Thermal-electrical Coupled Analysis and Experimental Investigation on Spark Plasma Sintering of SiC Ceramics

Finite element simulations were conducted to study the mechanism of spark plasma sintering. The spark plasma sintering of SiC ceramics was simulated by the Marc software based on the load current curve and temperature-time curve deserved by SPS experiment. The concept of equivalent radiation coefficient was presented and applied during the simulation. The temperature distribution regularity of SiC ceramics sintered by SPS technology was got by thermal-electrical coupled finite element simulation. The experimental results show that by thermal-electrical coupled finite element analysis, the temperature rising and distribution regularity of nonconductive material can be preferable forecasted in the sintering process of SPS. In the initial stage of the heat preservation, the temperature of the central part of the sample has achieved sintering temperature, but now, the temperature of the sample is not uniform. The temperature for each part of the die is also quite different and the sample temperature in the center is higher than that in the edge. In the end of heat preservation, the central temperature of the sample is 50 ℃higher than the required sintering temperature, and the temperature gap for each part of the die decreases gradually.

Fast Calculation Method of Energy Flow for Combined Electro-Thermal System and Its Application

In recent years, Combined electro-thermal system has developed rapidly. In order to provide the initial data for the analysis of the combined electro-thermal system, a practical energy flow calculation method for the combined electro-thermal system is proposed in this paper. Based on the detailed analysis of the topology structure of the heating network and its hydraulic and thermodynamic model, the forward-backward sweep method for the heat flow of the heating network is established, which is more suitable for the actual radial heating network. The electric and thermal coupling model for heating source, such as thermoelectric unit and electric boiler is established, and the heat flow of heating network and the power flow of power grid are calculated orderly, thus a fast calculation method for the combined electro-thermal system is formed. What’s more, a combined electro-thermal system with two-stage peak-shaving electric boiler is used as the example system. This paper validates the effectiveness and rapidity of this method through the example system, and analyzes the influence for the energy flow of combined electro-thermal system caused by the operating parameters such as the installation location of electric boiler, the outlet water temperature of heat source and the outlet flow rate, etc.

ANALYSIS OF SHAKEDOWN OF FG BREE PLATE SUBJECTED TO COUPLED THERMAL-MECHANICAL LOADINGS

The static and kinematic shakedown of a functionally graded （FG） Bree plate is analyzed. The plate is subjected to coupled constant mechanical load and cyclically varying temperature. The material is assumed linearly elastic and nonlinear isotropic hardening with elastic modulus,yield strength and the thermal expansion coeffcient varying exponentially through the thickness of the plate. The boundaries between the shakedown area and the areas of elasticity,incremental collapse and reversed plasticity are determined,respectively. The shakedown of the counterpart made of homogeneous material with average material properties is also analyzed. The comparison between the results obtained in the two cases exhibits distinct qualitative and quantitative difference,indicating the importance of shakedown analysis for FG structures. Since FG structures are usually used in the cases where severe coupled cyclic thermal and mechanical loadings are applied,the approach developed and the results obtained are significant for the analysis and design of such kind of structures.

Simulation of District Cooling Plant and Efficient Energy Air Cooled Condensers (Part I)

In hot arid countries with severe weather, the summer air conditioning systems consume much electrical power at peak period. Shifting the loads peak to off-peak period with thermal storage is recommended. Model A of residential buildings and Model B of schools and hospitals were used to estimate the daily cooling load profile in Makkah, Saudi Arabia at latitude of 21.42°N and longitude of 39.83°E. Model A was constructed from common materials, but Model B as Model A with 5 - 8 cm thermal insulation and double layers glass windows. The average data of Makkah weather through 2010, 2011 and 2012 were used to calculate the cooling load profile and performance of air conditioning systems. The maximum cooling load was calculated at 15:00 o’clock for a main floor building to a 40-floor of residential building and to 5 floors of schools. A district cooling plant of 180,000 Refrigeration Ton was suggested to serve the Gabal Al Sharashf area in the central zone of Makkah. A thermal storage system to store the excess cooling capacity was used. Air cooled condensers were used in the analysis of chiller refrigeration cycle. The operating cost was mainly a function of electrical energy consumption. Fixed electricity tariff was 0.04 $/kWh for electromechanical counter, and 0.027, 0.04, 0.069 $/kWh for shifting loads peak for the smart digital counter. The results showed that the daily savings in consumed power are 8.27% in spring, 6.86% in summer, 8.81% in autumn, and 14.55% in winter. Also, the daily savings in electricity bills are 12.26% in spring, 16.66% in summer, 12.84% in autumn, and 14.55% in winter. The obtained maximum saving in consumed power is 14.5% and the daily saving in electricity bills is 43% in summer when the loads peak is completely shifted to off-peak period.

Analysis and FDTD Modeling of the Influences of Microwave Electromagnetic Waves on Human Biological Systems

The interactions of electromagnetic waves with the human body are complex and depend on several factors related to the characteristics of the incident wave, including its frequency, its intensity, the polarization of the tissue encountered, the geometry of the tissue and its electromagnetic properties. That’s to say, the dielectric permittivity, the conductivity and the type of coupling between the field and the exposed body. A biological system irradiated by an electromagnetic wave is traversed by induced currents of non-negligible density;the water molecules present in the biological tissues exposed to the electromagnetic field will begin to oscillate at the frequency of the incident wave, thus creating internal friction responsible for the heating of the irradiated tissues. This heating will be all the more important as the tissues are rich in water. This article presents the establishment from a mathematical and numerical analysis explaining the phenomena of interaction and consequences between electromagnetic waves and health. Since the total electric field in the biological system is unknown, that is why it can be determined by the Finite Difference Time Domain FDTD method to assess the electromagnetic power distribution in the biological system under study. For this purpose, the detailed on the mechanisms of interaction of microwave electromagnetic waves with the human body have been presented. Mathematical analysis using Maxwell’s equations as well as bio-heat equations is the basis of this study for a consistent result. Therefore, a thermal model of biological tissues based on an electrical analogy has been developed. By the principle of duality, an electrical model in the dielectric form of a multilayered human tissue was used in order to obtain a corresponding thermal model. This thermal model made it possible to evaluate the temperature profile of biological tissues during exposure to electromagnetic waves. The simulation results obtained from computer tools show that the temperature in the biological tissue is a linear function of the duration of exposure to microwave electromagnetic waves.

Optimized scheduling of integrated energy systems for low carbon economy considering carbon transaction costs

With the introduction of the“dual carbon”goal and the continuous promotion of low-carbon development,the integrated energy system(IES)has gradually become an effective way to save energy and reduce emissions.This study proposes a low-carbon economic optimization scheduling model for an IES that considers carbon trading costs.With the goal of minimizing the total operating cost of the IES and considering the transferable and curtailable characteristics of the electric and thermal flexible loads,an optimal scheduling model of the IES that considers the cost of carbon trading and flexible loads on the user side was established.The role of flexible loads in improving the economy of an energy system was investigated using examples,and the rationality and effectiveness of the study were verified through a comparative analysis of different scenarios.The results showed that the total cost of the system in different scenarios was reduced by 18.04%,9.1%,3.35%,and 7.03%,respectively,whereas the total carbon emissions of the system were reduced by 65.28%,20.63%,3.85%,and 18.03%,respectively,when the carbon trading cost and demand-side flexible electric and thermal load responses were considered simultaneously.Flexible electrical and thermal loads did not have the same impact on the system performance.In the analyzed case,the total cost and carbon emissions of the system when only the flexible electrical load response was considered were lower than those when only the flexible thermal load response was taken into account.Photovoltaics have an excess of carbon trading credits and can profit from selling them,whereas other devices have an excess of carbon trading and need to buy carbon credits.

Impacts of Startup,Shutdown and Load Variation on Transient Temperature and Thermal Stress Fields within Blades of Gas Turbines

Based on the actual operation parameters and temperature-dependent material properties of a gas turbine unit,composite cooling blade model and corresponding reliable boundary conditions were established.Transient thermal-fluid-solid coupling simulations were then comprehensively conducted to analyze the transient flow and the temperature field of the blade under startup,shutdown,and variable loads condition.Combined with the obtained transient temperature data,the non-linear finite element method was exploited to examine the effect of these transient operations on the turbine blade thermal stress characteristics.Results show that the temperature and pressure on the blade surface increase with the load level and vice versa.As the startup process progresses,the film cooling effectiveness and the heat convection of airflows inside the blade continuously grow;high-temperature areas on the pressure surface and along the trailing edge of the blade tip gradually disappear.Locally high-temperature zones with the maximum of 1280 K are generated at the air inlet and outlet of the blade platform and the leading edge of the blade tip.The high thermal stresses detected on the higher temperature side of the temperature gradient are commonly generated in places with large temperature gradients and significant geometry variations.For the startup/shutdown process,the rate of increase/decrease of the thermal stress is positively correlated with the load variation rate.A slight variation rate of the load(1.52%/min)can lead to an apparent alteration(41%)to the thermal stress.In operations under action of the variable load,although thermal stress is less sensitive to the load variation,the rising or falling rate of the exerted load still needs to be carefully controlled due to the highly leveled thermal stresses.

Size and temperature effects on band gaps in periodic fluid-filled micropipes

A new model is proposed for determining the band gaps of flexural wave propagation in periodic fluid-filled micropipes with circular and square thin-wall cross-sectional shapes, which incorporates temperature, microstructure, and surface energy effects. The band gaps depend on the thin-wall cross-sectional shape, the microstructure and surface elastic material constants, the pipe wall thickness, the unit cell length, the volume fraction, the fluid velocity in the pipe, the temperature change,and the thermal expansion coefficient. A systematic parametric study is conducted to quantitatively illustrate these factors. The numerical results show that the band gap frequencies of the current non-classical model with both circular and square thin-wall cross-sectional shapes are always higher than those of the classical model. In addition,the band gap size and frequency decrease with the increase of the unit cell length according to all the cases. Moreover, the large band gaps can be obtained by tailoring these factors.

A MULTI-COUPLED FINITE ELEMENT ANALYSIS OF RESISTANCE SPOT WELDING PROCESS

A two-dimensional axisymmetric finite element model is developed to analyze the transient thermal and mechanical behaviors of the Resistance Spot Welding （RSW） process using commercial software ANSYS. Firstly a direct-coupled electrical-thermal Finite Element Analysis （FEA） is performed to analyze the transient thermal characteristics of the RSW process. Then based on the thermal results a sequential coupled thermo-elastic-plastic analysis is conducted to determine the mechanical features of the RSW process. The thermal history of the whole process and the temperature distribution of the weldment are obtained through the analysis. The mechanical features, including the distributions of the contact pressure at both the faying surface and the electrode-workpiece interface, the stress and strain distributions in the weldment and their changes during the RSW process, the deformation of the weldment and the electrode displacement are also calculated.

Steady state electrical–thermal coupling analysis of TSV

This paper presents a blended analytical electrical–thermal model for steady state thermal analysis of through-silicon-via（TSV） in three-dimensional（3 D） integrated circuits. The proposed analytical model is validated by the commercial FEM tool—COMSOL. The comparison between the results of the proposed analytical formulas and COMSOL shows that the proposed formulas have very high accuracy with a maximum error of 0.1%.Based on the analytical model, the temperature performance of TSV is studied. Design guide lines of TSV are also given as：（1） the radius of the TSV increases, the resistance decreases and the temperature can be increased;（2） the thicker the dielectric layer, the higher the temperature;（3） compared with carbon nanotube, the Cu enlarges the temperature by 34 K, and the W case enlarges the temperature by 41 K.

Study on the Temperature of the Bridge Wire in the Initiator Used in Nuclear Explosion Valve

This paper established the mathematical model of bridge wire temperature rise under direct current condition and gave the solution. It computed bridge wire temperature by using the thermal-electric coupling method provided by ANSYS-Workbench finite element analysis software. In the end, the temperature bridge wire applied to different electric current was measured by the infrared thermal imaging temperature measurement method. The result shows that the ANSYS simulation results are in agreement with the theoretical calculation and the experimental results. It is feasible to compute bridge wire temperature of initiator by using ANSYS-Workbench software, and it is an important method to analyze complex structure of pyrotechnics.

Study on Temperature Distribution of Specimens Tested on the Gleeble 3800 at Hot Forming Conditions

Taking Ti-6Al-4V specimens into consideration, the coupled thermal-electrical finite element model has been developed in Abaqus/Explicit to simulate the heating process in Gleeble 3800 and to study the temperature history and distribution in the specimen. In order to verify the finite element （FE） results, thermal tests are carried out on Gleeble 3800 for a Ti-6Al-4V specimen with a slot to in the centre of the specimen. The effects of the specimen size, heating rate, and air convection on the temperature distribution over the specimen have been investigated. The conclusions can be drawn as： the temperature gradient of the specimen decreases as the specimen size, heating rate, and vacuuming decrease.

温度与荷载共同作用下钢筋混凝土桩的细观损伤

为探究港口码头不同环境因素对码头桩身材料特性的劣化影响而降低桩身承载能力,通过颗粒流分析程序(particle flow code 3D,PFC3D)建立三维颗粒流离散元钢筋混凝土桩模型开展研究。对温度-应力模型进行建立,选取热学参数,构建了温度热管模型,通过分级加热,得到了钢筋混凝土桩的横向拉伸应变、纵向压缩应变以及微裂缝生长数量随温度变化曲线;调整模型混凝土粗骨料占比与强度等级,研究其对钢筋混凝土桩受热损伤的影响;通过施加温度场的模型进行水平加荷载后,得到的应力应变曲线;基于模型微裂隙数量的损伤变量,并构建了损伤变量-轴向应变曲线,进一步分析了温度-荷载共同作用的损伤规律。结果表明:混凝土轴向压缩应变和横向拉伸应变会随温度的增加而逐渐升高,细观微裂隙数量会随温度的升高而增长;粗骨料占比升高会使受热初始损伤增加;温度的升高,材料的宏观力学性能出现了不同程度的降低。

锂电池在机械滥用下的耦合仿真模型研究

随着新能源汽车保有量的增加,因锂电池故障而引起的起火、爆炸等问题引起了各界的密切关注。锂电池在机械滥用下的热失控行为复杂、实验成本高、可重复性低,难以为研究提供有效、完备的数据。因此,利用高置信度仿真模型研究和评估锂电池的安全性能是一种可行的途径。基于Ls-Dyna软件建立了锂电池机-电-热耦合仿真模型。结果表明,该模型能够准确预测电池在受到压痕时的机械响应和电响应,且能合理地模拟电池的温度分布,具有较高的置信度。利用该模型对控制因素(压头半径,冲压方式)进行了研究,并综合分析了相关参数对锂电池安全性能的影响。所获得的结果可为车载锂电池包的设计和安全系统构建提供参考。

考虑下游氢负荷的氢-电耦合配电网容量规划

针对大规模光伏并网下配电网灵活性不足以及当前市场环境下氢能交易价格过高的问题,提出一种考虑下游氢负荷的氢-电耦合配电网协同规划模型。计及氢能设备的运行特性,构建包含电制氢、燃料电池、储氢罐和电储能的氢-电耦合配电网运行模型,并进一步基于光伏出力和负荷的波动性确定配电网的灵活性供需情况;对不同领域的用氢负荷进行建模,以系统总体投资和运行成本最小为优化目标,在满足所有设备投资和运行约束的前提下,构建考虑氢负荷需求的氢-电耦合配电网规划模型;以IEEE 33节点配电网为算例进行测试,结果表明氢-电耦合能够有效提升配电网的经济性(综合成本降低了3.8%)和灵活性(上调、下调灵活性分别提升了34.7%、37.6%),并大幅削减下游用氢负荷的购氢成本。

基于UIS测试的Si/SiC级联器件雪崩特性分析

与机械式断路器相比,使用半导体功率器件构成的直流固态断路器在响应时间方面有较大的优势。由低压硅金属—氧化物—半导体场效应晶体管(Si MOSFET)和高压碳化硅结型场效应晶体管(SiC JFET)构成的Si/SiC级联型器件具有优异的开断特性。半导体功率器件可靠性一直是直流固态断路器所关注的焦点问题,非箝位感性负载开关(unclamped inductive switching,UIS)测试是评估半导体功率器件可靠性的重要方法。文中通过实验和仿真的方式分析了Si/SiC级联器件在非箝位感性负载开关过程的雪崩特性。首先,通过增加器件导通时间得到了不同负载电流下的雪崩特性,结果表明,随着导通时间的增加,Si/SiC级联器件在雪崩期间出现了雪崩电压下降的异常特性。随后,通过分立式Si/SiC级联器件进行UIS测试,发现异常特性是由于SiC JFET在雪崩期间出现导通而形成的。最后,通过Si/SiC级联器件的三维电—热耦合仿真,结果表明雪崩期间SiC JFET芯片栅极铝金属层和键合线温度升高,导致SiC JFET栅极等效电阻增加,最终使得SiC JFET在雪崩期间出现导通。

考虑多场耦合高压电脉冲作用下岩体破碎响应

基于电学理论、热学理论和力学理论建立高压电脉冲作用下岩体破碎多物理场耦合数值模型,提出一种考虑电击穿的电–热–力耦合数值模型揭示岩体在高压电脉冲下的破碎过程。利用随机分布模型模拟岩体中可能出现的导体矿物颗粒,综合分析电击穿过程中等离子体通道的形成规律。与现场试验进行对比,验证该数值模型的准确性。计算结果表明:击穿场强是主导等离子体通道形成的关键因素。岩体在高压电脉冲作用下的破碎过程可分为3个阶段,等离子体通道初步形成阶段、等离子体通道扩展阶段和等离子体通道形成阶段。在等离子体通道形成前,通道处的温度保持在500 K左右,应力达到10–2MPa左右;当等离子体通道形成时,温度和应力会在短时间内剧增,温度达到10~3 K,应力达到10 MPa。在电脉冲持续作用下,等离子体通道处的温度和应力持续增加。当最大应力超过岩体的临界应力强度后,岩体将发生破碎;同时通道也会继续分支扩展,更大范围地对岩体造成破坏。导体矿物颗粒会引导等离子体通道的形成,颗粒分布越密,对通道的形成越有利。脉冲电压到达峰值的时间越长,岩体的破坏速率相对越快。数值模型的计算结果有助于加深对高压电脉冲过程中岩体破碎过程的理解。

基于荷-储碳流模型的电力系统双层优化调度

为减少高耗能机组出力,同时增加风电消纳能力,考虑负荷和储能两类灵活调用资源,提出基于荷-储碳放流模型的电力系统双层经济低碳优化调度方法。基于电力系统碳排放流理论,分别建立负荷和储能设备的碳排放流模型;设计考虑荷-储协同优化的低碳调度策略,在负荷侧建立基于负荷节点碳势的电-碳耦合价格需求响应模型,同时鉴于荷侧降碳调节的局限性,在储能侧建立基于碳流模型的低碳调度策略,实现荷-储协同低碳调度策略;考虑经济性和低碳性,建立包含上层经济调度、下层低碳调度的双层优化调度模型。通过改进IEEE-14节点系统对优化调度方法进行仿真验证,结果表明:提出的优化调度方法在保证经济性的同时,减少了弃风,并降低了高耗能机组出力,从而有效降低了全系统的碳排放。

BMS电路板多模块协同热-力耦合建模及仿真分析

针对现有电动汽车电池管理系统(BMS)电路板研究仅仅考虑单一功能模块的温度场及其散热效果,缺乏考虑BMS多个功能模块在温度场和力场下的相互影响及协同效应的研究的情况,以某商用BMS电路板为研究对象,采用ANSYS构建了表征BMS多模块协同作用下的热-力耦合数值仿真分析模型并验证了其有效性.在此基础上,针对BMS电路板各功能模块温度场及热变形行为开展了数值仿真研究.结果表明:BMS电路板温度分布不均,最大温差达20.5℃.均衡模块存在积热,温度高达54.4℃.高温导致电路板组件发生热膨胀变形,同时电路板约束诱发均衡模块及供电模块边缘的贴片电阻出现热应力集中,两者共同作用致使BMS均衡模块、供电模块产生凸起翘曲变形,且Z轴热变形量随着温度升高而增大,最大变形量达9.5μm,应针对BMS电路板上积热模块开展散热优化设计.

垂直洋流下500 kV海缆电热耦合场和载流量研究

发展海上风电是实现“双碳”目标的重要举措。直流海缆是海上风电输电工程的重要装置,而海缆稳态载流量等研究对推动远海风电大规模开发具有重要意义。近年来高压直流海缆稳态载流量的相关研究考虑海洋环境因素较为单一且未充分考虑绝缘层温差的限制。文中建立了500 kV直流海缆与海水系统的电-热-流耦合模型,研究了单根和双极海缆在不同敷设方式下垂直洋流(垂直于海缆长度方向流动的洋流)流速,考虑绝缘层温差限制、双极不同间距等对载流量的影响。结果表明,相较于仅考虑线芯温度70℃限制,综合考虑绝缘层温差20℃限制的载流量更小,且相较于其他敷设方式,直埋敷设时绝缘层温差20℃限制对载流量的影响更小;双极海缆的载流量随双极间距增大而增加,流速为0.1 m/s时涡旋对海缆载流量有较小的提升作用;在绝缘层温差为6℃附近,电场发生翻转。研究结果可为敷设方式的选择以及载流量的预测和评估提供重要指导和参考。