SOI-MOS器件的自热效应仿真及产热机理研究

随着微电子器件日益微型化和高速化,自热效应已逐渐成为限制其性能提升的重要因素,深入理解纳米尺度器件产热机理对电子器件的设计和优化具有重要意义.针对绝缘体上硅金属-氧化物半导体场效应晶体管(SOIMOS)进行了电热仿真,基于漂移扩散模型详细计算和分析了焦耳热、重组热和帕尔贴-汤姆逊热的生成及其影响.计算结果显示,焦耳热在器件内是主要的功耗来源,主要分布在栅极下方的导电沟道处,最大值出现在漏极端.与此相比,重组热的量级极小,主要分布在沟道区和源漏结区,其对温度场和器件性能的影响较弱.帕尔贴-汤姆逊热与焦耳热的产热量级相当,会影响器件温度分布.然而,由于其在栅极下方存在独特的冷热源交替分布,加热效应和制冷效应得到了抵消,同时引起的温度变化集中在源漏电极下方,导致其对器件性能基本不产生影响.此外,帕尔贴-汤姆逊热的影响与边界条件有关,在基底散热时,忽略帕尔贴-汤姆逊热会导致温度场预测发生较大偏差,这对于评估器件的寿命和可靠性非常关键.

车用动力锂电池产热机理研究现状

精确的锂离子电池产热量是电动汽车电池包热管理设计的基础。总结了现有锂离子电池产热模型,指出Bernadi产热模型在计算电池产热时通用性较高。整理了3种测量温熵系数dE/dT的方法:直接测量法、可逆热等值法以及极化热扣除法。给出了Bernadi产热模型关键参数温熵系数dE/dT特征值,为各类锂离子电池包产热计算提供了依据。

低真空度下土工离心机产热机理试验研究

目的为1000 g以上的大型高速土工离心机提供散热方案,保证土工离心机的正常工作。方法通过试验研究和理论分析相结合的方法,研究低真空度下高速转子的产热机理,分析散热模式。结果绝对压力越高,离心室内的升温速度越快。不同真空度下(绝对压力10000、5000、3000、2000、1000 Pa),离心机驱动电机的输入功耗分别为2.17、3.79、5.17、7.66、11.56 kW。超重力高速土工离心机的产热主要由空气与高速转子的摩擦引起的第一热源,由高速旋转空气与离心舱壁面摩擦产生的第二热源,还有其他机构摩擦、空气与底部顶部摩擦产生的少量热源。结论第一热源产生的壁面热量可以通过设置冷却夹套快速带走,离心舱中心产生的第二热源的热量可以通过通入适量的冷风加以冷却,还可以通过注入冷却剂快速蒸发,利用汽化潜热进行快速冷却。

热塑性复合材料感应植入焊技术研究进展

热塑性复合材料(TPC)感应植入焊(IIW)是一种利用TPC层合板搭接区域植入的电磁感受加热元件在高频交变磁场作用下自发热,使界面区域热塑性树脂熔融黏合,从而实现TPC结构连接的新技术。该技术具有操作简单、绿色高效、非接触等优点,近30年来受到工业部门的广泛关注。本文围绕TPC的IIW焊接工艺,系统地介绍产热机理、加热效应、工艺参数等对焊接头质量的影响;重点阐释了引起焊接区域温度不均匀的原因,提出了调控焊接区域温度分布的方法,揭示温度场均匀性与焊接头质量的关系;最后讨论了在参数优化中缺少准确的产热传热温度场模型以及实际生产中缺少适配大型TCP结构焊接专门设备的问题,为IIW技术的未来发展方向提供了一定的指导。

中医学中的热力学问题

热力学是自然科学中最普遍、最基本的规律之一。本文对中医学中的热力学内容进行了初步的探讨,阐述了中医学与热力学的有机联系及热力学原理对中医研究的意义。

Performance analysis of aircraft low-power thermoelectric refrigeration system

An optimal design method for an aircraft low-power thermoelectric refrigeration system（TRS）is proposed using an existing experimental model as the research platform under given aircraft flight conditions.The variation curves of the cooling capacities and the refrigeration coefficients of the system running at three flight altitudes are investigated.The performance of the system is evaluated by the minimum-entropy-generation method and the performance penalty is also calculated.The power variation curves of the cooling system are obtained by an electric power experiment.The peak values of these curves are less than the maximal electric power supply of airborne equipment,proving that the use of the low-power TRS for airborne equipment is feasible.The COP,cooling capacity and entropy generation of the system are relative to the flight altitude and the current of the TRS.Through the analyses of these data,the optimal values of the COP are obtained,and the optimization measures are proposed to maximize the use of the advantages of the TRS.

Estimate of China's energy carbon emissions peak and analysis on electric power carbon emissions

China＇s energy carbon emissions are projected to peak in 2030 with approximately 110% of its 2020 level under the following conditions： 1） China＇s gross primary energy consumption is 5 Gtce in 2020 and 6 Gtce in 2030; 2） coal＇s share of the energy consumption is 61% in 2020 and 55% in 2030; 3） non-fossil energy＇s share increases from 15% in 2020 to 20% in 2030; 4） through 2030, China＇s GDP grows at an average annual rate of 6%; 5） the annual energy consumption elasticity coefficient is 0.30 in average; and 6） the annual growth rate of energy consumption steadily reduces to within 1%. China＇s electricity generating capacity would be 1,990 GW, with 8,600 TW h of power generation output in 2020. Of that output 66% would be from coal, 5% from gas, and 29% from non-fossil energy. By 2030, electricity generating capacity would reach 3,170 GW with 11,900 TW h of power generation output. Of that output, 56% would be from coal, 6% from gas, and 37% from non-fossil energy. From 2020 to 2030, CO2 emissions from electric power would relatively fall by 0.2 Gt due to lower coal consumption, and rela- tively fall by nearly 0.3 Gt with the installation of more coal-fired cogeneration units. During 2020--2030, the portion of carbon emissions from electric power in China＇s energy consumption is projected to increase by 3.4 percentage points. Although the carbon emissions from electric power would keep increasing to 118% of the 2020 level in 2030, the electric power industry would continue to play a decisive role in achieving the goal of increase in non-fossil energy use. This study proposes countermeasures and recommendations to control carbon emissions peak, including energy system optimization, green-coal-fired electricity generation, and demand side management.

Simulation and performance analysis of organic Rankine cycle combined heat and power system

To improve the overall thermal efficiency of the organic Rankine cycle（ ORC）, a simulation study was carried out for a combined heat and power（ CHP） system, using the Redlich-Kuang-Soave（ RKS） equation of state. In the system,R245 fa was selected as the working fluid. A scroll expander was modeled with empirical isentropic expansion efficiency.Plate heat exchangers were selected as the evaporator and the condenser, and detailed heat transfer models were programmed for both one-phase and two-phase regions. Simulations were carried out at seven different heat source temperatures（ 80,90, 100, 110, 120, 130, 140 ℃） in combination with eight different heat sink temperatures（ 20, 25, 30, 35, 40, 45, 50,55 ℃）. Results showthat in the ORC without an internal heat exchanger（ IHE）, the optimum cycle efficiencies are in the range of 7. 0% to 7. 3% when the temperature differences between the heat source and heat sink are in the range of 70 to90 ℃. Simulations on CHP reveal that domestic hot water can be produced when the heat sink inlet temperature is higher than40 ℃, and the corresponding exergy efficiency and overall thermal efficiency are 29% to 56% and 87% to 90% higher than those in the non-CHP ORC, respectively. It is found that the IHE has little effect on the improvement of work output and efficiencies for the CHP ORC.

New type steam turbine for cogeneration

A concept of energy saving & efficiency improving from cold source for cogeneration steam turbine was discussed herein. A new type "NCB" cogeneration steam turbine was proposed,which could considerably increase heat supply capacity,thermal efficiency and electric power. Taking 300 MW cogeneration steam turbine as an example,the results show that heat supply capacity reaches the maximum,i.e. increases by 30 %,thermal efficiency is improved by 12 %,and electric power is enhanced by 15 MW during peak heat load.

循环过程的教学探讨

循环过程是一个重要的热力学基本过程.本文旨在探讨循环过程的教学及其在热力学理论和热机循环上的应用.

Performance Analysis and Retrofit on 350-MW China-Made Supercritical Steam Turbines

In this paper the development status and background of 350-MW China-made supercritical steam turbines are introduced.Through the study on the eight turbines that are put into operation,their technical performances are compared and summarized.The major factors affecting the heat consumption rate are analyzed in details and the technical measures to reduce the heat consumption rate are put forward.These measures have been applied to several such units with significant improvements,which can provide important references for the maintenance and retrofit of 350-MW super critical steam turbines.

Making Use of the Eddy Currents Effect in the Examination of the Tribological Characteristics of Strip Rolling Mill Rolls

The key element in the proper performance of a rolling mill is the careful planning of the rolls operational conditions, since this factor constitutes the restricting element in the manufacturing process. In the article, a collection of operation and research steel strips hot-rolling mill information was presented, which was processed based on the advanced computer programmes for rolls grinders. The research outcomes were produced, presenting the application of eddy currents to detect materials flaws in metallurgical mill rolls.

Impact of Planting Position and Planting Material on Root Yield of Cassava （Manihot esculenta Crantz）

Cassava （Manihot esculenta Crantz） is a perennial woody shrub with an edible root, which grows in tropical and subtropical areas of the world. In Africa, cassava provides a basic daily source of dietary energy. It plays an important role in food security and incomes of many rural households in the southern Ethiopia. However, information available on production practices of cassava for the region is insufficient. Hence, field experiment was conducted at Awassa Agricultural Research Center for two successive cropping seasons from 2004 to 2006 to investigate the response of cassava to planting position and planting material. The treatments used were three planting positions （slant, vertical and horizontal） and five planting materials （main stem top part, main stem middle part, main stem bottom part, branch stake top part and branch stake bottom part） were combined in factorial arrangement and laid out in randomized complete block design with three replications. The result revealed that root yield was significantly （P 〈 0.05） affected by the interaction effects of the planting position and planting material. The highest yield （25.2 ton ha^-1） was obtained from the main stem top part planted in slant position whereas the least yield （6.5 ton ha^-1） was obtained from main stem bottom part planted in horizontal position. Based on the findings of this study, areas like Awassa with moderate rainfall slant and vertical planting of main stem top and middle parts could be used as planting material.

Design and Sizing Electric Micro Generator Using Thermoelectric Modules

This paper presents the development of a methodology for calculating sizing electric micro sources of power generation using TEG （thermoelectric modules） to capture energy industrial process waste. Since the thermoelectric modules are able to convert a temperature gradient directly into electricity and still occupy a small space, and have no vibration or noise during operation. Furthermore, the cogeneration using thermoelectric modules is totally clean and reuses part of the residual thermal energy to generate power, or improve the overall yield of the process and avoid the emission of gases to the environment. Therefore, this research contributes to the development of a green energy to numerical modeling for the design and dimensioning of micro-sources of electric power generation from performance curves and predetermined temperature gradients industrial processes. The result is an effective methodology for the design and conditioning the voltage level and power of micro allowing the size of the electrical quickly and securely for many industrial applications, varying the types of modules used area, voltage and power generated.

Mathematical model of absorption and hybrid heat pump

Recovering waste heat from industrial processes is bene ficial in order to reduce the primary energy demands and heat pumps can be used to this purpose.Absorption heat pumps are energy-saving and environment-friendly because use working fluids that do not cause ozone depletion and can reduce the global warming emissions.The hybrid heat pump processes combine the conventional vapor-compression and the absorption heat pump cycles.Studies about the simulations and modeling of hybrid heat pumps are few in literature.In this research a mathematical model for single effect absorption and hybrid heat pump is carried out with Chem Cad? 6.0.1.LiBr–H_2O is used as working fluid while electrolytic NRTL and electrolytes latent heat are used as thermodynamic model due to the better results.Binary parameters of activity coef ficients are regressed from experimental vapor pressure data while default constants are used for the solubility expressions.A design of heat pumps is developed and a new modeling of generator is analyzed.The coef ficient of performance of absorption heat pump and hybrid heat pump is equal to 0.7 and 0.83 respectively.For absorption heat pump a sensitivity analysis is carried out to evaluate the effect of temperature and pressure generator,the concentration of Li–Br solution on coef ficient of performance,cooling capacity and working fluid temperature.For hybrid heat pump,the different coef ficients of performance,the primary energy ratio,the generator heat,and the compressor power are analyzed for different values of compressor proportion.Results show that comparing the two systems the hybrid pump allows to save more primary energy,costs and carbon dioxide emissions with respect to absorption heat pump with the increasing of compressor proportion parameter.Future researches should focus on the construction of this heat pumps integrated in chemical processes as a biogas plant or trigeneration systems.

Exergetic Performance Analysis of a Cogeneration Plant at Part Load Operations

A cogeneration plant can run at off-design due to change of load demand or ambient conditions. The cogeneration considered for this study is gas turbine based engine consists of variable stator vanes （VSVs） compressor that are re-staggered for loads greater than 50% to maintain the gas turbine exhaust gas temperature at the set value. In order to evaluate the exergetic performance of the cogeneration, exergy model of each cogeneration component is formulated. A 4.2 MW gas turbine based cogeneration plant is analysed for a wide range of part load operations including the effect of VSVs modulation. For loads less than 50%, the major exergy destruction contributors are the combustor and the loss with the stack gas. At full load, the exergy destructions in the combustor, turbine, heat recovery, compressor and the exergy loss with stack gas are 63.7, 14.1, 11.5, 5.7, and 4.9%, respectively. The corresponding first and second law cogeneration efficiencies are 78.5 and 45%, respectively. For comparison purpose both the first and second law efticiencies of each component are represented together. This analysis would help to identify the equipment where the potential for performance improvement is high, and trends which may aid in the design of future plants.

An Energy and Exergy Analysis of a Microturbine CHP System

The micro-turbine is known as a producer of high-grade energy （work） and also low energy （heat）. The following low grade heat energy have been modeled under ISO ambient conditions （international standard organization）, i.e. 15 ℃ and 1 bar, to utilize the waste heat energy of a 200 kW micro-turbine combined with a single effect absorption chiller, an organic ranking cycle using R245fa （ORC-R245 fa） as a working fluid, a multi-effect distillation desalination （MED） and a thermal vapor compression MED Desalination unit （TVC-MED）. The thermal comparison was carried out based on an energy and exergy analysis in terms of electric efficiency, exergetic efficiency, carbon footprint, and energy utilization factor （EUF）. The software package IPSEpro has been used to model and simulate the proposed power plants. As a result, utilizing the exhaust waste heat energy in single-effect absorption chillier has contributed to stabilize ambient temperature fluctuation, and gain the best exergetic efficiency of 39%, while the EUF has reached 72% and the carbon footprint was reduced by 75% in MED and TVC-MED Desalination respectively. The results also reveal that TVC-MED is more efficient than traditional MED as its gain output ratio （GOR） is improved by 5.5%. In addition, ORC-245fa generates an additional 20% of the micro-turbine electricity generation.

Step-Loading Characteristics of Gas Engine Cogeneration System Using Doubly-Fed Induction Generator in Stand-Alone Operation

Application of a DFIG （doubly-fed induction generator）, which is one of adjustable speed generators, to a gas engine cogeneration system has been investigated. To operate during a blackout as an emergency power supply is one of important roles for the gas engine eogeneration system. In the case of conventional constant speed of synchronous generator, the amount of the allowed step load is limited to around 30% of the rated power. On the other hand, DFIG is expected to increase the amount of step load during the stand-alone operation. In this paper, it has been demonstrated that an increase in the gas engine speed resulted in an increase in the maximum amount of step load using experimental equipment with a real gas engine. It has been concluded that the proposed system can improve the performance of an emergency power supply at step-loading.

Local Entropy Production in Turbulent Shear Flows:A Tool for Evaluating Heat Transfer Performance

Performance evaluation of heat transfer devices can be based on the overall entropy production in these devices. In our study we therefore provide equations for the systematic and detailed determination of local entropy production due to dissipation of mechanical energy and due to heat conduction, both in turbulent flows. After turbulence modeling has been incorporated for the fluctuating parts the overall entropy production can be determined by integration with respect to the whole flow domain. Since, however, entropy production rates show very steep gradients close to the wall, numerical solutions are far more effective with wall functions for the entropy production terms. These wall functions are mandatory when high Reynolds number turbulence models are used. For turbulent flow in a pipe with an inserted twisted tape as heat transfer promoter it is shown that based on the overall entropy production rate a clear statement from a thermodynamic point of view is possible. For a certain range of twist strength there is a decrease in overall entropy production compared to the case without insert. Also, the optimum twist strength can be determined. This information is unavailable when only pressure drop and heat transfer data are given.

Analysis of an electricity-cooling cogeneration system for waste heat recovery of gaseous fuel engines

Waste heat recovery(WHR)is one of the most useful ways to improve the efficiency of internal combustion engines,and an electricity-cooling cogeneration system(ECCS)based on Rankin-absorption refrigeration combined cycle for the WHR of gaseous fuel engines is proposed in the paper.This system can avoid wasting the heat in condenser so that the efficiency of the whole WHR system improves,but the condensing temperature of Rankin cycle(RC)must increase in order to use absorption refrigeration system,which leads to the decrease of RC output power.Therefore,the relationship between the profit of absorption refrigeration system and the loss of RC in this combined system is the mainly studied content in the paper.Because the energy quality of cooling and electricity are different,cooling power in absorption refrigeration is converted to corresponding electrical power consumed by electric cooling system,which is defined as equivalent electrical power.With this method,the effects of some important operation parameters on the performance of the ECCS are researched,and the equivalent efficiency,exergy efficiency and primary energy rate are compared in the paper.