Novel heat spreader coatings for high power electronic devices

A new set of heat spreader coatings consisting of multilayers of diamond/AlN/diamond were deposited on high heat capacity substrates of molybdenum and silicon nitride. Bonding of the heat spreaders to the device wafers using gold-tin eutectic solder was carried out after metallization layers of titanium, gold and copper were deposited on diamond. Prior to bonding, backside of the silicon wafers was also metallized with titanium, gold and copper and the gallium arsenide wafers with titanium, copper-germanium alloy and gold. Characterization of the multilayer diamond films was carried out by Raman spectroscopy, X-ray diffraction and scanning electron microscopy. The bonded wafers were tested for adhesion strength, resistance against peeling due to thermal cycling and failure under stress. Further, the bonded regions were characterized by scanning electron microscopy, energy dispersive spectroscopy and X-ray mapping of different elements. The heat spreader characteristics of the single layer diamond and the multilayer diamond substrates were tested by infrared imaging. The results illustrate that the multilayer diamond heat spreader coatings provide better heat dissipation and also possess better adhesion strength and resistance against peeling under thermal cycling. These novel multilayer diamond/AlN/diamond heat spreaders are expected to considerably improve the life of high frequency power devices.     

Characterisation of heat spreader materials for pulsed IGBT operation

Insulated gate bipolar transistors (IGBTs) have a very high output power and generate correspondingly large amounts of heat. If not dissipated efficiently, this heat will destroy the IC (integrated circuit). Furthermore, since the input to the IGBT is often in the form of a pulsed wave, the rapid repeated heating and cooling of the chip and the surrounding packaging cause physical stresses, which in turn eventually lead to delamination and breakdown. Reducing the magnitude of thermal excursion in pulsed mode operations reduces the amount of stress caused by expansion and contraction, thereby reducing delamination and maintaining component efficiency for a longer period of time. It is therefore important to maintain a low rate of thermal expansion, or have a slow enough change in temperature for the physical stresses not to be damaging. This is normally done with heat sink assemblies, which form an integral part of IGBT design. This study investigates, via simulations using the transmission line matrix method, the thermal responses of some of the popular heat spreader materials. Material combinations within the layered structure of the heat sink assembly will give different thermal responses, and thus an analysis of operational behaviour of these components, with attention given to the input frequency as well as duty cycle, would provide a better guide to designing more suitable and efficient packaging assemblies and heat sinks     

Multidisciplinary Design Optimization Procedure for Improved Design of a Cooled Gas Turbine Blade

A multidisciplinary optimization procedure for gas turbine blade design has been developed and demonstrated on a generic 3-D blade. The blade is cooled both internally and externally (film cooling). Aerodynamic and heat transfer design criteria are integrated along with various constraints on the blade geometry. The blade is divided into numerous spanwise sections and each section is represented by a Bezier-Bernstein polynomial. A comprehensive solver for 3-D Navier-Stokes equations is used for the viscous flow calculations. The finite element method is used to obtain the blade interior temperatures. The average blade temperature and maximum blade temperature at each spanwise section are minimized, with aerodynamic and geometric constraints on the blade geometry. The constrained multiobjective optimization problem is solved using the Kreisselmeier-Steinhauser function approach. The results for a generic turbine blade design problem show significant improvements after optimization.     

Elevated-pressure mixed-coolants Joule-Thomson cryocooling

This paper explores the potential of mixed coolants at elevated pressures for Joule-Thomson cryocooling. A numerical model of a Joule-Thomson cryocooler is developed that is capable of simulating operation with mixtures of up to 9 components consisting of hydrocarbons, non-flammable halogenated refrigerants, and inert gases. The numerical model is integrated with a genetic optimization algorithm, which has a high capability for convergence in an environment of discontinuities, constraints and local optima. The genetic optimization algorithm is used to select the optimal mixture compositions that separately maximizes following two objective functions at each elevated pressure for 80, 90 and 95 K cryocooling: the molar specific cooling capacity (the highest attainable is 3200 J/mol) and the produced cooling capacity per thermal conductance which is a measure of the compactness of the recuperator. The optimized cooling capacity for a non-flammable halogenated refrigerant mixture is smaller than for a hydrocarbon mixture; however, the cooling capacity of the two types of mixtures approach one another as pressure becomes higher. The coefficient of performance, the required heat transfer area and the effect of the number of components in the mixture is investigated as a function of the pressure. It is shown that mixtures with more components provide a higher cooling capacity but require larger recuperative heat exchangers. Optimized mixtures for 90 K cryocooling have similar cooling capacity as those for 80 K. Optimized compactness for 80 K is about 50% higher than can be achieved by pure nitrogen. For 90 K, no mixture provides a more compact recuperator than can be achieved using pure argon. The results are discussed in the context of potential applications for closed and open cycle cryocoolers.     

Optimal scheduling of biocide dosing for seawater-cooled power and desalination plants

Thermal desalination systems are typically integrated with power plants to exploit the excess heat resulting from the power-generation units. Using seawater in cooling the power plant and the desalination system is a common practice in many parts of the world where there is a shortage of freshwater. Biofouling is one of the major problems associated with the usage of seawater in cooling systems. Because of the dynamic variation in the power and water demands as well as the changes in the characteristics of seawater and the process, there is a need to develop an optimal policy for scheduling biocide usage and cleaning maintenance of the heat exchangers. The objective of this article is to introduce a systematic procedure for the optimization of scheduling the dosing of biocide and dechlorination chemicals as well as cleaning maintenance for a power production/thermal desalination plant. A multi-period optimization formulation is developed and solved to determine: the optimal levels of dosing and dechlorination chemicals; the timing of maintenance to clean the heat-exchange surfaces; and the dynamic dependence of the biofilm growth on the applied doses, the seawater-biocide chemistry, the process conditions, and seawater characteristics for each time period. The technical, economic, and environmental considerations of the system are accounted for. A case study is solved to elucidate the applicability of the developed optimization approach.     

露点蒸发冷却装置性能评价指标的研究

本文通过搭建逆流式露点蒸发冷却装置,实验研究了空气入口温度、湿度和风速对露点效率、湿球效率、?效比等各性能评价指标的影响,提出了能够反映湿通道潜热交换的强弱和装置性能的适用于露点蒸发冷却的评价指标——换热放大系数.研究结果表明:进口温度为33、相对湿度为22％时,当风速从1 m/s增至3 m/s,制冷量从29.5 kW...     

Effect of jet length and ambient temperature on the performance of a two-phase jet impingement heat sink refrigeration system

The jet impingement heat sink integrated with a compact oil-free R-134a vapor compression refrigeration system introduced in a previous work (Oliveira and Barbosa, 2017) is now further evaluated in terms of the influence of the compressor piston stroke, applied thermal load, orifice-to-heater distance (jet length) and ambient (hot end) temperature. The proposed heat sink is a compact active thermal solution for concentrated heat loads because it integrates the evaporator and the expansion device into a single unit, making use of a single two-phase impinging jet as the cooling mechanism. The present analysis is based on the coefficient of performance and other steady-state heat transfer parameters associated with the impinging jet (heat transfer coefficient and heater surface temperature). A reduction of the jet length promoted a more vigorous splattering of the jet on the heated surface, enhancing the droplet breakup, which in turn reduced significantly the critical heat flux. An increase of the hot reservoir temperature increased the jet impingement heat transfer coefficient.     

用于批量快速筛选最佳低温保存程序的生物芯片技术

低温生物学应用中,筛选最佳的冻结、复温程序以及相应的保护剂配方,通常需要大量繁琐、费时且高度重复性的测试工作.将样品准备及其活性检测功能加以集成,首次在低温保存程序优化方面引入了生物芯片技术的概念.设计制作了相应的原型器件并开展实验研究.结果表明,流道式芯片用于样品分配时效果不佳,而点样式芯片则可实现快速、可靠的样品加载,红外实验进一步表明其传热一致性较好.在此基础上,利用点样式芯片与集成化的半导体制冷器件相结合,对多种生物样品的低温冷冻及复温效果进行了测试,基于对结果的比较分析可以筛选出最优的降温、复温程序及低温保护剂浓度配比.此外,还对批量测定低温保护剂溶液的热物性也进行了考察.研究表明,借助于功能集成化及检测自动化的生物芯片,可以实现大规模快速优化复杂低温保存程序.     

Thermal characteristics of a Hartmann-Sprenger tube

This paper describes the thermal characteristics of a water-cooled Hartmann-Sprenger (HS) tube as an expansion device for refrigeration and cryogenic applications. In this arrangement, a jet issuing from a convergent nozzle and expanded to a pressure below the critical value is directed towards the HS tube closed at the opposite end and maintained at resonant conditions. The interaction of the steady jet entering this tube, the generation and the propagation of the acoustic waves within the tube and the resulting non-linear flow oscillations result in strong thermal effects and heating of the entrapped gases. Effective heat removal at the surface of the HS tube results in a pseudo-positive Joule-Thomson coefficient. The emerging gas from such a nozzle-HS tube arrangement under resonant conditions will be much cooler when compared to the throttling process. The intense heating experienced in this arrangement using primary and secondary smaller tubes may find other industrial applications such as the flameless ignition of rocket engines. This experimental work suggests further investigations coupled with analytical modelling and optimization resulting in a device having either maximum cooling of the emerging stream or a high temperature heat source.     

冷热互联系统研究及其能效计算准则讨论

随着节能减排的不断深入和能源效率的逐步提高,同时利用冷量和热量的冷热互联系统将得到进一步的推广应用。与传统的制冷系统和制热系统的能效计算相比,冷热互联系统能综合利用冷热两部分的能量,原来单独冷、热量的能效计算法则是否适用于新的系统需要重新考虑。本文构建了复叠机组和热泵机组互联(A系统)、以及常规制冷机组和热泵互联(B系统)两种冷热互联系统,提出了3种能效计算方式,通过具体实验操作和分析给出了3种系统的COP计算方式和结果,其中第3种计算方法综合考虑了制冷系统制冷量和热泵系统制热量作为收益,将整个系统的轴功率看作补偿能量,最为合理。     

考虑热漏损失的实际空气制冷机制冷率密度优化

以制冷率密度作为热力性能目标,综合考虑热漏、热阻和循环内不可逆性,对不可逆简单空气制冷机进行分析,导出了制冷率密度和制冷系数解析关系式,对制冷率密度进行了优化,并由数值计算分析了热漏、压比、热导率分配等参数对制冷率密度的影响特点.     

The potential of solar energy use in desiccant cooling cycles

The use of heat produced by solar thermal collectors is an interesting option for thermal driven air conditioning processes. A thermal driven cooling technique which fits well to non-tracking solar collectors is the desiccant cooling technique. Recently several projects have been carried out which focus on the connection of desiccant cooling systems with solar thermal energy for regeneration of the sorbents. This communication deals with three main topics: (1) experiences achieved in a realized system which is coupled to a solar collector are discussed, (2) a new concept is presented, in which a solar air collector is integrated into the desiccant cooling cycle as the only heat source and (3) a comparative study is presented which compares system performance for different system configurations and different climatic situations.     

芯片封装均温板壳体的传热特性研究

高热流密度、微型化芯片的发展使传统金属材料的热扩散能力受限.本文设计加工了一款具有微针筋的均温板,应用于芯片封装壳体,实验研究了充液率、芯片尺寸、散热器运行参数(水流量、温度)对均温板壳体(VC IHS)传热性能的影响,并与同工况条件下芯片封装金属铜壳体(Cu IHS)的传热性能进行对比.结果表明:VC IHS的充液率...     

磁性纳米制冷剂冷却回路热磁对流特性研究

建立磁性纳米制冷剂Fe3O4-R600a冷却回路的热磁对流特性实验系统,研究了磁场分布、磁场强度、加热功率、冷却温度等对热磁对流特性的影响。结果表明：外磁场对磁性纳米流体热磁对流过程的影响非常明显,可无须机械泵驱动而实现能量的自主传递过程,冷却回路中的磁流体循环流动和传热性能取决于外磁场与温度的协同作用,应用外磁场有效可控制冷却回路的运行特性。     

基于自然循环预冷过程高效低温传热方法的初步研究

提出将自然循环预冷法与低温热管技术有机结合的设想,综合自然循环和低温热管的优点,可以实现连续、快速冷却,保证被冷却物体的温度波动较小,同时具有自反馈功能.详细介绍了基于自然循环预冷及低温热管的高效低温传热单元的设计及初步试验结果.给出了该低温传热单元在微机械(MEMS)电源开发中的应用实例.     

Effect of heat transfer on the performance of thermoelectric generator-driven thermoelectric refrigerator system

A model of thermoelectric generator-driven thermoelectric refrigerator with external heat transfer is proposed. The performance of the combined thermoelectric refrigerator device obeying Newton’s heat transfer law is analyzed using the combination of finite time thermodynamics and non-equilibrium thermodynamics. Two analytical formulae for cooling load vs. working electrical current, and the coefficient of performance (COP) vs. working electrical current, are derived. For a fixed total heat transfer surface area of four heat exchangers, the allocations of the heat transfer surface area among the four heat exchangers are optimized for maximizing the cooling load and the coefficient of performance (COP) of the combined thermoelectric refrigerator device. For a fixed total number of thermoelectric elements, the ratio of number of thermoelectric elements of the generator to the total number of thermoelectric elements is also optimized for maximizing both the cooling load and the COP of the combined thermoelectric refrigerator device. The influences of thermoelectric element allocation and heat transfer area allocation are analyzed by detailed numerical examples. Optimum working electrical current for maximum cooling load and COP at different total number of thermoelectric elements and different total heat transfer area are obtained, respectively.     

恒温恒湿空调系统的优化控制与性能模拟

针对传统恒温恒湿空调系统表冷器采用固定露点方法导致热湿补偿损失较大的缺点,采用热湿独立控制装置和PID分程控制方法,研制了一套恒温恒湿空调系统。在实验的基础上,利用TRNSYS 16软件建模,对系统在不同热湿负荷下的运行状况及节能效果进行了模拟分析。结果表明,该系统能自动调节表冷器冷冻水流量与温度,以及加热器或加湿器的投入量,实现对空气温湿度的独立控制,并达到设定的温湿度;在设计此类表冷器时,换热面积应该以较高的冷冻水进口温度(如12℃而不是通常的7℃)来进行计算。该系统节能效果显著,比传统系统在低温高湿工况下节能30%以上;在高温低湿工况下节能50%左右。     

变温热源不可逆布雷顿制冷循环制冷率密度优化

用有限时间热力学分析方法,制冷率密度为热力学优化目标,分析了变温热源条件下不可逆布雷顿制冷循环的性能,得到了普适的解析关系式,并由数值计算分析了压比、热导率分配以及工质和热源间热容率匹配等参数对制冷率密率的影响特点.     

工业余热热泵及余热网络化利用的研究现状与发展趋势

当前工业能源消耗中所排放的低品位余热量大面广,若采用高效的余热利用技术将这部分余热回收,将具有显著的节能效果。工业余热热泵技术可以实现余热品位的提升或容量的扩大,一方面可以将回收的热量应用到工业流程中,另一方面可以在区域供热及供冷方面发挥作用。本文分析了压缩式热泵、吸收式热泵与化学热泵的特点与发展趋势。目前三种热泵技术都在工质、循环以及系统创新方面得到了较大的发展,但是在容量、能效比、温升与可靠性方面存在不可兼得的瓶颈问题。此外,工业余热根据种类以及温度品位的不同,适用场合与特点也各不相同。但目前在余热回收利用的设备与系统方面,缺乏针对不同余热特点的指导性设计准则。未来的研究需要集中在发展效率高、容量大、热适应性好、稳定可靠的热泵技术,形成各余热热泵互补利用的广谱化设计准则。同时需要通过对余热的热、电、冷、储、运的网络化利用进行余热系统高质化集成,实现工业余热的高效利用。     

冰晶在肾组织中生长特点之初探

在微电脑控制的小样品升降温控制装置上，用透射电子显微镜研究了鼠肾组织在快速冷却后冰晶生长的一些特点，并结合传热分析方法和结晶动力学理论，定量地研究了肾细胞核内冰晶随位置的分布。