Least-energy optimization of air-cooled heat sinks for sustainable development

The development of heat sinks for microelectronic applications, which are compatible with sustainable development, involves the achievement of a subtle balance between a superior thermal design, minimum material consumption, and minimum pumping power. This presentation explores the potential for the least-energy optimization of natural and forced convection cooled rectangular plate heat sinks. The results are evaluated in terms of a heat sink coefficient of performance, relating the cooling capability to the energy invested in the fabrication and operation of the heat sink, and compared to the entropy generation minimization methodology (EGM).     

Optimal numerical design of forced convection heat sinks

The objective of this paper is to describe the development of a computationally efficient computer-aided design (CAD) method, which uses a finite element numerical model (FEM) coupled with empirical correlations, to create an optimum heat sink design, subject to multiple constraints. A thermal optimization "challenge" problem, representative of anticipated heat sink requirements in the near future, is solved to demonstrate the proposed methodology. Particular emphasis is placed upon micro-processor central processing unit (CPU) chip cooling applications where, in addition to thermal requirements, the heat sink design specification includes constraints upon size, total mass, and air coolant pressure drop across the heat sink.     

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.     

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.     

Parametric optimization of multichanneled heat sinks for VLSI chipcooling

This paper presents an optimization study of multichannel heat sinks for electronic devices. Specifically, we present a method of determining optimum values of the channel diameter, flow rate and number of channels for minimum pumping power or minimum pressure drop. Optimized parameters are expressed in dimensionless form. The calculated results for both laminar and turbulent regimes present several important relationships among the parameters. A criterion for choice of the flow regime to be used is presented. For a current electronic cooling requirement, the optimized diameter of a channel lies in the micro-scale range when water is used as working fluid. Several advantages of an optimized heat sink and its' feasibility toward actual cooling problems are discussed     

Design and optimization of air-cooled heat sinks for sustainable development

The development of heat sinks for microelectronic applications, which are compatible with sustainable development, involves the achievement of a subtle balance between a superior thermal design, minimum material consumption, and minimum pumping power. Due to the rapid proliferation of electronic systems, substantial material streams and energy consumption rates are associated with the cooling of computers, as well as other categories of electronic equipment. This presentation explores the potential for the least-energy optimization of natural- and forced-convection cooled rectangular plate heat sinks. The results are evaluated in terms of a heat sink coefficient of performance, relating the cooling capability to the energy invested. Guidelines for "sustainable" heat sink designs are suggested.     

高功率板条激光介质的纵向强制对流换热技术

液体强制对流换热因具有较高的可靠性和性能稳定性而被广泛使用于高功率板条激光介质介质的制冷,但沿流场方向产生的温度梯度会显著改变激光介质的热应力状态而带来不良影响。提出了基于冷却流场与目标温度匹配控制思路的双大面侧泵激光介质纵向强制对流冷却方案（Longitudinal forced convection）,利用非定常边界条件的流?固耦合有限元仿真方法对比了全腔浸泡对流冷却（Cavity forced convection）、微通道传导冷却技术方案（Micro-channel conduction）,针对入口流量、流场状态、流道壁面条件等因素进行了详细研究。在30 L/min入口流量下,该方案热交换区域固液界面平均对流换热系数达104 W·m?2·K?1量级,且均匀分布。此外,通过改变壁面粗糙程度能够获得更高的对流换热系数。根据设计结果研制了一套板条激光放大器,实验监测点的温度结果与模拟仿真预测结果相吻合,冷却性能达到预期。     

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。     

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.     

Fabrication and characterization of microscale heat sinks

In the field of thermal management, engineers are well aware of the challenges posed by the increasing level of dissipation. Among the many possible solutions to counter the threat of overheating, one is dealing with the usage of microscale heat sinks, where the forced air or liquid cooling solution is integrated into the electronic package itself. As the System-on-Package integration is not a straightforward task, many fabrication steps have to be fully developed before a successful chip-level cooling system is ready to be used. In this paper, as one of these many steps, we present a refined manufacturing technology which offers the possibility to create the microscale heatsink integrated together with the electronic devices. With the refined manufacturing technology, several channel patterns can be created relatively easily. Nevertheless, only simple channel patterns with integrated diodes are presented now which are tested with an enhanced thermal characterization method developed for microchannel based cooling structures in the last years.     

Investigation of internally finned LED heat sinks

A novel heat sink is proposed,which is composed of a perforated cylinder and internally arranged fins.Numerical studies are performed on the natural convection heat transfer from internally finned heat sinks;experimental studies are carried out to validate the numerical results.To compare the thermal performances of internally finned heat sinks and externally finned heat sinks,the effects of the overall diameter,overall height,and installation direction on maximum temperature,air flow and heat transfer coefficient are investigated.The results demonstrate that internally finned heat sinks show better thermal performance than extemally finned heat sinks;the maximum temperature of internally finned heat sinks decreases by up to 20％ compared with the externally finned heat sinks.The existence of a perforated cylinder and the installation direction of the heat sink affect the thermal performance significantly;it is shown that the heat transfer coefficient of the heat sink with the perforated cylinder is improved greater than that with the imperforated cylinder by up to 34％,while reducing the mass of the heat sink by up to 13％.     

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.     

Heat transfer in forced convection through fins

A novel structure for cooling silicon chips involving passage of water through fins etched in the back of the chips has recently been described in the literature. The properties of silicon and the nature of the structure are such that approximations that allow an analytic solution to the heat transfer problem in the structure can be introduced. Formulas for the fin and channel dimensions that provide optimum cooling under various conditions can then be derived. The results are also presented in graphical form and by means of examples.     

High-power IMPATT diodes on diamond heat sinks

This paper presents calculated and experimental results which demonstrate that the performance of IMPATT diodes is significantly improved by the use of diamond heat sinks. Oscillator test results on germanium IMPATT diodes at 6.2 GHz indicate about 50 to 100 percent increase in power output for diamond versus copper heat-sinked units without compromising other oscillator characteristics. An increase in thermal conductance of about 40 percent is realized for diodes mounted on selected high-conductivity diamonds compared to units mounted on copper. Considerations of IMPATT wafer design for optimum power performance on high thermal conductance heat sinks are discussed. Thermal conductivity of naturally occurring diamonds ranges from 1.0 to 5.0 times that of copper which necessitates selection of stones to realize maximum thermal conductance. This paper presents the results of a study of diamond thermal conductivity, its measurement, and its relationship to diamond optical properties. The dependence of diode thermal conductance on die area for diamond heat-sinked devices has been obtained by computer solution of the heat flow equations for the relevant geometries. These calculations have been corroborated by measurement of the thermal conductance of diodes with various die diameters.     

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%.     

Thermal compact modeling of parallel plate heat sinks

Growing complexity of electronic systems has resulted in an increased computational effort in CFD modeling of electronic systems. To reduce the computational effort, one or several heat sinks can be represented by a compact "porous block" model, with an effective thermal conductivity and pressure loss coefficient. In this study of parallel plate heat sinks in laminar forced convection, a methodology is developed to rigorously determine the thermal properties of compact heat sink models that provide a high level of accuracy. The results of an extensive set of CFD simulations for a three heat sink channel covering two distinct heat sink geometries, air velocities from 0.25 m/s to 2 m/s and various spacings between the heat sinks, were used to create and evaluate the fidelity of compact models. The results of this study establish the validity and value in using the porous block compact model representation for noncritical heat sinks in an electronic assembly. The results also reveal that a location-independent porous-block representation can yield excellent agreement in the prediction of the thermal characteristics of state-of-the-art heat sinks.     

Thermal resistance of heat sinks with temperature-dependent conductivity

Kirchhoff's transformation is summarised in a form appropriate for semiconductor-device heat sinks and then illustrated with a brief application to the thermal resistance of a GaAs laser. Under the most common semiconductor boundary conditions his transformation immediately converts the steady-state linear temperature rise (based on a temperature-independent conductivity σ₀) of a uniform heat sink of any shape into the nonlinear rise [based on a temperature-dependent conductivity σ(T) of any functional form].     

Microchannel heat sinks for two-dimensional high-power-densitydiode laser arrays

The operation of a two-dimensional GaInAsP/InP diode laser array with CW power dissipation up to 500 W/cm² into a Si microchannel heat sink is discussed. The approximately 1×4-mm² laser array was used to characterize the heat sink, and the value of 0.040°C cm²/W was obtained for the thermal resistance per unit area. The extrapolated value for a 1-cm² heated area is 0.070°C cm²/W     

A micromachined Pirani gauge with dual heat sinks

This paper reports a micromachined Pirani gauge with dual heat sinks that can be integrated with microelectromechanical systems (MEMS) devices inside a vacuum package to monitor long-term pressure changes and stability inside the package. The Pirani gauge utilizes small gaps (<1 /spl mu/m) between its heater and two thermal heat sinks to obtain large dynamic range (20 mtorr to 2 torr) and high sensitivity (3.5/spl times/10/sup 5/ (K/W)/torr). The gauge is 2/spl times/2 mm/sup 2/ in size, is fabricated using the dissolved wafer process (DWP) on a glass substrate, and utilizes dielectric bridges for signal routing. Measurements show the low end of the dynamic range can be extended by reducing the gap distance between the heater and thermal sinks, which matches well with analytical modeling. This gauge shows an uncertainty of 50 /spl mu/torr and a detectable leak rate of 3.1/spl times/10/sup -16/ cm/sup 3//s, assuming a common micropackage volume of 1.6/spl times/10/sup -5/ cm/sup 3/, which represents at least four orders of magnitude improvement over traditional leak testing.     

浅谈带散热片产品的封装

带散热片封装的产品主要是功率器件,其产品在使用过程中会产生热能,主要借助散热片来释放,其产生的热能对散热片上的焊线质量提出了更大的挑战。带散热片封装的集成电路分为两种,一种是散热片上打线的集成电路,一种是散热片不打线的集成电路。本文主要讨论了对散热片打线集成电路的散热和工艺方面的改进。