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提出了一种在第三类边界条件下,根据LED灯瞬态温度场的变化规律,通过对其表面温度的实际数值测定来推算LED灯表面对流换热系数的快速测定方法。基于对流热平衡理论,设计了一种可以在较高表面换热强度条件下进行测试的装置,通过实验测定LED灯上下表面的温度,结合曲线拟合对实测数据进行数理分析,得到较宽范围内的表面对流换热系数。实验结果表明:该测试方法简单、实用,测试时间较短(实验准备与数据测定大约需要30 min),测试精度较高(数据拟合误差不高于0.2%),可靠性强,可以用于工程热设计等多种相关发热体表面对流换热系数的测定。 相似文献
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热复杂边界条件三维热应力场数值模拟研究 总被引:1,自引:0,他引:1
本文以制动盘为研究对象,基于三维对称有限元模型,运用顺序耦合数值模拟方法对制动盘制动过程传热与受力进行了探讨,分析了在热流密度、对流换热系数、辐射换热系数与时间相关的复杂的二、三类边界条件下,温度场与应力场的瞬时变化。研究结果表明,数值模拟结果与实验结果吻合程度高,证明了采用数值模拟方法对具有复杂边界条件的对象进行热应力研究与预测的可行性,同时为其他领域的传热与应力研究提供了理论依据。 相似文献
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基于半导体器件的物理模型,联立并求解由电磁场、半导体物理及热力学方程构成的多物理场方程组,实现半导体器件及电路的电磁效应计算。为了更加准确地仿真半导体器件的温度变化,深入研究了多物理场计算中的热边界条件。以肖特基二极管HSMS-282c为例,采用多物理场算法仿真并对比了器件在相同激励(幅值为2V的阶跃脉冲)、不同边界条件下的温度变化情况。实际测量了器件在正向偏置下的表面温度,并于多物理场计算结果进行对比。结果表明,采用热对流边界可以准确仿真半导体器件的热效应。 相似文献
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针对低超声速飞行器非稳态飞行条件下内外流固耦合一体化计算的复杂性,将飞行器外部流场的实时气动热转化为浮动的第三类边界条件进行解耦.以加速俯冲的超声速三维头锥体为例,分别采用浮动温差法和辐射平衡法提取表面对流换热系数进行解耦计算,并与直接耦合计算结果进行比较,验证两种解耦算法的可靠性.结果表明,将非稳态飞行过程离散为不同飞行状态点,通过提取对流换热系数解耦计算得到的不同状态点的锥体表面温度分布与直接耦合计算得到的结果吻合较好.两种解耦算法在计算效率方面均要优于耦合计算方法;在外界气动环境发生剧烈变化的过程中,最大相对误差均不超过2%. 相似文献
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聚焦型太阳能集热器中腔体吸收器的热性能研究 总被引:1,自引:0,他引:1
本文对采用菲涅尔透镜一半圆式腔体吸收器的聚焦型太阳能集热装置进行了实验研究和理论分析计算.在相同天气情况下,针对具有不同形状玻璃盖层(半圆盖型YG,平板型PB,V型)和未加盖层(开口型KK)时的腔体吸收器在35~90℃温度范围内进行瞬时热效率测试得出热效率曲线,并且在室内测量了此温度范围内不同工况下的热损失.实验结果表明,半圆盖型(YG)吸收器热损失系数最小.本文还借助于CFD软件Fluent建立4种腔体模型,计算了腔体吸热面温度为90℃时的热损失,最后通过与实验结果的分析比较,发现计算值与实验值基本吻合(偏差小于10%). 相似文献
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利用CFD软件数值研究了颗粒三维有序堆积多孔介质的对流换热问题. 采用颗粒直径分别为14 mm,9.4 mm和7 mm的球形颗粒有序排列构成多孔介质骨架,在多孔骨架的上方有一恒热流密度的铜板. 采用流固耦合的方法研究了槽通道内温度分布和局部对流换热系数的分布以及对流换热的影响因素. 研究结果表明:热渗透的厚度和温度边界层的厚度在流动方向上逐渐增大,并且随流量的增加而减小;当骨架的导热系数比较高时,对流换热随颗粒直径的减小而略有增大;对流换热系数随聚丙烯酰胺溶液浓度的增大而减小,黏性耗散减弱了对流换热.
关键词:
多孔介质
温度场
局部对流换热系数
数值模拟 相似文献
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This article presents a measuring method for determination of convective heat transfer in rotating environments. The method is used to obtain temperature and Nusselt number distributions on optically accessible objects inside real operating environments, without the need for implementation of complex surface heat flux measurements. Temperature maps of the observed surfaces are acquired non-intrusively by infrared (IR) thermography, whereas heat flux data is computed numerically by computational fluid dynamics (CFD) tools. The method was employed on a rotating hollow blade, heated internally by secondary air flow. Experimental and numerical results for the observed blade side are compared in terms of surface temperature 2D distributions. Temperature distributions are further statistically evaluated and show good agreement, which is the basic precondition for combining experimental and numerical data by the method. Results are presented in terms of combined experimental-numerical Nusselt number shown as two-dimensional distribution on the blade pressure side. 相似文献
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研究超临界CO2在高温吸热管内的传热特性是将其应用于聚光太阳能热发电技术中的基础.本文对此进行了数值模拟研究,分析了流体温度、流动方向、系统压力、质量流率和热流密度对对流传热系数和Nu数的影响.结果表明:高温区(800—1050 K)的对流传热系数和Nu数受流动方向和系统压力的影响均很小,但都随着质量流率的增大以及热流密度的减小而明显增大;而随着流体温度的升高,对流传热系数近似线性增大,Nu数则近似线性减小.另外,本文研究发现在高温区可忽略浮升力对传热的影响,而由高热流密度引起的流动加速效应会明显恶化传热.最后,选取了八种管内超临界流体传热关联式与模拟结果进行对比,发现使用基于热物性修正的关联式对高温区传热数据预测的结果优于使用基于无量纲数修正的关联式得到的结果,且其中预测效果最优的关联式得到的计算结果与模拟结果之间的平均绝对相对偏差为8.1%. 相似文献
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高超声速后台阶流动是大气层内高速飞行器发动机设计、表面热防护以及高超声速拦截器红外成像窗口气动光学效应校正等诸多先进高超声速技术研发过程中所涉及的一类基础流动问题. 研究高超声速后台阶流动特性对有效提升飞行器综合性能, 进一步掌握高超声速流动机理具有重大基础 意义. 本文以二维高超声速后台阶流动为研究对象, 在KD-01高超声速激波风洞中测量了二维后台阶模型表面传热系数和表面静压, 并将实测台阶下游表面传热系数分布同采用高超声速边界层理论所得估计值进行了比较. 为进一步验证实验结果, 使用NPLS技术测量了其中一种实验状态下台阶周围流动结构. 研究发现, 对于二维高超声速后台阶流动, 台阶下游表面传热分布受台阶处边界层外缘流动特性的直接影响; 在台阶下游分离区和再附区内, 气体黏性占主导作用; 在台阶下游远场区域, 边界层流动特性趋同于平板边界层; 下游边界层基本结构取决于台阶处边界层相对厚度. 对高超声速后台阶流动, 若使用数值模拟方法研究气动热问题, 应当使用湍流模型. 相似文献
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An experimental study of condensation heat transfer characteristics of flow inside horizontal micro-fin tubes is carried out using R410A, R22, and R32 as the test fluids. This study especially focuses on the influence of heat transfer area upon the condensation heat transfer coefficients. The test sections were made of double tubes using the counter-flow type; the refrigerants condensation inside the test tube enabled heat to exchange with cooling water that flows from the annular side. The saturation temperature and pressure of the refrigerants were measured at the inlet and outlet of the test sections to defined state of refrigerants, and the surface temperatures of the tube were measured. A differential pressure transducer directly measured the pressure drops in the test section. The heat transfer coefficients and pressure drops were calculated using the experimental data. The condensation heat transfer coefficient was measured at the saturation temperature of 48°C with mass fluxes of 50–380 kg/(m2s) and heat fluxes of 3–12 kW/m2. The values of experimental heat transfer coefficient results are compared with the predicted values from the existing correlations in the literature, and a new condensation heat transfer coefficient correlation is proposed. 相似文献
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振荡流共轭换热现象广泛存在于热声热机等工程应用中.基于双分布格子-Boltzmann模型,对平行平板间振荡流共轭换热进行了数值模拟.通过假定共轭界面处流体和固体的未知内能分布函数均为对应的平衡态滑移修正格式,提出了一种处理共轭换热边界的新方法.模拟结果表明,该方法可以保证共轭界面上温度连续和热流连续.分析了不同流体与固体导热系数比情况下振荡流共轭换热的速度场、温度场以及热流分布的特点. 相似文献
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Abstract This article aims to employ a two-dimensional inverse heat conduction technique in designing an experiment for accurately estimating the local convective heat transfer coefficient in slot jet impingement, given temperature measurements at some interior locations in the target plate. The method uses a sequential procedure together with the Beck function specification approach. Solution accuracy and experimental errors are examined using simulated temperature data. It is concluded that a good estimation of the space variable heat transfer coefficient can be made from the knowledge of the transient temperature recordings. The technique is used in a series of numerical experiments to provide the optimum experimental design for a slot jet impingement heat transfer investigation. 相似文献
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This article describes an experimental procedure conducted to estimate and investigate the transient thermal contact conductance (or thermal contact resistance) between the electrodes and workpieces during resistance spot welding. A fine thermal metrology was developed to collect thermal histories near the welding region. Indeed, the electrode tip was instrumented with several interior microthermocouples for measuring the transient temperature response during the welding process. A simple mathematical model, using an inverse heat transfer method, was built for the estimation of the transient heat transfer coefficient from interior transient temperature measurements. A simple resistance welding case of two steel sheets was investigated. The initial transient values of thermal contact conductance were found to be in agreement with those observed in the dry copper–steel solid contact case. At the end of the process, the transient heat transfer coefficient reaches a high value corresponding to the best heat transfer phenomenon at the interface during the welding process. When the metal is melted, the contact quality increases due to the high-applied electrode force. Higher electrode force and heating temperatures produce lower thermal contact resistance. The results obtained show the capabilities and the power of the coupled thermal metrology and transient inverse technique developed to investigate thermal history of resistance spot welding. 相似文献