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     

Thermal design of a broadband communication system with detailed modeling of TBGA packages

This paper presents a thermal modeling of a broadband network communication box partitioned into two stacked modules. A printed circuit board (PCB) is inside each module where an array of 16 tape ball grid array (TBGA) packages is surface mounted to the PCB. The TBGA package dissipates 6 W power each. In addition, 12 W of power is dissipated from four plastic ball grid array (PBGA) packages on the PCB. Pin-fin heat sinks are attached to the TBGA packages using silica-filled epoxy to enhance heat dissipation. Pin-fin heat sinks are also attached to the PBGA packages. Two exhaust fans are mounted at the flow exit to draw ambient air into the system at approximately 200 linear feet per minute (LFM) of velocity. The full Navier–Stokes equations for airflow are solved to simulate the forced convection cooling in the electronic module. Buoyancy effect was considered in the numerical model by incorporating Boussinesq-approximation. The TBGA packages are modeled in detail in order to obtain the package junction temperatures for system reliability evaluation and thermal design optimization. Detailed models of the attached pin-fin heat sinks and the epoxy interfaces are also utilized in this study. Compact heat sink model composed of a base plate and a resistance fluid volume is applied to model heat dissipation from the heat sinks attached to the four PBGA packages. System fan curve is used to simulate the fan operating conditions. The effect of changing system thermal design on the TBGA package junction temperatures as well as the hydraulic operating conditions of the system fans are examined and reported herein. The effect of radiation heat transfer is also examined. The importance of detailed modeling of the high power TBGA packages is demonstrated in this study. Simulation results were compared with JEDEC thermal test data under similar conditions of airflow.     

Optimization of pin-fin heat sinks using entropy generation minimization

In this study, an entropy generation minimization, EGM, technique is applied as a unique measure to study the thermodynamic losses caused by heat transfer and pressure drop in cylindrical pin-fin heat sinks. The use of EGM allows the combined effect of thermal resistance and pressure drop to be assessed through the simultaneous interaction with the heat sink. A general expression for the entropy generation rate is obtained by considering the whole heat sink as a control volume and applying the conservation equations for mass and energy with the entropy balance. Analytical/empirical correlations for heat transfer coefficients and friction factors are used in the optimization model, where the characteristic length is used as the diameter of the pin and reference velocity used in Reynolds number and pressure drop is based on the minimum free area available for the fluid flow. Both in-line and staggered arrangements are studied and their relative performance is compared on the basis of equal overall volume of heat sinks. It is shown that all relevant design parameters for pin-fin heat sinks, including geometric parameters, material properties and flow conditions can be simultaneously optimized.     

Characterization of compact heat sink models in natural convection

In this study, an approximate analytical-numerical procedure is used to model natural convection cooling of heat sinks using electronics cooling software. The analysis evolves in two stages: a numerical simulation of the detailed heat sink, and a simulation of a compact model that exhibits similar thermal and flow resistance characteristics to those of the actual heat sink. From the analysis, the thermal resistance of the heat sink is evaluated. Subsequently, the effective thermal conductivity that must be assigned to the compact heat sink is determined using the Nusselt number correlation for free convection over a vertical plate. Due to the algebraic form of the Nusselt number correlation, the effective thermal conductivity is determined in an iterative fashion. The purpose of a compact heat sink is to reduce computational effort while retaining a desired level of accuracy. In this article, the compact modeling scheme is first applied to either an extruded or a pin-fin heat sink in order to validate the procedure under laminar conditions. Subsequently, the same approach is applied to a multichip system consisting of a set of pin-fin heat sinks placed in series. At both individual and system-level models, it is found that the compact approach results in substantial savings in mesh size and computing time. These savings are accompanied by a small acceptable error that is less than 10% relative to the detailed model predictions     

Analysis and Control of Equivalent Physical Simulator for Nanosatellite Space Radiator

A realistic prediction of the in-orbit transient performance of a nanosatellite space radiator requires a ground-based equivalent space radiator with a small size, simple configuration, and fast response. For this purpose, we present in this paper the design concept, operating principle, and analysis algorithm of a novel equivalent physical simulator (EPS) consisting of a thermoelectric cooler (TEC), a plate-fin heat sink, and a forced cooling fan. The TEC-based EPS achieves the purpose of simulating the in-orbit transient heat radiation in earth's atmospheric environment by adapting two key parameters: the TEC cooling capacity and the thermal resistance of the heat sink cooling fan. This paper offers results of in-depth numerical parametric studies leading to an EPS design that enables robust simulations under both hot-case and cold-case operations. In addition, we present the design and evaluation of a fuzzy controller for the EPS as an attractive alternative to the traditional PID controller. The fuzzy control presented here will have other potential thermal control applications where TECs and forced cooling heat sinks are employed.      

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.      

Performance Analysis of Pin-Fin Heat Sinks With Confined Impingement Cooling

This work assesses the performance of pin-fin heat sinks with confined impingement cooling using numerical simulation. The extent to which the Reynolds number, the height and the width of the fins, the nozzle-to-heat sink distance, the thermal conductivity, the upper confining plate and the fin number affect the thermal resistance are considered. The work shows that increasing the Reynolds number reduces the thermal resistance, but the effect decreases slowly as the Reynolds number increases. Although increasing the fin height can reduce the thermal resistance, reduction decreases. The fin width that is associated with the minimum thermal resistance increases with the Reynolds number. The optimal nozzle-to-heat sink distance increases with the Reynolds number. The thermal resistance decreases with an increasing thermal conductivity; however, the drop in the thermal resistance becomes smaller. The presence of the upper confining plate increases the thermal resistance. Additionally, the thermal resistance initially decreases and then increases slowly as the fin number increases.     

Modeling of Cylindrical Pin-Fin Heat Sinks for Electronic Packaging

Analytical models are developed for determining heat transfer from in-line and staggered pin-fin heat sinks used in electronic packaging applications. The heat transfer coefficient for the heat sink and the average temperature of the fluid inside the heat sink are obtained from an energy balance over a control volume. In addition, friction coefficient models for both arrangements are developed from published data. The effects of thermal conductivity on the thermal performance are also examined. All models can be applied over a wide range of heat sink parameters and are suitable for use in the design of pin-fin heat sinks. The present models are in good agreement for high Reynolds numbers with existing experimental/numerical data.      

CPU空气强迫对流冷却系统设计

根据空气强迫对流冷却系统一体化设计理念,对9238CPU风扇进行空气动力设计,由Fortran程序输出三维空间曲线文件,导入Pro/E实现实体造型.通过标准风洞对CNC铣床雕刻出的样品进行风扇性能测试.根据风扇数值模拟结果(风扇出口流场特性)设计系列放射状散热器.采用分块六面体网格技术,应用多参考旋转坐标系模型和RNG k-ε模型对风扇和曲线型散热器进行整体数值模拟,模拟结果表明曲线型散热器相对传统垂直型散热器热阻值降低15.9％,最后通过实验证明数值模拟的可信性.一体化设计思想指导下的系列散热器能达到高性能散热效果.     

Heat rejection limits of air cooled plane fin heat sinks for computer cooling

Current desktop computers typically use fan-heat sinks for cooling the CPU, referred to as active heat sinks. This work seeks to determine the heat rejection limits for such fan-heat sinks, within specific fan and heat sink space limits. A fixed volume, 80 /spl times/ 60 /spl times/ 50 mm is chosen as the limiting dimensions, which includes the fan volume. The present work addresses plane fin heat sinks, on which a typical 60 mm fan is mounted. Both duct flow and impinging flow are considered. Analytically based models are used to predict the optimum geometry (minimum convection resistance) for plane fins with duct and impinging flow configurations. Also assessed are the effects of increased fan speed (up to 25%) and heat sink base size (33% increase) on air-cooling limits in duct and impinging flow. Tests on fan-heat sinks are done to validate the predictions. Optimization is also done for an enhanced (offset-strip) fin geometry in duct flow. The plane fin is found to outperform the enhanced geometry.     

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.     

Numerical Study of Heat Transfer From Pin-Fin Heat Sink Using Steady and Pulsated Impinging Jets

This paper investigates numerically the heat transfer characteristics of confined slot jet impingement on a pin-fin heat sink. A variety of pin-fin heat sinks is investigated, and the resulting enhancement of heat transfer studied. The distribution of heat transfer coefficient on the top surface of the base plate and that along the fin height are examined. Both steady and pulsated jets are studied. It is observed that for a steady jet impingement on a pin-fin heat sink, the effective heat transfer coefficient increases with fin height, leading to a corresponding decrease in base plate temperature for the same heat flux. In the case of pulsated jets, the influence of pulse frequency and the Reynolds number is examined, and their effect on the effective heat transfer coefficient is studied.      

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.     

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.     

Improvement of Cooling Performance of a Thermoelectric Air Cooling System Using a Vapor Chamber Heat Sink

Since vapor chambers exhibit excellent thermal performance, they are suited to use as the basis of a heat sink. This work presents the results of tests carried out to investigate the potential application of a vapor chamber heat sink for improving the cooling performance of a thermoelectric (TE) air cooling system. To this end, two sets of TE air coolers were constructed. The cold side of the TE module of both sets was fixed to a conventional plate-fin heat sink. The hot side of one set was fixed to a vapor chamber heat sink, whereas the other set was fixed to a conventional plate-fin heat sink. The effects of air flow rate and electric current supplied to the TE module on the cooling performance were considered. Experimental data were compared with corresponding data for a conventional plate-fin heat sink. It also has been experimentally proven that the use of a vapor chamber heat sink increases the coefficient of performance (COP) by up to 34.2%.     

Performance analysis of heat pipe aided NEPCM heat sink for transient electronic cooling

An experimental investigation on the thermal performance of Nano Embedded Phase Change Material (NEPCM) heat sink with heat pipe has been conducted for electronic cooling in Personal computers. The NEPCM and heat pipe configuration in the heat sink effectively eliminates the use of electronic fan. A flat plate heater was used to simulate the computer's microprocessor. The heat sink configurations were placed above the flat plate heater and tested for multiple head load conditions. The addition of NEPCM increases the heat storage capacity, causes a delay effect on the sensible temperature rise and maintained the core temperature of the heat sink at room temperature for prolonged time. Heat pipe charged with R134a refrigerant placed inside the heat sink cavity for regeneration of NEPCM in heat sink. The results showed that use of heat pipe aided NEPCM heat sink caused a 3 °C decrease in the heater's surface plate temperature during six hours of the operating period without the help of electronic fan or any other forced convection.     

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.     

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％.     

Design for manufacturability of SISE parallel plate forcedconvection heat sinks

The study reported herein extends a previously reported “design for manufacturability” methodology, to forced convection cooled rectangular plate heat sinks. Using a well validated analytical model, the thermofluid performance of the side-inlet-side-exit (SISE) heat sink has been characterized, parametric optimization carried out, and the maximum heat transfer capabilities for a range of operating points has been determined. A least-material optimization has been performed to achieve optimal material use. The analysis indicates the least-material design to provide significant mass savings for a moderate penalty in thermal performance. Empirical criteria for manufacturability obtained from several heat sink manufacturers lead to qualitative guidelines     

固体激光器新型冷却热沉的设计和CFD数值研究

为固体激光器设计了一种新型内部结构扰流柱结构的冷却热沉,采用计算流体力学（CFD）方法对此水冷热沉的三种典型设计方案以及传统的空腔结构和等截面小通道结构热沉分别进行了数值模拟,据此研究了冷却水流量对各种方案的增益介质最高温度、冷却面温度分布以及热沉的压力损失等特性的影响。在相同传热量和相同冷却水流量前提下,等截面小通道热沉和扰流柱热沉的传热特性都明显优于空腔结构热沉。与等截面小通道水冷热沉相比较,扰流柱热沉传热热阻更小,而流动压力损失较大。数值模拟结果表明扰流柱热沉传热性能优于传统的两种热沉（空腔结构和等截面小通道结构）设计方案,具有更好的冷却效果。在较高流量下工作时,扰流柱热沉传热性能略优于等截面小通道热沉,在较低流量下工作时则显著优于等截面小通道热沉。