The Experts below are selected from a list of 20736 Experts worldwide ranked by ideXlab platform
Qunte Dai - One of the best experts on this subject based on the ideXlab platform.
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cfd investigation on characteristics of Oscillating Flow and heat transfer in 3d pulse tube
International Journal of Heat and Mass Transfer, 2015Co-Authors: Qunte Dai, Yanyan Chen, Luwei YangAbstract:Abstract A CFD method is used to investigate the three dimensional Oscillating Flow and heat transfer in the pulse tube (PT) and heat exchangers (HEs) of a pulse tube refrigerator (PTR). Some interesting phenomena and characteristics have been found in the present work, and quantitative analyses in detail have been made. The transient temperature variation resembles sinusoidal in the central part of the pulse tube, while exhibits non-sinusoidal within 10 mm away from the two end HEs, respectively. The lowest periodically averaged temperature appears not in the cold end HE but on the cross-section about 1 mm away from the cold end HE, while the highest averaged temperature appears at about 3 mm away from the hot end HE. This would increase the conduction loss, but benefits the coaxial space arrangement for a PTR. The heat transfer efficiency of the two HEs has significant influence on the PV power loss. Poor heat transfer can lead to a higher loss, even reaching to 10% of the total PV power when the heat transfer coefficient decreases to 10 2 W/m 2 K. The efficiency of a pulse tube has been newly proposed, which can be used to describe the loss of pulse tube quantitatively. In summary, the effects of a series of factors on the loss of the pulse tube have been discussed, including the phase angle, the heat transfer coefficient of the HEs, the mass Flow rate, and the gravity. The present study would give a better understanding on the mechanism of losses in a PT.
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lbm numerical study on Oscillating Flow and heat transfer in porous media
Applied Thermal Engineering, 2013Co-Authors: Qunte Dai, Luwei YangAbstract:Abstract Oscillating Flow and heat transfer in regenerative cryocoolers, are very important for the optimization of cryocooler's performance. A numerical study was conducted in such a system by Lattice Boltzmann Method (LBM), which is an efficiently new way compared to that of the traditional continuum Navier–Stokes method. The simulation work was firstly developed in a two-dimensional empty planar channel, and then followed by porous media. The Oscillating Flow is driven by a periodic pressure wave, with the isothermal or adiabatic planar wall. A coupled double distribution function model, which is one of the typical thermal LBMs, is used to investigate the thermo-hydrodynamics problem. As a key step, the extrapolation and bounce back schemes are used to treat the boundaries. The simulation results have shown a great effectiveness of the implementation of the LBM in the present study. LBM would serve as a promising method for predicting Flow and heat transfer characteristics in regenerative cryocoolers, such as pulse tube cryocoolers. In this work, the effects of the characteristic system parameters on the fluid Flow and the heat transfer are investigated. Detailed information for system behavior, especially in porous media, are also included in this paper.
Luwei Yang - One of the best experts on this subject based on the ideXlab platform.
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cfd investigation on characteristics of Oscillating Flow and heat transfer in 3d pulse tube
International Journal of Heat and Mass Transfer, 2015Co-Authors: Qunte Dai, Yanyan Chen, Luwei YangAbstract:Abstract A CFD method is used to investigate the three dimensional Oscillating Flow and heat transfer in the pulse tube (PT) and heat exchangers (HEs) of a pulse tube refrigerator (PTR). Some interesting phenomena and characteristics have been found in the present work, and quantitative analyses in detail have been made. The transient temperature variation resembles sinusoidal in the central part of the pulse tube, while exhibits non-sinusoidal within 10 mm away from the two end HEs, respectively. The lowest periodically averaged temperature appears not in the cold end HE but on the cross-section about 1 mm away from the cold end HE, while the highest averaged temperature appears at about 3 mm away from the hot end HE. This would increase the conduction loss, but benefits the coaxial space arrangement for a PTR. The heat transfer efficiency of the two HEs has significant influence on the PV power loss. Poor heat transfer can lead to a higher loss, even reaching to 10% of the total PV power when the heat transfer coefficient decreases to 10 2 W/m 2 K. The efficiency of a pulse tube has been newly proposed, which can be used to describe the loss of pulse tube quantitatively. In summary, the effects of a series of factors on the loss of the pulse tube have been discussed, including the phase angle, the heat transfer coefficient of the HEs, the mass Flow rate, and the gravity. The present study would give a better understanding on the mechanism of losses in a PT.
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lbm numerical study on Oscillating Flow and heat transfer in porous media
Applied Thermal Engineering, 2013Co-Authors: Qunte Dai, Luwei YangAbstract:Abstract Oscillating Flow and heat transfer in regenerative cryocoolers, are very important for the optimization of cryocooler's performance. A numerical study was conducted in such a system by Lattice Boltzmann Method (LBM), which is an efficiently new way compared to that of the traditional continuum Navier–Stokes method. The simulation work was firstly developed in a two-dimensional empty planar channel, and then followed by porous media. The Oscillating Flow is driven by a periodic pressure wave, with the isothermal or adiabatic planar wall. A coupled double distribution function model, which is one of the typical thermal LBMs, is used to investigate the thermo-hydrodynamics problem. As a key step, the extrapolation and bounce back schemes are used to treat the boundaries. The simulation results have shown a great effectiveness of the implementation of the LBM in the present study. LBM would serve as a promising method for predicting Flow and heat transfer characteristics in regenerative cryocoolers, such as pulse tube cryocoolers. In this work, the effects of the characteristic system parameters on the fluid Flow and the heat transfer are investigated. Detailed information for system behavior, especially in porous media, are also included in this paper.
Zhihua Gan - One of the best experts on this subject based on the ideXlab platform.
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heat transfer of laminar Oscillating Flow in finned heat exchanger of pulse tube refrigerator
International Journal of Heat and Mass Transfer, 2014Co-Authors: Ke Tang, Tao Jin, Yufei Wang, Weiyu Tang, Zhihua GanAbstract:Abstract In order to characterize the heat transfer of heat exchangers employed by pulse tube refrigerators, an experimental apparatus was built to investigate the heat transfer performance of a water-cooled finned heat exchanger operating in laminar Oscillating Flow. The test results summarized into the Nusselt number with respect to the maximum Reynolds number and the Valensi number were presented. The increases in the maximum Reynolds number and the Valensi number both lead to a rise in the Nusselt number. The comparisons of the experimental results and the available typical correlations were conducted and discussed. A new correlation of the Nusselt number to the maximum Reynolds number and the Valensi number was proposed, with which the results have a maximum deviation of 6.3% compared with the experimental values.
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Influence of compression-expansion effect on Oscillating-Flow heat transfer in a finned heat exchanger
Journal of Zhejiang University SCIENCE A, 2013Co-Authors: Ke Tang, Tao Jin, Zhihua GanAbstract:Compression and expansion of a working gas due to the pressure oscillation of an Oscillating Flow can lead to a temperature variation of the working gas, which will affect the heat transfer in the Oscillating Flow. This study focuses on the impact of the compression-expansion effect, indicated by the pressure ratio, on the heat transfer in a finned heat exchanger under practical operating conditions of the ambient-temperature heat exchangers in Stirling-type pulse tube refrigerators. The experimental results summarized as the Nusselt number are presented for analysis. An increase in the pressure ratio can result in a marked rise in the Nusselt number, which indicates that the compression-expansion effect should be considered in characterizing the heat transfer of the Oscillating Flow, especially in the cases with a higher Valensi number and a lower maximum Reynolds number.
Tormartin Tveit - One of the best experts on this subject based on the ideXlab platform.
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Oscillating Flow in a stirling engine heat exchanger
Applied Thermal Engineering, 2012Co-Authors: Maunu Kuosa, Kari Saari, Ari Kankkunen, Tormartin TveitAbstract:Abstract Three heat exchangers exist in modern Stirling engines: a heater, a cooler, and a regenerator. Here a study that deals principally with tubular heaters and coolers is carried out. The calculation procedure for the Oscillating Flow heat transfer is presented. Literature sources are studied to find the most suitable correlations by comparing them to each other and to the classical turbulent Flow correlations encountered in the literature. The enhancement of heat transfer by means of a few circumferential slots inside the tubes and the pressure losses of oscillatory Flow are discussed. Non-circular cross-section conduits with rectangular and triangular cross-sections are investigated and compared to the smooth circular tubes. The increment of the performance of an idealised Stirling engine with slotted heat exchanger tubes is compared to the case with smooth ones. The ratio of the gain in the shaft power and pumping losses is 2.22. The Carnot efficiency increment is 2.7%.
K.c. Leong - One of the best experts on this subject based on the ideXlab platform.
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Heat Transfer Performance of Metal Foam Heat Sinks Subjected to Oscillating Flow
IEEE Transactions on Components and Packaging Technologies, 2006Co-Authors: Liwen Jin, K.c. LeongAbstract:This paper reports the results of an experimental investigation on the heat transfer performance of metal foam as a heat sink subjected to Oscillating Flow. The measured pressure drops, velocities, and surface temperatures of Oscillating Flow through aluminum 40 PPI foam are presented in detail. The calculated cycle-averaged local temperatures and Nusselt numbers for different kinetic Reynolds numbers were analyzed. The variation of total heat transfer rate with a kinetic Reynolds number suggests that Oscillating Flow at relative low frequency has a substantial effect on heat transfer enhancement in a metal foam heat sink. A comparison of the length-averaged Nusselt numbers between Oscillating and steady Flows indicates that higher heat transfer rates can be obtained in metal foams subjected to Oscillating Flow. The relation between pumping power and total heat transfer rates for the Oscillating Flow cooling system was also analyzed with a view to designing a novel heat sink using metal foam. The results show that high heat transfer performance of metal foam heat sinks subject to Oscillating Flow can be obtained with moderate pumping power
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Heat Transfer Characteristics of Oscillating Flow Through Highly Porous Medium
Heat Transfer Volume 1, 2006Co-Authors: Liwen Jin, K.c. LeongAbstract:Heat transfer in porous media has been investigated extensively with the motivation of enhancing heat removal in electronics cooling applications. Many investigations have been conducted on heat transfer in a channel filled with porous media. However, steady Flow through a porous channel still yield a higher temperature difference along the Flow direction. It is conceivable that Oscillating Flow through a porous channel will produce a more uniform temperature distribution due to the two thermal entrance regions of Oscillating Flow. As compared to a porous channel packed with metal particles, spheres or woven-screens, the highly porous open-cell metal foam possesses a different configuration. The polyhedral pore and reticulated ligament structures provide the extremely large fluid-to-solid contact surface area and tortuous coolant Flow path inside the metal foam, which could increase dramatically the overall heat transfer rate. A survey of the literature shows that heat transfer in open-cell metal foam were mostly investigated under steady Flow condition. Published literature on heat transfer in metal foams subjected to Oscillating Flow is scarce. This paper presents both experimental and numerical investigations on the heat transfer characteristics for Oscillating Flow through highly porous medium. Experiments were carried out to study the effect of the oscillatory frequency on the heat transfer in metal foams with various pore densities. The results show that the local Nusselt number increases with the kinetic Reynolds number. Higher total heat transfer rates for Oscillating Flow can be obtained by using high pore density metal foam. The numerical simulation is focused on the study of the variations of the transient temperature and Nusselt number at different locations in the porous channel during a complete cycle. The numerical results show that the profile of the transient temperature decreases with the increase of the distance along the vertical direction and the variation of the instantaneous Nusselt number at entrance region is more significant than that at the location close to the center of the porous channel. It is also found that the two-dimensional temperature distributions in the numerical domain are symmetric about the center of the channel at the cycle-steady state. The comparison shows that the results obtained by the simulation are in reasonably good agreement with the experimental data.Copyright © 2006 by ASME
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Heat Transfer and Fluid Flow in Metal Foam Subjected to Oscillating Flow
Heat Transfer: Volume 1, 2005Co-Authors: K.c. Leong, Liwen JinAbstract:The need for higher performance and an increased level of functional integration as well as die size optimization on the microprocessor leads to preferential clustering of higher power units on the processor. Conventional natural or forced convection cooling methods are not capable of removing such a high heat flux for maintaining a proper operational temperature. It is imperative to look for new methods of cooling the modern high-speed electronic components. The porous medium has emerged as an effective method of heat transfer enhancement due to its large surface area to volume ratio and intense mixing of fluid Flow. Many researchers have studied heat transfer and fluid Flow in a channel filled with metal particles or woven-screens. However, uni-directional Flow through the porous channel yields a relatively high temperature difference along the Flow direction on the substrate surface. For modern high-speed microprocessors, the reliability of transistors and operating speed are not only influenced by the average temperature but also by temperature uniformity on the substrate surface. Therefore, maintaining the uniformity of on-die temperature distribution below certain limits is imperative in thermal design. It is conceivable that Oscillating Flow through a porous channel will produce a more uniform temperature distribution, due to the presence of two thermal entrance regions for Oscillating Flow. In the present investigation, a novel porous material of open-cell metal foam was employed to study heat transfer and fluid Flow of Oscillating Flow through a porous channel. The metal foam with fully inter-connected structure, large surface area to volume ratio and high permeability lends itself to applications in electronics cooling. This paper describes an experimental study on heat transfer and pressure drop behavior of Oscillating Flow through a channel filled with open-cell aluminum foam. Both cycle-averaged and length-averaged local Nusselt numbers were calculated to evaluate heat transfer rate of Oscillating Flow in metal foam channel. The effects of the dimensionless Flow amplitude and frequency of Oscillating Flow on heat transfer were analyzed. A correlation equation of maximum friction factor of Oscillating Flow in metal foam was obtained and compared with the results for wire-screens obtained by other investigators under the Oscillating Flow condition. The results revealed that heat transfer performance can be enhanced substantially by Oscillating Flow through metal foam with moderate pressure drop.Copyright © 2005 by ASME
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an experimental study of heat transfer in Oscillating Flow through a channel filled with an aluminum foam
International Journal of Heat and Mass Transfer, 2005Co-Authors: K.c. Leong, Liwen JinAbstract:Abstract An experimental study has been conducted on the heat transfer of Oscillating Flow through a channel filled with aluminum foam subjected to a constant wall heat flux. The surface temperature distribution on the wall, velocity of Flow through porous channel and pressure drop across the test section were measured. The characteristics of pressure drop, the effects of the dimensionless amplitude of displacement and dimensionless frequency of Oscillating Flow on heat transfer in porous channel were analyzed. The results revealed that the heat transfer in Oscillating Flow is significantly enhanced by employing porous media in a plate channel. The cycle-averaged local Nusselt number increases with both the kinetic Reynolds number Re ω and the dimensionless amplitude of Flow displacement A 0 . The length-averaged Nusselt number is effectively increased by increasing the kinetic Reynolds number from 178 to 874 for A 0 = 3.1–4.1. Based on the experimental data, a correlation equation of the length-averaged Nusselt number with the dimensionless parameters of Re ω and A 0 is obtained for a porous channel with L / D h = 3.
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Effects of Displacement and Frequency of Oscillating Flow on Heat Transfer in a Porous Channel
Heat Transfer Volume 1, 2004Co-Authors: Liwen Jin, K.c. LeongAbstract:The development in modern electronics has resulted in rapid increases in power densities for electronic packages. Traditional cooling methods are not capable of removing such high heat fluxes. It is imperative to find new methods to cool high-speed electronic components. One of these methods is to implement a channel filled with a high conductivity porous medium. Many investigations have been conducted on the heat transfer of a channel filled with porous media. However, steady Flow through a porous channel still yield a higher temperature difference along the Flow direction. It is conceivable that Oscillating Flow through a porous channel will produce a more uniform temperature distribution due to the two thermal entrance regions of Oscillating Flow. Some researchers have investigated forced convective heat transfer in porous channels in Oscillating Flow with different kinds of porous media. Their results showed that the operating temperatures of electronic components can be reduced significantly when an oscillatory Flow device is employed. However, research into the two critical factors of displacement and frequency for Oscillating Flow in a porous channel is very sparse. This paper presents the experimental results of an investigation into the effects of varying Flow displacement and frequency on heat transfer enhancement in a porous channel subject to Oscillating Flow. A comparison was made between the heat transfer performance of Oscillating Flow through a plate channel without a porous medium and a channel filled with sintered metal foam. The maximum displacements of Oscillating Flow were varied from 52 to 68 mm and frequencies of oscillation ranged from 1 to 10 Hz. The characteristics of pressure drop, the effects of the dimensionless amplitude of displacement and dimensionless frequency of Oscillating Flow on heat transfer in porous channel were analyzed. The results revealed that heat transfer in Oscillating Flow is significantly enhanced by employing porous media in a plate channel. The cycle-averaged local Nusselt number increases with both kinetic Reynolds number Reω and the dimensionless amplitude of Flow displacement A0 . Based on the experimental data, a correlation equation of the length-averaged Nusselt number with the dimensionless parameters of Reω and A0 is obtained for a porous channel with L/Dh = 3. This correlation equation will be useful to determine heat transfer rates in Oscillating Flow through a porous channel for applications in electronics cooling.Copyright © 2004 by ASME