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.     

Analysis of Convective Thermal Resistance in Ducted Fan-Heat Sinks

The thermal performance of plate fin, round pin-fin, and offset strip-fin heat sinks with a duct-flow type fan arrangement was analytically evaluated. Heat sinks of 65mm$times hbox60, hboxmm hboxplan hboxareatimes hbox50 hboxmm hboxheight$with a 4300-RPM dc fan (60mm$times$15mm) were chosen for the performance comparison. A constant temperature, 6-mm thick heat sink base plate is assumed so that thermal spreading resistance is not involved. The operating point on the fan curve is based on the flow pressure drop impedance curve through a heat sink using the friction factor correlation for the chosen heat sink. The loss coefficients at both the entrance and the exit of the heat sink are included in the flow impedance curve. The operating point is defined by the balance point of the flow impedance curve and the fan performance curve. After determining the operating air velocity, the convective thermal resistance of heat sinks is evaluated from the Nusselt number correlation for the chosen heat sink. Results obtained show that optimized round pin-fin heat sinks provide 32.8%–46.4% higher convective thermal resistance compared to an optimized plate-fin heat sink. The optimized offset strip-fin heat sink shows a slightly lower convective thermal resistance than the plate-fin heat sink. As the offset strip length decreases, however, thermal performance seriously deteriorates.     

小型轴流CPU风扇设计与数值模拟

根据空气强迫对流冷却系统一体化设计理念,对小型轴流CPU风扇进行空气动力设计,由Fortran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.为了减少费用和缩短设计周期,利用CFD对风扇性能预测,风扇出口流向角结论为曲线型散热器设计提供依据;数值模拟结果与实验特性曲线比较吻合,为一体化数值模拟积累了经验.     

Geometric optimization of a micro heat sink with liquid flow

Over the course of the past decade, a number of investigations have been conducted to better understand the fluid flow and heat transfer in microchannel heat sinks, particularly as it pertains to applications involving the thermal control of electronic devices. In the current investigation, a detailed numerical simulation of the heat transfer occurring in silicon-based microchannel heat sinks has been conducted in order to optimize the geometric structure using a simplified, three-dimensional (3-D) conjugate heat transfer model [two-dimensional (2-D) fluid flow and 3-D heat transfer]. The micro heat sink modeled in this investigation consists of a 10 mm long silicon substrate with rectangular microchannels fabricated with different geometries. The rectangular microchannels had widths ranging from 20 /spl mu/m to 220 /spl mu/m and a depth ranging from 100 /spl mu/m to 400 /spl mu/m. The effect of the microchannel geometry on the temperature distribution in the microchannel heat sink is presented and discussed assuming a constant pumping power. The model was validated by comparing the predicted results with previously published experimental results and theoretical analyses, and indicated that both the physical geometry of the microchannel and the thermophysical properties of the substrate are important parameters in the design and optimization of these microchannel heat sinks. For the silicon-water micro heat sink, the optimal configuration for rectangular channel heat sinks occurred when the number of channels approached 120 channels per centimeter.     

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.     

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.      

Thin Thermoelectric Generator System for Body Energy Harvesting

Wearable thermoelectric generators (TEGs) harvest thermal energy generated by the body to generate useful electricity. The performance of these systems is limited by (1) the small working temperature differential between the body and ambient, (2) the desire to use natural air convection cooling on the cold side of the generator, and (3) the requirement for thin, lightweight systems that are comfortable for long-term use. Our work has focused on the design of the heat transfer system as part of the overall thermoelectric (TE) system. In particular, the small heat transfer coefficient for natural air convection results in a module thermal impedance that is smaller than that of the heat sink. In this heat-sink-limited regime, the thermal resistance of the generator should be optimized to match that of the heat sink to achieve the best performance. In addition, we have designed flat (1?mm thickness) copper heat spreaders to realize performance surpassing splayed pin heat sinks. Two-dimensional (2-D) heat spreading exploits the large surface area available in a wristband and allows patterned copper to efficiently cool the TE. A direct current (DC)/DC converter is integrated on the wristband. The system generates up to 28.5???W/cm² before the converter and 8.6???W/cm² after the converter, with 30% efficiency. It generates output of 4.15?V with overall thickness under 5?mm.     

高功率轴快流CO2激光器激励源热沉结构优化设计

为了提高激励源的热稳定性,保证4kW轴快流CO₂激光器的光束质量,采用计算流体动力学的方法,理论分析了激光器激励源热沉的散热机理,对热流密度为106W/m2、面积为16cm2的激励源热沉结构进行了优化设计。结果表明,经过优化之后的热沉其表面的最高温度低于340K,完全能够满足激光器正常工作时激励源核心功率MOSFET对散热指标的要求;同时经过数值模拟得到了带凹槽微通道热沉的优化结构尺寸,分别是微通道凹槽间距P=0.6mm,微通道凹槽倾角θ=45°,微通道凹槽交错距离s=0.1mm,同时当雷诺数Re=546.9时,热沉有最优的散热效果,激光输出功率的稳定度可以控制在±2%以内。此研究为设计具有高效散热能力的微通道热沉提供了理论指导。     

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.     

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.     

照射角度对大功率LED筒灯散热性能影响的分析

为了满足照明需求,有时需要将LED灯具设计成照射角度可调的结构,采用有限元软件分析了三款搭配常见散热器的大功率LED筒灯在不同照射角度下的散热性能,结果发现搭配辐射状散热器的LED筒灯在低于30°照射角下散热效果较佳;搭配平板状散热器的LED筒灯绕不同方向转动照射时散热效果不同,在绕文中所示X轴方向转动时散热效果较好,适合多角度照射;搭配柱状散热器的LED筒灯在多角度照射情况下都具有较好的散热效果。研究结果为以后的筒灯设计提供了参考依据。     

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     

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.      

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.     

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     

Forced Air Cooling of CPUs With Heat Sinks: A Numerical Study

A common ATX form factor personal computer system is modeled in detail. The flow and temperature fields inside the chassis are numerically investigated as a conjugate heat transfer problem. The computational effort is concentrated on the forced air cooling of the CPU using a heat sink. Three different commercial heat sink designs are analyzed by using commercial computational fluid dynamics software packages Icepak and Fluent. The grid independent, well converged, and well posed simulations are performed, and the results are compared with the experimental data. It is observed that flow obstructions in the chassis and the resulting air recirculation affect the heat sink temperature distribution. The specific thermal resistance values for the heat sinks are compared. It is observed that although they have different geometries, all of the three heat sinks have similar specific thermal resistances. The best heat sink is selected and modified in order to have a lower maximum temperature distribution in the heat sink by changing the geometry and the material. Especially, replacing aluminum with copper as the heat sink material improved the performance. The importance of modeling the entire chassis is demonstrated by comparing the simulation results with the results from a model of only the CPU-heat-sink-fan assembly.      

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     

Design and Optimization of Single-Phase Liquid Cooled Microchannel Heat Sink

Semiconductor devices for demanding automotive applications generate a large amount of heat $({≫}{rm 100}~{rm W}/{rm cm}^{2})$. These high power devices can be cooled off very effectively by liquid coolant flowing through the microchannel heat sink. Microchannel heat sinks are very attractive because of their compactness, light weight, and large surface-to-volume ratio. Higher surface-to-volume ratio results in enhanced cooling performance. In this paper, a systematic robust analytical method is presented for design and optimization of single-phase liquid cooled microchannel heat sink. Effects of various design parameters such as eccentricity and footprint of heat source or device, thickness of the heat sink base, channel aspect ratio, number of microchannels or fins, coolant flow rate, and thermal conductivity of heat sink material on heat sink thermal resistances and pressure drop are delineated. Finally, analytical results are compared with experimental data and good agreement is obtained. The analytical method helps to reduce the design cycle time and time-to-market significantly.      

Thermal design for the high-power LED lamp

This paper summarizes different kinds of heat sinks on the market for high power LED lamps. Analysis is made on the thermal model of LED, PCB and heat sink separately with a simplified mode provided. Two examples of simulation are illustrated as a demonstration for the thermal simulation as guidance for LED lamp design.