Thermal performance measurement of heat sinks with confined impinging jet by infrared thermography

In this paper, the thermal performance of heat sinks with confined impingement cooling is measured by infrared thermography. The effects of the impinging Reynolds number, the width and the height of the fins, the distance between the nozzle and the tip of the fins, and the type of the heat sinks on the thermal resistance are investigated. The results show that increasing the Reynolds number of the impinging jet reduces the thermal resistance of the heat sinks consistently. However, the reduction of the thermal resistance decreases gradually with the increase of the Reynolds number. The thermal resistance can be decreased by increasing the fin width combined with an appropriate Reynolds number. Increasing the fin height to enlarge the area of heat transfer also decreases the thermal resistance, but the effects are less conspicuous than those on altering the fin width. An appropriate impinging distance with minimum thermal resistance can be found at a specific Reynolds number, and the optimal impinging distance increases as the Reynolds number increases. Generally speaking, the thermal performance of the pin–fin heat sinks is superior to that of the plate–fin heat sinks because the pin–fin heat sinks consist of smaller volumes but greater exposure surfaces.     

Measurement of performance of plate-fin heat sinks with cross flow cooling

This work assesses the performance of plate-fin heat sinks in a cross flow. The effects of the Reynolds number of the cooling air, the fin height and the fin width on the thermal resistance and the pressure drop of heat sinks are considered. Experimental results indicate that increasing the Reynolds number can reduce the thermal resistance of the heat sink. However, the reduction of the thermal resistance tends to become smaller as the Reynolds number increases. Additionally, enhancement of heat transfer by the heat sink is limited when the Reynolds number reaches a particular value. Therefore, a preferred Reynolds number can be chosen to reduce the pumping power. For a given fin width, the thermal performance of the heat sink with the highest fins exceeds that of the others, because the former has the largest heat transfer area. For a given fin height, the optimal fin width in terms of thermal performance increases with Reynolds number. As the fins become wider, the flow passages in the heat sink become constricted. As the fins become narrower, the heat transfer area of the heat sink declines. Both conditions reduce the heat transfer of the heat sink. Furthermore, different fin widths are required at different Reynolds numbers to minimize the thermal resistance.     

Thermal optimization of plate-fin heat sinks with fins of variable thickness under natural convection

In this study, thermal performance of a vertical plate-fin heat sink under natural convection was optimized for the case in which the fin thickness varied in the direction normal to the fluid flow. For this optimization, the averaging approach presented in an earlier paper for the case of the heat sinks under forced convection was extended to study the performance of heat sinks under natural convection. In the case of an air-cooled heat sink, the thermal resistance decreases by up to 10% when the fin thickness is allowed to increase in the direction normal to the fluid flow. However, the difference between the thermal resistances of heat sinks with uniform thickness and the heat sinks with variable thickness decreases as the height decreases and as the heat flux decreases.     

Effects of fin shapes on heat transfer in microchannel heat sinks

In the present study, compact water cooling of high‐density, high‐speed, very‐large‐scale integrated (VLSI) circuits with the help of microchannel heat exchangers were investigated analytically. This study also presents the result of mathematical analysis based on the modified Bessel function of laminar fluid flow and heat transfer through combined conduction and convection in a microchannel heat sink with triangular extensions. The main purpose of this paper is to find the dimensions of a heat sink that give the least thermal resistance between the fluid and the heat sink, and the results are compared with that of rectangular fins. It is seen that the triangular heat sink requires less substrate material as compared to rectangular fins, and the heat transfer rate per unit volume has been almost doubled by using triangular heat sinks. It is also found that the effectiveness of the triangular fin is higher than that of the rectangular fin. Therefore, the triangular heat sink has the ability to dissipate large amounts of heat with relatively less temperature rise for the same fin volume. Alternatively, triangular heat sinks may thus be more cost effective to use for cooling ultra‐high speed VLSI circuits than rectangular heat sinks.     

Thermal performance of plate-fin vapor chamber heat sinks

Since vapor chambers exhibit excellent thermal performance, they are suited to use as bases of heat sinks. This work experimentally studies the thermal performance of plate-fin vapor chamber heat sinks using infrared thermography. The effects of the width, height and number of fins and of the Reynolds number on the thermal performance are considered. Experimental data are compared with corresponding data for conventional aluminum heat sinks. The results show that generated heat is transferred more uniformly to the base plate by a vapor chamber heat sink than by a similar aluminum heat sink. Therefore, the maximum temperature is effectively reduced. The overall thermal resistance of the vapor chamber heat sink declines as the Reynolds number increases, but the strength of the effect falls. The effect of the fin dimensions on the thermal performance is stronger at a lower Reynolds number. At a low Reynolds number, a suitable number of fins must be chosen to ensure favorable thermal performance of the vapor chamber heat sink. However, at a high Reynolds number, the thermal performance improves as the fin number increases.     

复合热沉环路热管的热点散热性能模拟研究

针对芯片功耗与集成度提高而导致的局部热点问题,设计了一种用于芯片散热的复合热沉环路热管系统。建立了环路热管蒸发段模型,通过数值模拟的方法,证明了复合热沉环路热管系统能够降低热点温度,提高散热表面的温度均匀程度,且散热效果与热点的分布位置有关。当热点的热流密度为160W/cm2,热沉横向、纵向导热率分别为1500W/(m?K)、24W/(m?K)时,热点温度为88.88°C,相比于无热沉时降低了5.96°C。研究了不同热沉导热率下的热沉厚度对热点温度的影响,结果表明：若导热率各项同性,热点温度随热沉厚度的增加而降低,之后趋向不变;若为各项异性,存在最优的热沉厚度,使热点温度最低。     

Forced convective heat transfer across a pin fin micro heat sink

This paper investigates heat transfer and pressure drop phenomena over a bank of micro pin fins. A simplified expression for the total thermal resistance has been derived, discussed and experimentally validated. Geometrical and thermo-hydraulic parameters affecting the total thermal resistance have been discussed. It has been found that very low thermal resistances are achievable using a pin fin heat sink. The thermal resistance values are comparable with the data obtained in microchannel convective flows. In many cases, the increase in the flow temperature results in a convection thermal resistance, which is considerably smaller than the total thermal resistance.     

The hydraulic‐thermal performance of miniature compact heat sinks using SiO2‐water nanofluids

Ever since the rapid increase in both the demand for the miniature electronic devices and their applications, heat dissipation in the electronic components has been a serious issue. A miniature plate‐pin heat sink model with square, circular, and elliptic pins is considered to enhance the hydrothermal performance of this kind of compact heat sink (CHS). Water and 3% of SiO₂‐water nanofluids of volume fraction were used with different Reynolds number ranges (100‐1000). The findings show that the base temperature of heat sink reduces while the Nusselt number enhances by using nanofluids and increasing Reynolds number. The lowest value of the base temperature is nearly 25% for the square pins and circular pins CHSs compared with a plate–fin heat sink at 3% of nanofluids. Furthermore, the highest value of the Nusselt number is about 98% at 3% SiO₂ for circular pin CHSs compared with the plate–fin heat sink. However, the pressure drop of CHSs is higher than that of plate–fin heat sink. Moreover, the most significant hydrothermal performance value is about 1.44 for water and around 1.51 for SiO₂ as using the CHS with circular and elliptic pins depends on the Reynolds number. Thus, applying CHSs with nanofluids instead of the traditional heat sinks might produce a substantial enhancement in the hydrothermal performance of heat sinks.     

An experimental study on thermal management of concentrated photovoltaic cell using loop heat pipe and heat sink

One of the most critical innovations in the solar energy conversion is the use of concentrators for generating power from a smaller area of the cell. The thermal management has an exceptional role in the concentrated photovoltaic (CPV) cell, without which the operating temperature will increase owing to the thermal degradation. In the present study, a prototype of low CPV with single‐cell configuration using a Fresnel lens and a manual tracker with geometrical concentration ratio of up to 25 Suns is made. The performance of the CPV with passive cooling arrangements, such as heat sink and loop heat pipes (LHPs), is analyzed under real‐time outdoor conditions. The results obtained infer that the LHP‐based cooling system has brought down the average temperature rise above ambient to 37.8°C from 54.16°C and 72.6°C in the heat sink and bare CPV systems, respectively. Also, the LHP managed to reject the heat to the surrounding with an average thermal resistance of 1.005°C/W, which is the least when compared with the heat sink. Apart from the instabilities caused by the interference of clouds, the CPV with the LHP cooling system could generate 10% more power output than the one with a heat sink.     

Multidisciplinary optimization of a pin-fin radial heat sink for LED lighting applications

In this study, the cooling performance and mass of a pin-fin radial heat sink were optimized. A radial heat sink with pin fins was examined numerically to obtain a lighter heat sink while maintaining a similar cooling performance to that of a plate-fin heat sink investigated in a previous study. Both natural convection and radiation heat transfer were considered. Experiments were performed to validate the numerical model. The average temperature and mass of the heat sink for various types of fin arrays were compared to determine an appropriate reference configuration. The effects of various geometric parameters on the thermal resistance and mass of the heat sink were investigated; these indicated that the system was sensitive to the number of fin arrays, as well as the length of the long and middle fins. Multidisciplinary optimization was carried out using the three design variables to minimize the thermal resistance and mass simultaneously, and Pareto fronts were obtained with various weighting factors. A design for the optimum radial heat sink is proposed, which reduces the mass by more than 30% while maintaining a similar cooling performance to that of a plate-fin heat sink.     

Thermal-fluid characteristics of plate-fin heat sinks cooled by impingement jet

This work experimentally and numerically studies the thermal-fluid characteristics of plate-fin heat sinks under impingement cooling by adjusting the impinging Reynolds number, the impingement distance, and the fin dimensions. The parameters and the ranges under consideration are the impinging Reynolds number (Re = 5000–25,000), the impingement distance (Y/D = 4–28), the fin width (W/L = 0.08125–0.15625) and the fin height (H/L = 0.375–0.625). The results show that the heat transferred by the heat sink increases with the impinging Reynolds number. The thermal performance can be improved significantly even at low impinging Reynolds number. However, the improvement becomes indistinct as the impinging Reynolds number increases. The thermal resistance declines as the impingement distance increases, and is minimal at Y/D = 20 for various impinging Reynolds numbers. Additionally, the thermal resistance increases as the impingement distance increases further. Increasing the fin width can effectively reduce the thermal resistance. However, as the fin width increases beyond a particular value, the thermal resistance increases dramatically. Reducing the thermal resistance by increasing the fin height depends on a suitable impinging Reynolds number and fin width. Therefore, the effect of the fin height is weaker than that of the impinging Reynolds number or the fin width.     

Multiwalled Carbon Nanotube Nanofluid for Thermal Management of High Heat Generating Computer Processor

Minichannel heat sink geometries with varying fin spacing were tested with de‐ionized water and MWCNT (1 wt %) nanofluid to evaluate their performance with flow components of a liquid cooling kit. Four heat sinks with fin spacing of 0.2 mm, 0.5 mm, 1.0 mm, and 1.5 mm were used in this investigation. Heat sink base temperature was analogous to processor operating temperature which was the prime parameter of interest in this investigation. The base temperature decreased by reducing the fin spacing and using multiwalled carbon nanotube (MWCNT) nanofluid. The lowest value of heat sink base temperature recorded was 49.7 ^°C at a heater power of 255 W by using a heat sink of 0.2 mm fin spacing and MWCNT nanofluid as a coolant. Moreover, as a result of reduced fin spacing and using MWCNT nanofluid as a coolant the value of overall heat transfer coefficient increased from 1200 W/m²K to 1498 W/m²K, translating to about a 15% increase. The value of thermal resistance also dropped by reducing the fin spacing and using MWCNT nanofluid. The most important aspect of the study is that the heat sinks and MWCNT nanofluid proved to be compatible with the pump and radiator of the commercial CPU liquid cooling kit. The pump was capable to handle the pressure drop which resulted by reducing the heat sink fin spacing and by using MWCNT nanofluid. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(7): 653–666, 2014; Published online 11 November 2013 in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21107     

A study of an LED backlight thermal module

The present study uses a heat sink plate to conduct natural convection in order to examine different areas of the heat sink and the effects of mounting different quantities of LEDs on the same surface on the thermal mechanism performance. Based on the experimental results, when a heat sink plate is arranged vertically, the channel flow between the fins is parallel to gravity. The LED substrate plate temperature is different from that at the end of the fin, and rises with the increase of total power. The thermal resistance rises slowly and then declines with the increase of LED electric power. As for temperature change of the LED substrate and at the end of the fin, when the temperature difference is increased, it also increases the natural convection thrust. For thermal resistance, the environmental thermal resistance at the bottom of the heat sink plate is lower than at the middle and top sections. These LED power emissions will be changed synchronously. Regarding the LED quantity control, the rate of increase is the highest for the heat sink plate with 30 pcs LED, and the temperature is very high for the heat sink plate with 45 and 60 pcs LEDs when the power approaches 1 W. Moreover, the rising rate is the lowest for the heat sink plate with 60 pcs LEDs. Depending on the brightness requirement, the illuminant is provided by 60 pcs LEDs to obtain a lower temperature so that the system can reduce the thermal protective design. Evidence shows that a high conductivity heat pipe embedded in the channel can provide a more uniform temperature distribution. The present study provides a further understanding on the influence of different illuminant densities on the heat sink structure and the temperature difference in an LED heat transfer device, in order to provide a reference for heat sink design of a backlight module and LED illuminant module evaluation. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20321     

The heat transfer characteristics of liquid cooling heat sink with micro pin fins

This paper numerically and experimentally investigated the liquid cooling efficiency of heat sinks containing micro pin fins. Aluminum prototypes of heat sink with micro pin fin were fabricated to explore the flow and thermal performance. The main geometry parameters included the diameter of micro pin fin and porosity of fin array. The effects of the geometrical parameters and pressure drop on the heat transfer performance of the heat sink were studied. In the experiments, the heat flux from base of heat sink was set as 300 kW/m². The pressure drop between the inlet and the outlet of heat sink was set < 3000 Pa. Numerical simulations with similar flow and thermal conditions were conducted to estimate the flow patterns, the effective thermal resistance. It was found that the effective thermal resistance would reach an optimum value for various pressure drops. It was also noted that the effective thermal resistance was not sensitive to porosity for sparsely packed pin fins.     

Effect of the angle of inclination of a plate shield on the thermal and hydraulic performance of a plate-fin heat sink

Using CFD software FLUENT, we investigated the effect of the angle of inclination of a plate heat shield on the thermal and hydraulic performance of a plate-fin heat sink. The variation of this angle causes a substantial and complicated variation of the flow field in space both upstream and downstream near such a heat sink. This distinctive behavior modifies the pressure drop between the inlet and outlet of the investigated duct, but that variation influences only slightly the flow field in the space from fin to fin, and thus the thermal resistance of the heat sink. This trend is further smoothed with increasing Reynolds number and height of the heat sink. As a compromise between the demands of small thermal resistance and a small pressure drop, the angle of inclination of a plate heat shield must be chosen carefully.     

基于烟囱效应的通信基站热沉优化设计

利用数值模拟的方法,探究了烟囱效应对通信基站热沉自然对流散热的强化作用,对影响热沉散热性能的主要因素及其机理进行了分析,并以热沉热阻作为优化目标,通过优化翅片间距与隔板间隙的取值提升了热沉的散热性能。在优化设计过程中,通过模糊均值聚类对拉丁超立方抽样所得的样本点进行筛选,快速并有效的缩减了设计区间,使用Kriging模型对新设计区间内的均匀样本点进行拟合,构建了热沉热阻与设计变量间的代理模型,并结合遗传算法寻优,确定了最优设计参数取值。在最优参数布置下,相比于初始热沉,热沉的发热面温度降低了15.23 K,总热阻降低了34.29%。     

Study of heat transfer enhancement in a nanofluid-cooled miniature heat sink

This paper reports numerical solution for thermally developing temperature profile and analytical solution for fully developed velocity profile in a miniature plate fin heat sink with SiO₂–water nanofluid as coolant. The flow regime is laminar and Reynolds number varies between 0 and 800. The heat sink is modeled using porous medium approach. Modified Darcy equation for fluid flow and the two-equation model for heat transfer between the solid and fluid phases are employed to predict the local heat transfer coefficient in heat sink. Results show that the nanofluid-cooled heat sink outperforms the water-cooled one, having a considerable higher heat transfer coefficient. The effects of channel aspect ratio and porosity on heat transfer coefficient of the heat sink are studied in detail. Based on the results of our analysis, it is found that an increase in the aspect ratio or the porosity of the plate fin heat sink enhances the heat transfer coefficient.     

热沉几何参数对侧面泵浦板状激光介质热效应影响分析

以不均匀换热系数模型为基础,数值研究了侧面泵浦板状激光介质在热沉冷却情况下,热沉的几何参数对介质最高温度及最大应力的影响。结果表明,热沉材料对激光介质热效应的影响表现在热阻效应和温度均匀化效应两个方面：热沉材料的导热性能较差时,介质最高温度及最大应力随介质厚度的增加而增加;热沉材料的导热性能较好时,不同热沉厚度下介质最高温度及最大应力变化很小。随着热沉长度的增加,介质内最高温度和最大应力均下降。     

Partially heated heat sinks in a zero-bypass

The need to improve the thermal performance of heat sinks remains a design priority for thermal engineers. Most of the considerations so far have involved various shapes and sizes of the fin designs. This numerical study evaluates the influence of the heating position on the thermal performance of a plate-fin heat sink in a zero-bypass characterized by the thermal resistance data obtained from experiments. For the heating positions evaluated, the central heating position offers the least thermal resistance. In practice, many cooling systems, like in electronic components, involve heat sinks with partially heated sections; therefore, evaluating the best position to place the heat sinks could be a fairly cheap way of enhancing the thermal performance.     

The correlation between the number of fins and the discharge time for a finned heat pipe latent heat storage system

The concept of a solar energy heat pipe latent heat storage system is presented. In order to assure large charging and discharging rates, finned heat pipes are used to transfer heat to and from the phase-change material (paraffin in this case). The evolution of the solid - liquid interface is studied by considering the radial heat transfer (due to the heat pipe wall) and the angular one (due to the fin). Two mathematical models, corresponding to exponential, respectively polynomial functions describing the fin temperature profile are presented and the results are compared. The two models allow the evaluation of the discharge time of the storage unit for a certain number of fins for a single heat pipe. When the discharge time has a fixed value, the methods presented in the paper allow to conclude whether the number of fins is sufficiently large to assure the complete solidification of the phase-change material.