New Physical Model for Thermoelectric Generators

In this paper we describe a new analytical physical model for thermoelectric generators (TEGs). The model includes the Thomson effect, the Peltier heat, a parameterization of the Joule heat, as well as all thermal and electrical resistances. Geometry optimization and investigations of the influence of Peltier heat and the heat source, as well as heat sink conditions and the load resistance, which affect the output power, are presented. The results are compared with measurements of commercially available thermoelectric generators and the fundamental thermodynamic limit. A comparison between the generators is performed.     

射流微通道耦合高效散热器传热实验研究

针对光导开关高重复频率运行时产生丝电流加热,使光导开关温度迅速超过材料最高允许使用温度,造成开关失效或损伤的难题,本文结合微通道散热技术和射流冷却技术的优点,设计了射流微通道耦合高效散热器。通过实验测试,对不同运行工况下射流微通道耦合高效散热器的传热特性进行了研究,并与美国进口的蜂窝型微通道散热器进行散热性能对比。实验结果表明：体积流量为3 L/min的情况下,射流微通道耦合高效散热器的换热系数超过35 000 W/(K·m²),散热量高达1 000 W,相比蜂窝型微通道散热器散热量提升了45%。在测试流量下,随着体积流量的增加,射流微通道耦合高效散热器的平均换热系数接近线性增加,而蜂窝型微通道散热器的平均换热系数在大流量下却增加缓慢。此外,采用射流微通道耦合高效散热器冷却的热源面温度均匀性明显优于采用蜂窝型微通道散热器冷却的热源面温度均匀性,采用射流微通道耦合高效散热器的热源面温度波动能降低58%,更有利于降低光导开关热应力。     

Two-dimensional simulation of thermal runaway in a nonplanarGTO-thyristor

The problem of electrothermal stability due to different cooling conditions has been investigated by computing the thermal transients in a nonplanar GTO-thyristor. In the first simulation, a steady state occurs with a heat sink removing all the dissipated power. In the second simulation severe thermal runaway is induced due to bad cooling conditions, allowing the analysis of destructive electrothermal interaction. The simulations are based on an advanced model for self-heating effects in silicon devices derived from first principles of irreversible thermodynamics. Self-consistently incorporating a phenomenological model of band gap narrowing in order to take account of heavy doping effects. The system of governing equations is valid in both the steady state and the transient regimes. Four characteristic effects contributing to the heat generation can be identified: Joule heating, recombination heating, Thomson heating, and carrier source heating. Thermal runaway is significantly accelerated in the simulations based on the thermodynamic model of thermoelectric transport compared to a conventional heuristic theory of thermoelectricity. The importance of the entropy balance equation is emphasized in order to derive the mathematical form of the heat flux and the current relations for electrons and holes. Limitations of underlying assumptions are discussed. It is shown that the heat generation implies the Thomson relations     

高功率微波装置散热热沉传热流动特性

高功率微波装置在运行时面临的高热流密度散热是当前热控必须解决的难题。微小通道热沉散热结构简单,换热能力突出,在一定程度上能够解决高热流密度散热的问题。但使用微小通道热沉散热时,散热面温度在沿工质流动方向不断升高,这对器件稳定运行不利。而射流冲击技术中流体垂直于热源喷射,温度边界层薄,温度梯度大,换热效果强。将射流冲击技术与微通道热沉相结合,不仅能提高换热系数,增大换热量,而且能实现良好的温度均匀性。对高热流密度下射流冲击微小通道热沉进行数值模拟,分析不同射流孔径对其传热和流动特性的影响。结果表明,增大远离出口处的射流孔径,有利于提高传热效率和减小流动阻力。优化后的射流微通道热沉,在质量流量为14 g/s时,换热系数接近39 000 W/(m2·K)。     

不同环境与加热路径下的微波加热岩石的数值研究

硬质岩隧道开挖是一个难题,文章通过采用有限元软件建立玄武岩的微波加热模型,分析了岩石外界环境温度、换热系数、照射时间以及加热路径对微波照射岩石的影响。计算结果发现降低环境温度、增大换热系数两者实质相似,均是使得岩石表面温度降低较大,在岩石内形成较大温度梯度,从而产生温度应力,引起岩石破坏。延长微波照射时间虽然可以提高温度应力,但破坏效果与照射时间并未呈现正比关系。通过改变微波加热路径,在总时间不变的情况下,在加热中途增加一个自然冷却过程,可以显著提高微波照射效果。     

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.      

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。     

基于LTCC的微通道散热设计

设计了基于LT℃C(低温共烧陶瓷)的微通道散热模型,运用ANSYS软件对其进行了热—流耦合仿真分析,并制作了试验样件.测试结果显示,在环境温度25℃、冷却水入口水温25℃、入口流量27 mL/min、热源功率30 W的工况下,系统平衡时的最高温度为79.3℃,与仿真结果的85.7℃较为吻合,等效散热通量达到120 W/...     

适用于大功率光电芯片散热的一体化平板热管

为解决大功率光电芯片散热问题,构造了一种新结构一体化平板热管。利用超轻多孔泡沫金属作为毛细吸液芯,以水、丙酮和乙醇为工质,在不同充液比、加热功率和倾角条件下对新结构热管的热性能进行了研究,结果表明,这种新结构平板热管不仅消除了热管与散热片间的接触热阻,而且使整个散热翅片也处于均温状态,当功率达到380W、热流密度超过445 W/cm2时,热管仍具有较好的均温特性,且热阻较小,可达0.04℃/W。在3种工质中,水是最佳工质选择,且当充液比为30%时具有较好的效果。实验表明,以泡沫金属为吸液芯的新结构一体化平板热管具有很好的传热性能,并扩展了承载大热流密度的能力。     

An analysis of the heat pipe as a heat sink for solid-state RF sources

Equations are developed for determining the temperature of a steady-state power flux source incident on the heat pipe as a function of the pipe wall thickness. The analysis shows the heat pipe to be no better than a semi-infinite heat sink operating at an elevated temperature for practical solid-state RF devices having power flux densities of 10⁴-10⁶watts/cm².     

基于AT89S52的温度控制系统设计

文章所设计的温度控制器以AT89S52单片机为核心控制单元,用温度传感器DS18B20采集散热片表面温度,采用TIP122来构成水泥电阻和风扇的驱动电路。将由温度传感器DS18B20采集到的实际温度数据与设定温度数据进行比较,得到的误差经PWM补偿网络调整后反馈到驱动电路控制端,实现水泥电阻对散热片的加温和风扇对散热片的降温,从而对散热片表面温度进行准确的显示及控制,散热片表面温度控制误差小于1％。     

Spatial and Temporal Resolution of Conjugate Conduction-Convection Thermal Resistance

A transient, 3-D solution to the heat conduction equation with a small square heat source on an adiabatic surface and Newtonian convection on the opposite side was obtained using Green's functions. The geometry conservatively models conduction spreading resistance encountered by small, concentrated heat sources such as light-emitting diodes and integrated circuits in general, mounted to larger substrates such as the base of a heat sink experiencing Newtonian convection. The solution is presented for a range of nondimensional parameters. Superposition techniques can also be used to extend the applicability of the current solution to the temperature prediction of arbitrary heat flux patterns in certain cases. This technique only holds for applications where the heat transfer coefficient is not a function of temperature, such as thermal management strategies designed to rely on forced convection with air.     

Temperature stabilization in semiconductor laser diodes

Active layer temperature stabilization in semiconductor lasers is treated theoretically. Laser diodes are assumed to be mounted on a submount which is in contact with a heat sink block. The active layer temperature fluctuation signal is fed back to a Peltier device, an injection current, or a resistor layer in the chip. Active layer temperature stability and conditions required for the control circuit are analyzed theoretically and numerically.     

Thermal Effect of Ceramic Substrate on Heat Distribution in Thermoelectric Generators

In thermoelectric generators (TEG), poor system design and load matching, which make the system less efficient, have been limiting factors in achieving high conversion efficiency. In this work, to consider the effect of the inlet plenum arrangement and the laminar coolant flow temperature variation in the heat sink, a parallel microchannel heat sink is applied to a real TEG. The focus of this study is a discussion of the temperature difference variation between the cold/hot sides of the TEG legs versus the variation of the thermal conductivity of the ceramic substrate and the thickness of the substrate on the hot side. While the imposed heat flux on the TEG is homogeneously constant, different pressure drops are applied along the microchannel heat sink. The three-dimensional governing equations for the fluid flow and heat transfer are solved using the finite-volume method. The results show that the temperature difference is affected remarkably by the pressure drops in the heat sink, the thermal conductivity of the ceramic substrate, and the thickness of the substrate on the hot side.     

半导体制冷在机械泵热管控温中的应用

机械泵驱动环路式热管冷却系统是近年来空间散热的研究热点,其工作点的温度控制,特别是对降温速率的控制一直是一项技术难题.新型的设计结构将系统回路同半导体制冷片有机结合,既可以保证热端热量即时释放,又能对储液器有效冷却.通过验证,该方法切实可行且效率较高.     

电子器件散热片换热特性的数值研究

对三种不同截面形状的散热片,在不同风速和相同加热功率下的换热特性进行数值模拟。得到三种散热片的底面芯片最高温度、传热系数以及压降在不同风速下的变化关系。通过对计算结果的分析可知：三种模型的底面芯片最高温度随着风速的增加而下降,传热系数和压降随着风速的增加而增大,这与相关实验数据的变化趋势一致。提高风速可以有效增强换热效果,但是压降的影响不容忽视。对比三种模型,收缩式散热片模型较另外两种模型具有换热效果好、压降小的优点,可为高热流密度的电子设备冷却方案的设计和改进提供参考。     

LED筒灯复合结构热管散热器的数值模拟

为解决LED筒灯使用单纯自然对流散热扩散热阻过大、温度分布不均的问题,提出一种基于平板热管和热虹吸管的复合结构热管散热器,并用数值模拟的方法研究了热功率、翅片高度、翅片数目、辐射换热对该散热器性能的影响。模拟结果表明应用于LED筒灯的复合结构热管散热器的热阻随着热功率的增加而减小,翅片高度和翅片数目存在一个最优值,使得散热器温度和热阻最小,自然对流情况下不可忽视辐射换热的作用。     

激光填丝多层焊温度场和应力场的数值模拟

基于有限元计算软件MARC,对16 mm厚低合金高强钢激光填丝多层焊温度场和应力场进行了三维数值模拟。利用生死单元法,采用热流密度线性衰减高斯圆柱热源模拟匙孔效应,双椭球模型模拟焊丝受热过程。计算结果与实际结果对比,两者基本吻合。计算结果表明,层间保温能够有效降低接头冷却速度,减小激光填丝焊残余应力,改善厚板多层焊接头性能;多层焊应力集中主要位于中下部焊道及其热影响区;焊接中坡口有收缩趋势,焊后工件有一定角变形。     

脉冲方波驱动强化热电制冷的瞬态特性

采用有限差分法对脉冲电压驱动下的瞬态热电效应及其动态特性过程进行了理论分析,探索了非稳态工况下帕尔帖效应、焦耳热效应与傅里叶导热效应之间的耦合关系及其关键制约因素对制冷性能的影响规律,进而探讨了脉冲驱动强化热电制冷性能的作用机理。分析结果得到,在合理电压域值内采用主动控制方法,对热电模块周期性施加数倍于稳态工况理想电压的脉冲突变电压,有益于充分利用帕尔贴制冷效应而推迟出现以焦耳热和傅里叶热耗散形式为主的内部热积聚对热电模块冷端引起的负效应,并能瞬态实现冷端面的制冷强化作用和最大程度实现输入电能的有效转换。该结论不仅为进一步提出脉冲驱动模式的优化控制策略提供了理论依据,也为瞬态热电制冷效应的应用开辟了一条新思路。