Thermal Management of Electronic Packages for Space Applications

This paper describes the state of the art for thermal mathematical modeling of electronic packages during transient operation. The methods for calculating thermal contact conductance, view factors, and heat transfer coefficients are reviewed, and an algorithm for computer software is provided. Monte Carlo treatment of the data uncertainties is explained. The computer algorithm uniquely incorporates the subroutines for calculating the thermal contact conductance, absorption factor, and statistical representation of the thermal parameters for Monte Carlo analysis.     

Thermal Contact Analysis Using Identification Method

The system identification method is one of the most important topics in engineering. An interesting application of this method is to investigate the heat transfer from the exhaust valve, especially the valve burning at high temperatures. This study consists of experimental and analytical work. During experimentation, two co-axial rods were used to transfer heat at their contact surfaces. Using the measured temperatures at different locations on the rods and the analytical method, the temperature distribution of the rods and the heat transfer coefficient of the contact surface were calculated. Using the above calculated temperatures at both sides of the contact surface and applying the system identification method, the temperature transfer function was estimated. Using the transfer function, a computational model was created. The results were compared to previous research work. An experimental apparatus, including an analog to digital board, was designed and set up for the experiment.     

The Impact of Thermal Contact Conductance on the Spreading and Solidification of a Droplet on a Substrate

The interfacial thermal contact conductance between an impinging molten droplet and a cold substrate plays an important role in the droplet spreading and solidification. In this paper, a simple correlation for the thermal contact conductance during a rapid contact solidification process was obtained. By introducing this correlation into the numerical model, a non-constant thermal contact conductance that varies with time and position was adopted for the first time to simulate the spreading and solidification of a molten droplet on a substrate. It was found that the droplet spreading and final bump shape are sensitive to the thermal contact conductance. Experiments were also performed to observe the final bump shape of the droplet. Qualitative agreement between the numerical and the experimental results justified the present method. Because the thermal contact conductance is not required to be prescribed, the present method is applicable to different operation conditions.     

Thermal Stress in Fabrication of Thermal Barrier Coatings

Thermal stress in the fabrication process of thermal barrier coating system (TBCs) has a significant effect on the quality of TBCs and the durability of gas turbine. In this work, a new analytical model was developed to calculate the thermal stress during the fabrication process of TBCs. Variations of the material properties with temperature of TBCs were well considered in the present model. Several spraying factors: such as pre-heating temperature, cold gas dynamic spraying (CGDS) method, thickness of top coating and thickness of substrate, which has significant effects on thermal stress generation, are also discussed in this work.     

等离子喷涂热障涂层组织结构及热导率研究

采用扫描电子显微镜（SEM）、激光脉冲等方法研究了204NS和204NS-G粉末对等离子喷涂热障涂层组织结构及热导率的影响。结果表明：相比204NS-G粉末,204NS粉末制备的YSZ涂层具有较高的密度和较低的孔隙率。在1 000℃下,204NS粉末制备的YSZ涂层热导率为0.78 W/m·K,比204NS-G粉末制备的YSZ涂层热导率高约20%。     

利用辐射壁提高燃油锅炉热效率的研究

针对一台立式燃油热水锅炉的结构特点,设计了在炉膛安装燃烧反应器对锅炉进行节能改造的方案,通过流体计算软件Fluent 对锅炉改造前后的燃烧换热状况进行了数值计算,并进行了锅炉改造前后热平衡对比试验,数值计算和试验结果基本一致.改造后提高了炉膛辐射换热量,增加了热烟气在炉内的停留时间,改变了原来锅炉炉膛受热不均的状况,换...     

基于计算流体力学的数据中心机器学习热模型数据增强技术

基于人工智能的热模型可以有效地提升数据中心制冷能效比.受到机房实际采集数据的数量不足和覆盖范围不足的影响,使用实际采集数据集训练的热模型常常在准确度和泛化能力上存在不足.文章介绍了一种基于计算流体力学(Computational Fluid Dynamics,CFD)的人工合成数据增强技术,采用增强数据源对人工智能热模...     

燃气轮机应用的热障涂层

简要叙述了燃气轮机热燃气通流部件上热障涂层镀数工艺的进展情况,最新开发的EB－PVD方法是TBC技术的重大突破,简介了EB－PVD方法及其设备。     

Shape Optimization of a Dimpled Channel to Enhance Heat Transfer Using a Weighted-Average Surrogate Model

Shape optimization of a rectangular channel with the opposite walls roughened by staggered arrays of dimples has been performed not only to enhance turbulent heat transfer but also to reduce friction loss. The dimpled channel shape is defined by three geometric design variables, and the design points within design space are selected using Latin hypercube sampling. The shape of the channel is optimized with three-dimensional (3-D) Reynolds-averaged Navier–Stokes analysis and surrogate approximation methods. A weighted-sum method for multi-objective optimization is applied to integrate multiple objectives related to heat transfer and friction loss into a single objective. A weighted-average surrogate model is employed for this optimization. By the optimization, the objective function value is improved largely and heat transfer rate is increased much higher than pressure loss increase due to shape deformation. The optimum design results in lower channel height, wider dimple spacing, and deeper dimple. The flow mechanism shows the heat transfer rate is increased mainly in the rear portion of the dimple.     

A Numerical Method for Studying Thermal Deformation in 3-D Double-Layered Thin Films with Imperfect Interfacial Thermal Contact Exposed to Ultrashort-Pulsed Lasers

Ultrashort-pulsed lasers have been attracting worldwide interest in science and engineering communities. Studying the thermal deformation induced by ultrashort pulsed lasers is important for preventing thermal damage. In this article, we consider a three-dimensional (3-D) double-layered metal thin film, where the interface between layers is imperfectly thermal contact, and present a finite difference scheme and an iterative algorithm for studying thermal deformation in the metal thin film exposed to ultrashort pulsed lasers. The method is demonstrated by investigating the thermal deformation in a 3-D gold-chromium thin film.     

Measurement of Total Hemispherical Emittance of Spacecraft Thermal Control Coatings at Low Temperatures

Spacecraft payloads that operate at cryogenic temperatures often use passive thermal control systems that incorporate a variety of thermal control coatings to reject heat to space. The thermal performance of these systems depends significantly on the emittance of their thermal control coatings. This paper presents total hemispherical emittance measurements carried out at the ISRO Satellite Centre (ISAC) for thermal control coatings: Aeroglaze Z307 absorptive conductive polyurethane black coating (from 8 0K to 150 K) and PUC conductive black polyurethane coating (from 70 K to 200 K). The experiments were conducted in vacuum using a steady-state calorimetric method. This paper highlights the importance of obtaining a steady state for accurately estimating the emittance at cryogenic temperatures and the criterion for achieving this. The results indicate that the emittance in the cryogenic temperature range increases with temperature for the coatings considered in this paper. Determination of the uncertainty in the experimental results is also presented. Further, the sensitivity of emittance estimates to chamber wall emittance is discussed.     

国内首台火电机组省煤器分级改造提高SCR入口烟温实践

北仑电厂2号锅炉低负荷时省煤器出口烟温过低,不能保证机组的脱硝投运率,通过省煤器的分级改造,提高了SCR入口烟气温度,既满足了脱硝设备的烟温要求,又不影响锅炉热效率,为国内同类机组脱硝改造提供了借鉴.     

A New Inverse Method Using Model Synthesis: Application to Thermal Systems

We propose a new inverse method which consists of building an “inverse model.” The model synthesis [1 G. Lefebvre , E. Palomo , and A. Ait-Yahia , Substructured Modelling of Linear Thermal Systems: The Model Synthesis , Numer. Heat Transfer B , vol. 39 , pp. 303 – 324 , 2001 . [CSA] [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]], which allows us to gather several coupled elementary models in a single one, can be used to permute some outputs with some inputs of the direct model, solving a special coupling between the direct model and a particular one called “inversor.”

The model synthesis then provides an inverse model which can be used to perform usual simulations. We show the principles of the method, the practical “ticks,” and demonstrate with an example that it is an easy-to-use and efficient method.     

采用径向基函数神经网络的热工过程在线辨识方法

基于M-RAN算法的RBF神经网络是一种动态神经网络,适合于过程的在线建模。对M-RAN算法的删除策略进行了改进,不仅删除那些连续对网络输出贡献较小的隐层单元,同时还将相似的隐层单元合并,使网络结构更加紧凑。将基于这种算法的RBF神经网络用于电厂非性线模型热工过程的在线辨识,仿真研究表明了这种建模方法的有效性,且所得模型精度高,计算量小,可直接应用于基于模型的控制算法。图4表1参18     

Thermal Analysis of Orthotropic Pin Fins With Contact Resistance: A Closed-Form Analytical Solution

Light weight composite fins are considered to deal with thermal management problems for many microelectronic components. These composite fins are inherently anisotropic, therefore cannot be handled by a traditional one-dimensional approach; however, these materials can be designed to provide high thermal conductivity values in the desired direction to handle application-specific demands. In this article, we present analytical solutions for temperature distribution and heat transfer rate for orthotropic two-dimensional pin fins subject to convective-tip boundary condition and the contact resistance at the fin base. The generalized results are presented in terms of fin aspect ratio (fin length-to-radius ratio) and three dimensionless fin parameters that relate the internal conductive resistance to three convective resistances discussed in terms of dimensionless variables such as contact, tip, and axial Biot numbers, in addition to the axial-to-radial conductivity ratio. Several special cases including the insulated tip boundary condition are presented. It is demonstrated that the temperature distribution and heat transfer rate from the two-dimensional isotropic annular fin introduced earlier in the literature, can easily be recovered from the benchmark solutions presented in this article. Furthermore, dimensionless heat transfer rates are presented for the pin fins with contact resistance that can help to solve design and optimization problems of many natural-to-forced convection composite fins that are typically encountered in many microelectronic applications.     

The Design of Cold Plates for the Thermal Management of Electronic Equipment

Cold plates, devices used for the thermal management of electronic equipment, consist of a fluid flow space that is bounded by metallic walls. The fluid passages are designed to optimize the heat extraction from the electronics. This paper deals with the fluid flow and heat transfer in cold plates in which both the fluid flow and heat transfer experience periodic variations in the streamwise direction. The motivation for the work was to devise a methodology for dealing with problems that are highly complex and also computationally demanding. The first goal of the work was to transform the combined problems of fluid flow and conjugate heat transfer into one in which the wall heat transfer can be solved separately. The decoupling was achieved by first focusing on the solution of the full conjugate heat transfer problem for a portion of the periodic array. From this solution, heat transfer coefficients were extracted and subsequently employed for the solution of the wall heat conduction problem for the entire cold plate. The second focus was the development of enhancements of the heat transfer performance of cold plates. Consideration was given to manufacturing as well as thermal and fluid flow issues.     

用于电子设备热管理的相变热沉实验研究

为了探究在不同加热功率下肋片结构对相变热沉性能的影响,本文选择相变材料石蜡,对三种不同的相变热沉结构进行了实验研究.结果表明,不同肋片结构在不同加热功率下表现出完全不同的底面温度变化趋势,中心阀杆和径向肋显著提高了热沉的热性能,同时热沉内部结构的设计需要综合考虑加热功率和临界温度的影响.     

Thermal Control of Protruding Electronic Components with PCM: A Parametric Study

This work deals with the melting and natural convection in a rectangular enclosure heated from three discrete protruding electronic components (heat sources) mounted on a conducting vertical plate (substrate). The heat sources generate heat at a constant and uniform volumetric rate. A part of the power generated in the heat sources is dissipated to the phase change material (PCM, n-eicosane with a melting temperature T _m  = 36°C) that filled the enclosure. To investigate the thermal behavior of the proposed heat sink, a mathematical model, based on the mass, momentum, and energy conservation equations was developed. The model has been verified and then validated comparing the melting front with available experimental results. Numerical investigations have been conducted in order to examine the effects of the electronic components thickness and the plate thermal diffusivity on the maximum temperature of electronic components. The percentage contribution of plate heat conduction on the total removed heat and temperature profile in the plate have also been analyzed. Correlations for the nondimensional secured working time (time to reach the threshold temperature, T _cr  = 75°C) and its corresponding melt fraction were derived.     

Thermal Modeling of the Effect of Interstitial Fluid on Contact Resistance between Two Dissimilar Materials

Contact resistance between two dissimilar materials of finite thickness is formulated as two cylinders in contact over an area at their centers. The noncontact gap between the two cylinders is assumed to be filled with a thermally conducting fluid. The lateral surfaces are insulated, while the top and bottom surfaces are kept at constant temperatures. Heat diffusion equations in the cylinders are transformed to two integral equations for the heat flux through the contact and noncontact areas with the interstitial fluid conductance as a parameter. The integral equations are solved numerically. Therefore, no assumption on the heat flux distribution on the contact and noncontact surfaces is made. An expression for the dimensionless overall resistance is developed using the rate of heat transfer through the contact and noncontact areas. The effects of the length of the cylinders and the gap conductance on the overall and contact resistances were evaluated. Radial heat flux and temperature distributions over the contact and noncontact regions were determined. The results are reported in dimensionless form convenient for a parametric study and design analysis.