Effect of Header Configuration on Refrigerant Distribution in Parallel Flow Microchannel Evaporators

The refrigerant flow distribution in the parallel flow microchannel evaporators is experimentally investigated to study the effect of header configuration.Six different configurations are tested in the same evaporator by installing insertion device and partition plate in the header to ensure the consistency of the other structure parameters.The results show that the uniformity of refrigerant flow distribution and the heat transfer rate are greatly improved by reducing the sectional area of header.The heat transfer rate can increase by 67.93% by reducing the sectional area of both inlet and outlet headers.The uniformity of refrigerant flow distribution and the heat transfer rate become worse after installing the partition plate in the insertion devices and changing the inner structure of the header further.     

回热器对跨临界CO2热泵系统性能的影响

为了研究跨临界CO2热泵热水系统中,回热器传热面积对系统性能的影响,在不同的制冷剂充注量条件下实验研究了CO2热泵系统的性能.实验中,通过调节变频压缩机频率与电子膨胀阀开启度,保持了一定的制热量与蒸发器出口过热度.实验结果表明:在最佳制冷剂充注量条件下,随着回热器传热面积的增加,压缩机的压缩比下降,排气温度与吸气温度上升.采用回热器可以提高系统的最大制热系数,当回热器的无量纲传热面积为0.2时,可使最大制热系数提高约3.2%～5.1%.     

Geometry Modeling of an Electronic Expansion Valve Head

This paper proposed that the flow characteristic of electronic expansion valve should be adapted to the evaporator superheat gain to refrigerant flow rate under different working conditions. Two native methods of geometry modeling of electronic expansion valve head were introduced. By analysis of them, some shortcoming was detected and a universal modeling method of electronic expansion valve head was put forward. Through this model, the flow characteristic of EEV and the influence factors can be investigated more deeply.     

A New Experimental Rig of Testing Flow Boiling Heat Transfer of Refrigerant and Lubricant Mixture

This paper proposed a new experimental rig of testing flow boiling heat transfer of refrigerant and lubricant oil mixture. The quantity of oil in the test section can be controlled and regulated conveniently and accurately by connecting separate lubricant oil circuit with test section in parallel. It was built up by retrofitting a multiple air-conditioner and installing three oil-separators in serials at the compressor outlet. And so the lubricant oil in the discharged refrigerant gas of compressor can be removed completely. The refrigerant flow rate through test section can be bypassed by the by-path circuit of indoor unit. This experimental rig has advantages such as on-line and continuous oil injection, short time of obtaining stability, flexible operation, simple control, which lead to high efficiency in the research of flow boiling heat transfer of refrigerant and lubricant oil mixture.     

Convective Boiling of Near-Azeotropic Refrigerant R410A in the Horizontal Micro-fin Tube

Using near-azeotropic refrigerant R410A as the working fluid, the experimental studies on the horizontal micro-fin tubes were conducted. Several factors affecting heat transfer coefficients were analyzed, and the characteristics of flow boiling of the refrigerant in the horizontal micro-fin tubes were discussed. The local heat transfer coefficients increase with mass flux, heat flux and quality. And the heat transfer enhancement factor of those testing tubes is about 1.6 to 2.2.     

Dynamic simulation and performance investigation of no-frost refrigerator: Part I mathematical model

A dynamic approach for the modeling, simulation and analysis of no-frost Refrigerator (RF) is discussed. In Part I, the complex interactions among the components in the cooling system are analyzed in detail, based on which the modeling simplifications are proposed. Then, the mathematical models for the evaporator, cabinet and duct-fan are presented. The whole system is divided into two subsystems—refrigerant cycling system and air cycling system. In order to simplify the model, two closed-loop systems are broken into the compressor component and the evaporator component, respectively. A general distributed parameter model is employed for evaporator with homogeneous flow to simplify the two-phase evaporating flow region. The z-transfer function model is used to describe the cabinet load. Computational fluid dynamics (CFD) method is employed to obtain the pressure drop and flow rate curve of the duct-fan model.

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无接触网供电车辆电磁-热场耦合计算

无接触网供电技术在城市轨道交通中的应用受到越来越广泛的关注，大功率无接触电能传输的实际应用还有许多问题需要论证，其中电磁感应导致的涡流发热问题引起人们的普遍重视. 依据电磁感应原理和传热学，建立无接触网供电车辆感应加热模型，采用有限元法计算无接触网供电车辆热场分布，对不同载荷工况下的车辆的发热情况进行数值仿真，并对采用散热器和风冷两种散热方式的接收线圈的散热性能进行对比研究. 研究结果表明:接收线圈和转向架温度升高明显；随着发射线圈电流增加以及气隙距离的减小，车辆各个部位的温度都有上升趋势；装有散热器的接收线圈最高温度比不含散热器时降低了126.0 ℃，通过改变散热器的传热系数能进一步提高散热器的散热性能；采用风冷散热方式接收线圈温度降低了131.2 ℃，与散热器相比，风冷的散热性能略好，且随着风速增加风冷效果更加突出.      

通道内矩形涡对涡发生器强化换热的数值研究

用数值模拟方法研究了在矩形通道底壁安装矩形涡产生器对(RWP)时纵向涡对层流换热的影响.在雷诺数变化范围为500~7 000,通道底壁安装RWP和不安装RWP两种情况下,比较了流体流动和换热性能.同时对涡产生器的高度和攻角对表面换热性能的影响也做了研究.结果表明:通道的底壁安装RWP可以显著提高换热性,雷诺数越大,换热性越强.随着涡产生器高度的增大,换热性增强,但阻力系数会急剧增加.当攻角为29°时,强化换热效果是最强的.     

车辆通风式制动盘内部通道对流换热研究综述

总结了通风式制动盘内部通道对流换热的研究成果,从内部通道的质量流量、对流换热系数和有效散热表面积三方面,分析了不同结构设计对制动盘内部通道换热的影响;从解析法、数值分析法和试验测试法三方面,综述了国内外在对流换热分析和检测方法的研究概况。研究结果表明:在径向叶片制动盘通道内,主要存在2种流动方式,由紧邻叶片吸力侧气流分离引起的回流和在径向通道内部旋转的二次流,抑制回流区的形成可以提高泵送空气质量流量,使通道内的温度分布更加均匀,二次流将促进通道间的空气混合流动和湍流的发展,加强局部剪切应力,改善制动盘散热性能;综合应用射流冲击强化方式(多束流、旋流和多方向射流等)、高孔隙率和类柱状结构优化设计也能够改变流体在通道中的流动状态,这些措施都会使得通道内流体扰动增大,热边界层变薄,壁面附近的速度梯度增大,有效提高了制动盘的对流换热系数,增强了散热能力;采用解析法和数值分析法得到的结果具有很强的理论参考价值,而采用试验测试法所获得的结果更加接近制动盘实际内部温度和气体流速的变化,因此,若能将三者无缝结合,实现优势互补,则最具有科学研究价值;在对高速车辆制动盘结构进行优化设计时,为了获得最大的散热效率,往往忽略了通道内摩擦压降和流动阻力,因此,如何平衡散热与摩擦压降、流动阻力之间的关系,还需进一步深入探索与研究。      

Error Analysis of Liquid Holdup Measurement in Gas-Liquid Annular Flow Through Circular Pipes Using High-Speed Camera Method

Accurate measurement of gas-liquid phase fraction is essential for the proper modelling of the pressure drop, heat transfer coefficient, mass transfer rate and interfacial area in two-phase flows. In this paper, taking the issue of optical distortion into account, an analytical model was proposed to estimate and correct the liquid holdup in gas-liquid annular flow through a circular pipe using high-speed camera method. The error in the liquid holdup measurement generated from different refractive indices among transparent circular pipe, liquid film and air core was firstly theoretically analyzed based on the geometric optics. Experimental tests were then carried out to identify the difference as well as to validate the proposed model. Results indicated that the prediction of the liquid holdup has a good performance with the experimental data (i.e., mean relative error is 4.1%) and the measured liquid holdup is larger than the real one. It was found that the measured liquid holdup is larger than the real one. Generally, when the real liquid holdup gets smaller, the discrepancy between the measured liquid holdup by image and the real liquid holdup becomes more significant. Thus, after measuring the liquid holdup from the images, the value of the measured liquid holdup must be corrected by the present model in order to obtain the real liquid holdup.     

Dynamic Simulation and Performance Investigation of No-frost Refrigerator: Part Ⅰ Mathematical Model

A dynamic approach for the modeling, simulation and analysis of no-frost Refrigerator (RF) is dis-cussed. In Part Ⅰ, the complex interactions among the components in the cooling system are analyzed in detail, based on which the modeling simplifications are proposed. Then, the mathematical models for the evaporator, cabinet and duct-fan are presented. The whole system is divided into two subsystems-refrigerant cycling system and air cycling system. In order to simplify the model, two closed-loop systems are broken into the compressor component and the evaporator component, respectively. A general distributed parameter model is employed for evaporator with homogeneous flow to simplify the two-phase evaporating flow region. The z-transfer function model is used to describe the cabinet load. Computational fluid dynamics (CFD) method is employed to obtain the pressure drop and flow rate curve of the duct-fan model.     

毛细相变流体回路中蒸发器的预热启动特性研究

通过分析毛细管内液柱的动量方程,从力平衡的角度获得毛细相变流体回路系统的启动判别条件,并建立蒸发器的三维导热模型来研究系统的启动特性.研究表明:蒸发器的启动预热时间随启动热流的增大而减小;减小液体补偿腔的高度可以加快蒸发器的启动过程,且启动热流愈小该现象愈显著;在较低的启动热流条件下,减小蒸气槽道的宽度,可以减小启动预热时间,改善蒸发器启动性能,而在较高的热流密度下,其对蒸发器的启动性能影响不大.     

Integrated fluid-thermal-structural numerical analysis for the quenching of metallic components

The quenching of a metal component with a channel section in a water tank is numerically simulated. Computational fluid dynamics (CFD) is used to model the multiphase flow and the heat transfer in film boiling, nucleate boiling and convective cooling processes to calculate the difference in heat transfer rate around the component and then combining with the thermal simulation and structure analysis of the component to study the effect of heat transfer rate on the distortion of the U-channel component. A model is also established to calculate the residual stress produced by quenching. The coupling fluid-thermal-structural simulation provides an insight into the deformation of the component and can be used to perform parameter analysis to reduce the distortion of the component.     

Convective Heat Transfer Characteristics of the Elliptic Cylinder with Axis Ratio 4 : 1 in Crossflow

The heat transfer features around the elliptic cylinder of axis ratio 4: 1 in crossflow were investigated experimentally within a wide range of Reynolds number. By means of heat-mass transfer analogy and the naphthalene sublimation technique, the local heat transfer distribution and the mean heat transfer coefficient are clarified.The result shows that the mean heat transfer coefficient is higher than that of a circular cylinder in most Reynolds number range regarded, and this superiority turns to be more significant with the increase of flow speed. Moreover, the effect of axis ratio on mean heat transfer coefficient was investigated tentatively. The oil-lampblack technique was employed to enable visualization of the flow pattern around the cylinder and on the cylinder wall.     

发泡条件对基质沥青发泡膨胀率的影响

通过建模软件Solidworks对沥青发生装置进行三维建模, 采用有限元仿真软件Fluent分析了不同参数条件下基质沥青的发泡过程, 并对比了试验结果和仿真结果, 分析了应用有限元仿真技术研究基质沥青发泡膨胀率的可靠性; 对发泡腔和发泡腔内各流体材料进行有限元仿真, 利用Fluent中的后处理功能得到了发泡腔的温度、速度、压力和各相的分布云图。仿真结果表明: 在整个发泡过程中, 基质沥青温度的增大使沥青黏度下降, 发泡腔内水蒸汽增加, 当基质沥青温度从120℃升高到160℃时, 基质沥青的发泡膨胀率从4增大到11, 说明基质沥青温度的变化对其发泡膨胀率的影响很大; 基质沥青流量的增大起到增加发泡腔内基质沥青总量和减少基质沥青之间相互接触时间和接触面积的作用, 当基质沥青入口流量从60 g·s-1增大到120 g·s-1时, 基质沥青的发泡膨胀率为7~11, 表明基质沥青流量的变化对其发泡膨胀率的影响很大; 当用水量从2.0%增大到3.5%时, 基质沥青的发泡膨胀率基本不变, 说明用水量对基质沥青发泡膨胀率的影响不大; 仿真得到的最低发泡膨胀率为3.57, 此时发泡条件参数分别是基质沥青流量为120 g·s-1, 基质沥青温度为120℃, 发泡用水量为3.0%。      

The Effect of Circulation Fan on Energy Consumption in Nature Convective Refrigerator-Freezer

The effect of the circulation fan installed in fresh food compartment on energy consumption of natural convective refrigerator/freezers (RFs) was experimentally studied. Five different RF models with different cycles were tested. The experimental results showed that the energy consumption of the single-loop cycle RF increased by 2.4%~3.8%, that of the bypass two-circuit cycle RF decreased by 1.0%, and that of the two-circuit cycle RF with its evaporators in parallel when the geometry parameters of refrigeration system and the refrigerant charge were not changed after the circulation fan was installed decreased by 3.3%. When the optimization on the refrigerant charge and the evaporator was carried out, the energy consumption of the single-loop cycle RF , the bypass two-circuit cycle RF and the two-circuit cycle RF with its evaporators in parallel, decreased by 1.0%~6.4%, 3.25% and 3.26% respectively. The present conclusions will provide a guideline to the optimum design for the RF with the circulation fan.     

不同空间结构的有轨电车超级电容热行为

为了减轻有轨电车超级电容模组因温度引起的性能衰减，基于超级电容器的单体结构，研究单体不同空间结构对超级电容模组热行为的影响. 首先，建立超级电容电化学-热耦合模型，并搭建实验平台验证模型的有效性；其次，定义“自然对流换热比表面积”，通过最高温度、最大温差、单体温度波动率和空间利用率4个指标对截面为3 × 6、2 × 9的长方体结构、截面为4 × 4的正方体结构和六面体结构的超级电容模组的温度特性和体积特征进行评估. 研究表明:气流路径的长度、对流换热比表面积以及强制对流换热的单体数量会影响散热的效果，具有短而宽流动路径的空间结构冷却效果更好；正方体结构是冷却效果和均温方面的最优选择；对于空间利用率和冷却效率而言，六面体结构是最佳选择.      

前挤压工件和模具的温度分布有限元分析

在高精密冷成形加工中，工件和模具的温度变化直接影响工件的成形精度，通过对前挤压加工过程机械热力偶合有限元模拟，对材料的流动，由于塑料变形和接触面之间的摩擦所产生的热量，工件和模具中的热传导，工件与模具之间的热交换，在成形期间和其后冷却过程工件和模具中温度的分布等进行了分析，对工件和模具的机械和热力学性能和诸如冲头的速度，摩擦系数等加工条件对温度在工件和模具中的分布的影响进行了研究，有限元模型的结果表明，在成形加工中由于热膨胀和冷却的影响，工件和模具中温度的变化将影响工件的成形精度，工件的性能对热的产生和温度分布有决定性的影响，加工条件的变化会影响温度的高低和分布。     

电动汽车无线供电系统电能发射线圈设计与切换控制

针对采用级联式发射线圈的电动汽车无线供电系统中线圈切换时存在的互感急剧下降及汽车位置检测困难的问题,提出了一种对嵌式电能发射线圈,并根据互感稳恒原则及其计算方法,给出了对嵌式电能发射线圈主要参数的设计方法,提出了一种双线圈式车体位置检测传感器,给出了传感器的尺寸参数设计方法及电能传输系统对传感器的干扰抑制方法,阐述了级联式发射线圈的切换控制策略.基于Ansoft Maxwell平台、Matlab/Simulink平台和电动汽车ICPT无线供电系统实验平台分别对研究成果进行了仿真分析和实验验证,结果表明:实验实测互感值波动率约为8%,车载拾取电压波动率约为10%,对嵌式能量发射线圈能够有效地缓解ICPT无线供电电动车在切换过程中的互感下降问题;双线圈式车体位置检测系统能够有效地在40 kHz能量通道电磁场的干扰中拾取位置信号,表明该位置检测方案及切换控制策略的可行性.