Enhancement of shell side forced convective heat transfer in the shell tube‐type heat exchanger using thin plate‐type supports

The shell side heat transfer and pressure drop in counterflowing water were experimentally investigated on the basis of the overall heat transfer coefficient. The investigation was intended to identify ways to get higher performance for the cooler in a BWR nuclear power plant. The following three conclusions were reached in the study. (1) Predicted performance of the heat exchanger, using the overall heat transfer coefficient based on the outside area of the tube K_o, indicated an enhancement by 92% compared with the measured performance of the conventional segmental baffle‐type heat exchanger. (2) The tube side pressure drop ΔP_t=20 kPa and the shell side pressure drop ΔP_s=70 kPa were obtained, and were within the allowable value ΔP_a=80 kPa. The shell side pressure drop of the low‐pressure drop spacer could be decreased by 20% as compared with that of the standard spacer. (3) The enhancement constant of the shell side heat transfer using the low‐pressure drop spacer was about 1.2 times as large as that of the standard spacer, regardless of the pumping power. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(5): 455–471, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10097     

Prediction of heat exchanger capacity by thermal network method (Influence of thermal conduction in fins on capacity of a condenser)

This paper describes the influence of heat flow from high‐temperature refrigerant to low‐temperature refrigerant through fins by thermal conduction. To estimate that influence, we applied a thermal network method that can consider refrigerant quality distribution in the heat exchanger. At the same time, for verifying the estimation, an experiment was performed with a two‐row, two‐pass heat exchanger. Prediction shows that the heat transfer capacity of a condenser is reduced by 3% for a simple two‐row, two‐pass heat exchanger by heat conduction in fins. Comparison of experimental results and predicted results proves that the prediction error was within 1% for condenser capacity. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(2): 101–114, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20184     

Simple method to support optimization of layouts for vacuum insulation panels (VIPs) for refrigerators

We proposed a technique of analysis that supports the optimization of layouts for vacuum insulation panels (VIPs) for refrigerators, using a one‐dimensional technique of calculation to simulate the heat loss caused by VIP envelope materials. VIP thermal characteristics were described by approximating system efficiency by using the panels' average length (L_p). We compared this simplified method to three‐dimensional numerical analysis of 1 to 6µm thick, vacuum‐packed aluminum foil and 1.5 to 6 mW/mK thermally conductive heat‐insulated core materials, and verified them to be within a 1% margin of error. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(7): 451–463, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20132     

Performance Analysis of Aluminum and Graphite Foam Heat Exchangers Under Countercurrent Arrangement

Due to the increasing power requirement and the limited available space in the vehicles, a countercurrent heat exchanger (HEX) is proposed for the position on the roof of the vehicle compartment. Furthermore, a new material, graphite foam with high thermal conductivity and low density, is a potential material for HEXs in vehicles. In order to evaluate the performance of the graphite foam HEX, the CFD computational fluid dynamics (CFD) approach is applied in a comparative study between the graphite foam and the aluminum HEXs under countercurrent flow condition. The analysis is conducted for the thermal performance (heat transfer coefficient) and the pressure loss. The simulation results show that the graphite foam HEX proves higher thermal performance than the aluminum HEX. However, due to the high pressure loss in the graphite foam HEX, the coefficient of performance in the graphite foam HEX is much lower than that of the aluminum HEX. A specific case study is carried out to evaluate the performance of graphite foam HEX as well. Useful recommendations are highlighted and provided to promote the development of the countercurrent flow HEXs in vehicles.     

Performance analysis of a closed regenerated Brayton heat pump with internal irreversibilities

This paper analyses the performance of a real heat pump plant via methods of entropy generation minimization or finite‐time thermodynamics. The analytical relations between heating load and pressure ratio, and between coefficient of performance (COP) and pressure ratio of real closed regenerated Brayton heat pump cycles coupled to constant‐ and variable‐temperature heat reservoirs are derived. In the analysis, the irreversibilities include heat transfer‐irreversible losses in the hot‐ and cold‐side heat exchangers and the regenerator, the non‐isentropic expansion and compression losses in the compressor and expander, and the pressure drop loss in the pipe and system. The optimal performance characteristics of the cycle may be obtained by optimizing the distribution of heat conductances or heat transfer surface areas among the two heat exchangers and the regenerator, and the matching between working fluid and the heat reservoirs. The influence of the effectiveness of regenerator, the effectiveness of hot‐ and cold‐side heat exchangers, the efficiencies of the expander and compressor, the pressure recovery coefficient and the temperature of the heat reservoirs on the heating load and COP of the cycle are illustrated by numerical examples. Published in 1999 by John Wiley & Sons, Ltd.     

Effect of pressure on thermal aspects in the riser column of a pressurized circulating fluidized bed

In the present paper the effect of pressure on bed‐to‐wall heat transfer in the riser column of a pressurized circulating fluidized bed (PCFB) unit is estimated through a modified mechanistic model. Gas–solid flow structure and average cross‐sectional solids concentration play a dominant role in better understanding of bed‐to‐wall heat transfer mechanism in the riser column of a PCFB. The effect of pressure on average solids concentration fraction ‘c’ in the riser column is analysed from the experimental investigations. The basic cluster renewal model of an atmospheric circulating fluidized bed has been modified to consider the effect of pressure on different model parameters such as cluster properties, gas layer thickness, cluster, particle, gas phase, radiation and bed‐to‐wall heat transfer coefficients, respectively. The cluster thermal conductivity increases with system pressure as well as with bed temperature due to higher cluster thermal properties. The increased operating pressure enhances the particle and dispersed phase heat transfer components. The bed‐to‐wall heat transfer coefficient increases with operating pressure, because of increased particle concentration. The predicted results from the model are compared with the experimentally measured values as well as with the published literature, and a good agreement has been observed. The bed‐to‐wall heat transfer coefficient variation along the riser height is also reported for different operating pressures. Copyright © 2005 John Wiley & Sons, Ltd.     

Second Law Efficiency Analysis of Heat Exchangers

Analytical analysis of unbalanced heat exchangers is carried out to study the second law thermodynamic performance parameter through second law efficiency by varying length‐to‐diameter ratio for counter flow and parallel flow configurations. In a single closed form expression, three important irreversibilities occurring in the heat exchangers—namely, due to heat transfer, pressure drop, and imbalance between the mass flow streams—are considered, which is not possible in first law thermodynamic analysis. The study is carried out by giving special influence to geometric characteristics like tube length‐to‐diameter dimensions; working conditions like changing heat capacity ratio, changing the value of maximum heat capacity rate on the hot stream and cold stream separately and fluid flow type, i.e., laminar and turbulent flows for a fully developed condition. Further, second law efficiency analysis is carried out for condenser and evaporator heat exchangers by varying the effectiveness and number of heat transfer units for different values of inlet temperature to reference the temperature ratio by considering heat transfer irreversibility. Optimum heat exchanger geometrical dimensions, namely length‐to‐diameter ratio can be obtained from the second law analysis corresponding to lower total entropy generation and higher second law efficiency. Second law analysis incorporates all the heat exchanger irreversibilities. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21109     

The effect of a metal plate barrier with holes blocking channel in the forced convection of rectangular modules

The experimental work reported here has provided an analysis of the effect of a perforated barrier, fully spanning the flow passage upstream of a pair of modules in a duct, on heat transfer and pressure drop characteristics of heated, rectangular modules that are commonly encountered in electronic equipment. The barrier has been shown to be an effective means towards providing heat transfer enhancement. Heat transfer was increased with increasing barrier hole diameter d, and decreasing barrier porosity σ and module‐barrier distance L. The enhancing effect of the barrier was found to change dramatically at L/d = 3.5 and 18. Experimental data on heat transfer coefficients were correlated as a function of L/d, σ, and Reynolds number. The pressure loss coefficient of the barrier is influenced by porosity σ, and is insensitive to the other factors experimentally investigated. The average pressure loss coefficient was correlated as a function of σ. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20348     

Study on high performance evaporator with micro‐grooves (Measurement of capillary force in a single groove and modeling of heat and mass transfer)

A micro‐grooved evaporator is composed of µm‐wide grooves on a heat transfer plate in which the inter‐line regions at the liquid–vapor meniscus of coolant become identifiable. The high‐heat performance of the evaporator is realized by this inter‐line region (ILR) where the liquid thin film reduces the thermal resistance on the heat transfer surface. In this report, we propose a numerical simulation model of heat and mass transfer in a single groove to predict its capillary force and heat flux. The capillary force performance (capillary‐rise length in a groove) of a single groove was measured for samples of varying width, superheat, and inclination. The performance was found to be a maximum at a specific groove width of 200–400 µm, which is in good agreement with the predicted results calculated by the proposed model. For a better prediction of capillary‐rise length, the effective capillary force and the effective flow resistance were considered. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20257     

Experimental studies on heat transfer enhancement of the inside and outside spirally triangle finned tube with small spiral angles for high‐pressure preheaters

A new heat transfer enhanced tube—the inside and outside spirally triangle finned tube with small spiral angles (IOSTF tube)—was developed and manufactured for improving the performance of high‐pressure preheaters. The triangle flutes with small spiral angle on the outside surface of the IOSTF tube perform like the vertically fluted tube, and the triangle flutes with small spiral angle on the inside surface of the IOSTF tube perform like the spirally fluted tube. The experiments show that the total heat transfer coefficient of the vertical IOSTF tube is 63–95 per cent larger than that of the smooth tube with only a slight increase in the inside flowing friction and the field results show that a 43 per cent increase in the total heat transfer coefficient of the high‐pressure preheater with the IOSTF tubes can be obtained. Copyright © 2000 John Wiley & Sons, Ltd.     

ANN modeling of compact heat exchangers

This paper focuses on the heat transfer analysis of compact heat exchangers through artificial neural network (ANN). The ANN analysis includes heat transfer coefficient, pressure drop and Nusselt number in the compact heat exchangers by using available experimental results in a case study. In this study, data sets are established in 15 different test channel configurations. A feed‐forward back‐propagation algorithm is used in the learning process and testing the network. The learning process is applied to correlate the heat transfer analysis for different ratios of rib spacing and height, various Reynolds numbers, different inlet–outlet temperatures, heat transfer areas and hydraulic diameters. Various hidden numbers of the network are trained for the best prediction of the heat transfer analysis. Heat transfer coefficient, pressure drop and Nusselt number values are predicted by the network algorithm. The results are then compared with the experimental results of the case. The trained ANN results perform well in predicting the heat transfer coefficient, pressure drop and Nusselt number with an average absolute mean relative error of less than 6% compared with the experimental results for staggered cylindrical ribbed and staggered triangular ribbed of test channels in the case study. The ANN approach is found to be a suitable method for heat transfer analysis in compact heat exchangers. Copyright © 2007 John Wiley & Sons, Ltd.     

Performance of hemisphere algorithm for fast form factor calculation

A fast and accurate algorithm is required for carrying out radiative heat transfer simulations designing thermally efficient devices. This paper describes the performance of the hemisphere algorithm, which was originally developed for fast form factor calculation for obtaining photorealistic three‐dimensional computer graphics. We compare the performance of the hemisphere algorithm with that of two conventional algorithms that are widely used for radiative heat transfer simulations. The hemisphere algorithm is found to be significantly faster than the other algorithms, but it has an absolute error of 1.0×10^?5. In addition, the result indicates that the hemisphere algorithm is suitable for simulating the trial and error process in the practical analysis of large‐scale models due to its tolerable visualization of form factor distribution. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20259     

Heat transfer and pressure loss characteristics of a heat exchanger for recovering latent heat (effects of straight fin length and fin pitch on the heat transfer and pressure loss characteristics)

In recent years, the requirement for the reduction of energy consumption has been increasing to solve the problems of global warming and the shortage of petroleum resources. A latent heat recovery type heat exchanger is one of the effective methods for improving thermal efficiency by recovering latent heat. This paper describes the heat transfer and pressure loss characteristics of a latent heat recovery type heat exchanger having straight fins (fin length: 65 mm or 100 mm, fin pitch: 2.5 mm or 4 mm). These were clarified by measuring the exchange heat quantity, the pressure loss of the heat exchanger, and the heat transfer coefficient between the outer fin surface and gas. The effects of fin length and fin pitch on heat transfer and pressure loss characteristics were clarified. Furthermore, equations for predicting the heat transfer coefficient and pressure loss which are necessary for heat exchanger design were proposed. ©2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(4): 230– 247, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20153 Copyright © 2004 Wiley Periodicals, Inc.     

The heat transfer and pressure loss characteristics of a heat exchanger for recovering latent heat (the heat transfer and pressure loss characteristics of the heat exchanger with wing fin)

In recent years the requirement for reduction of energy consumption has been increasing to solve the problems of global warming and the shortage of petroleum resources. A latent heat recovery type heat exchanger is one of the effective methods of improving thermal efficiency by recovering latent heat. This paper described the heat transfer and pressure loss characteristics of a latent heat recovery type heat exchanger having a wing fin (fin pitch: 4 mm, fin length: 65 mm). These were clarified by measuring the exchange heat quantity, the pressure loss of heat exchanger, and the heat transfer coefficient between outer fin surface and gas. The effects of condensate behavior in the fins on heat transfer and pressure loss characteristics were clarified. Furthermore, the equations for predicting the heat transfer coefficient and pressure loss which are necessary in the design of the heat exchanger were proposed. ©2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(4): 215–229, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20154     

保温材料热物性测试的实验及数值研究

针对保温材料导热系数低,采用常规的导热系数测试方法难以获得准确结果的问题,根据瞬态法导热系数测试原理,对常功率平面热源法进行了研究。建立传热的二维瞬态数学模型,借助FLUENT有限体积软件对常功率平面热源法中试样的温度分布和热量传递规律进行数值模拟,开发了一套保温材料导热系数测试装置。测试结果与文献数据能较好的吻合,最大误差不超过4％。测试结果可靠,测试精度较高。     

Heat transfer research on vapor‐gas mixture with condensation in a vertical tube

The convection‐condensation heat transfer of vapor‐gas mixtures in a vertical tube was studied theoretically and experimentally. The effects of the condensation of a small amount of water vapor (8 to 20%) on heat transfer in a vertical tube were discussed. Comparisons show that theoretical solutions obtained through modified film model and experimental results are in good agreement. The results show that the condensation heat transfer of a small amount of water vapor and single‐phase convection heat transfer in the vapor‐gas mixtures are of the same order of magnitude, and these two modes of heat transfer could not be neglected. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(7): 531–539, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10055     

Study on carbon dioxide gas cooler heat transfer process under supercritical pressures

In carbon dioxide transcritical air‐conditioning and heat pump systems, the high‐pressure‐side heat exchanger operating at supercritical pressures is usually called as gas cooler. The carbon dioxide gas cooler displays much difference from the traditional heat exchangers employing constant property fluids. The commonly used logarithmic mean temperature difference (LMTD) and effectiveness—heat transfer unit (ε‐NTU) fail for the gas cooler design calculation as the carbon dioxide properties change sharply near the critical or pseudo‐critical point in the heat transfer processes. The new effective heat transfer temperature difference expression for variable fluid property derived by the authors is verified by numeric simulation of the carbon dioxide gas cooler. Moreover, the available correlated models for the cooled carbon dioxide supercritical heat transfer are used to simulate the gas cooler. Detail analysis is made for the deviations among the different models, and for the distributions of local convective coefficient, heat flux, and local temperature of carbon dioxide along the flow path in the gas cooler. Copyright © 2002 John Wiley & Sons, Ltd.     

A finite volume method on distorted quadrilateral meshes for discretization of the energy equation's conduction term

A finite volume method (FVM) on distorted meshes for discretizing the energy equation's conduction term is presented. In this method, it is possible to compose the computational mesh of general quadrilateral elements (cells), namely, the cells are not required to be rectangular. The gradient of temperature on the cell's surface is computed to be second‐order accurate. Therefore, the error of numerical results by this method is smaller than using the traditional multilateral element method (MEM). The error does not depend on the degree of mesh distortion. The formulation based only on Taylor's theorem is straightforward. These are advantageous features to revise the fluid flow computation programs (based on FVM) that neglected the heat conduction term of the energy equation. The test calculations show that the convergence tendency of the numerical error using this method with the distorted mesh is the same as using an ordinary 2‐node central difference scheme on a constant‐interval rectangular mesh. By this method a conduction term was added to the energy equation of a SALE [ 1 ] program which had neglected that term originally, and z numerical calculation of a fluid flow with a heat transfer problem was performed. The numerical result of the present method with the distorted mesh well agrees with the analytical solution and the result of REM with a rectangular mesh. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20375     

Control of turbulent channel flow over a backward‐facing step by suction or injection

Experiments have been performed for turbulent channel flow over a backward‐facing step. The backward‐facing step is controlled by equipping a slit at the bottom corner of the step. Low momentum fluids in the recirculation region are sucked or high momentum fluids are injected from the slit. The width of the slit is changed between 2, 3, and 5 mm, and the flow ratio is varied from 0.00 to 0.15. The wall static pressure and local heat transfer coefficient are measured behind the backward‐facing step. The wall shear stress is measured using a micro flow sensor. In addition, the velocity profiles and turbulent intensities are measured by a split hot film probe. It is found that the heat transfer and pressure drop characteristics are controlled by the flow ratio. When the suction flow ratio is 0.06, the highest performance is obtained. Enhancement of the heat transfer is related to the increase of turbulence intensity. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(8): 490–504, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20036     

Enhancement of natural convective heat transfer from tall,vertical heated plate to water

An enhancement technique was developed for natural convection heat transfer from a tall, vertical heated plate to water. Rectangular grid fins attached to the base plate were utilized as a heat transfer promoter. These grid fins redirect the high‐temperature fluid ascending along the base plate toward the outside of the boundary layer and introduce the low‐temperature ambient fluid toward the base plate instead. The heat transfer coefficients of thus‐treated surfaces were measured and compared with a nontreated surface and a surface with conventional vertical plate‐fins. The highest performance was achieved for the experimental surfaces. In particular, the experimental surfaces with 5‐mm‐high, nonconducting grids and with 10‐mm‐high, conducting grid fins show 27% and 80% higher heat transfer coefficients compared to the turbulent heat transfer coefficients of the nontreated surface, respectively. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(2): 178–190, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10083