channel orientation are 45° and 90°, respectively, and the aspect ratios are 1:2, 1:1, 2:1. The inlet Reynolds number changes from 1e4 to 4e4 and rotational speeds include 0, 550 rpm, 1,100 rpm. Local heat transfer coefficient, endwall surface heat transfer coefficient ratio and augmentation factor are the three primary criteria to measure channel heat transfer. Ribs increase the heat transfer area and improve heat transfer coefficient of ribbed surfaces significantly, especially in the 1st pass, while the endwall surface contributes more to channel heat transfer because of the larger area and relatively smaller heat transfer coefficient. The wide channel (AR =2:1) owns the better augmentation factor than the narrow channel (AR =1:2) and ribs heat transfer weight increases with an increase of the inlet Reynolds number. Rotating slightly reduces the ribs heat transfer weight in channel and the trailing surface in 1st pass is the main influence object of rotating.

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Dai, Chuan Shan, Shuai Wang, and Wei Xing Qin. "U-Tube Diameter Dependence of Heat Output for Borehole Heat Exchangers." Applied Mechanics and Materials 170-173 (May 2012): 2613–16. http://dx.doi.org/10.4028/www.scientific.net/amm.170-173.2613.

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The heat output for borehole heat exchangers due to the variation of U-tube diameter was theoretically analyzed using the steady heat conduction model of a hollow cylinder. In the present model, except of the U-tube diameter, the other influencing factors on the heat output, such as the heat transfer coefficient inside U-tube, tube thickness and thermal conductivity, have been taken into account.

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Cui, Yu Zhou. "Analysis on Heat Transfer Energy Efficiency of U-Tube Buried Pipe under Variable Entering Water Temperature Conditions." Advanced Materials Research 960-961 (June 2014): 603–8. http://dx.doi.org/10.4028/www.scientific.net/amr.960-961.603.

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Taken as the carrier of heat extraction between rock-soil body and ground source heat pump systems, U-tubed pipe heat transfer efficiency was the key for ensuring the long-term and high-performance operation of ground source heat pump systems by means of improving the heat transfer effect. The efficiency coefficient, E, is defined as the ratio of the actual heat transfer capacity to the theoretically maximal heat transfer capacity from the U-tube into rock-soil body, which illustrated the effect of heat transfer ability and the variable heating or cooling loads. Aim at Variation characteristics of heat transfer coefficient of energy efficiency under the variable temperature inflow condition, decomposed into the product of the ratio of biggest buried tube heat transfer temperature difference φ and heat pump outlet water temperature difference σ. Use of u-shaped buried pipe three-dimensional heat transfer model which based on the multipole theory, the influence law of its change which caused by the construction load, buried pipe flow and the unit performance were analyzed, it can provide technical support to optimize the design of ground source heat pump system.

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Garrote, R. L., E. R. Silva, R. D. Roa, and R. A. Bertone. "Note. Overall Heat Transfer Coefficient to Canned Liquid During End-over-end Sterilisation." Food Science and Technology International 12, no. 6 (December 2006): 515–20. http://dx.doi.org/10.1177/1082013206072940.

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The overall heat transfer coefficient as a function of rotation speed (5–20rpm) was calculated for cans containing a 2% NaCl and 1.5% sucrose aqueous solution during end-over-end heat sterilisation at 120°C. The values obtained for the overall heat transfer coefficient, U (W/m2 °C), were: 544.4±85.3 at 5rpm, 710.7±24.5 at 10rpm, 760.5±17.7 at 15rpm and 941.6±22.1 at 20rpm. A correlation was developed in terms of Nusselt, rotational Reynolds and Prandtl numbers to predict U(Nu = 1.866Re0.379 Pr0.38). The characteristic dimension in Nu and Re was the diameter of the can. This correlation (R2 = 0.88) was valid for Re within the range of 3,012–14,820 and Pr within 2.02–2.63 values.

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Krasoń, Joanna, Przemysław Miąsik, Lech Lichołai, Bernardeta Dębska, and Aleksander Starakiewicz. "Analysis of the Thermal Characteristics of a Composite Ceramic Product Filled with Phase Change Material." Buildings 9, no. 10 (October 12, 2019): 217. http://dx.doi.org/10.3390/buildings9100217.

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The article presents a comparative analysis carried out using three methods, determining the heat transfer coefficient U for a ceramic product modified with a phase change material (PCM). The purpose of the article is to determine the convergence of the resulting thermal characteristics, obtained using the experimental method, numerical simulation, and standard calculation method according to the requirements of PN-EN ISO 6946. The heat transfer coefficient is one of the basic parameters characterizing the thermal insulation of a building partition. Most often, for the thermal characteristics of the partition, we obtain from the manufacturer the value of the thermal conductivity coefficient λ for individual homogeneous materials or the heat transfer coefficient U for the finished (prefabricated) partition. In the case of a designed composite element modified with a phase change material or other material, it is not possible to obtain direct information on the above parameter. In such a case, one of the methods presented in this article should be used to determine the U factor. The U factor in all analyses was determined in stationary conditions. Research has shown a significant convergence of the resulting value of the heat transfer coefficient obtained by the assumed methods. Thanks to obtaining similar values, it is possible to continue tests of thermal characteristics of partitions by means of numerical simulation, limiting the number of experimental tests (due to the longer test time required) in assumed different partition configurations, in stationary and dynamic conditions.

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Alagha, Mohamed Sobhi, Botond Szucs, and Pal Szentannai. "Numerical study of mixing and heat transfer of SRF particles in a bubbling fluidized bed." Journal of Thermal Analysis and Calorimetry 142, no. 2 (December 13, 2019): 1087–96. http://dx.doi.org/10.1007/s10973-019-09135-2.

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AbstractIn this article, numerical investigations on mixing and heat transfer of solid refused fuel (SRF) particles in a bubbling fluidized bed are carried out. The numerical model is based on the Eulerian–Eulerian approach with empirical submodels representing gas–solid and solid–solid interactions. The model is verified by experimental data from the literature. The experimental data include SRF vertical distribution in SRF–sand mixtures of different sand particle sizes ($$d_{\mathrm{pm}} = 654,810$$ d pm = 654 , 810 and 1110 $$\upmu$$ μ m) at different fluidization velocities ($$u/u_{\mathrm{mf}} = 1.2$$ u / u mf = 1.2 –2.0). We proposed magnification of drag force exerted by the gas on SRF particles based on Haider and Levenspiel (Powder Technol 58(1):63–70, 1989) drag coefficient. The proposed model shows good agreement with the experimental data at high fluidization velocities ( $$u/u_{\mathrm{mf}} = 1.5$$ u / u mf = 1.5 –2.0) and poor predictions at low fluidization velocities ($$u/u_{\mathrm{mf}} = 1.2$$ u / u mf = 1.2 –1.5). Heat transfer results showed that the present model is valid and gives good agreement with the experimental data of wall–bed heat transfer coefficient.

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Yu, Guo Qing, Gang Feng Gao, and Xin Feng Lin. "Identification of Building Envelope Overall Coefficient of Heat Transfer Using Recursive Least Squares Algorithm." Advanced Materials Research 250-253 (May 2011): 3239–44. http://dx.doi.org/10.4028/www.scientific.net/amr.250-253.3239.

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This paper introduces the methodology and procedures of identification of overall coefficient of heat transfer (U-factor) of building envelopes using recursive least squares algorithm and dynamic heat transfer data. Application this method to three types of typical to examine the correctness and feasibility of this method. The following conclusions can be obtained: 1) Identification of U-factor of building envelopes using recursive least squares algorithm is feasible for engineering purpose, the identified U-factor can be near to its real value; 2)The testing periods can be much shorter than the steady testing; 3)The identification error is associated with the thermal inertia. The error is larger as the thermal inertia of building envelope is large within the same testing circumstances.

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Andrzejczyk, Rafal, Tomasz Muszynski, and Przemysław Kozak. "Experimental investigation on straight and u-bend double tube heat exchanger with active and passive enhancement methods." MATEC Web of Conferences 240 (2018): 02001. http://dx.doi.org/10.1051/matecconf/201824002001.

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Authors in this work want to demonstrate the possibility to increase the heat transfer efficiency by using simple wire coil inserts to create turbulent flow in the boundary layer as well as air blowing into the annulus of the pipe. In the study, Wilson plot approach was applied in order to estimate heat transfer coefficients for all heat exchanger (HX) configurations. The study focuses on experimental values of heat transfer coefficient (HTC) and pressure drops. The primary objectives of the work are to: I. Provide an experimental comprehensive database for HTC and pressure drops; II. Analysis effect of different flow conditions e.g. water mass flow rate, the void fraction on heat transfer and hydraulic performance of tested elements. III. Compare influences of both passive and active methods at the efficiency of simple heat exchangers constructions; IV. Validation experimental results with selected experimental models from the open literature.

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Rasheed, Adnan, Jong W. Lee, and Hyun W. Lee. "Development of a model to calculate the overall heat transfer coefficient of greenhouse covers." Spanish Journal of Agricultural Research 15, no. 4 (February 7, 2018): e0208. http://dx.doi.org/10.5424/sjar/2017154-10777.

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A Building Energy Simulation (BES) model based on TRNSYS, was developed to investigate the overall heat transfer coefficient (U-value) of greenhouse covers including polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), and horticultural glass (HG). This was used to determine the influences of inside-to-outside temperature difference, wind speed, and night sky radiation on the U-values of these materials. The model was calibrated using published values of the inside and outside convective heat transfer coefficients. Validation of the model was demonstrated by the agreement between the computed and experimental results for a single-layer PE film. The results from the BES model showed significant changes in U-value in response to variations in weather parameters and the use of single or double layer greenhouse covers. It was found that the U-value of PC, PVC, and HG was 9%, 4%, and 15% lower, respectively, than that for PE. In addition, by using double glazing a 34% reduction in heat loss was noted. For the given temperature U-value increases as wind speed increases. The slopes at the temperature differences of 20, 30, 40, and 50 °C, were approximately 0.3, 0.5, 0.7, and 0.9, respectively. The results agree with those put forward by other researchers. Hence, the presented model is reliable and can play a valuable role in future work on greenhouse energy modelling.

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Jung, Gun, Geun Oh, Chul Chung, and Han Kim. "Heat transfer on grooved high density poly ethylene tube for surface water source heat pump." Thermal Science 18, no. 4 (2014): 1327–41. http://dx.doi.org/10.2298/tsci130513017j.

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High density polyethylene (HDPE) tube has been successfully utilized in surface water source heat pump (SWSHP) system as a surface water heat exchanger (SWHE). Since the heat transfer coefficient (U value) of the HDPE tube directly affects performance and energy efficiency of SWSHP, this research aims to increase U value of HDPE tube by grooving external surface of conventional 32A HDPE tube to reducing cross sectional volume. The final shape of grooved HDPE tube is similar to that of fin. In order to verify the performance of grooved HDPE tube, the U values of grooved and smooth tube were compared experimentally. According to the results, U value of grooved tube showed approximately 21.5% increase with natural convection and 23.5% with forced convection system than U values obtained from smooth tube. The reason for such increase in U value was found to be the reduction in cross sectional volume of the HDPE tube.

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12

Alammar, Khalid. "Turbulent flow and heat transfer characteristics in U-tubes: A numerical study." Thermal Science 13, no. 4 (2009): 175–81. http://dx.doi.org/10.2298/tsci0904175a.

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Using the standard k-e model, 3-dimensional turbulent flow and heat transfer characteristics in U-tubes are investigated. Uncertainty is approximated using experimental correlations and grid independence study. Increasing the Dean number is shown to intensify a secondary flow within the curved section. The overall Nusselt number for the tube is found to decrease substantially relative to straight tubes, while the overall skin friction coefficient remains practically unaffected. Local skin friction coefficient, Nusselt number, and wall temperature along the tube wall are presented.

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Iacovides, Hector, David C. Jackson, George Kelemenis, and Brian E. Launder. "The Measurement of Local Wall Heat Transfer in Stationary U-Ducts of Strong Curvature, With Smooth and Rib-Roughened Walls." Journal of Turbomachinery 122, no. 2 (February 1, 1999): 386–92. http://dx.doi.org/10.1115/1.555459.

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The paper presents some of our recent experimental investigations of convective heat transfer in flow through stationary passages relevant to gas turbine blade-cooling applications. The main objective of this effort is to produce local heat transfer data for CFD validation. Local Nusselt number measurements in flows through round-ended U-bends of square cross section, with and without artificial wall roughness, are presented. Our earlier LDA measurements of flows through these passages are first briefly reviewed and then the liquid-crystal technique for the measurement of local wall heat transfer inside passages of complex geometries is presented. Tightly curved U-bends generate strong secondary motion and cause flow separation at the bend exit, which substantially raise turbulence levels. Wall heat transfer is significantly increased, especially immediately downstream of the U-bend, where it is over two times higher than in a straight duct. The local heat transfer coefficient around the perimeter of the passage is also found to vary considerably because of the curvature-induced secondary motion. The introduction of surface ribs results in a further increase in turbulence levels, a reduction in the size of the curvature-induced separation bubble, and a complex flow development after the bend exit with additional separation regions along the outer wall. Heat transfer levels in the straight sections are more than doubled by the introduction of ribs. The effects of the bend on the overall levels of Nusselt number are not as strong as in the smooth U-bend, but are still significant. The effects of the bend on the perimetral variation of local heat transfer coefficients within the ribbed downstream section are also substantial. [S0889-504X(00)00802-3]

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Yam, Kah Wei, Khar San Teh, Patrick Loi, and David W. Yarbrough. "Reflective insulation assemblies for above-ceiling applications." Journal of Building Physics 44, no. 3 (May 5, 2020): 272–83. http://dx.doi.org/10.1177/1744259120914644.

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Previously published hot-box data have been used to construct equations for the thermal resistance of enclosed reflective air spaces (reflective insulation assemblies) for a wide range of temperatures, air gap dimensions, thermal emittances, and heat flow directions. The thermal resistances or R-values (RSI) calculated with the equations compare favorably with previously published thermal resistances. Significant differences from RSI values (m2 K/W) calculated using ISO 6946 were observed. Equations for calculating heat transfer coefficients for conduction–convection with constants for the heat flow directions up, 45° up, horizontal, 45° down, and down are contained in this article. The conduction–convection coefficient for planar air spaces oriented at any angle and heated above can be obtained by interpolation between heat flow down and heat flow at a downward angle of 45° or heat flow down at an angle of 45° and horizontal heat flow. The overall heat transfer coefficient is obtained by adding the thermal radiation contribution to the conduction–convection contribution. The RSI of enclosed reflective air spaces is the reciprocal of the overall heat transfer coefficient for the air space. This air space RSI is especially useful as input for the calculation of U-values for ceiling–roof assemblies located in hot climates.

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Krzywanski. "Heat Transfer Performance in a Superheater of an Industrial CFBC Using Fuzzy Logic-Based Methods." Entropy 21, no. 10 (September 20, 2019): 919. http://dx.doi.org/10.3390/e21100919.

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The heat transfer coefficient in the combustion chamber of industrial circulating flidized bed (CFB) boilers depends on many parameters as it is a result of multifactorial mechanisms proceeding in the furnace. Therefore, the development of an effective modeling tool, which allows for predicting the heat transfer coefficient is interesting as well as a timely subject, of high practical significance. The present paper deals with an innovative application of fuzzy logic-based (FL) method for the prediction of a heat transfer coefficient for superheaters of fluidized-bed boilers, especially circulating fluidized-bed combustors (CFBC). The approach deals with the modeling of heat transfer for the Omega Superheater, incorporated into the reaction chamber of an industrial 670 t/h CFBC. The height above the grid, bed temperature and voidage and temperature, gas velocity, and the boiler’s load constitute inputs. The developed Fuzzy Logic Heat (FLHeat) model predicts the local overall heat transfer coefficient of the Omega Superheater. The model is in good agreement with the measured data. The highest overall heat transfer coefficient is equal 220 W/(m2K) and can be achieved by the SH I superheater for the following inputs l = 20 m, tb = 900 °C, v = 0.95, u = 7 m/s, M-C-R = 100%. The proposed technique is an effective strategy and an option for other procedures of heat transfer coefficient evaluation.

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Hsieh, Shou-Shing, and Hsiu-Cheng Liao. "Local Heat Transfer and Pressure Drop in a Rotating Two-Pass Ribbed Rectangular Channel." International Journal of Rotating Machinery 7, no. 3 (2001): 183–94. http://dx.doi.org/10.1155/s1023621x01000173.

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The influences of rotation and uneven heating condition as well as passage aspect ratio on the local heat transfer coefficient and pressure drop in a rotating, two pass ribroughened (rib heighte/DH≈0.27; rib pitchp/e=8) rectangular channel with a crosssection aspect ratio of 3 was studied for Reynolds numbers from 5000 to 25,000 and rotation numbers from 0 to 0.24. Regionally averaged Nusselt number variations along the duct have been determined over the trailing and leading surfaces for two pass straight channels and U-bend region. Implementing with the data from Hsieh and Liu (1996) forAR=1and 1.5 withp/e=5ande/DH=0.17and 0.20, passage aspect ratio effect was further examined. Furthermore, data for180∘U-bend region with ribroughened turbulator on heat transfer were also measured. It was found that a complicated three-dimensional accelerated flow and secondary flow in this U-bend region caused higher heat transfer on both leading/trailing walls. Enhancement performance ratios are also presented and discussed. Results again indicate a slight decrease in heat transfer coefficient for an increase in passage aspect ratio as compared to those of previous studies.

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Hu, Ping Fang, Zhong Yi Yu, Fei Lei, Na Zhu, Qi Ming Sun, and Xu Dong Yuan. "Performance Evaluation of a Vertical U-Tube Ground Heat Exchanger Using a Numerical Simulation Approach." Advanced Materials Research 724-725 (August 2013): 909–15. http://dx.doi.org/10.4028/www.scientific.net/amr.724-725.909.

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A vertical U-tube ground heat exchanger can be utilized to exchange heat with the soil in ground source heat pump systems. The outlet temperature of the working fluid through the U-tube not only accounts for heat transfer capacity of a ground heat exchanger, but also greatly affects the operational efficiency of heat pump units, which is an important characteristic parameter of heat transfer process. It is quantified by defining a thermal effectiveness coefficient. The performance evaluation is performed with a three dimensional numerical model using a finite volume technique. A dynamic simulation was conducted to analyze the thermal effectiveness as a function of soil thermal properties, backfill material properties, separation distance between the two tube legs, borehole depth and flow velocity of the working fluid. The influence of important characteristic parameters on the heat transfer performance of vertical U-tube ground heat exchangers is investigated, which may provide the references for the design of ground source heat pump systems in practice.

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Jamiru, Tamba, Oludaisi Adekomaya, Rotimi Sadiku, and Zhongie Huan. "Analysis of Overall Heat Transfer Coefficient of Composite Panels for Thermal Insulation." Applied Mechanics and Materials 864 (April 2017): 179–83. http://dx.doi.org/10.4028/www.scientific.net/amm.864.179.

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Heat infiltration through the external wall of refrigerated vehicles has been a concern to food industries considering high thermal load required to sustain unbroken cold chain. In this research, experiments were carried out with known fibres contents laid out at various orientations and the effect on the heat transfer measured. The results indicate that the estimated overall heat transfer coefficient of the composite reinforced with 10%wt. of fibre at 0o orientation (G10E) offers the lowest U value of 0.386950 W/m2K and 0.196680 W/m2K for 50 mm and 100 mm insulation thicknesses respectively. The effect of fiber orientation in the composite panel in energy saving was to a large extent minimal when compared to the un-oriented composite panel

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Vafai, Kambiz, Ambreen Afsar Khan, Saba Sajjad, and Rahmat Ellahi. "The Study of Peristaltic Motion of Third Grade Fluid under the Effects of Hall Current and Heat Transfer." Zeitschrift für Naturforschung A 70, no. 4 (April 1, 2015): 281–93. http://dx.doi.org/10.1515/zna-2014-0330.

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AbstractThis article is concerned with the peristaltic pumping of an incompressible, electrically conducting third grade fluid in a uniform channel. The Hall effect under the influence of wall properties and heat transfer is taken into account. Mathematical modelling is based upon continuity, momentum, and energy equations. Closed form solutions for velocity, temperature, concentration, and heat transfer coefficient are obtained. Effects of pertinent parameters, such as third grade parameter Γ, Hall parameter M, amplitude ratio ε, Brickman number Br, Soret number Sc, wall tension E1 and elasticity parameters E2 and E3 on the velocity u, temperature θ, concentration φ, and heat transfer coefficient Z, are discussed through graphs.

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Alkhalidi, Ammar, Suhil Kiwan, and Haya Hamasha. "A Comparative Study between Jordanian Overall Heat Transfer Coefficient (U-Value) and International Building Codes, With Thermal Bridges Effect Investigation." Sustainable Development Research 3, no. 1 (January 12, 2021): p10. http://dx.doi.org/10.30560/sdr.v3n1p10.

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Depletion of fossil fuel and the environmental effect associated with the use of it have made the topic of “thermal insulation regulations” a major concern in country Jordan and worldwide. This paper reviews the overall heat transfer coefficient U-value in Jordanian code for the building envelope, which represents how much the building envelope transfer heat to the outside environment. U-value was reviewed with respect to the following factors, heating degree days, the heating load required to achieve thermal comfort. Based on the review a new U-value of 0.65 W/m2.K was proposed and it was found that this value reduces the energy demand almost 50%. Moreover, the thermal bridge effect was investigated and it was found that an obvious increase in the U-value is present when having thermal bridges; this will affect the energy demand, almost 200%.

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Guan, Chang Sheng, and Zhao Wan. "The Simulation Study on Buried Ground-Source Heat Pipe Transient Temperature Field Distribution." Advanced Materials Research 383-390 (November 2011): 6621–25. http://dx.doi.org/10.4028/www.scientific.net/amr.383-390.6621.

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In order to provides the theory basis for the optimization design of ground source heat pump underground U-shaped buried tube, ANSYS software was used to simulate the temperature field distribution of GSHP buried tube summer cooling process. The dynamic simulation was base on analyzing the GSHP heat exchanger unsteady heat transfer model. Comparing the temperature field distribution radius in different soil heat transfer rate, the simulation results show that the buried tube heat transfer efficiency increases with soil coefficient of thermal conductivity, soil hot effect radius increased over time and tend to be gentle.

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Flimel, Marián. "Differences U_g - Values of Glazing Measured In Situ with the Influence Factors of the Internal Environment." Advanced Materials Research 649 (January 2013): 61–64. http://dx.doi.org/10.4028/www.scientific.net/amr.649.61.

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This paper presented the results of experiments to determine Ug values of heat transfer coefficient on glazed window in the apartment block during heating period. For assessing the values of heat transfer coefficient of the window glazing was used heat flow measurements. Measurements are performed with optimal conditions (without the internal effects of environment) and the other hand with real conditions, when factors such as noise or artificial light affect on the construction of the glazing. Differences Ug - values is demonstrated by comparing the partial results due to transformation of noise and luminous energy from an internal environment to the heat flow in window glazing.

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Zhu, Lingbo, Yiping Lu, Jianfei Tong, Tianjiao Liang, Youlian Lu, Weida Fu, Bin Wang, and Yunan Zhang. "Sensitivity Analysis of Influencing Factors of Supercritical Methane Flow and Heat Transfer in a U-Tube." Energies 14, no. 18 (September 10, 2021): 5714. http://dx.doi.org/10.3390/en14185714.

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Due to the existence of a Dean vortex in a U-tube, the flow and heat transfer process of supercritical methane is complex, and its thermophysical property are greatly influenced by different factors. Based on computational fluid dynamics theory, the numerical simulation of the turbulent flow and heat transfer characteristics of supercritical methane in a U-tube with an inner diameter of 10 mm and a radius of curvature of 27 mm carried out by using the finite volume method. On the basis of verifying the reliability of the model, the influences of inlet mass flux (G), heat flux on the tube wall boundary (q), pressure on the outlet (P), and gravity acceleration factors (g) on heat transfer characteristics were analyzed. The calculation results show that the sensitivity of the effects of G, q, P, and g on the heat transfer coefficient is, from large to small, in the order of P, G, g, and q. Compared with a horizontal straight tube, a U-tube can significantly improve heat transfer in the elbow part, but the presence of the elbow reduces heat transfer in the subsequent straight pipe section. The research in this paper has significance as a reference for the construction of the LNG gasification process.

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Zhang, Dan, Fa Hui Wang, Bo Lei, Yan Ping Yuan, and Xiao Ling Cao. "Study on Heat Transfer Capacity Calculation of Multi-Hole Heat Source for Vertical U-Tube Ground Heat Exchangers." Applied Mechanics and Materials 71-78 (July 2011): 94–99. http://dx.doi.org/10.4028/www.scientific.net/amm.71-78.94.

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By studying the features of vertical u-tube ground heat exchangers, with the consideration of the mutual interference between heat exchanger wells on heat transfer, this thesis puts forward the numerical model and calculation method for the heat exchange study of the well group, on the basis of analyzing heat exchange for single well. The paper adopts a nine-well model which is convenient and represents the general patterns of the heat exchange between well groups. The amount of the heat exchange between well groups can be calculated through testing the heat exchange of the single well by means of the heat exchange correction coefficient.

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Maciejewski, P. K., and R. J. Moffat. "Heat Transfer With Very High Free-Stream Turbulence: Part II—Analysis of Results." Journal of Heat Transfer 114, no. 4 (November 1, 1992): 834–39. http://dx.doi.org/10.1115/1.2911890.

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Correlations describing the effect of free-stream turbulence on heat transfer have been offered by Simonich and Bradshaw (1978), Pedisius et al. (1983), and Blair (1983a), but they fail to describe the present data. The present data can be represented by a function of St, St/St0, ReΔ2Tu, and Λ/Δ2 within ±20 percent, but equally well by a simple correlation relating the rms fluctuating velocity in the free stream, u′, to the heat transfer coefficient, h. A new Stanton number, St′, based on u′max, the maximum standard deviation in the streamwise component of velocity found in the wall affected region, collects the data of Blair (1983b), Pedisius et al. (1983), Vogel (1984), MacArthur (1986), and Hollingsworth et al. (1989), as well as the data from the present experiment, all within ± 15 percent. The fact that h can be expressed as a function of local u′ alone suggests the possibility of geometry-independent correlations for turbulent heat transfer.

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Li, Jianhua, and Wenjing Chen. "Heat Transfer Dynamic Analyses for Recycled-Concrete Wall Combined with Expanded Polystyrene Template." Advances in Materials Science and Engineering 2018 (2018): 1–7. http://dx.doi.org/10.1155/2018/9692806.

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Due to the benefits of pollution reduction, energy saving, and recycling of resources associated with the recycled concrete, together with the apparent thermal storage thermal insulation yield of expandable polystyrene (EPS) template, the heat transfer dynamics of their combination has become a contemporary study topic. In this research work, an investigation of the heat transfer coefficient (U) of EPS template recycled-concrete shear wall has been carried out. Four different concrete mixtures shear wall samples having different insulation types were developed for the purpose of quantifying their thermal outputs. Both temperature (T) and humidity (H) affection to thermal conductivity coefficient (λ) of reinforced concrete and the EPS template were investigated, correspondingly. The λ0°C (relative variation for a 0°C of temperature variation in T) of cement mortar, recycled-concrete shear wall, and ordinary concrete shear wall were measured being 0.7526, 1.2463, and 1.3750 W·m−1·K−1, respectively. And the λ calculation of EPS was carried out being 0.0396 W·m−1·K−1. A corrected calculation method was put forward to application in practical work that could reflect the real U value in a more precise manner. These results brought to light the fact that the heat preservation output of recycled-concrete shear wall posed to be comparatively more improved than that of ordinary concrete shear wall. We put forth the suggestion for the use of corrected calculation method in the calculation and analysis of U of EPS template recycled-concrete composite shear wall in the climatic conditions of Beijing. The results revealed the fact that the U of EPS template recycled-concrete shear wall was dominantly controlled by the change of thermal conductivity changes of EPS template. The monthly mean U increased with increasing Tout and decreased with decreasing Tout. The smaller the U of the enclosure wall was, the better the thermal stability of the wall was experienced.

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Dewar, H., J. Graham, and R. Brill. "STUDIES OF TROPICAL TUNA SWIMMING PERFORMANCE IN A LARGE WATER TUNNEL - THERMOREGULATION." Journal of Experimental Biology 192, no. 1 (July 1, 1994): 33–44. http://dx.doi.org/10.1242/jeb.192.1.33.

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The body temperatures (Tb) of nine yellowfin tuna (Thunnus albacares) were monitored while fish swam in a large water tunnel at controlled velocities (U) and ambient temperatures (Ta). Monitoring Tb during step changes in Ta at constant U permitted estimation of the thermal rate coefficient (k), an index of heat transfer. In the yellowfin, k is dependent on both Ta and the direction of the thermal gradient (i.e. whether Ta is greater or less than Tb). Modulation of k in response to Ta was further demonstrated during tests in which U was varied; the elevation of Tb in response to equal increases in U was 34 times less at 30 C than at 25 and 20 C. These experiments demonstrate that the yellowfin tuna can modulate heat transfer. This ability could prevent overheating during intense activity, retard heat loss during a descent into cool water and permit increased heat gain upon returning to warm surface waters (i.e. when Tb<Ta).

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Zubair, S. M., P. V. Kadaba, and R. B. Evans. "Second-Law-Based Thermoeconomic Optimization of Two-Phase Heat Exchangers." Journal of Heat Transfer 109, no. 2 (May 1, 1987): 287–94. http://dx.doi.org/10.1115/1.3248078.

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This paper presents a closed-form analytical method for the second-law-based thermoeconomic optimization of two-phase heat exchangers used as condensers or evaporators. The concept of “internal economy” as a means of estimating the economic value of entropy generated (due to finite temperature difference heat transfer and pressure drops) has been proposed, thus permitting the engineer to trade the cost of entropy generation in the heat exchanger against its capital expenditure. Results are presented in terms of the optimum heat exchanger area as a function of the exit/inlet temperature ratio of the coolant, unit cost of energy dissipated, and the optimum overall heat transfer coefficient. The total heat transfer resistance represented by (1/U = C1 + C2 Re−n) in the present analysis is patterned after Wilson (1915) which accommodates the complexities associated with the determination of the two-phase heat transfer coefficient and the buildup of surface scaling resistances. The analysis of a water-cooled condenser and an air-cooled evaporator is presented with supporting numerical examples which are based on the thermoeconomic optimization procedure of this paper.

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Abrahamson, S. D., and J. K. Eaton. "Heat Transfer Through a Pressure-Driven Three-Dimensional Boundary Layer." Journal of Heat Transfer 113, no. 2 (May 1, 1991): 355–62. http://dx.doi.org/10.1115/1.2910569.

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An experimental investigation of heat transfer through a three-dimensional boundary layer has been performed. An initially two-dimensional boundary layer was made three dimensional by a transverse pressure gradient caused by a wedge obstruction, which turned the boundary layer within the plane of the main flow. Two cases, with similar streamwise pressure gradients and different lateral gradients, were studied so that the effect of the lateral gradient on heat transfer could be deduced. The velocity flowfield agreed with previous hydrodynamic investigations of this flow. The outer parts of the mean velocity profiles were shown to agree with the Squire-Winter theorem for rapidly turned flows. Heat transfer data were collected using a constant heat flux surface with embedded thermocouples for measuring surface temperatures. Mean fluid temperatures were obtained using a thermocouple probe. The temperature profiles, when plotted in outer scalings, showed logarithmic behavior consistent with two-dimensional flows. An integral analysis of the boundary layer equations was used to obtain a vector formulation for the enthalpy thickness, HH≜∫0∞ρuisdyρ∞ii,o(u∞2+w∞2)1/2,0,∫0∞ρwisdyρ∞is,o(u∞2+w∞2)1/2 (where is is the stagnation enthalpy), which is consistent with the scalar formulation used for two-dimensional flows. Using the vector formulation, the heat transfer data agreed with standard two-dimensional correlations of the Stanton number and enthalpy thickness Reynolds number. It was concluded that although the heat transfer coefficient decreased faster than its two-dimensional counterpart, it was similar to the two-dimensional case. The vector form of the enthalpy thickness captured the rotation of the mean thermal energy flux away from the free-stream direction. Boundary layer three dimensionality increased with the strength of the transverse pressure gradient and the heat transfer coefficients were smaller for the stronger transverse gradient.

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Li, Guo Neng. "Numerical Simulation of Characteristics of Cross-Flow Heat Transfer in Pulsating Flow." Advanced Materials Research 187 (February 2011): 242–46. http://dx.doi.org/10.4028/www.scientific.net/amr.187.242.

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In order to investigate the characteristics of heat transfer in oscillating flow, the computational fluid dynamics method was employed to study the effects of pulsating flow on the heat transfer process in a cross-flow heat exchange pipe, and to analyze the underling mechanism which controls the improvement of heat transfer in pulsating flow through the distribution of temperature. Several pulsating frequencies (f=0, 5, 10, 50, 100, 150 Hz) and a wide range of pulsating amplitudes (inlet velocity u=2.0+Asin(2πft) m/s, A=0, 2, 5, 10, 15, 20 m/s) were explored to find out the best pulsating parameters for heat transfer. Results showed that pulsating flow with a low pulsating frequency (the magnitude of ~101 Hz) should be selected to obtain large heat transfer coefficient, and that pulsating flow with larger pulsating amplitude results in greater heat transfer coefficient. On the other hand, results revealed that only a limited length of the cross-flow exchange pipe was affected by the pulsating flow compared to the whole length, and that the affected length is longer with lower pulsating frequency and larger pulsating amplitude.

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Lalovic, Milisav, Zarko Radovic, and Nada Jaukovic. "Characteristics of heat flow in recuperative heat exchangers." Chemical Industry 59, no. 9-10 (2005): 270–74. http://dx.doi.org/10.2298/hemind0510270l.

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A simplified model of heat flow in cross-flow tube recuperative heat exchangers (recuperators) was presented in this paper. One of the purposes of this investigation was to analyze changes in the values of some parameters of heat transfer in recuperators during combustion air preheating. The logarithmic mean temperature (Atm) and overall heat transfer coefficient (U), are two basic parameters of heat flow, while the total heated area surface (A) is assumed to be constant. The results, presented as graphs and in the form of mathematical expressions, were obtained by analytical methods and using experimental data. The conditions of gaseous fuel combustions were defined by the heat value of gaseous fuel Qd = 9263.894 J.m-3, excess air ratio ?= 1.10, content of oxygen in combustion air ?(O2) = 26%Vol, the preheating temperature of combustion air (cold fluid outlet temperature) tco = 100-500?C, the inlet temperature of combustion products (hot fluid inlet temperature) thi = 600-1100?C.

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Shen, Zhongyang, Yonghui Xie, Di Zhang, and Gongnan Xie. "Numerical Calculations on Flow and Heat Transfer in Smooth and Ribbed Two-Pass Square Channels under Rotational Effects." Mathematical Problems in Engineering 2014 (2014): 1–7. http://dx.doi.org/10.1155/2014/981376.

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U-shaped channel, which is also called two-pass channel, commonly exists in gas turbine internal coolant passages. Ribbed walls are frequently adopted in internal passage to enhance the heat transfer. Considering the rotational condition of gas turbine blade on operation, the effect of rotation is also investigated for the coolant channel which is close to real operation condition. Thus, the objective of this study is to discuss the effect of rotation on fluid flow and heat transfer performance of U-shaped channel with ribbed walls under high rotational numbers. Investigated Reynolds number is Re=12500and the rotation numbers areRob=0.4and 0.6. In the results, the spatially heat transfer coefficient distributions are exhibited to discuss the effect of rotation and roughened walls. It is found that ribbed walls enhance the heat transfer rate significantly. Under the rotational condition, theNuin the first pass with outward flow is increased while that in the second pass is decreased. Finally, averageNuratio, friction ratio, and thermal performance are all presented to discuss the thermal characteristics.

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Kim, Hyung-Kweon, Young-Sun Ryou, Young-Hwa Kim, Tae-Seok Lee, Sung-Sik Oh, and Yong-Hyeon Kim. "Estimating the Thermal Properties of the Cover and the Floor in a Plastic Greenhouse." Energies 14, no. 7 (April 2, 2021): 1970. http://dx.doi.org/10.3390/en14071970.

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This study comprehensively analyzed the heat loss and total heat transfer coefficient (U-value) of a single-span experimental plastic greenhouse covered with a double layer of 0.1 mm thick polyethylene. The air temperature and heat flux (W m−2) of the greenhouse components were measured from 18:00 to 06:00, and the energy balance equations under steady-state conditions were determined. The heat flux and U-value of the roof, sides, front and rear, and floor of the greenhouse were determined and compared. The results showed that these values for the roof play an important role in determining the heat load in the greenhouse, and that the average heat transfer through the floor is very small. The average U-value of the greenhouse cover is a comprehensive value which takes the U-values of the roof, sides, and front and rear into account through the use of an area–weighted average method. Finally, an average U-value of 3.69 W m−2 °C −1 was obtained through the analysis of the variations in the U-value, as it is related to the difference in air temperature between the interior and exterior of the greenhouse, as well as to the outdoor wind speed. The relationships between the average U-value and those of the roof, sides, and front and rear of the experimental greenhouse were modeled, and were shown to have a highly linear relationship.

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Sourtiji, Ehsan, and Mofid Gorji-Bandpy. "Numerical analysis of mixed convection characteristics inside a ventilated cavity including the effects of nanoparticle suspensions." Thermal Science 21, no. 5 (2017): 2205–15. http://dx.doi.org/10.2298/tsci130804001s.

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A numerical study of mixed convection flow and heat transfer inside a square cavity with inlet and outlet ports is performed. The position of the inlet port is fixed but the location of the outlet port is varied along the four walls of the cavity to investigate the best position corresponding to maximum heat transfer rate and minimum pressure drop in the cavity. It is seen that the overall Nusselt number and pressure drop coefficient vary drastically depending on the Reynolds and Richardson numbers and the position of the outlet port. As the Richardson number increases, the overall Nusselt number generally rises for all cases investigated. It is deduced that placing the outlet port on the right side of the top wall is the best position that leads to the greatest overall Nusselt number and lower pressure drop coefficient. Finally, the effects of nanoparticles on heat transfer are investigated for the best position of the outlet port. It is found that an enhancement of heat transfer and pressure drop is seen in the presence of nanoparticles and augments with solid volume fraction of the nanofluid. It is also observed that the effects of nanoparticles on heat transfer at low Richardson numbers is more than that of high Richardson numbers. This article has been retracted. Link to the retraction <a href="http://dx.doi.org/10.2298/TSCI190625278E">10.2298/TSCI190625278E</a>

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Nor Zanariah, Safiei, Mohamed Nor Noor Naimah, Norzita Ngadi, Zaki Yamani Zakaria, and Jusoh Mazura. "Progressive Freeze Concentration of Coconut Water: Effect of Coolant Temperature on Process Efficiency and Heat Transfer." Applied Mechanics and Materials 695 (November 2014): 447–50. http://dx.doi.org/10.4028/www.scientific.net/amm.695.447.

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In this research, coconut water was concentrated by applying progressive freeze concentration (PFC) using coil crystallizer. Overall heat transfer coefficient (U) was analyzed from the process by varying different coolant temperature values since both of them are closely related. In this case, heat transfer efficiency depends strongly on ice crystal formed on the inner cooled surface and is explained theoretically from that angle. At optimum flowrate, operation time and initial concentration best results were observed at-10oC of coolant temperature where the concentration efficiency and effective partition constant (K) obtained were 48% and 0.2 respectively. Meanwhile, U obtained at the first and second stages were 183.0046 W/m2oC but dropped at lower value at later stage at 154.9625 W/m2oC due to ice fouling.

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Aguilar Osorio, Rita, and K. Cliffle. "Experimental and Theoretical Research of the Shell Side Heat Transfer Coefficient and Pressure Drop in a Plastic Shell and Tube Heat Exchanger." Defect and Diffusion Forum 312-315 (April 2011): 187–92. http://dx.doi.org/10.4028/www.scientific.net/ddf.312-315.187.

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The aim of this work is to present an experimental research of the shell side heat transfer coefficient and pressure drop in a plastic shell and tube heat exchanger with single segmental baffle. The tube bundle consisted of 110 U-tubes constructed of high-density polyethylene, the inside diameter was 9.2 mm, the tube pitch was 1.5 the out side diameter. The shell was constructed of polypropylene with a diameter of 315 mm. Shell side heat transfer coefficients and pressure drop were determined varying the flow rates. An experimental rig for the experimental research was designed and constructed. The overall experimental rig consisted of two operation cycles. The two fluids used in this system were hot and cold water. The experimental results were compared with theoretical predictions using the Bell-Taborek and Wills and Johnston Methods. The heat transfer coefficient predictions, for Reynolds number greater than 780, showed that the Bell-Taborek and Wills-Johnston methods are in general agreement with the experimental data with only 5% difference, Wills-Johnston overpredicts it and Bell underpredicts it, except at the lower Reynolds number than 780 where there was an average underprediction of 15%. The pressure drop predictions by Wills-Johnston and Bell-Taborek methods were generally acceptable including the inlet and outlet nozzles with the highest experimental data (Reynolds number greater than 780) within a 15% overprediction, however, at the lower data the pressure drop was overpredicted up to 2 times the measured values.

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Ahmad, Naveed, Christian Ghiaus, and Moomal Qureshi. "Error Analysis of QUB Method in Non-Ideal Conditions during the Experiment." Energies 13, no. 13 (July 2, 2020): 3398. http://dx.doi.org/10.3390/en13133398.

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Overall heat transfer coefficient, also known as the intrinsic performance measurement of the building, determines the amount of heat lost by a building due to temperature difference between indoor and outdoor. QUB (Quick U-value of Buildings) is a short-term method for measuring the overall heat transfer coefficient of buildings. The test involves heating and cooling the house with a power step and measuring the indoor temperature response in a single night. Ideally, the outdoor temperature during QUB experiment should remain constant. To compare the influence of variable outdoor temperature, the QUB experiments are simulated on a well-calibrated model with real weather conditions. The experiments at varying outdoor temperature and constant outdoor temperature during the night show that the results in both conditions are nearly similar. A ±2 °C increase or decrease in the outdoor temperature during the QUB experiment can change the results in the measured overall heat transfer coefficient by ±5%. QUB experiments simulated during the months of winter show that the majority of results are ±15% of the steady-state overall heat transfer coefficient. The QUB results during the months of summer show relatively large variation. The large errors coincide with the small temperature difference between indoor and outdoor temperatures before the start of QUB experiment. The median error of multiple QUB experiments during summer can be reduced by increasing the setpoint temperature before the start of QUB experiment.

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Baughn, J. W., H. Iacovides, D. C. Jackson, and B. E. Launder. "Local Heat Transfer Measurements in Turbulent Flow Around a 180-deg Pipe Bend." Journal of Heat Transfer 109, no. 1 (February 1, 1987): 43–48. http://dx.doi.org/10.1115/1.3248065.

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The paper reports extensive connective heat transfer data for turbulent flow of air around a U-bend with a ratio of bend radius:pipe diameter of 3.375:1. Experiments cover Reynolds numbers from 2 × 104 to 1.1 × 105. Measurements of local heat transfer coefficient are made at six stations and at five circumferential positions at each station. At Re = 6 × 104 a detailed mapping of the temperature field within the air is made at the same stations. The experiment duplicates the flow configuration for which Azzola and Humphrey [3] have recently reported laser-Doppler measurements of the mean and turbulent velocity field. The measurements show a strong augmentation of heat transfer coefficient on the outside of the bend and relatively low levels on the inside associated with the combined effects of secondary flow and the amplification/suppression of turbulent mixing by streamline curvature. The peak level of Nu occurs halfway around the bend at which position the heat transfer coefficient on the outside is about three times that on the inside. Another feature of interest is that a strongly nonuniform Nu persists six diameters downstream of the bend even though secondary flow and streamline curvature are negligible there. At the entry to the bend there are signs of partial laminarization on the inside of the bend, an effect that is more pronounced at lower Reynolds numbers.

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Bai, Li, and Tan Liu. "Analysis of Dirt Resistance Based on the Double-Pipe Device." Advanced Materials Research 671-674 (March 2013): 2563–66. http://dx.doi.org/10.4028/www.scientific.net/amr.671-674.2563.

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The double-pipe heat exchanger device is used for simulating sewage water heat exchanger. The double-pipe heat exchanger system with the sewage water flow in the inner tube and intermediary (tap) water flow in the annular tube. The pt100 thermometer measure inlet and outlet temperature of sewage water and intermediary water. According the debugging temperature data, the error of double-pipe device heat transfer coefficient ΔU/U≤±20%.It is proved that the double-pipe system is feasible to monitor the fouling resistance dynamically.

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Némethová, Michaela, Jana Lendelová, Veronika Šranková, Miroslav Žitňák, and Ľubomír Botto. "Verification of Thermo-Technical Characteristics of Selected Floor Constructions for Dairy Cows (Pilot Study)." Acta Technologica Agriculturae 23, no. 2 (June 1, 2020): 87–91. http://dx.doi.org/10.2478/ata-2020-0014.

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AbstractThe purpose of this study was to theoretically and practically investigate the thermo-technical properties of two bedding surface materials under real farm conditions during the hot summer period. The study was focused on the research of cubicles with water mattresses and straw bedding for dairy cows. The results of thermal-technical calculations showed that straw belongs to the category of warm floors, the thermal effusivity value of cubicle with straw is b = 173.55 W·s1/2·m−2·K−1; the heat transfer coefficient is U = 0.36 W·m−2·K−1. Water mattress belongs to the category of cold floors with the thermal effusivity value b = 572.46 W·s1/2·m−2·K−1 and the heat transfer coefficient U = 4.504 W·m−2·K−1. On the basis of calculations, the results showed that U was 12.5 higher for water mattresses than for straw, and b was 3.3 times higher for water mattresses than for straw. Based on thermographic measurements under field conditions of dairy farm, it was observed that the surface temperature of the water mattresses after one hour of lying was lower by 4.95 ±1.88 °C in comparison to chopped straw. In practice, suitability of the material structure of water mattresses was verified on the basis of physical properties for summer period.

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yan, Dong, Dong Ji-xian, and Qiao Li-jie. "Research on Flow and Condensation Heat Transfer Coefficient of multi-channel cylinder dryer in U-shaped Section." Journal of Physics: Conference Series 1948, no. 1 (June 1, 2021): 012135. http://dx.doi.org/10.1088/1742-6596/1948/1/012135.

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Martic, Igor, Aleksandar Maslarevic, Nikola Milovanovic, and Miloš Markovic. "Effect of baffle cut and baffle spacing on pressure drop in shell and tube heat exchanger with U tubes." Technium: Romanian Journal of Applied Sciences and Technology 2, no. 2 (April 13, 2020): 72–78. http://dx.doi.org/10.47577/technium.v2i2.355.

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A general procedure for heat exchanger design has been presented in the Heat Exchanger Design Handbook (HEDH) [1], but no precise criterion for determining baffle cut nor baffle spacing has been offered, and the emphasis is only on heat exchanger’s permissible range of application. In this paper, an optimization program has been used to calculate pressure drop, fluid velocity, heat power, overall heat transfer coefficient and middle temperature difference for various baffle cut and baffle spacing for the same type of heat exchanger, using the procedure in HEDH. This could be considered as complementary to the HEDH recommendations and can be used by designers and, generally, engineers for determining the right baffle cut and baffle spacing for their specific cases.

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Ali, Asif, Lorenzo Cocchi, Alessio Picchi, and Bruno Facchini. "Experimental Determination of the Heat Transfer Coefficient of Real Cooled Geometry Using Linear Regression Method." Energies 14, no. 1 (December 31, 2020): 180. http://dx.doi.org/10.3390/en14010180.

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The scope of this work was to develop a technique based on the regression method and apply it on a real cooled geometry for measuring its internal heat transfer distribution. The proposed methodology is based upon an already available literature approach. For implementation of the methodology, the geometry is initially heated to a known steady temperature, followed by thermal transient, induced by injection of ambient air to its internal cooling system. During the thermal transient, external surface temperature of the geometry is recorded with the help of infrared camera. Then, a numerical procedure based upon a series of transient finite element analyses of the geometry is applied by using the obtained experimental data. The total test duration is divided into time steps, during which the heat flux on the internal surface is iteratively updated to target the measured external surface temperature. The final procured heat flux and internal surface temperature data of each time step is used to find the convective heat transfer coefficient via linear regression. This methodology is successfully implemented on three geometries: a circular duct, a blade with U-bend internal channel, and a cooled high pressure vane of real engine, with the help of a test rig developed at the University of Florence, Italy. The results are compared with the ones retrieved with similar approach available in the open literature, and the pros and cons of both methodologies are discussed in detail for each geometry.

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Fokaides, Paris A., and Soteris A. Kalogirou. "Application of infrared thermography for the determination of the overall heat transfer coefficient (U-Value) in building envelopes." Applied Energy 88, no. 12 (December 2011): 4358–65. http://dx.doi.org/10.1016/j.apenergy.2011.05.014.

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45

Mahmoodzadeh, Milad, Voytek Gretka, Katie Hay, Casey Steele, and Phalguni Mukhopadhyaya. "Determining overall heat transfer coefficient (U-Value) of wood-framed wall assemblies in Canada using external infrared thermography." Building and Environment 199 (July 2021): 107897. http://dx.doi.org/10.1016/j.buildenv.2021.107897.

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46

Battula, Sreedhar Rao, Keerthana Reddy Chittireddy, Meena Pullurwar, and Kishore Kumar Sriramoju. "Thermal performance of corrugated plate heat exchanger using ethylene glycol as test fluid." Journal of Mechanical and Energy Engineering 4, no. 2 (November 24, 2020): 167–72. http://dx.doi.org/10.30464/jmee.2020.4.2.167.

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This paper reports an experimental comparative thermal analysis of a flat plate heat exchanger and corrugated plate heat exchanger (CPHE) of different corrugation angles using ethylene glycol as test fluid. The experiments were carried out counter current mode using water as hot fluid at 75°C. Design of each plate provided with eleven thermocouple sensors to determine the temperatures, in which seven were used to measure the surface temperature of plate and four were used to measure the inlet and outlet bulk temperature of cold and hot fluids. The mass flow rate of test fluid, varied between 0.5 to 4 liters per minute and corresponding steady state temperatures is measured. Using experimental readings, temperature difference between the inlet and outlet streams (DT), logarithmic mean temperature difference (LMTD) and overall heat transfer coefficient (U) are determined. The obtained DT and U values of corrugation angles (300, 500) of CPHE were compared with those of flat plate heat exchangers. For corrugation angle of 30° and 50°, the DT and U values increases with increase of mass flow rate of the fluid.

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Cuce, Erdem. "Experimental and numerical investigation of a novel energy-efficient vacuum glazing technology for low-carbon buildings." Indoor and Built Environment 26, no. 1 (July 28, 2016): 44–59. http://dx.doi.org/10.1177/1420326x15599188.

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In this study, a recently developed innovative window technology called vacuum tube window is introduced, and its performance assessment is presented through an experimental and numerical research. The novel design of vacuum tube window consists of evacuated tubes surrounded by Argon as inert gas to eliminate conductive and convective effects inside the window and thus to produce a building element with remarkably low overall heat transfer coefficient (U-value). Heat transfer inside the window was modelled via a reliable commercial computational fluid dynamics software ANSYS FLUENT. The accuracy of simulations was verified by environmental chamber tests. For the vacuum tube diameter of 28 mm, an excellent agreement between experimental and numerical data was achieved. For different values of design parameters such as pane thickness, tube thickness, tube diameter and Argon gap, total heat loss and U-value of the vacuum tube window and optimum data were evaluated. Optimum tube diameter was found to be 60 mm in terms of thermal performance characteristics, cost, lightness and aesthetic issues. It is concluded that the vacuum tube window is able to provide a U-value lower than 0.40 W/m2K, which is very promising for both retrofitting of existing buildings and new-build applications.

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Poyraz, Kağan. "Passive House and Construction Standard: Example Design and Multi-Objective Optimization." Applied Mechanics and Materials 719-720 (January 2015): 177–80. http://dx.doi.org/10.4028/www.scientific.net/amm.719-720.177.

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Due to environmental and energy matters, importance of future construction trend-Passive House Design is increasing all over the world. In Europe, already recommended values for passive buildings are included in thermal insulation standards and energy regulation directives. There is a wide range of construction materials nowadays. The key point is using proper techniques by harmonizing correct practice and materials. In this regard, smart optimization set-up approach is necessary in order to achieve the most suitable design which has the lowest CO2 and SO2 values and appears as the cheapest option. The sample given in this paper is an example of an exterior wall design for residential passive houses (heat transfer coefficient (U) value through the cross section is 0,108 W/m²K). Connected with the aim of the paper, which is showing an multi-objective optimization method for choosing the best thermal insulation design in the case of that more than one projection, results of given example design in the paper is used. Simultaneously, criteria of total thickness, heat transfer coefficient (U) through the cross section, global warming potential (GWP), acid produce (AP), primary energy content (PEI) non renewable and cost in 2013 per m2 are included in “Smart optimization set-up approach diagram”.

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Rahimi-Gorji, Mohammad, Oveis Pourmehran, Mofid Gorji-Bandpy, and Davood Ganji. "The effect of variable magnetic field on heat transfer and flow analysis of unsteady squeezing nanofluid flow between parallel plates using Galerkin method." Thermal Science 21, no. 5 (2017): 2057–67. http://dx.doi.org/10.2298/tsci160524180r.

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This paper presents a thermal and flow analysis of an unsteady squeezing nanofluid flow and heat transfer using nanofluid based on Brinkman model in presence of variable magnetic field. Galerkin method is used to solve the non-linear differential equations governing the problem. Squeezing flow between parallel plates is very applicable in the many industries and it means that one or both of the parallel plates have vacillation. The effects of active parameters such as the Hartman number, squeeze number, and heat source parameter are discussed. Results for temperature distribution and velocity profile, Nusselt number, and skin friction coefficient by Galerkin method are presented. As can be seen in results, the values of Nusselt number and skin friction coefficient for CuO is better than Al2O3. Also, according to figures, as nanofluid volume fraction increases, Nusselt number increases and skin friction coefficient decreases, increase in the Hartman number results in an increase in velocity and temperature profiles and an increase in squeeze number can be associated with the decrease in the velocity. This article has been corrected. Link to the correction <a href="http://dx.doi.org/10.2298/TSCI171204246E">10.2298/TSCI171204246E</a>

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Mei, Xianzhi, Yaping Chen, Jiafeng Wu, and Xiaoyu Zhou. "Simulation on heat transfer performances of hollow tube electric heaters with dual-side longitudinal flow." Engineering Computations 37, no. 7 (February 22, 2020): 2213–27. http://dx.doi.org/10.1108/ec-01-2019-0033.

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Purpose Conventional electric heaters mostly use U-shaped electric heating tubes and the hollow tube electric heaters are new type ones that rely on the heat transfer tubes as heating elements. However, in the original design, the fluid flows through the annular gaps between the shell wall and the supporting plates, the chambers between supporting plates are generally stagnant zones. The purpose of study is to overcome these deficiencies. Design/methodology/approach A modified approach is proposed in which the heating tubes are surrounded by holes on the supporting plates, thus the stagnant flow zone can be eliminated and the heating surfaces of both inside and outside the tube can be fully used. Numerical simulations were carried out on four schemes of hollow tube electric heaters, i.e. plate blocked, countercurrent, parallel and split. The results show that the two schemes of parallel and split can reduce the temperature difference between the two sides of the fixed tube plate, and thus reduce thermal stress and prolong the service life. Findings The split scheme of electric heater has the highest comprehensive index, moderate heat transfer coefficient and minimum pressure drop on the shell side. Its average heat transfer coefficient and comprehensive index are, respectively, 15.7% and 52.9% higher and its average pressure drop and tube wall temperature are, respectively, 57.6% and 19 K lower than those of the original plate blocked scheme, thus it can be recommended as the best scheme of the hollow tube electric heaters. Originality/value Based on the original design of hollow tube electric heater with plate blocked scheme, three plate perforated schemes were proposed and investigated. The thermal and flow features of the four schemes were compared in terms of heat transfer coefficient, pressure drop and comprehensive index ho·Δpo−1/3. The split scheme can reduce the temperature difference between two sides of the fixed tube plate with reduced thermal stress. It has moderate tube wall temperature and heat transfer coefficient, the smallest shell side pressure drop and the highest comprehensive index ho·Δpo−1/3, and it can be recommended as the optimal scheme.

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Journal articles on the topic 'Heat transfer coefficient U'

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