基于微通道致冷的大功率LED阵列封装热分析

采用微通道致冷技术,设计了大功率LED阵列封装的微通道致冷结构,并应用热分析软件模拟了其热性能,探讨不同鳍片结构尺寸、流速、功率等参数对LED多芯片散热效果的影响.文中提出了采用交错通道以提高LED封装的散热能力,模拟结果显示,交错微通道致冷的封装结构能很好地满足大功率LED阵列的散热需要.     

Study of the optimal layout of cooling fins in forced convection cooling

In this work the influence of the cooling fin shape on the pressure drop caused by flow resistance of a heat sink is studied. A new manner to optimise heat sinks is developed, bringing the emphasis not only on maximum heat transfer flux, but also on minimum flow resistance. The study is done numerically using the computational fluid dynamic software FLUENT. The results show the advantages of using aerodynamic shaped fins if the Reynolds number, based on the spacing between the cooling fins, is greater or equal than about 800. Some preliminary profile shapes are suggested. The authors consider this research as a quite unique approach as compared to other research where the flow resistance has not been taken into account.     

Thermal analysis of LED lighting system with different fin heat sinks

This paper designs a 3×3 light emitting diode(LED) array with a total power of 9 W,presents a thermal analysis of plate fin,in-line and staggered pin fin heat sinks for a high power LED lighting system,and develops a 3D one-fourth finite element(FE) model to predict the system temperature distribution.Three kinds of heat sinks are compared under the same conditions.It is found that LED chip junction temperature is 48.978℃when the fins of heat sink are aligned alternately.     

A novel hybrid heat sink using phase change materials for transient thermal management of electronics

A hybrid heat sink concept which combines passive and active cooling approaches is proposed. The hybrid heat sink is essentially a plate fin heat sink with the tip immersed in a phase change material (PCM). The exposed area of the fins dissipates heat during periods when high convective cooling is available. When the air cooling is reduced, the heat is absorbed by the PCM. The governing conservation equations are solved using a finite-volume method on orthogonal, rectangular grids. An enthalpy method is used for modeling the melting/re-solidification phenomena. Results from the analysis elucidate the thermal performance of these hybrid heat sinks. The improved performance of the hybrid heat sink compared to a finned heat sink (without a PCM) under identical conditions, is quantified. In order to reduce the computational time and aid in preliminary design, a one-dimensional fin equation is formulated which accounts for the simultaneous convective heat transfer from the finned surface and melting of the PCM at the tip. The influence of the location, amount, and type of PCM, as well as the fin thickness on the thermal performance of the hybrid heat sink is investigated. Simple guidelines are developed for preliminary design of these heat sinks.     

A numerical study of the thermal performance of an impingement heat sink-fin shape optimization

This paper presents the results of a numerical analysis of the performance of an impingement heat sink designed for use with a specific blower as a single unit. These self-contained heat sink/blower units, which cause impingement type flow on the heat sink fins, are now commonly used for desktop microprocessors. One of the objectives of this study is to examine the effect of the shape of the heat sink fins, particularly near the center of the heat sink, on the thermal performance of the package. The pressure gradient at the center of the heat sink, near the base, tends to be high. It significantly reduces the airflow, and hence, transport in that region. Different fin shapes and airflow rates have been studied with the objective of searching for an optimal heat sink design that would improve the thermal performance without increasing the pressure drop across the heat sink. Parallel plate fins have been studied by removing fin material from the region near the center of the heat sink along the length and height of the fins. Seventeen different designs have been compared, and an "optimum" heat sink shape is reported that results in a lower operating temperature and pressure drop. It is found that removal of fin material from the central region of the heat sink enhances the thermal as well as hydraulic performance of the heat sink.     

Heat Transfer and Thermal Design of Finned Frames for TEFC Variable-Speed Motors

This paper addresses the evaluation of the heat transfer capability of a finned frame for different velocities of the cooling fan and different numbers and dimensions of the fins. As the heat transfer is highly dependent on the air speed and turbulence, separate evaluations are done in four axial sectors of four different frames. For each frame, each sector is thermally isolated and evenly heated by an internal cylindrical heater with controlled losses. The experimental results allow computing the local transfer coefficient on each axial sector in terms of the fin dimensions and cooling air velocity, and using these empirical coefficients, it is possible to evaluate the thermal capability of the frames and/or to compute the temperature gradient needed to dissipate certain losses. Based on these results, a simple and accurate method to size finned frames is proposed.      

Modeling of the thermal and hydraulic performance of plate fin,strip fin, and pin fin heat sinks-influence of flow bypass

Tests have been conducted in a wind tunnel with seven types of heat sinks including plate fin, strip fin, and pin fin heat sinks. In the case of strip fin, and pin fin heat sinks, both in-line and staggered arrays have been studied. The pin fin heat sinks had circular and square cross-sections. For each type, tests were run with fin heights (H) of 10, 15, and 20 mm while the heat sink width (B) was kept constant and equal to 52.8 mm. In total, 42 different heat sinks were tested. The width of the wind tunnel duct (CB) was varied in such a way that results were obtained for B/CB=0.84, 0.53, and 0.33. The wind tunnel height (CH) was varied similarly, and data were recorded for H/CH=1, 0.67, and 0.33 while the duct Reynolds number was varied between 2000 through 16500. An empirical bypass correlation has been developed for the different fin designs. The correlation predicts the Nusselt number and the dimensionless pressure drop and takes into account the influence of duct height, duct width, fin height, fin thickness, and fin-to-fin distance. The correlation parameters are individual for each fin design. Further, a physical bypass model for plate fin heat sinks has been developed to describe the bypass effect     

Thermal Comfort Study of a Compact Thermoelectric Air Conditioner

This paper evaluates the cooling performance and thermal comfort of a compact thermoelectric (TE) air conditioner. The compact TE air conditioner is composed of three TE modules. The cold and hot sides of the TE modules were fixed to rectangular fin heat sinks and fans. Thermal acceptability assessment was performed to find out whether the cooled air met the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standard-55’s 80% acceptability criteria. A suitable condition occurred at 1 A current flow with a corresponding cooling capacity of 29.2 W, giving an average cooled air temperature of 28°C and 0.9 m/s cooled air velocity. The coefficient of performance was calculated and found to be ∼0.34. Economic analysis indicates that the payback period is 0.75 years when one compact TE air conditioner unit is used instead of a 1-ton conventional air conditioner.     

微针鳍散热器结构参数模拟及优化

通过数值模拟研究了交错式微针鳍散热器的散热效应,分析了针鳍阵列间距和高度对散热器壁温和压降的影响。结果表明,压降随针鳍间距和针鳍高度的减小而呈非线性增加；壁温随针鳍间距的增大而上升,随针鳍高度的增加则呈现出波动趋势。基于上述研究,进一步利用响应表面近似法对微针鳍的横向间距、纵向间距和高度进行了优化,优化后压降最大可降低61.11%。     

Pressure Drop and Heat Transfer Correlations for Triangular Folded Fin Heat Sinks

Experiments have been performed to investigate the cooling performance of triangular folded fin heat sinks made of 6000 series aluminum in a duct flow. The dimension of the triangular folded fin heat sink is 70mm in width and 92 mm in length with an 8-mm-thick base plate. The fin height is varied from 19 to 36 mm and the fin pitch from 5.0 to 9.0 mm. The duct air velocity is in the range of 1.0 to 5.0 m/s and the corresponding Reynolds number based on the hydraulic diameter is varied from 212 to 1974. The experimental results show that the cooling performance of triangular folded fin heat sink is influenced by the fin pitch, the Reynolds number, and the fin height. It increases substantially as the fin pitch decreases and the Reynolds number and the fin height increase. By compiling the experimental data, the heat transfer and the friction factor correlations with plusmn6.5% and plusmn20% accuracy, respectively, are provided for effective design of triangular folded fin heat sinks     

翅片截面形状对风冷翅片散热器性能的影响

基于牛顿粘性定律和计算流体力学(CFD),在实际项目的基础上探究了五种不同垂直截面形状的翅片式散热器在强迫对流条件下的散热性能,最终根据其各自的散热性能和经济性筛选出最佳垂直截面形状的散热器为三角形截面翅片散热器,与传统的矩形截面翅片散热器相比,其散热性能提升了4.23%,材料成本下降了17.95%。     

Numerical investigation of liquid cooling cold plate for power control unit in fuel cell vehicle

This paper proposed fifteen structure schemes of the liquid-cooled plate for thermal control of the power control unit (PCU) in fuel cell vehicle (FCV). At the given serpentine channel with inconstant width, pin fin arrays with various configurations were arranged to improve the performance of three heating zones with multiple heat sources. Based on the same setup and boundary conditions, numerical simulations were conducted for different schemes. The solutions were validated by grid independence check and comparison with previous researches. Effects of fin geometrical parameters (such as diameter, height, fin pitch and shape) on pressure drop and heat transfer characteristics were investigated. Furthermore, two dimensionless factors η_H and η_P were quantified to evaluate the heat transfer enhancement and pressure drop augmentation. The dimensionless performance evaluation factor P_EF was cited to assess overall performance of the cold plate. Based on three factors mentioned above, cooling performances of three heating zones and the whole plate were compared among all schemes. According to the performance comparison, scheme 12 employing circular fins with diameter of 4 mm was selected as the optimal solution for the cold plate.     

Heat transfer from square pin-fin heat sinks using air impingement cooling

Experimental and numerical results are presented for heat transfer from a C4 mounted organic land grid array (OLGA) thermal test chip cooled by air impingement. Five heat sink geometries were investigated for Reynolds numbers ranging from 9,000 to 26,000. The dimensionless nozzle-to-heat sink vertical spacing z/D was varied between 2 and 12. In this study, we investigate the interactions between heat sink geometry, flow conditions and nozzle setting and how they affect the convective heat transfer and overall cooling of the test chip as measured by total thermal resistance /spl theta//sub ja/. Optimizing fin arrays by minimizing the overall heat sink thermal resistance instead of focusing solely on maximizing the heat transfer from the fins is shown to be a better design criterion. We also provide results that show cooling performance gains can be obtained by inserting a deflector plate above the heat sink.     

肋片截面及安装角度对LED散热性能的影响

为提高LED的散热性能,研究了肋片截面形状及安装角度对LED散热性能的影响,获得了较优的肋片横截面形状和最佳肋片安装角度。首先,利用Matlab软件对矩形截面和三角形截面进行数值计算,选择具有较优截面形状的肋片制作3个实物模型;接着,通过温度场测试实验,对3种不同肋片安装角度的模型进行温度场分析,比较并利用Ansys仿真反求出各个模型的表面对流换热系数,进一步验证安装角度对LED散热性能的影响;最终获得较优的肋片截面形状为矩形,最佳安装角度为90°(即垂直于水平面)。     

大功率LED路灯叉排式散热器的热学特性研究

本文结合有限体积数值模拟建立散热器热学模型,可准确计算散热器系统中温度场以及流体场分布,为有效评价散热器的散热效率提供重要参考依据。基于散热器热学模型．分析比较叉排式以及顺排式散热器的温度场以及流体场分布,发现又排式散热器中交错分布翅片可有效破坏散热器层流底层,增强了流体扰动,加大了换热效果,为优化叉排式散热器结构提供了可靠依据,进而通过分析优化散热器系统送风方向、粘结层材料、散热器材料对总体散热性能以及重量的交叉影响。     

Design and Simulation of the CPU Fan and Heat Sinks

Traditional design methods to achieve improvement in heat sink performance are not suitable for meeting new thermal challenges. Revolutionary rather than evolutionary concepts are required for removing heat from the electronic components. We have recently developed an emerging novel approach, the integration design of the forced convection air cooling system. The aerodynamic design for the miniature axial-flow fan is conducted and a CPU fan is designed to be integrated with the radial fins in order to form a complete fan-heat sink assembly. The 3-D data of the fan generated by FORTRAN program are imported into Pro/E to create its 3-D model. The performance curve of the fan prototype fabricated by the computer numerically controlled machine is tested in a standard wind tunnel. To reduce the economic cost and prompt the design efficiency, the computational fluid dynamics is adopted to estimate the initial fan's performance. A series of radial heat sinks is designed in accordance with the outflow angle of airflow discharged from the fan. The inlet angle of the fin is arranged so that the incoming flow from the upstream impeller matches the fin's angle of heat sinks. Using the multi-block hexahedral grid technique, the numerical simulation of the system, including the fan and heat sinks, is performed by means of Multiple Reference Frame (MRF) and RNG k-$varepsilon$ Model. Our results indicate that the thermal resistance of the streamlined heat sink is decreased by 15.9% compared to the traditional heat sink and the entropy generation rate of the streamlined heat sink is lower. The experiments support our simulation results. The series of heat sinks is able to achieve the productive thermal performance when the integration design concept is utilized.      

一种改进型百叶窗翅片的性能数值模拟研究

传统导航大功率设备大多采用平板翅片换热，导致实际空气侧换热系数较低，换热效果不理想。传统板式百叶窗翅片虽然能克服上述缺点，但其压降比平板翅片高。本文提出一种改进型 S 型百叶窗翅片，具有较大的扰流及导流作用，从而增加换热力、减少压降。本文针对平板翅片、传统板式百叶窗翅片及 S 型百叶窗翅片进行数值建模，并对速度场、温度场、压力场、 换热系数，拟合传热因子、阻力系数与雷诺数的关系式进行模拟分析。仿真结果表明，在相同工况下，的综合换热性能最优。     

Single chamber compact two-phase heat spreaders withmicrofabricated boiling enhancement structures

Presents the thermal performance evaluation of a compact single-chamber two-phase heat spreader. The heat spreader setup has a central evaporator section with integrated fins for cooling along the edges. The evaporator employs a micro-fabricated three-dimensional (3-D) copper structure for enhancing boiling heat transfer. The thermal performance of the system was characterized at various power levels and condenser cooling conditions. The size of the boiling enhancement structure and effects of liquid fill volumes on performance were also investigated. Incorporation of the enhancement structure resulted in an improvement in the spreader thermal performance by decreasing the wall temperature at the evaporator by 8°C, for a power dissipation of 36 W/cm² at an air speed of 1 m/s. The maximum heat flux obtained based on a maximum evaporator temperature of 75°C for an air speed of 1 m/s was 42.5 W/cm². Variation in the liquid fill volume showed negligible effect on the maximum temperature at the evaporator, as long as the enhanced structure was fully flooded     

Investigation of planted pin fins for heat transfer enhancement in plate fin heat sink

The present study carries out numerical computations of the plate-circular pin-fin heat sink and provides physical insight into the flow and heat transfer characteristics. The governing equations are solved by adopting a control-volume-based finite-difference method with a power-law scheme on an orthogonal non-uniform staggered grid. The coupling of the velocity and the pressure terms of momentum equations are solved by the SIMPLEC algorithm. The plate-circular pin-fin heat sink is composed of a plate fin heat sink and some circular pins between plate fins. The purpose of this study is to examine the effects of the configurations of the pin-fins design. The results show that the plate-circular pin-fin heat sink has better synthetical performance than the plate fin heat sink.     

高热流密度热沉散热能力数值仿真分析

固体激光器增益介质的热效应问题严重制约了高功率固体激光器的发展。本文从实际应用角度出发,通过数值仿真实验对比散热热沉的主要几何参数(包括热沉基底厚度、肋片高度、肋片宽度、肋片间距)对散热效果的影响;同时也分析了不同的外部流量条件下热沉的散热性能。计算结果表明:优化热沉几何参数,选取适宜的流量,热沉散热效果会有一定提升。