高压直流海底电缆电–热–流多物理场耦合仿真

高压直流电缆运行时径向温度和电场分布是反映其运行状态的重要参数,考虑流场的海底电缆电热耦合规律研究具有重要意义。依据南澳直流工程±160 kV高压直流海底电缆,利用COMSOL Multiphysics有限元分析软件,建立了海缆本体及其敷设环境的3维电–热–流耦合模型,以控制变量法研究了铺设和埋设2种敷设方式下海缆载流量、海水温度和海水流速对海缆径向温度和电场分布的影响。结果表明:载流量是海缆径向温度和电场分布的主要影响因素;在该模型下海缆导体温度和绝缘层温差与海水温度存在线性关系;很小的海水流速能显著降低海缆温度,因此提出静止海水散热的流速修正系数;海水流动有利于海缆散热,导致海缆温度分布发生变化,同时影响海缆绝缘材料电导率而导致电场分布发生改变。

应用三维电磁–热–流耦合场分析法计算换流变压器干式套管的温度场分布

换流变压器阀侧干式套管主绝缘材料为环氧树脂/皱纹纸复合材料,散热能力较差,随着输送功率的提高,套管载流量的升高,发热问题已成为制约换流变干式套管安全稳定运行的瓶颈。该文以400k V换流变干式套管为研究对象,采用三维电磁–热–流耦合场分析方法,考虑了热辐射、热传导和对流传热的影响,计算分析了其三维温度场分布,得出了套管内部的温度分布规律。同时,为了验证所用仿真方法的准确性,对400k V换流变干式套管进行了温升试验,对比了测量点的仿真计算结果与温升试验结果,试验结果表明仿真结果与测量结果的差值低于8%,证明了该方法的合理性,可为换流变干式套管的设计提供计算依据。

不同敷设环境下高压交流海底电缆导体温度和载流量的计算分析

为了提高海底电缆容量利用率、安全性、可靠性,针对传统的导体温度与载流量计算方法仅适用于特定敷设条件的缺陷,以某风电项目的三芯220 kV光纤复合海缆为研究对象,使用COMSOL有限元软件,建立了海缆及其敷设环境的二维有限元模型。对电磁–热–流多物理场耦合进行了仿真分析,研究了海水温度、海水流速、埋设深度和载流量对海缆导体温度的影响,并通过拟合仿真结果推导了导体温度和载流量的经验公式。结果显示,在工程领域常用的传统模型和IEC解析公式的默认流速和埋深条件下,该仿真模型及经验公式的载流量计算结果与传统模型和IEC解析公式的相对误差都在7%以内;仿真模型与经验公式之间的误差在5%以内。该结果表明,利用所提仿真模型及经验公式可以分析不同敷设环境下的载流量变化规律。

基于流热固多物理场耦合的电主轴热误差建模研究

针对电主轴热误差仿真建模中忽略冷却液自身的温度变化对冷却效果的影响,导致预测精度不准确的问题。建立流–热–固多物理场耦合有限元模型,在热–结构耦合模型中引入流体域,通过流–固交界面将冷却液的温度场作为热分析中螺旋冷却管道的精确热边界条件、压力场作为结构分析中的力约束,更为真实地反映冷却液的实际换热能力和螺旋冷却管道的实际受力情况。采用基于热流密度的载荷施加方式与流–热–固多物理场耦合方法相结合的ANSYS仿真模型,仿真结果表明电主轴最大轴向热变形为51 μm,与实验测得的值相比,残差在5.2 μm左右。可以有效地实现高速电主轴热误差预测。

热补偿条件下双井EGS产能和寿命预测方法研究

增强型地热系统(Enhanced Geothermal System,EGS)作为干热岩资源开采的有效手段,具有广阔的发展前景和巨大的利用价值,因此,对其进行产能和寿命预测显得尤为重要。为实现双井EGS产能和寿命预测,利用理论推导和数值模拟的方法对不同工况下的EGS系统进行产能分析,最终得到双井EGS产能和寿命预测方法。首先,以Dupuit公式与吸放热公式为基础,建立EGS产能和寿命控制方程,为EGS寿命预测提供理论支撑。然后,根据地下水流动方程和热传导方程,结合牛顿冷却公式,分析出影响EGS产能和寿命控制方程中4个未知参数(热储减少热量、大地热补偿热量、生产井平均产出温度和热储形状系数)的5个因素分别为热储初始温度、热媒介质注入温度、热储体积、热储比表面积和EGS运行时间。在考虑大地热补偿的情况下,利用双井EGS的3维数值模拟分别对不同工况下的热储发生热突破时各未知参数的影响因素进行分析、修正和定量化研究,得到4个未知参数随5个因素变化的具体预测公式。基于上述结果得到一种适用于双井EGS产能和寿命的预测方法,即:利用EGS产能和寿命控制方程、4个未知参数的预测公式及热储渗透率对双井EGS产能和寿命进行预测。最后,利用于双井EGS产能和寿命的预测方法预测已有文献的工况并进行比较,两者结果较吻合,证明了控制方程和预测公式的适用性和预测方法的准确性。

采用充水电缆沟敷设方案的海缆登陆段载流量计算

为了检验近海风电场海缆登陆段由土壤直埋改为充水电缆沟敷设的载流量提升效果,建立了充水电缆沟内二维流–热耦合求解的数学模型,利用COMSOL Multiphysics软件对某条置于充水电缆沟的海缆载流量进行计算,得到沟内流场和温度场分布,验证了模型的正确性。由于水的自然对流可有效地改善电缆的散热条件,与直埋时相比,采用充水电缆沟敷设方案的海缆载流量提升了43.8%。基于该模型仿真分析了不同因素对充水电缆沟内海缆载流量的影响规律:电缆沟高度或宽度增大时,载流量均会增大,但增大宽度比增大高度能带来更明显的载流量提升效果;海缆在沟内的放置高度变化对载流量基本无影响。

考虑气流场影响的GIS温升计算与实验研究

准确计算GIS温升对于产品优化设计、缩短研发周期和降低研发成本等具有重要意义。为此,针对一台126kV三相共箱式GIS,考虑接触电阻、邻近与趋肤效应以及涡流效应的作用,首先建立了电磁–热耦合仿真模型,仿真分析了2 200 A电流条件下GIS的损耗分布及温升特性;接着为了进一步研究气流场对温升的影响,建立了GIS的电磁–热–流耦合模型,对比分析了仅计及GIS内部SF6气体流体域、同时考虑GIS内部SF6和外部空气流体域两种方法的温升计算结果;最后开展了2 200 A电流下的温升实验。结果表明:隔离开关导体的损耗密度要高于断路器导体,且接触电阻的损耗密度最大;考虑内、外流体域的计算方法精度最高,最大相对误差小于10%。研究为GIS温升特性的工程设计提供了有效的方法,也可为其他电力设备的温升计算提供技术参考。

Effect of working parameters on performance characteristics of hydrostatic turntable by using FSI-thermal model

Effects of working parameters on performance characteristics of hydrostatic turntable are researched by applying the fluid-structure-thermal coupled model.Fluid-structure interaction(FSI)technique and computational fluid dynamics(CFD)method are both employed by this new model,and thermal effects are also considered.Hydrostatic turntable systems with a series of oil supply pressures,various oil recess depth and several surface roughness parameters are studied.Performance parameters,such as turntable displacement,system flow rate,temperature rise of lubrication,stiffness and damping coefficients,are derived from different working parameters(rotational speed of turntable and exerted external load)of the hydrostatic turntable.Numerical results obtained from this FSI-thermal model are presented and discussed,and theoretical predictions are in good agreement with the experimental data.Therefore,this developed model is a very useful tool for studying hydrostatic turntables.The calculation results show that in order to obtain better performance,a rational selection of the design parameters is essential.

Cast-rolling force model in solid-liquid cast-rolling bonding(SLCRB) process for fabricating bimetal clad strips

Based on twin-roll casting, a cast-rolling force model was proposed to predict the rolling force in the bimetal solid-liquid cast-rolling bonding(SLCRB) process. The solid-liquid bonding zone was assumed to be below the kiss point(KP). The deformation resistance of the liquid zone was ignored. Then, the calculation model was derived. A 2D thermal-flow coupled simulation was established to provide a basis for the parameters in the model, and then the rolling forces of the Cu/Al clad strip at different rolling speeds were calculated. Meanwhile, through measurement experiments, the accuracy of the model was verified. The influence of the rolling speed, the substrate strip thickness, and the material on the rolling force was obtained. The results indicate that the rolling force decreases with the increase of the rolling speed and increases with the increase of the thickness and thermal conductivity of the substrate strip. The rolling force is closely related to the KP height. Therefore, the formulation of reasonable process parameters to control the KP height is of great significance to the stability of cast-rolling forming.

Heat transfer analysis and experimental study of unequal diameter twin-roll casting process for fabricating Cu/Al clad strips

Unequal diameter twin-roll casting(UDTRC)can improve the formability,surface conditions,and production efficiency during the fabrication of clad strips.Using Fluent software,a numerical simulation is used to study the asymmetric heat transfer characteristics of Cu/Al clad strips fabricated by UDTRC.The effects of roller velocity ratio,Cu strip thickness,and inclination angle on the kissing point position,as well as the entire temperature distribution are obtained.The heat transfer model is established,and the mechanism is discussed.The Cu strip and rollers are found to be the main causes of asymmetric heat transfer,indicating that the roller velocity ratio changes the liquid zone proportion in the molten pool.The Cu strip thickness determines the heat absorption capacity and the variations in thermal resistance between the molten Al and the big roller.The inclination angle of the small roller changes the cooling time of big roller to molten Al.Moreover,the microstructure of Al cladding under different roller velocity ratios is examined.The results show significant grain refinement caused by the shear strain along the thickness direction of Al cladding and the intense heat transfer at the moment of contact between the metal Al cladding and Cu strip.

Fluid-solid coupling numerical simulation of charge process in variable-mass thermodynamic system

Abstract： A joint solution model of variabk：-mass flow in two-phase region and fluid-solid coupling heat transfer, concerned about the charge process of variable-mass thermodynamic system, is built up and calculated by the finite element method （FEM）. The results are basically consistent with relative experimental data. The calculated average heat transfer coefficient reaches 1.7~105 W/（m2. K）. When the equal percentage valve is used, the system needs the minimum requirements of valve control, but brings the highest construction cost. With the： decrease of initial steam pressure, the heat transfer intensity also weakens but the steam flow increases. With the initial water filling coefficient increasing or the temperature of steam supply decreasing, the amount of accumulative steam flow increases with the growth of steam pressure. When the pressure of steam supply drops, the steam flow gradient increases during the maximum opening period of control valve, and causes the maximum steam flow to increase.

Mathematical model for coupled reactive flow and solute transport during heap bioleaching of copper sulfide

Based on the momentum and mass conservation equations, a comprehensive model of heap bioleaching process is developed to investigate the interaction between chemical reactions, solution flow, gas flow, and solute transport within the leaching system. The governing equations are solved numerically using the COMSOL Multiphysics software for the coupled reactive flow and solute transport at micro-scale, meso-scale and macro-scale levels. At or near the surface of ore particle, the acid concentration is relatively higher than that in the central area, while the concentration gradient decreases after 72 d of leaching. The flow simulation between ore particles by combining X-ray CT technology shows that the highest velocity in narrow pore reaches 0.375 m/s. The air velocity within the dump shows that the velocity near the top and side surface is relatively high, which leads to the high oxygen concentration in that area. The coupled heat transfer and liquid flow process shows that the solution can act as an effective remover from the heap, dropping the highest temperature from 60 to 38 ℃. The reagent transfer coupled with solution flow is also analyzed. The results obtained allow us to obtain a better understanding of the fundamental physical phenomenon of the bioleaching process.

A non-monotonic blow-off limit of micro-jet methane diffusion flame at different tube-wall thicknesses

In order to provide guideline for choosing a suitable tube-wall thickness(d)for the micro-jet methane diffusion flame,the effect of tube-wall thickness on the blow-off limit is investigated via numerical simulation in the present work.The results show that the blow-off limit of micro-jet methane diffusion flame firstly increases and then decreases with the increase of tube-wall thickness.Subsequently,the underlying mechanisms responsible for the above non-monotonic blow-off limit are discussed in terms of the flow filed,strain effect and conjugate heat exchange.The analysis indicates that the flow field is insignificant for the non-monotonic blow-off limit.A smaller strain effect can induce the increase of the blow-off limit fromd=0.1 to 0.2 mm,and a worse heat recirculation effect can induce the decrease of the blow-off limit fromd=0.2 to 0.4 mm.The non-monotonic blow-off limit is mainly determined by the heat loss of flame to the tube-wall and the performance of tube-wall on preheating unburned fuel.The smallest heat loss of flame to the tube-wall and the best performance of tube-wall on preheating unburned fuel result in the largest blow-off limit atd=0.2 mm.Therefore,a moderate tube-wall thickness is more suitable to manufacture the micro-jet burner.

Coupled Seepage and Heat Transfer Intake Model

In the beach well intake system, heat is transferred from soil to fluid when seawater is filtered through the aquifer, providing higher temperature source water to the seawater source heat pump (SWHP) system in winter. A 3-D coupled seepage and heat transfer model for studying beach well intake system is established by adopting the computer code FLUENT. Numerical results of this model are compared with the experimental results under the same conditions. Based on the experiment-verified coupled model, numerical simulation of the supply water tem-perature is studied over a heating season. Results show that the minimum temperature of supply water is 275.2 K when this intake system continuously provides seawater with flow rate of 35 m3/h to SWHP. Results also indicate that the supply water temperature is higher than seawater, and that the minimum temperature of supply water lags behind seawater, ensuring effective and reliable operation of SWHP.

Specific Heat of a Two-Layer Magnetic Superlattice

The specific heats of both a two-layer ferromagnetic superlattice and a two-layer ferrimagnetic one arestudied.It is found that the spin quantum numbers,the interlayer and intralayer exchange couplings,the anisotropy,theapplied magnetic field,and the temperature all affect the specific heat of these superlattices.For both the ferromagneticand ferrimagnetic superlattices,the specific heat decreases with increasing the spin quantum number,the absolutevalue of interlayer exchange coupling,intralayer exchange coupling,and anisotropy,while it increases with increasingtemperature at low temperatures.When an applied magnetic field is enhanced,the specific heat decreases in the two-layerferromagnetic superlattice,while it is almost unchanged in the two-layer ferrimagnetic superlattice at low fieldrange at low temperatures.

Thermal analysis of high speed permanent magnetic generator

High-speed permanent magnetic generators (HSPMG) are common and important power generation equipments used in distributed generation systems. A 100 kW level HSPMG is investigated in this paper, and it is fluid-thermal coupling analyzed. The transient 2D electromagnetic field while machine is under rated operating is analyzed by using the time-stepping FEM, from which the electromagnetic performances and the loss distributions are obtained. Then, an analysis model for fluid-solid temperature field analysis is established. Taking losses as the distributed heat sources, the 3D thermal field is coupling calculated. The variations of heat transfer coefficient and temperature of fluid in stator grooves along the axial direction, as well as the whole region 3D temperature distribution in HSPMG are obtained. Then, considering the variations of heat sources distributions and heat transfer conditions, 3D temperature fields of HSPMG operating under different speeds are calculated, and the influences of machine operating speed on the HSPMG thermal performance are studied, based on which, the functions of machine temperature with operating speed and stator windings resistance are proposed. The obtained conclusions may provide a useful reference for the design and research of HSPMG.