Experimental Investigation on Pressure Drop and Heat Transfer Characteristics of Copper Metal Foam Heat Sink

Abstract

The effect of the cooling performance of a copper metal foam heat sink under buoyancy-induced convection is investigated in this work. Experiments are conducted on copper metal foam of 61.3% porosity with 20 pores per inch. The pressure drop experiment is carried out to find the permeability and foam coefficient of the porous media. It is found that the property of porous media changes by changing the angle of inclination of the porous media from a horizontal to a vertical position while keeping the orientation and porosity the same. The Hazen-Dupuit Darcy model is used to curve-fit the longitudinal global pressure drop versus the average fluid speed data from an isothermal steady-flow experiment across the test section of the porous medium. The study concludes that the permeability and foam coefficient for copper foam is found to be 1.11 × 10^?7 m² and 79.9 m^?1, respectively. The heat transfer study shows that the thermal performance of copper metal foam is 35–40% higher than the conventional aluminum metal heat sink under an actual conventional mode.     

纳米石墨烯片-正十八烷复合相变材料制备及热物性研究

本文分别制备了纳米石墨烯片质量分数为0%, 0.5%, 1%, 1.5%, 2%的纳米石墨烯片-正十八烷复合相变材料,并通过扫描电镜测试、红外光谱分析、差示扫描量热实验及导热分析等实验对其形貌结构及热物性进行表征和研究.实验表明本文制备的纳米石墨烯-正十八烷复合相变材料具有很好的相变稳定性;当纳米石墨烯片的质量分数达到2%时,复合相变材料的导热系数相对于纯十八烷高出了89.4%.     

空调蓄冷材料研究现状及其新进展

分析了空调蓄冷材料研究现状及存在的一些问题 ,提出研制一种新型空调复合蓄冷材料 ,通过实验 ,分析该蓄冷材料的融点、融解热等热学性能。并通过实验研究寻找到了一种新型空调蓄冷材料 ,测试结果表明该蓄冷材料具有较高的相变潜热、适宜的相变温度和较好的热稳定性 ,因此可被应用于蓄冷空调系统中。     

Prediction of aerodynamic noise reduction by using open-cell metal foam

As the speed of high-speed train (HST) increases continuously, aerodynamic noise has become more remarkable compared with the wheel/rail noise, which affects the inhabited environment along the railway and the riding comfort. This paper preliminarily investigates the feasibility of using open-cell metal foam covering layer to reduce the low Mach number aerodynamic noise generated by the flow around a circular cylinder which is the typical section of pantographs. The aerodynamic noises radiated from the circular cylinder with and without metal foam are calculated. The hybrid method combining two-dimensional large eddy simulation (LES) with Ffowcs Williams–Hawkings (FW–H) equation is employed. The calculated Strouhal number, time-averaged drag coefficient, base pressure and overall sound pressure level agree well with some available experimental data. Then, the influences of metal foam porosity, pore density, thickness of covering layer and the speed of train on the aerodynamic noise and the aerodynamic forces are investigated, and some detailed comparisons of flow field are made. The numerical results indicate that as a passive scheme, the open-cell metal foam with high porosity can modify the flow, adjust the vortex shedding frequency and regularize the wake, leading to a significant reduction of aerodynamic noise. The results are expected to provide useful information for the control of aerodynamic noise using this new material.     

热管吸液芯的研究进展

文中对热管内吸液芯的研究进展进行了阐述,着重从对热管传热性能起主要影响作用的比表面积、孔隙率、渗透率、有效毛细半径、密度、有效导热系数等结构参数方面进行了分析,最后介绍了多孔泡沫金属这一新型的热管吸液芯,并指出了今后的研究方向.     

封装有相变材料的金属泡沫复合散热器实验研究

相变材料的固液相变具有较高的相变潜热且相变体积变化小,在间歇性工作的电子器件的温控中得到广泛的应用。本文采用将铜泡沫嵌入相变材料中的方法来强化固液相变的传热性能的方法,提出一种封装有金属泡沫和相变材料的复合式散热器结构,实验研究了该散热器的加热表面的温度与时间的变化关系,分析铜泡沫孔隙率、孔密度以及石蜡物性等各个参数对该复合式热沉散热效果的影响。     

通孔金属泡沫表面的池沸腾实验研究

本文对烧结有厚度为30 mm的高孔隙率通孔铜泡沫的水平表面的池沸腾进行实验研究.并采用高速摄像仪对泡沫表面的汽泡生长形貌进行了可视化研究,研究了壁面过热度对热流密度、汽泡脱离直径、汽泡生长周期的影响关系.结果表明由于本文所研究的通孔泡沫厚度较大,限制了汽泡的脱离,使传热性能低于光表面,但是使沸腾起始点降低至3℃.     

方腔内相变材料固液相变传热研究

基于相变材料(PCM,phase change material)的相变储能设备具有储能密度高的特点。本文建立了基于相变储能元件伪焓模型的固液相变格子Boltzmann模型,研究了内部管道位置、方腔倾斜角度对PCM融化过程的影响规律。结果表明,在内管道靠近方腔上部时,由于上部界面(固液相变界面或上壁面)对自然对流阻碍作用,使PCM的融化速率减慢。但是,在此时使方腔发生倾斜,会改变管道热流体到上部界面的距离,强化PCM的热质传递过程,使融化加快。     

高浓度润滑油对泡沫金属池沸腾特性的影响

实验研究了高油浓度的制冷剂/油混合物在泡沫金属加热表面池沸腾换热特性。使用三种泡沫铜作为加热表面,其参数分别为10ppi/90%孔隙率、10 ppi/95%孔隙率和30 ppi/98%孔隙率,厚度均为10 mm。制冷剂为R113,润滑油为VG68,油浓度为0%～40%。实验结果表明,泡沫金属总是强化池沸腾换热,换热系数最多提高450%;润滑油恶化制冷剂在泡沫金属加热表面池沸腾换热,换热系数最多降低90%。开发了高油浓度的制冷剂/油混合物在泡沫金属加热表面池沸腾换热关联式,预测值与95%的实验值误差在±30%以内。     

Forced convection heat transfer from porous heat sinks placed in partially open cavity: Some case studies

In this present study, the forced convection heat transfer from aluminum foam heat sinks with 10, 20, 40 PPI pore density placed in a discrete form in a partially open cavity were experimentally investigated. Air was used as working fluid. The uniform heat flux was applied to 3 × 3 array of foam heat sinks horizontally mounted in the cavity. The experimental studies were performed for the 3363–9743 range of Reynolds number and the 2.7 x 10⁶ and 7.5 x 10⁶ range of modified Grashof number. The effects of the Reynolds number, the modified Grashof number and the pore density of foam heat sink on the heat transfer were investigated. The results obtained were compared with the results obtained without foam heat sink cases. In addition, the most heated elements within the cavity were identified and solution proposals were presented. In addition, the most heated elements within the cavity were identified and solution proposals were presented.     

Thermal energy storage behaviour of nanoparticle enhanced PCM during freezing and melting

The present research work aimed to investigate the melting and solidification characteristics of NPCM. The NPCM was prepared using paraffin as the PCM and high conductive MWCNT as the nanomaterial without using any dispersant. The NPCM was prepared by dispersing MWCNTs with volume fractions of 0.3%, 0.6% and 0.9% in PCM as the base PCM. SEM morphology showed the uniform dispersion of MWCNTs in the paraffin wax. The MWCNT nano-additives PCMs showed two peaks in the heating curve by DSC measurement. Lessening in melting and solidification time of 30% and 43% was attained in the case of NPCM with 0.3% and 0.9%, respectively. It is observed from the DSC analysis that the latent heat of pure paraffin during freezing and melting cycle was 139.2 J/g (at 56.61 °C) and 131.8 J/g (at 57.55 °C), respectively. Whereas, the latent heat of NPCM with 0.9% of nanofluid was 150.7 J/g (at 56.36 °C) and 148.3 J/g (58.35 °C). It is construed that a maximum change in latent heat of 7.6% and 11% was observed between pure PCM and NPCM during freezing and melting cycle. For the lesser nanoparticle concentration (0.3% and 0.6%), the percentage change in latent heat was lesser than 0.9%.     

Effect of Heating Position on Thermal Energy Storage in Cavity With/Without Open-cell Metallic Foams

Thermal energy storage systems inherently store heat at different heating positions. In other words, the heat storage performance changes depending on the heating positions. In this study, the effects of the heating surface position and reinforcement of the open-cell metal foam on the phase change material melting fraction were experimentally investigated. For this purpose, a small-scale rectangular cube was made of plexiglass having a volume of 274 cm³. One of the surfaces of the cube was heated with a constant heat flux, whereas other surfaces were isolated from the room temperature in the environment. Three different constant heat fluxes were applied on the bottom, top, and side surfaces of the cube in the experiments. Paraffin (n-heptacosane), with a phase change point at 59°C–61°C and as phase change material with a rapid heat charge/discharge, was used in the thermal energy storage system. Depending on the heating position and surface heat flux, it was observed that the effect of natural convection significantly increased within the liquid phase change material. Additionally, the results indicate that the presence of metal foams can enhance the heat transfer rate of phase change materials. According to the sensitivity analysis, the effect of independent parameters on the melting ratio of the phase change material was listed in order of importance as time, surface heat flux, heating position, and metallic foam.     

Improving the Morphological Parameters of Aluminum Foam for Maximum Sound Absorption Coefficient using Genetic Algorithm

Fabricating of metal foams with desired morphological parameters including pore size, porosity and pore opening is possible now using sintering technology. Thus, if it is possible to determine the morphology of metal foam to absorb sound at a given frequency, and then fabricate it through sintering, it is expected to have optimized metal foams for the best sound absorption. Theoretical sound absorption models such as Lu model describe the relationship between morphological parameters and the sound absorption coefficient. In this study, the Lu model was used to optimize the morphological parameters of Aluminum metal foam for the best sound absorption coefficient. For this purpose, the Lu model was numerically solved using written codes in MATLAB software. After validating the proposed codes with benchmark data, the genetic algorithm (GA) was applied to optimize the affecting morphological parameters on the sound absorption coefficient. The optimization was carried out for the thicknesses of 5 mm to 40 mm at the sound frequency range of 250 Hz–8000 Hz. The optimized parameters ranged from 50% to 95% for porosity, 0.1 mm to 4.5 mm for pore size, and 0.07 mm to 0.6 mm for pore opening size. The result of this study was applied to fabricate the desired Aluminum metal foams for the best sound absorption. The novel approach applied in this study, is expected to be successfully applied in for best sound absorption in desired frequencies.     

Experimental research in the phase change materials based on paraffin and expanded perlite

In this study, paraffin (PA)/expanded perlite (EP) form-stable phase change material (PCM) was first fabricated using the direct impregnation method without vacuum treatment. Absorptive capacity results showed that the PA/EP composite can obtain good absorptive capacity with the temperature 80 °C and the time 2 h. Compared with the water absorption of EP, the decrease in the water absorption of PA/EP form-stable proved that the absorption of PA into porous EP has been carried out successfully. Scanning electron microscope (SEM) and Fourier transform infrared (FT-IR) results show that paraffin can be well impregnated into EP pores and has good compatibility with it. Differential scanning calorimetry (DSC) results reveal that paraffin/EP composite PCM has melting temperature and latent heat of 53.6 °C and 91.3 J/g, respectively. The durability cycles results suggest that form-stable PA/EP PCM shows good durability.     

Experimental investigation of metal foam for controlling centrifugal fan noise

This paper presents an experimental investigation on the metal foam for controlling a centrifugal fan noise. Nine samples of metal foam with different types of cells, i.e., open, semi-open and close, are employed to compare their effects on the aerodynamic performance and noise level of the centrifugal fan. Experimental data confirms that the open cell metal foam is the most effective to control the fan noise because it not only significantly suppresses the tonal noise but also attenuates the broadband noise. Moreover, the geometrical parameters of the open cell metal foam, i.e., pores per inch and porosity, are studied to investigate their effects on the aerodynamic performance and noise level of the centrifugal fan.     

Numerical simulation of the transient multiphase field during plasma deposition manufacturing composite materials

A solid/liquid/gas unified model has been developed to investigate the gradient composition formation during the plasma deposition manufacturing (PDM) composite materials process. In this model, an enthalpy porosity model was applied to deal with the melting and solidification of the deposited layer, and a level-set approach was introduced to track the evolution of the free surface of the molten pool and the deposited layer. Moreover, complicated physical phenomena occurring at the liquid/gas interface, including forced convection heat loss, heat emission and plasma heat source, have been incorporated into the governing equations by source terms. In this study, the numerical experiment of nickel base alloy powder deposited on the medium steel substrate by PDM technique was implemented based on the staggered grid and SIMPLEC algorithm. Concentration gradient distribution of the solute material at the composite material interface, fluid flow and temperature distribution in the molten pool and the deposited layer have been investigated in detail. Supported by the National Natural Science Foundation of China (Grant No. 50474053) and the High Technology Research and Development Program of China (Grant No. 2007AA04Z142)     

Effects of Solid Matrix and Porosity of Porous Medium on Heat Transfer of Marangoni Boundary Layer Flow Saturated with Power-Law Nanofluids

The effect of the solid matrix and porosity of the porous medium are first introduced to the study of power-law nanofluids,and the Marangoni boundary layer flow with heat generation is investigated.Two cases of solid matrix of porous medium including glass balls and aluminum foam are considered.The governing partial differential equations are simplified by dimensionless variables and similarity transformations,and are solved numerically by using a shooting method with the fourth-fifth-order Runge-Kutta integration technique.It is indicated that the increase of the porosity leads to the enhancement of heat transfer in the surface of the Marangoni boundary layer flow.     

Study on the properties of a novel shape-stable epoxy resin sealed expanded graphite/paraffin composite PCM and its application in buildings

In this study, a novel phase change material (PCM) of epoxy resin sealed expanded graphite/paraffin composite was developed as an independent attachment for building applications. A relatively high thermal energy storage density and a high thermal conductivity (2.141?W/(m·K)) were obtained in the composite PCM. The mass fraction of paraffin in the composite PCM could reach 94% without leakage of liquid paraffin when being heated at 50°C for more than 3 h, and the thermal cycle stability was good. Moreover, the thermal storage and release properties of this composite PCM with different thicknesses were studied by numerical simulation. The results showed that the thermal storage and release time are proportional to the thickness of the composite PCM, and there was almost no temperature gradient during the thermal storage and release process, which indicated that the thermal conductivity of this kind of composite PCM was high enough for building applications.