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.     

Acoustic Mismatch Model for Thermal Contact Conductance of Van Der Waals Contacts Under Static Force

Van der Waals interfaces play a major role in technology today. Thermal transport in material systems with van der Waals interfaces is mainly limited by the contact conductance. Although the effects of static force, such as pressure or the electrostatic part of hydrogen bonds, on the thermal contact conductance of van der Waals interfaces have been examined in a few studies, the focus was either on numerical simulation using techniques such as molecular dynamics or on experimental investigation. In this article, an analytical model of thermal contact conductance that accounts for the effects of static force and adhesion energy is presented. The application of static forces is found to cause a decrease in the intermolecular distance, which leads to increased interatomic forces across the interfaces and thus higher thermal conductance. The model is in good agreement with experimental data on the effect of pressure on thermal conductance collected by Gotsmann and Lantz (Nature Materials, Vol. 12, p. 59–65, 2012).     

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.     

An Experimental Study on the Air-Side Heat Transfer Coefficient and the Thermal Contact Conductance in Finned Tubes

The objective of this experimental study is to evaluate the heat transfer coefficient outside a tube with annular transverse fins, derived from strips of copper mechanically bound and coupled outside. Water is used as the heating medium, in turbulent conditions and flowing at different temperatures inside the tube. Petukhov's correlation has been selected to calculate the water heat transfer coefficient in the tube. The experimental data obtained are compared with a correlation from literature, and a similar trend is observed. A fitting of the data provides a correlation for the three tubes of different external diameter (30 mm, 22 mm, and 15.6 mm) that agrees very well with the experimental values. The thermal contact conductance is identified as the main reason for the difference between data and the original Briggs and Young correlation. An estimation of the contact conductance between fins and tubes provides values between 3500 and 11000 W/m²-K, slightly increasing with the air Reynolds number (based on the external diameter of the tube), whose range is 2000 to 8000. The thermal contact resistance is estimated and its importance is confirmed, contributing 30 to 50% to the total air-side thermal resistance in the tubes used in the experiments.     

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.     

Analysis for Thermal Conductance Effect on the Interfacial Thermal Stresses of Anisotropic Composites

The present work applies the regularized boundary integral equations that are newly developed to treat the thermoelastic field in thin anisotropic media. For the anisotropic thermal field, a direct domain mapping technique is applied with a unique interface condition that considers the heat conductance relation. By incorporating the heat conductance effect, the paper investigates how interfacial thermal stresses between generally anisotropic materials vary with the heat conductance coefficient. Accounting for the thermal conductance effect, the paper presents the complete algorithm for computing the thermal as well as the subsequent elastic fields on interfaces between dissimilarly adjoined anisotropic composites.     

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...     

Overall Thermal Performances of Double-Wall Effusion Cooling Covered by Simulated Thermal Barrier Coatings

A coupling configuration of double-wall cooling and exterior surface thermal barrier coating(TBC)is one of the most promising thermal protection methods of hot components of modem gas turbine.The combined influences of coating thickness,impingement layout,and cooling air flowrate on the overall thermal performances of such configuration were discussed deeply,to provide the valuable guidance of design.Overall effectiveness measurements were implemented under engine-matched Biot numbers and mainstream-to-coolant temperature ratio.Conjugate heat transfer simulations provided the additional information difficult to be acquired by the measurements.The results indicated that the contribution of TBC is much larger than that of increasing the cooling air amount.The thicker TBC can produce the stronger insulation,while the higher risk of thermal damage of itself.The larger coolant flowrate enlarges the benefit of TBC,while the trend is suppressed by the thick TBC.The constant coating thickness cannot bring to the uniform metal temperature,which can be solved through properly adjusting the backside impingement.The trends in overall effectiveness with TBC’s thickness are independent on the change of internal impingement.     

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。     

Effects of the Encapsulating Resin on the Junction Temperature of the QFN16 and QFN32 Electronic Packages Subjected to Free Convection

The junction temperature of the quad flat no-lead with 16 and 32 leads (QFN16 and QFN32) electronic packages subjected to free convection is highly affected by their encapsulating resin's thermal conductivity. This study considers a variation of this conductivity between ?80% and +100% of the average value measured on an industrial prototype by means of the Transient Plane Source method. The three dimensional numerical solution based on the control volume formulation shows that the thermal trend is of exponential type for these components but with different functions. The proposed relationships allow the calculation of the junction temperature of both QFN16 and QFN32 according to the power generated varying between 0.1 and 1W, and the inclinations relative to the horizontal plane in the range 0–90° (horizontal and vertical positions respectively). The law governing the influence of conductivity on the junction temperature shows that a more conductive resin does not significantly lower the junction temperature. However, for low conductivity values, the temperature can exceed the maximum recommended by the manufacturers, causing possible malfunction of the QFN and altering its technical performance that are directly related to its thermal state. In some cases, the device can be decommissioned.     

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.     

Generalized Procedure for Improved Accuracy of Thermal Contact Resistance Measurements for Materials With Arbitrary Temperature-Dependent Thermal Conductivity

Thermal contact resistance (TCR) is most commonly measured using one-dimensional steady-state calorimetric techniques. In these experimental methods, a temperature gradient is applied across two contacting beams and the temperature drop at the interface is inferred from the temperature profiles of the rods that are measured at discrete points. During data analysis, thermal conductivity of the beams is typically taken to be an average value over the temperature range imposed during the experiment. Here, a generalized theory is presented that accounts for temperature-dependent changes in thermal conductivity. The procedure presented enables accurate measurement of TCR for contacting materials whose thermal conductivity is any arbitrary function of temperature. For example, it is shown that the standard technique yields TCR values that are about 15% below the actual value for two specific examples of copper and silicon contacts. On the other hand, the generalized technique predicts TCR values that are within 1% of the actual value. The method is exact when thermal conductivity is known exactly and no other errors are introduced to the system.     

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.     

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.     

Effects of Crack Surface Conductance on Intensity Factors for a Functionally Graded Piezoelectric Material Under Thermal Load

Effects of crack surface conductance on intensity factors for a functionally graded piezoelectric material under thermal load are investigated. The heat flux through the crack is assumed to be proportional to the local temperature difference. Moreover, two models for more realistic crack face electric boundary conditions are proposed. By using the Fourier transform, the thermal and electromechanical problems are reduced to a singular integral equation and a system of singular integral equations, respectively, which are solved numerically. Detailed results are presented to illustrate the influence of the thermal and electric conductance on the stress and electric displacement intensity factors.