两级半导体制冷性能优化设计

在半导体制冷单元制冷基本公式的基础上,按照最大制冷系数的设计方法,得到了两级半导体制冷电堆中间温度的计算公式。根据建立的模型,对制冷单元的尺寸进行了优化设计,给出了级间元件个数比的最优分配,并分析了相应的影响因素。本文所得的结果对多级半导体制冷的优化设计具有一定的理论意义。     

优化半导体制冷工况的理论分析

对半导体制冷的原理进行简单介绍,同时对三种不同工况下半导体制冷进行理论分析,导出使制冷量和制冷系数达到最大值时的电流值,并由此得出设计用的主要参数,给半导体制冷器的设计提供了依据。     

Simulation of the transient temperature distribution in a high-power semiconductor device cooling apparatus using heat pipes

This study describes the transient temperature distributions in a cooling apparatus for high-power semiconductor devices used in electric-railcar drive systems. The cooling apparatus is composed of heat pipes, air-cooled fin arrays, and a metal block which is used for attaching several semiconductor packages, In our numerical simulation model, we substituted solid elements for the heat pipes, and determined their thermal properties by experiment. As a result, we could obtain transient temperature distributions for the cooling apparatus through a heat conduction analysis. Calculated results showed that when the amount of heat generated in the devices changes, the temperature of the cooling apparatus changes more slowly than that of the devices. A comparison between the transient-temperature distribution calculations and the experiments confirmed the accuracy of the modeling and prediction method. Thus, these calculations can be used to provide data for packaging design, especially concerning thermal stress and fatigue in the packages. © 1998 Scripta Technica, Inc. Heat Trans Jpn Res, 26(2): 107–115, 1997     

浅论防腐蚀节能管理中的腐蚀监测

讨论腐蚀监测以及它在防腐蚀节能管理中的作用,通过落实腐蚀监测管理,从而达到安全高效节能的目的。针对腐蚀行业的特殊性,实现节能降耗的深入化管理,必须先从源头上达到规范化的防腐蚀能力,利用信息技术,大量使用各种类型自动化仪表,再实现从预防性维护到预测性维护观念的根本转变,使腐蚀节能管理与资产管理的概念逐步系统化、统一化,才能实现真正意义上的大节能、大环保。     

Nonlinear optimal on-line heat-dissipation control methodology in electronic devices

The essential element in obtaining semiconductor electronic device enhanced reliability involves solving the heat-dissipating issue. Certain electronic components possess varying thermal properties and the strength of the heat generated by the semiconductor chip is unknown. Therefore, the heat dissipation control problem is both complicated and perplexing. This paper proposes a methodology, the LQG/IE tracking algorithm, to solve the nonlinear heat dissipation control problem. The IE method, which is a combination of an Extended Kalman filter and Recursive Least Squares Estimator, estimates (in real time) the unknown time-varying heat source generated by the semiconductor chip using temperature measurements of the package seal surface. The LQG tracking algorithm is adopted to analyze the feedback gain to control the heat dissipation. The simulation results reveal that an effective and optimal heat dissipation controller can be implemented for the cooling system using the LQG/IE tracking algorithm.     

Electrospray cooling for microelectronics

The challenge of effectively removing high heat flux from microelectronic chips may hinder future advancements in the semiconductor industry. Spray cooling is a promising solution to dissipate high heat flux, but traditional sprays suffer from low cooling efficiency partly because of droplet rebound. Here we show that electrosprays provide highly efficient cooling by completely avoiding the droplet rebound, when the electrically charged droplets are pinned on the heated conducting surface by the electric image force. We demonstrate a cooling system consisting of microfabricated multiplexed electrosprays in the cone-jet mode generating electrically charged microdroplets that remove a heat flux of 96 W/cm² with a cooling efficiency reaching 97%. Scale-up considerations suggest that the electrospray approach is well suited for practical applications by increasing the level of multiplexing and by preserving the system compactness using microfabrication.     

The analysis of triangular cycles of cooling and heating

Theoretical study of triangular cycle with cooling and heating at variable temperatures is investigated in this study. Simple approximated correlations for COP are obtained. By implementation of the cooling and heating using multistage machines, single-compressor machines accompanying with refrigerants mixtures, semiconductor thermopiles, and the supercritical cycles with variable temperature of heat rejection, the “triangular” cycle shows promising interesting features.     

Power consumption of semiconductor fabs in Taiwan

This paper reports and analyzes power consumption for nine representative semiconductor fabs in Taiwan. The power consumption data were obtained by surveys and site visits. Analysis results indicate that the average power consumption for the fabs is 2.18 kW/m² and the average cooling load is 0.434 RT/m². The average power consumption per unit product (wafer) area is 1.432 kWh/cm², which is consistent with the data (3.1 kWh/cm² in 1983 to 1.41 kWh/cm² in 1995) reported by the US Department of Commerce and Dataquest. The facility system consumes the most of the power consumption (about 56.6%) of the semiconductor fabs. Process tools are the next largest power consuming item, accounting for 40.4% of the power consumed in the fabs. A facility system includes the chiller plant, makeup air, recirculation air, exhaust air, gases, compressed dry air, process cooling water, vacuum and ultra-pure water systems. The power consumption of the different facility components is analyzed and compared.     

Modelling of a pin-fin heat converter with fluid cooling for power semiconductor modules

This paper presents a way to design a finite-element computer model of cooling system with a complicated geometry. The computer model is developed on the basis of a commercial software package ABAQUS. The steady state forced-convective fluid cooling of a pin-fin heat converter for power (∼1 kW heat power) semiconductor module has been investigated on the basis of computer simulation. A phenomenological equation has been used for calculation of the local value of the heat transfer coefficient for the liquid-solid interface. The impacts of the thermal conductivity of the pin-fin sink material, volume flow rate of the cooling liquid and geometrical design of the pin-fin sink on the thermal resistance of the converter are shown. Copyright © 2003 John Wiley & Sons, Ltd.     

Geometric optimization of thermoelectric coolers in a confined volume using genetic algorithms

The demand for thermoelectric coolers (TEC) has grown significantly because of the need for a steady, low-temperature operating environment for various electronic devices such as laser diodes, semiconductor equipment, infrared detectors and others. The cooling capacity and its coefficient of performance (COP) are both extremely important in considering applications. Optimizing the dimensions of the TEC legs provides the advantage of increasing the cooling capacity, while simultaneously considering its minimum COP. This study proposed a method of optimizing the dimensions of the TEC legs using genetic algorithms (GAs), to maximize the cooling capacity. A confined volume in which the TEC can be placed and the technological limitation in manufacturing a TEC leg were considered, and three parameters––leg length, leg area and the number of legs––were taken as the variables to be optimized. The constraints of minimum COP and maximum cost of the material were set, and a genetic search was performed to determine the optimal dimensions of the TEC legs. This work reveals that optimizing the dimensions of the TEC can increase its cooling capacity. The results also show that GAs can determine the optimal dimensions according to various input currents and various cold-side operating temperatures.     

Numerical simulation of thermal runaway phenomena in silicon semiconductor devices

A mathematical model for heat production due to thermal excitation of conductive electrons and positive holes in a semiconductor pn junction is derived and discussed. The model is applied to simulate the thermal runaway phenomena in power electronics semiconductor devices. Our discussion focuses especially on the modeling of unexpected huge currents due to an excessive temperature increase. Calculated dynamics of temperature distributions of a silicon wafer while cooling performance decreases proved it is possible for a silicon wafer to be heated over its melting point in a few milliseconds. Our results indicate that if a local hot spot arises in a wafer, the thermal intrinsic excitation carries an increased diffusion current of minor carriers and a recombination current in the depletion layer of a pn junction. Also it appears to be important that cooling performance should be uniform on the wafer to avoid the growth of hot spots and thermal‐runaway itself. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(6): 438–455, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10044     

Fluid and thermal analysis of a microchannel electronics cooler using computational fluid dynamics

Fluid flow and heat transfer of a microchannel electronics cooler is analyzed using computational simulation and experimental validation. The microchannel cooling technique appears to be a viable solution to high heat rejection requirements of today’s high-power electronic devices, such as diode lasers. The thermal design of these small electronics cooling devices is a key issue that needs to be optimized in order to keep the system temperatures at certain levels. However, this optimization should balance the heat transfer with pressure drop through the system by modifying the geometrical design. This technique is used in optimizing the performance of a microchannel cooler for high-power semiconductor diode laser applications in this study. The results show that symmetrical design modifications improve both pressure drop and heat transfer significantly, while resizing the channels may affect slightly.     

一种新型太阳能冷热联产系统的设计

基于节能环保的理念,设计了一种新型太阳能冷热联产系统。该系统利用太阳能作为能量来源,半导体制冷片作为制冷元件,同时回收系统的废热,整套系统的能源利用效率较高。以能量平衡与传热理论为基础,结合理论计算和数值模拟,证明该系统可实现冷热联产的功能,制冷能效COP为0.7,热量利用效率达73.5%。     

不可逆半导体固态热离子制冷器性能分析和优化

建立了考虑外部有限速率传热过程和热源间热漏的不可逆半导体固态热离子制冷器模型,基于非平衡热力学和有限时间热力学理论导出了热离子制冷器的制冷率和制冷系数的表达式;对比分析了不可逆热离子制冷器与可逆热离子制冷器的发射电流密度特性、电极温度特性以及制冷系数特性;研究了不可逆系统的制冷率与制冷系数最优性能,得到了制冷率和制冷系数的最优运行区间;通过数值计算,详细讨论了外部传热以及内部导热、热源间热漏损失、热源温度、外加电压、半导体材料势垒等设计参数对热离子装置性能的影响。在总传热面积一定的条件下,进一步优化了高、低温侧换热器的面积分配以获得最佳的制冷率和制冷系数特性。结果表明,由于存在内部和外部的不可逆性,热离子装置的发射电流密度及制冷系数都会明显降低;不可逆半导体固态热离子制冷器的制冷率与制冷系数特性呈扭叶型;合理地选外加电压、势垒等参数,可以使制冷器设计于最大制冷率或最大制冷系数的状态。     

Suppression of melt convection in a proposed Bridgman crystal growth system

Numerical simulations are performed for Bridgman crystal growth of several semiconductor materials, such as InAs, InSb, GaSe, CdTe, PbTe, and GaP. For materials with low Prandtl and low Grashof numbers, melt convection is weak and the traditional Bridgman technique is a suitable growth process. For the materials with high Prandtl numbers in their melt status and the growth system with high Grashof number, the temperature field and the growth interface are significantly influenced by melt flow, resulting in the complicated flow pattern and curved interface shape. A new Bridgman crystal growth system is proposed to suppress convection and improve solidification interface shape by cooling of the top melt. The results obtained from the proposed design demonstrate that melt convection may be controlled by adjusting the design parameters. Further, parametric studies are performed to determine the influence of the control parameters on melt flow and solidification interface.     

Thin semiconductor films for radiative cooling applications

Passive cooling systems use simple low-cost techniques to provide summer comfort in warm climates and can also be used to keep food, liquids and other materials at temperatures below ambient. Radiative cooling devices require a convective shield that should reject solar radiation but be transparent to mid-IR thermal radiation. In this paper, chemical solution deposition of thin semiconductor films (PbS and PbSe) onto polyethylene foils for radiative cooling applications is described. Optical and structural characterizations of the films were performed using UV–Vis, FTIR spectroscopies, X-ray diffraction and electron microscopy. Additionally, pigmented shields, which exhibit good radiation scattering properties, were prepared by incorporation of ZnS or ZnO into polyethylene. We also studied a combination of pigmented polyethylene foils coated with thin films of PbS that show improved optical properties for cooling purpose.     

Thermal effect of a thermoelectric generator on parallel microchannel heat sink

Thermoelectric generators (TEG) convert heat energy to electrical power by means of semiconductor charge carriers serving as working fluid. In this work, a TEG is applied to a parallel microchannel heat sink. The effect of the inlet plenum arrangement on the laminar flow distribution in the channels is considered at a wide range of the pressure drop along the heat sink. The particular focus of this study is geometrical effect of the TEG on the heat transfer characteristics in the micro-heat sink. The hydraulic diameter of the microchannels is 270 μm, and three heat fluxes are applied on the hot surface of the TEG. By considering the maximum temperature limitation for Bi₂Te₃ material and using the microchannel heat sink for cooling down the TEG system, an optimum pumping power is achieved. The results are in a good agreement with the previous experimental and theoretical studies.     

Application of two-phase vapor chamber technique for hard disk drive cooling of PCs

The internal mechanism of the hard disk drive is seriously damaged if it is subjected to forces outside the environmental specifications. The results of the investigation on the thermal cooling of vapor chamber for cooling hard disk drive of the personal computer are presented. It was found that the vapor chamber cooling technique has a significant effect on the thermal cooling of a hard disk drive. The average hard disk drive temperature with the vapor chamber cooling system is 15.21%, which is lower than those without the vapor chamber cooling system. The results of this study are of technological importance for the efficient design of cooling systems of personal computers or electronic devices to enhance cooling performance.     

Temperature effect on the electrical properties of pyrolytic MnO2 thin films prepared from Mn(C2H3O2)2·4H2O

Spray deposited MnO₂ thin films onto glass substrate were subjected to a post-deposition heat treatment and the effects of temperature on electrical transport properties were studied in details. The heating and cooling cycles of the samples are reversible after successive heat-treatments in air and vacuum. The films were polycrystalline in structure and the oxygen chemisorption–desorption process was found to play an important role in controlling the electronic properties. Various grain-boundary and energy band parameters were calculated by taking conventional extrinsic semiconductor theory and grain boundary trapping models into account. The samples were non-degenerate n-type semiconductors. The transport properties are interpreted in terms of Seto's model which was proposed for polycrystalline semiconducting films. The inter-crystallite boundaries of the thin films play an important role in the transport properties.     

Investigation of Natural Draft Cooling Tower in China

ABSTRACT

The natural draft cooling tower has been widely used in thermal power plants because of its stable operation, lower maintenance cost, and smaller environmental impact. Hundreds of natural draft cooling towers have been built in China, including different types and various capacities of conventional cooling towers, seawater cooling towers, flue gas injection cooling towers, cooling towers with water collecting device, dry cooling towers, and others. A wide range of investigation for natural draft cooling towers was carried out for the first time by the Electric Power Planning & Engineering Institute in 2013 in China. Based on the collected data and summarized information, the statistical results and conclusive opinions are analyzed. The development trend of natural draft cooling tower technology is also explored in this paper. The investigation results are expected to be a reference for designing and operating natural draft cooling towers in thermal power plants.