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.     

Optimization of convectively cooled heat sinks

Many factors of heat sink, such as its size and mass, component locations, number of fins, and fan power affect heat transfer. Owing to the opposite effects of these factors on heat sink maximum temperature, we have now a multi-objective optimization problem. A typical optimization case consists of hundreds of heat sink temperature field evaluations, which would be impractical to do with CFD. Instead, we propose to combine analytical results of convection and numerical solution of conduction to address these so-called conjugated heat transfer problems. We solve heat conduction in a solid numerically using the finite volume method and tackle convection with the analytical equation of forced convection in a parallel plate channel.This model is suitable for forced and natural convection heat sinks, and we have verified its validity by comparing its results to measured data and CFD calculations. We use the model to improve two industrial examples, using a multi-objective version of the particle swarm optimization (PSO) algorithm. The first example is a forced convection heat sink composed of nine heat generating components at the base plate, and the other is a natural convection case with two components. In both cases, mass is minimized; the other criterion is maximum temperature for the forced convection case and heat sink outer volume for the natural convection case. Our method is many orders of magnitude faster than CFD. Additionally, we provide some LES results of pin fins with natural convection for further use in similar optimizations.     

Optimization of plate fin heat sinks using entropy generationminimization

The specification and design of heat sinks for electronic applications is not easily accomplished through the use of conventional thermal analysis tools because “optimized” geometric and boundary conditions are not known a priori. A procedure is presented that allows the simultaneous optimization of heat sink design parameters based on a minimization of the entropy generation associated with heat transfer and fluid friction. All relevant design parameters for plate fin heat sinks, including geometric parameters, heat dissipation, material properties and flow conditions can be simultaneously optimized to characterize a heat sink that minimizes entropy generation and in turn results in a minimum operating temperature. In addition, a novel approach for incorporating forced convection through the specification of a fan curve is integrated into the optimization procedure, providing a link between optimized design parameters and the system operating point. Examples are presented that demonstrate the robust nature of the model for conditions typically found in electronic applications. The model is shown to converge to a unique solution that gives the optimized design conditions for the imposed problem constraints     

Ebullition characteristics of an isolated surface microstructure for immersion cooled heat sinks

An understanding of the fundamentals of the boiling mechanism is essential if phase-change liquid immersion cooling is to emerge as a cooling option for the next generation of data servers and other high performance electronics. The present work is an experimental study on the effect of cavity mouth size on the nucleation characteristics of a single isolated micro-pyramidal reentrant cavity. Cavity mouth size has long been known to be a primary variable determining the ebullition characteristics of microscopic structures present on a pool boiling heat sink surface. Isolated pyramidal shaped cavities with square mouth sizes of 7, 19, and 25/spl mu/m etched in polished silicon using an anisotropic etch were evaluated in this study. Serpentine thin film heaters (6.9mm /spl times/ 6.9mm) deposited on a Borofloat glass substrate and anodically bonded to the silicon cavity section served as heat sources. All experiments were conducted at atmospheric pressure in dielectric fluids, HFE-7100 and FC-72, popular in thermal management applications. High speed photography (up to 600frames/s) was used to record and quantify the effect of heat flux on bubble departure frequency and departure diameter under subcooled and saturated conditions. The bubble departure diameter increased with an increase in the cavity mouth size. Frequency and bubble departure size, both decreased with increased subcooling.     

Fluid flow and heat transfer in liquid cooled foam heat sinks for electronic packages

In this paper, the fluid flow and heat transfer of liquid cooled foam heat sinks (FHSs) were experimentally investigated. Eight Open-celled copper foam materials with two pore densities of 60 and 100 PPI (pores per inch) and four porosities varying from 0.6 to 0.9 were bonded onto copper base plates to form the FHSs, which were then assembled on flip chip BGA packages (FBGAs) with a common thermal grease as the thermal interface material. A liquid cooling test loop was established to obtain the pressure drops and overall thermal resistances. For the four 60 PPI FHSs, the one with the lowest porosity of 0.6 is found to possess the lowest thermal resistance level with the largest pressure drop. Generally the FHSs with 100 PPI had slightly lower thermal resistances at the same flowrates but much larger pressure drops than those with 60 PPI. In the overall performance assessment, the thermal resistances of the FHSs are plotted against the pressure drop and the pump power, together with a microchannel heat sink of similar unit cell scale and structural dimensions. The thermal resistances of the FHS with a porosity of 0.8 and pore density of 60 PPI were identified to be the lowest among all the FHSs, which outperformed the microchannel heat sink at large pressure drop and pump power. The reduced heat sink thermal resistance and Nusselt numbers for the present FHSs and microchannel heat sink are also presented and compared with the FHS reported in the literature.     

Staggered heat sinks with aerodynamic cooling fins

The effect of aerodynamic shaping of the cooling fins in staggered heat sinks is numerically studied. It is shown that by rounding the cooling fins, the aerodynamic efficiency is increased without affecting the thermal efficiency. Three different geometries (in-line rectangular, staggered rectangular and rounded staggered shape) have been compared. These three different layouts were studied to obtain the best ratio between the removed heat and the energy spent to drive the coolant flow through the cooling fins. The main purpose of the paper is to determine the influence of the rounded shape on the average performance. As an example, it was found that a rounded staggered fin layout removes the same heat for an incident air velocity of 4 m/s as a classical in-line fin layout with a higher air speed of 6 m/s, with a reduction of fan power consumption by more than 60%.     

Optimization study of stacked micro-channel heat sinks for micro-electronic cooling

With smaller inlet flow velocity, a micro-channel stack requires less pumping power to remove a certain rate of heat than a single-layered micro-channel, because it provides a larger heat transfer area. A simple thermal resistance network model was developed to evaluate the overall thermal performance of a stacked micro-channel heat sink. Based on this simple model, in this study, a single objective minimization of overall thermal resistance is carried out using genetic algorithms. The aspect ratio, fin thickness and the ratio of channel width to fin thickness are the variables to be optimized, subject to constraints of maximum pressure drop (4 bar) and maximum volumetric flow rate (1000 ml/min). During the optimization, the overall dimensions, number of layers and pumping power (product of pressure drop and flow rate) are fixed. The study indicates that reduction in thermal resistance can be achieved by optimizing the channel configuration. The effects of number of layers in the stack, pumping power per unit area, and the channel length are also investigated.     

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.     

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.     

Thermal design and optimization of natural convection polymer pin fin heat sinks

The design and optimization methodology of a thermally conductive polyphenylene sulphide (PPS) polymer staggered pin fin heat sink, for an advanced natural convection cooled microprocessor application, are described using existing analytical equations. The geometric dependence of heat dissipation and the relationships between the pin fin height, pin diameter, horizontal spacing, and pin fin density for a fixed base area and excess temperature are discussed. Experimental results of a pin finned thermally conductive PPS heat sink in natural convection indicate substantially high thermal performance. Numerical results substantiate analytical modeling results for heat sinks within the Aihara et al. fin density range. The cooling rates and coefficient of thermal performance, COP/sub T/, that relates cooling capability to the energy invested in the formation of the heat sink, has been determined for such heat sinks and compared with conventional aluminum heat sinks.     

Splitter plate application on the circular and square pin fin heat sinks

The main aim of this work is devoted to present a numerical analysis for studying effect of splitter on the hydro-thermal behavior of a pin fin heat sink. The concept of application of pins in the heat sinks arises from increasing the heat transfer area to reach maximum rate of heat losses in a limited space. On the other hand, flow separation behind the pin will enhance the pressure drop. To avoid or weaken the flow separation and reduce the pressure drop through the heat sink, a thin plate is located on the back of the pin. Two common pin fin heat sinks with circular and square pin shapes are compared together with and without splitters. Results showed that the use of splitter improves the hydro-thermal performance of both circular and square pins, so that the maximum improvement will be occurred for the case of Q = 10 W and V = 4.5 m/s. Results indicates that for circular pin fin heat sink with splitter pressure drop reduces by 13.4%, thermal resistance decreases by 36.8% and profit factor grows by 20%. Also for square pins the same results of 8.5% reduction for pressure drop, 23.8% reduction for thermal resistance and 14% increase in profit factor are observed. Also reliability analysis showed that for low-frequency and bipolar power transistor, the number of failure is reduced for circular and square splitter pin fin heat sinks.     

Optimal design methodology of plate-fin heat sinks for electronic cooling using entropy generation strategy

This paper presents a formal systematic optimization process to plate-fins heat sink design for dissipating the maximum heat generation from electronic component by applying the entropy generation rate to obtain the highest heat transfer efficiency. The design investigations demonstrate the thermal performance with horizontal inlet cooling stream is slightly superior to that with vertical inlet cooling stream. However, the design of vertical inlet stream model can yield to a less structural mass (volume) required than that of horizontal inlet stream model under the same amount of heat dissipation. In this paper, the constrained optimization of plate-fins heat sink design with vertical inlet stream model is developed to achieve enhanced thermal performance. The number of fins and the aspect ratio are the most responsive factors for influencing thermal performances. The heat sink used on AMD Thunderbird 1-GHz processor has been examined and redesigned by presenting optimization methodology. The optimal thermal analysis has a very good agreement to the both of vendors' announced information and using simulation of parabolic hyperbolic or elliptic numerical integration code series (PHOENICS). The optimum design that minimizes entropy generation rate in this paper primarily applied three criteria for plate-fins heat sink optimal design: formal constrained nonlinear programming to obtain the maximum heat dissipation; prescribed heat dissipation; prescribed surface temperature. As a result, the thermal performance can be notably improved; both the sink size and structural mass can apparently be reduced through the presented design method and process. This analysis and design methodology can be further applied to other finned type heat sink designs.     

U- and L-shaped heat pipes heat sinks for cooling electronic components employed a least square smoothing method

Heat pipes-heat sink modules transfer heat from a heat source to the heat pipes, and then to the heat sink and out into the surrounding ambient, and are suitable for cooling electronic components through a forced convection mechanism. The configuration and thermal performance of the heat sinks with inserted heat pipes were studied in the present paper. This article uses experimental procedures to investigate the thermal performance of two embedded U-shaped heat pipe and six embedded L-shaped heat pipe thermal modules with different fan speeds and heat source areas. And via the superposition method and least-square estimators in experimental data, the performance curves of individual U- and L-shaped heat pipes were derived and predicted. Results show that the lowest thermal resistances of U- and L-shaped heat pipe-heat sinks are respectively 0.246 °C/W and 0.166 °C/W given dual fans operating at 3000RPM and 30 × 30 mm² heat sources. Results for a single U-shaped heat pipe are 0.04 °C/W at 78.85 W, while sequential results for L-shaped heat pipes are 1.04 °C/W, 2.07 °C/W, 2.76 °C/W, 2.19 °C/W and 1.7 °C/W between 34 W and 40 W.     

Heat transfer from pin-fin heat sinks under multiple impinging jets

The enhancement of heat transfer from a discrete heat source using multiple jet impingement of air in a confined arrangement was experimentally investigated. A variety of pin-fin heat sinks were mounted on the heat source and the resulting enhancement studied. Average heat transfer coefficients are presented for a range of jet Reynolds numbers (2000相似文献   

机房空调及新风冷机组加湿水的水质处理

比较目前的几种加湿水水质处理方法 ,并在实验的基础上 ,提出新的水处理方法———综合法     

Heat removal by aluminum-foam heat sinks in a multi-air jet impingement

The present experiment investigates the effects of the pore density of aluminum foam heat sinks, the jet velocity, the jet-to-jet spacing and the nozzle plate-to-heated surface separation distance in a 3/spl times/3 square multi-jet impinging array on the averaged Nusselt number. Thermal performances of 10, 20, and 40 PPI (pores per inch) aluminum foam heat sinks and a conventional plate-fin heat sink are evaluated in terms of the averaged Nusselt number. The jet Reynolds number is varied in the range of Re=1000-13650. The highly permeable 10 PPI aluminum foam heat sink shows higher Nusselt numbers than the 20 and 40PPI aluminum foam heat sinks both in the multi-jet and the single jet impingements. For the single jet impingement, the aluminum foam heat sinks display 8-33% higher thermal performance compared to a conventional plate-fin heat sink while the enhancement is 2-29% for the multi-jet impingement. The multi-jet impingement shows higher heat transfer enhancement than the single jet impingement for high jet Reynolds number and smaller jet-to-jet spacing in the present experiment.     

Experimental investigation of discrete air cooled device thermal resistance dependence on cooling conditions

Temperature is an important factor influencing the operation of electronic devices, thus adequate thermal models should be used for their accurate simulations. Unfortunately, the information on device thermal characteristics provided by their manufacturers is very scarce and usually it is limited only to the specification of the junction-to-case thermal resistance, which is not sufficient for the prediction of device dynamic thermal behaviour.This problem is discussed here based on the practical example of an air cooled power device operating at different power dissipation levels and in variable cooling conditions. The experiments presented in this paper demonstrate that the notion of junction-to-case thermal resistance is ambiguous since the cooling conditions affect the heat diffusion processes inside the package and consequently influence the thermal resistance value. For the analysed device, a simple four-stage RC Foster ladder model is proposed here to simulate the device dynamic thermal behaviour. Owing to the fact that this model is generated in a structure preserving way, its element values can be assigned some physical meaning.     

电子产品散热器的设计

对电子产品使用的散热器的散热原理、主要影响因素进行了分析,建立了数理模型,并对如何选择散热器提供了一些可行的依据.     

Experimental and numerical investigation of circular minichannel heat sinks with various hydraulic diameter for electronic cooling application

This article presents the experimental thermal and hydraulic performances of heat sinks with various channel diameter for cooling electronic components. A heat sink with the length and width of 60 mm and total height of 16 mm fabricated from aluminum material. The heat sink is designed with four circular minichannels and three different values of hydraulic diameter of channel (D = 4 mm, D = 6 mm and D = 8 mm). The minichannel heat sink is heated with a uniform base heat flux. Also, numerical simulation of the problem is performed using Finite Volume Method (FVM). Comparing the experimental and numerical results show that numerical results are in a good agreement with experimental data. The variation of channel diameter affects the heat transfer and pressure drop characteristics of the circular shaped minichannel heat sink. The experimental results show that the increase of channel diameter reduces the pressure drop in the heat sink. Also, the minichannel heat sink with a hydraulic diameter of 4 mm has a much lower thermal resistance than the minichannel heat sinks with a hydraulic diameter of 6 mm and 8 mm. Furthermore, the optimization is done to have the maximum heat transfer coefficient and minimum of pressure drop along the heat sink.     

大功率LED散热器的空气强制对流冷却研究

为了解决大功率LED的散热问题,以数值计算的方法研究平片散热器内部流体的流动换热特性。该文基于COMSOL Multiphysics平台对三种不同湍流模型进行考核,并在此基础上对连续平片和分段平片散热器的散热性能进行比较分析。计算结果表明,标准k-ε模型精度最高;当入口风速由1 m/s增大到9 m/s时,分段平片相对于连续平片换热系数提高了5%~10%,阻力因子降低了3.5%~7.12%。此研究为散热器结构的优化设计提供了理论依据和计算数据。