Lumped-Parameter Thermal Network Model and Experimental Research of Interior PMSM for Electric Vehicle

A 25kW interior permanent magnet synchronous machine(IPMSM)applied to the electric vehicle is introduced in the paper.A lumped-parameter thermal network model is presented for IPMSM temperature rise calculation.Furthermore,a 3D liquid-solid coupling model considering the assembly clearance is compared with the 2D lumped-parameter thermal network model.Finally,a dynamometer platform for temperature rise measurement is established to verify the above-mentioned methods,which obtains the measured efficiency map at rated load case and overload case.At the same time,the measured no-load back electromotive Force(EMF),load line input voltage and load current are gathered.Thermocouple PTC100 is used to measure the temperature of the stator winding and iron core,and the FLUKE infrared thermal imager is applied to measure the surface temperature of PMSM and controller.Testing result shows that the lumped-parameter thermal network have a high accuracy to predict each part temperature.

Modeling of thermal conductivity for disordered carbon nanotube networks

Several theoretical models have been developed so far to predict the thermal conductivities of carbon nanotube(CNT)networks.However,these models overestimated the thermal conductivity significantly.In this paper,we claimed that a CNT network can be considered as a contact thermal resistance network.In the contact thermal resistance network,the temperature of an individual CNT is nonuniform and the intrinsic thermal resistance of CNTs can be ignored.Compared with the previous models,the model we proposed agrees well with the experimental results of single-walled CNT networks.

A Detailed Thermal Resistance Network Analysis of FCBGA Package

Using thermal models to describe the heat dissipation process of FCBGA is a significant topic in the field of packaging.However,the thermal resistance model considering the structure of each part of the chip is still ambiguous and rare,but it is quite desirable in engineering.In this work,we propose a detailed thermal resistance network model,and describe it by using thermal conduction resistance and thermal spreading resistance.For a striking FCBGA case,we calculated the thermal resistance of each part of the structure according to the temperature field simulated by COMSOL.The thermal resistance network can be used to predict the temperatures in the chip under different conditions.For example,when the power changes by 40%,the relative error of junction temperature prediction is only 0.24%.The function of the detailed thermal resistance network in evaluating the optimization space and determining the optimization direction is clarified.This work illustrates a potential thermal resistance analysis method for electronic devices such as FCBGA.

Numerical and experimental evaluation for density-related thermal insulation capability of entangled porous metallic wire material

Entangled porous metallic wire material(EPMWM)has the potential as a thermal insulation material in defence and engineering.In order to optimize its thermophysical properties at the design stage,it is of great significance to reveal the thermal response mechanism of EPMWM based on its complex structural effects.In the present work,virtual manufacturing technology(VMT)was developed to restore the physics-based 3D model of EPMWM.On this basis,the transient thermal analysis is carried out to explore the contact-relevant thermal behavior of EPMWM,and then the spiral unit containing unique structural information are further extracted and counted.In particular,the thermal resistance network is numerically constructed based on the spiral unit through the thermoelectric analogy method to accurately predict the effective thermal conductivity(ETC)of EPMWM.Finally,the thermal diffusivity and specific heat of the samples were obtained by the laser thermal analyzer to calculate the ETC and thermal insulation factor of interest.The results show that the ETC of EPMWM increases with increasing temperature or reducing density under the experimental conditions.The numerical prediction is consistent with the experimental result and the average error is less than 4%.

基于用户画像的暖通空调智能调控

目前,建筑物中的暖通中央空调系统基本上是根据行业准则设置的,然而,多项研究表明,由于用户的偏好、姿态和需求各异,这种传统做法不太可能满足大多数用户的热量需求。为了更精准地满足用户热量需求,使得基于用户行为模式来针对性提高热舒适性成为可能。文中采用深度强化学习的方法实现智能化暖通空调智能送风策略,该策略能够根据环境和用户行为模式动态地确定最佳暖通空调设置(温度设置和送风设置),从而极大提高用户的热舒适度,同时,实验结果还表明该智能调控策略相比传统固定值控制策略具有一定的节能效果。

基于神经网络的双面散热功率模块本构热阻建模与表征

双面散热(double-sided cooling,DSC)功率模块的结-壳热阻,是其电热设计、状态监测与失效分析的关键性能指标。然而,现有的结-壳热阻模型及其测试标准,仅针对单通道传热的功率模块,难以匹配多通道传热的DSC功率模块,无法识别DSC功率模块的本构热阻信息。首先提出DSC功率模块的本构热阻模型,阐释DSC功率模块本构热阻的物理意义,分析重构单通道传热本构热阻的可行性和唯一性;其次,评估所提本构热阻与传统测试热阻的本质差异。基于商业化DSC功率模块,采用多物理场分析方法,构建DSC功率模块的热阻数据库;然后,基于神经网络学习方法和所构建的数据库,建立DSC功率模块的本构热阻模型,并通过大量训练数据和测试数据的交叉验证及多款DSC功率模块的实测结果,验证神经网络重构本构热阻的泛化能力和兼容能力,为多通道散热功率模块的热阻建模与表征,提供新的研究思路和技术途径。

履带车辆油气弹簧生热机理和热模型研究

为研究油气弹簧工作过程中的生热机理,建立油气弹簧参数化热模型。采集试验数据对油气弹簧阻尼示功特性进行数值拟合,得到活塞运动速度-阻尼力关系的数学表达式。对油气弹簧的传热路径和换热特点分析,建立油气弹簧热阻网络模型,计算得到工作过程中油气弹簧2种工作介质的温度变化特性。设计试验对油气弹簧的热模型计算结果进行验证。试验结果表明:阻尼力做功是油气弹簧温度升高的主要热量来源,油液温度比气体温度上升更快、平衡温度更高,该模型可以准确地计算出油气弹簧不同工作介质的温升情况,为油气弹簧热-机耦合动力学研究提供了参考。

热管换热器间距对相变充填体蓄释热性能的影响

为了高效利用高温矿井的地热资源,解决高温环境对开采过程的影响,建立了热管-相变充填体矿井地热开采系统三维非稳态传热数值模型,研究了热管换热器与围岩布置间距对系统温度、相变材料液相分数、循环冷却水温度以及系统蓄热量、释热量的影响。结果表明:热管距离围岩越近,蓄热阶段相变材料熔化越快,蓄/释热共存阶段相变材料凝固越慢;随着热管与围岩间距的减小,热管冷凝端循环冷却水的出口温度和进出口温差增大,当热管与围岩间距从95 mm减小至20 mm时,系统稳定运行时冷却水进出口温差将由2.50 K增大至4.97 K;蓄热阶段,系统蓄热量随时间推移先逐渐增大,后维持恒定不变,蓄/释热共存阶段,系统释热量将以先逐渐减小,后恒定不变的速率持续增大;当热管与围岩布置间距由95 mm减小到20 mm时,系统总蓄热量提高72.89%,系统释热量提高91.10%,系统能效系数由81.71%增大到90.32%。研究结果可为热管-相变材料耦合系统在矿井地热高效开采与利用方面提供理论依据和技术指导。

基于形态空间格局分析与最小累积阻力模型的城市热环境生态网络优化研究

【目的】建立合理的城市热环境生态网络,以缓解城市热岛效应。【方法】以成都市中心城区为研究对象,基于“源-汇”理论,利用形态学空间格局分析方法(MSPA)与景观连通性指数,分别筛选研究区内景观稳定性好、连通性高的“源”“汇”景观作为生态源地;运用最小累积阻力模型、重力模型以及水文分析模块构建和筛选研究区内的重要生态廊道,从而建立缓解城市热环境问题的多层级“源-汇”景观网络。【结果】分别筛选出24个具有重要连通性的“源”“汇”核心斑块作为重要生态源地。构建“源-源”廊道102条,“汇-汇”廊道141条,“源-汇”廊道325条,生态节点103个,障碍点148个。通过综合相交分析,一级补偿廊道主要由岷江、毗河和其他河道构成,二级输送廊道主要分布在“汇”景观较为密集的区域,三级作用廊道主要分布在高强度建设区域。【结论】基于“源-汇”理论构建的多层级生态网络优化格局是有效缓解城市热岛效应的重要举措。图4表3参25.

综合考虑材料热各向异性与多种传热方式的磁性元件热阻网络精准模型

磁性元件正在向高频化、小型化、高功率密度的方向发展,随着功率密度的提高,散热已成为影响器件可靠运行的关键因素,因此对磁性元件的热分析提出更高的要求。传统的热分析模型存在运算时间长、传热方式单一等问题,该文引入已有研究中提出的三轴九热阻网络模型,在此基础上添加热对流与热辐射两种传热方式,综合考虑材料热各向异性与热传导、热对流、热辐射。并通过精细划分元件温度计算子区域、实际器件损耗场分析、热电耦合迭代提高模型的计算精度,提出一种更加完善的三轴十五热阻网络模型,基于该模型对实际磁性器件建模,验证了该模型的准确性,并于最后提出一种通用的针对EE、EI、UU等典型磁心构成的磁性元件的热阻网络建模方法。

基于热阻网络的高性能贴装设备温控设计和仿真分析

阐述利用热阻网络对高性能半导体贴装设备温控系统进行应用分析,通过热阻网络的构建能够快速评估出温控台隔热性能、降温速率等性能,给出有效的设计指导建议。通过仿真验证,显示优化后的温控台散热性能均达到设计指标要求,且与热阻网络分析结果接近。利用热阻网络分析方法可快速收敛设计方案。

Entransy dissipation,entransy-dissipation-based thermal resistance and optimization of one-stream hybrid thermal network

The one-stream hybrid thermal network is analyzed and discussed based on the entransy theory,and the results are compared with those from the entropy generation optimization.The theoretical analysis indicates that the minimum heat-flow-weighted temperature of the thermal networks corresponds to the minimum entransy dissipation rate and the minimum thermal resistance.For a simple hybrid thermal network consisting of three thermal components,the expression of entransy dissipation is conducted,and the heat transfer area and the mass flow rate are calculated and optimized.The optimal results are obtained in order to minimize the entransy dissipation and the thermal resistance.The optimal results are calculated for various combinations,such as series connection,parallel connection and other hybrid connections.The numerical results are in accordance with the theoretical analysis.Both the theoretical analysis and the numerical results show that the minimum entransy dissipation and the minimum thermal resistance correspond to the minimum heat-flow-weighted temperature of the thermal networks while the minimum entropy generation does not.

Thermal Analysis of Vehicular Twin-Tube Hydraulic Gas-Precharged Shock Absorbers

In this study of temperature rising in vehicular twin-tube hydraulic gas-precharged shock absorbers,thermodynamic analyses were conducted via simulations.Equations on heat conduction,heat convection as well as radiation were derived by applying certain laws governing heat transfer;an equivalent thermal resistance network model of a shock absorber undergoing heat transfer was established innovatively;moreover,the shock absorber’s thermodynamic model of control volume system was built by using the first law of thermodynamics;and finally,time required for shock absorber to reach thermal equilibrium and corresponding value of steady temperature were calculated by programming.In this way,a lower thermal equilibrium temperature will be achieved,hence help to improve reliability of shock absorbers in work by offering low ambient temperature,by reducing amplitudes and frequencies of external incentives exerted on them and by increasing flow rate of ambient air passing around them.

Improved thermal resistance network model of motorized spindle system considering temperature variation of cooling system

In the motorized spindle system of a computer numerical control (CNC) machine tool, internal heat sources are formed during high-speed rotation;these cause thermal errors and affect the machining accuracy. To address this problem, in this study, a thermal resistance network model of the motorized spindle system is established based on the heat transfer theory. The heat balance equations of the critical thermal nodes are established according to this model with Kirchhoffs law. Then, they are solved using the Newmark-β method to obtain the temperature of each main component, and steady thermal analysis and transient thermal analysis of the motorized spindle system are performed. In order to obtain accurate thermal characteristics of the spindle system, the thermal conduction resistance of each component and the thermalconvection resistance between the cooling system and the components of the spindle system are accurately obtained considering the effect of the heat exchanger on the temperature of the coolant in the cooling system. Simultaneously, high-precision magnetic temperature sensors are used to detect the temperature variation of the spindle in the CNC machining center at different rotational speeds. The experimental results demonstrate that the thermal resistance network model can predict the temperature field distribution in the spindle system with reasonable accuracy. In addition, the influences of the rotational speed and cooling conditions on the temperature increase of the main components of the spindle system are analyzed. Finally, a few recommendations are provided to improve the thermal performance of the spindle system under different operational conditions.

Entransy-dissipation-based thermal resistance analysis of heat exchanger networks

Heat exchanger network optimization has an important role in high-efficiency energy utilization and energy conservation. The thermal resistance of a heat exchanger network is defined based on its entransy dissipation. In two-stream heat exchanger networks, only heat exchanges between hot and cold fluids are considered. Thermal resistance analysis indicates that the maximum heat transfer rate between two fluids corresponds to the minimum entransy-dissipation-based thermal resistance; i.e. the minimum thermal resistance principle can be exploited in optimizing heat exchanger networks.

基于反馈神经网络的机身镀层抗热冲击性能研究

用磁控溅射离子镀设备在机身材料为高速钢M2的试件上制备Cr、Ti、N含量不同的4种镀层。用HADL2101DS8动静态电阻应变仪测试4种镀层在500℃热冲击下的水平方向、厚度方向的应力,输入反馈神经网络,计算不同镀层的破损率,评价其抗热冲击性能,确定最佳的镀层制备方案。用扫描电子显微镜观察镀层受热冲击前、后形貌。结果表明:当Cr、Ti、N的质量分数分别为56.89%、0.05%、43.06%时(方案1),镀层形貌无裂缝或脱落、氧化物白色颗粒最少,镀层破损率小于另外3种方案;方案1镀层抗热冲击性能最优。

层状Al_(2)O_(3)/EP复合材料的可控制备及性能研究

采用冰模板法构筑具有层状结构的Al_(2)O_(3)三维网络骨架,并通过真空浸渍工艺制备出Al_(2)O_(3)/环氧树脂(EP)复合材料。研究了楔形硅橡胶角度、浆料固相含量、冷冻温度对层状Al_(2)O_(3)三维网络骨架微观结构的影响,分析了片层间距对Al_(2)O_(3)/EP复合材料导热、介电和绝缘性能的影响。结果表明:楔形硅橡胶角度为10°和15°时Al_(2)O_(3)三维网络骨架的层状有序性最佳,固相含量的增加和冷冻温度的降低均会使片层间距减小;Al_(2)O_(3)/EP复合材料的热导率和介电常数随着片层间距的减小而增大,但体积电阻率呈降低趋势;当片层间距为45μm时,热导率达到0.52 W/(m·K),体积电阻率为10^(12)Ω·cm。

缓解城市热环境的多层级“源-汇”景观网络构建

以天津市六区和新四区为研究对象,首先运用形态学空间格局分析获得7种景观类型,从中提取稳定性较好、面积较大、连通性较高、热贡献度显著的核心区斑块为中心“源”“汇”;其次使用6个空间数据指标构建热环境格局评价模型,根据2009—2013、2013—2018年热环境格局的变化情况提出4类修正系数对基本阻力面进行修正;最后利用“源-源”、“汇-汇”、“源-汇”廊道构建能体现“补偿-输送-作用”过程的多层级“源-汇”景观网络。结果表明:(1)提取的Ⅰ、Ⅱ类中心“源”共27个,总面积为22773 hm^(2);中心“汇”共23个,总面积为50732 hm^(2)。中心“源”的整体抗干扰能力较小,容易受到种植类型和水体富营养化的影响。(2)多层级“源-汇”景观网络总长度约为1445 km,新四区的廊道占总廊道的70%。廊道在空间上分布不均,津南区分布稀疏,北辰区和市六区分布密集。(3)能量从中心“源”逐渐向中心“汇”流动的过程,可揭示网络之间的层级关系和各级廊道对热环境气候的调控作用。以生态格局与过程的角度构建缓解城市热环境的多层级“源-汇”景观网络体系,对合理规划廊道建设、高效缓解城市热环境效应具有积极意义。

基于热网络与数值仿真模拟的风电轴承瞬态温度分析

新疆达坂城风机齿轮箱的轴承温度超出限度是发生频率较高的故障之一,使用热网络法和数值仿真法分别计算轴承的温度变化并加以对比分析。热网络法首先计算风电齿轮箱轴承摩擦热量,分析轴承内部传热及其与外界换热行为,求解节点之间的热阻,然后根据能量守恒定律搭建瞬态温度方程组,形成风电齿轮箱输出轴轴承的热网络模型,最后利用Simulink求解各节点的温度变化。数值模拟法首先根据轴承尺寸建模,对模型离散化,然后根据实际运转情况确定轴承换热方式及换热量,最后计算各单元的温度变化,得到整体模型的温度变化情况。对比热网络法与数值模拟法,二者计算的轴承各节点温度误差很小,均适用于轴承温度的计算,但热网络法的计算速度远远高于数值模拟,并通过热网络法分析了不同工况下的轴承温度及其对轴承变形和接触应力的影响,结果表明:转速、径向载荷、环境温度提升均会引起轴承温度升高,温度升高会增大轴承的变形和接触应力。

非接触式太阳能蒸发的模拟与分析

零液体排放是高浓度盐水/废水处理的有效途径,其中非接触式太阳能蒸发是一种近年被提出的全新思路,兼具太阳能利用、结构简单、被动运行和不结垢的优势.针对非接触式太阳能蒸发缺乏有效预测模型用以指导实际装置优化的问题,首次构建了非接触式太阳能蒸发的稳态热阻网络模型,并对其蒸发性能进行了分析.结果显示,作为水体能量来源的辐射传热与空气层传热分别占比54.2%和45.8%,均对蒸发性能有重要影响.空气层厚度增加会对两种传热产生不利影响,10 mm空气层厚度下的蒸发率仅为4 mm空气层厚度下蒸发率的70%.此外,减小蒸汽扩散阻力是提升蒸发率的有效途径,当蒸汽扩散系数从5×10^(-6)m^(2)/s增大至2.5×10^(-5)m^(2)/s时,蒸发率提升了2倍.