Study of High Efficiency Micro Heat Exchanger and Refrigerant Distribution using Throttle Mechanism

高效微型换热器及节流机构制冷剂分配研究

基本信息

批准号：
16560173
负责人：
SAITOH Shizuo
金额：
$ 2.3万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2005
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-16560173/
关键词：
two-phase flow T-type distribution boiling heat transfer coefficient distributor compact heat exchanger refrigerant flow distribution oscillating flow

项目摘要

For the multi-path heat exchanger using small diameter tubes, a distributor supplies refrigerant to each passage of heat exchanger tubes. No evenness of refrigerant decreases the efficiency of the heat exchanger. In the present study, the distribution of refrigerant to parallel small tubes and the boiling heat transfer for refrigerant R-134a were investigated to provide useful data for the design of compact heat exchangers using small tubes. The distributor, which is connected to the parallel evaporator tubes, supplies refrigerant to each evaporator. Two orifice plates, which are three kinds of nozzle diameters(0.1mm, 0.15mm and 0.2mm), are installed in the distributor connected the front ends of the evaporator tubes. The experimental investigation was performed under the mass flux 100 to 250kg/m^2s, heat flux from 4.8 to 11.8kW/m^2 and inlet refrigerant vapor quality of the evaporator < 0. Results showed that 1) the distribution of refrigerant was not affected by nozzle diameter. 2) the refrigerant flow was steady with decreasing the nozzle diameter, which meant that the fluctuation of refrigerant flow decreased by throttle. 3) two-phase oscillating flow occurred in the evaporator was suppressed by throttle. For the effect of throttle for the boiling heat transfer, when mass fluxes were 100 and 150kg/m^2s, the boiling heat transfer coefficient for the nozzle diameter 0.1mm was better than for the diameter 0.2mm. But, in the case of the mass flux 250kg/m^2s, both the boiling heat transfer coefficients for the diameter 0.1mm and for 0.2mm were almost same values. The boiling heat transfer coefficient was improved at low mass flux. In previous study, it was known that the oscillating flow in the evaporator decreased the heat transfer coefficient. Throat on the entrance of evaporator suppressed flow instability and as a result, the boiling heat transfer coefficient was improved.

对于使用小直径管的多路热交换器，分配器将制冷剂供应到热交换器管的每个通道。制冷剂不均匀会降低热交换器的效率。在本研究中，研究了制冷剂到平行小管的分布以及制冷剂 R-134a 的沸腾传热，为使用小管的紧凑型换热器的设计提供有用的数据。连接到平行蒸发器管的分配器向每个蒸发器供应制冷剂。连接蒸发器管前端的分配器内安装有两个孔板，有三种喷嘴直径（0.1mm、0.15mm、0.2mm）。实验研究在质量通量100～250kg/m^2s、热通量4.8～11.8kW/m^2、蒸发器入口制冷剂蒸汽品质<0的情况下进行。结果表明：1）制冷剂分布不均匀。受喷嘴直径影响。 2）随着喷嘴直径的减小，制冷剂流量趋于稳定，这意味着通过节流，制冷剂流量的波动减小。 3）蒸发器内出现的两相振荡流被节流装置抑制。对于节流对沸腾传热的影响，当质量流量为100和150kg/m^2s时，喷嘴直径0.1mm的沸腾传热系数优于直径0.2mm的沸腾传热系数。但是，在质量流量为250kg/m^2s的情况下，直径0.1mm和0.2mm的沸腾传热系数几乎是相同的值。低质量通量下沸腾传热系数得到改善。在之前的研究中，我们知道蒸发器中的振荡流会降低传热系数。蒸发器入口处的喉部抑制了流动不稳定，从而提高了沸腾传热系数。