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Studies on the Clarification of Heat Transfer Characteristic for Flow Boiling in Small Channels and its Improvement

小通道流动沸腾传热特性的澄清及改进研究

基本信息

批准号：
18360103
负责人：
OHTA Haruhiko
金额：
$ 10.24万
依托单位：
Kyushu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-18360103/
关键词：
micro channel boiling heat transfer binary mixture self-wetting

项目摘要

Flow boiling heat transfer in a single small tube is investigated by using FC72 as a test fluid. The heat transfer coefficients were measured in the ranges of heat flux 2-24kW/m^2 and mass velocity 100-400kg/m^2s. Test tube, made of stainless steel, has an inner diameter of 0.51mm and a heated length of 200mm. The tube is located horizontally in a vacuum chamber to reduce the heat loss and to minimize the time to obtain data regarded as that of steady state. In the experiments of strict inlet flow rate regulation, heat transfer characteristics were similar to those observed in normal size tubes. But if the flow rate was fluctuated up to±20% of the total under the weak inlet flow rate regulation, the trend that the heat transfer coefficient was increased with increasing vapor quality in moderate vapor quality region was disappeared and heat transfer deterioration due to partial dryout started at lower vapor quality. Boiling heat transfer characteristics in minichannels could be changed … More considerably by the existence of flow fluctuation caused by the rapid axial growth of elongated bubbles at low vapor quality. The regulation of inlet flow rate seems to be one of key parameters to reduce the scattering in heat transfer data encountered in flow boiling of minichannels.In order to enhance flow boiling heat transfer in narrow channels, the effects of liquid supply method to channels on CHF and heat transfer coefficient were investigated using atmospheric water for various combinations with gap sizes of narrow channels and volumetric flow rates. An auxiliary unheated channel for liquid supply was installed in parallel with the back side of a narrow heated channel. These channels were connected by two sintered metal porous plates. Fine V-shaped grooves were machined on the heat transfer surface of heated channel. High CHF values of 2.0×10^6 W/m^2 were measured under conditions the total flow rate is 3.60 liter/min and gap sizes are 2 mm and 5 mm. In the series of the experiments for total flow rate of 3.60 liter/min, highest heat transfer coefficients as much as 1.1×10^5 W/m^2 for gap size of 2 mm and 7.8× 10^4 W/m^2 for 5 mm were measured.The selection of working fluid for the high-performance thermal systems by applying boiling phenomena was examined. For mixtures of 1-propanol/ water, 2-propanol/ water and water/ ethylene glycol, nucleate boiling heat transfer characteristics were investigated. Alcohol aqueous solutions can be expected heat transfer enhancements due to "Marangoni effect". At low alcohol concentration region, CHF is decreased sharply by the increase in alcohol concentration. After reaching a minimum value, CHF is increased gradually up to the value of the azeotropic concentration with the increase in alcohol concentration at the region of moderate alcohol concentration. Less

以FC72为试验流体，研究了单管内的流动沸腾传热。换热系数在热流密度2 ~ 24kw /m^2和质量速度100 ~ 400kg/m^2s范围内测量。试管由不锈钢制成，内径0.51mm，加热长度200mm。该管水平放置在真空室中，以减少热损失，并最大限度地减少获得稳态数据的时间。在严格调节进口流量的实验中，传热特性与正常尺寸管相似。但当流量波动到总流量的±20%时，在中等汽质区域换热系数随汽质增加而增加的趋势消失，在较低汽质区域开始部分干化导致换热恶化。在低汽质条件下，由于细长气泡轴向快速增长而产生的流动波动的存在，可以显著改变微通道内的沸腾换热特性。入口流量的调节是减少小通道流动沸腾传热数据散射的关键参数之一。为了增强窄通道内的流动沸腾换热，以大气水为对象，研究了不同通道供液方式对窄通道间隙大小和体积流量的CHF和换热系数的影响。在一个狭窄的加热通道的背面平行安装一个辅助的供液不加热通道。这些通道由两个烧结金属多孔板连接。在加热通道的传热表面加工出细小的v形槽。在总流量为3.60 l /min，间隙尺寸为2mm和5mm的条件下，测得高CHF值2.0×10^6 W/m^2。在总流量为3.60 l /min的一系列实验中，在间隙尺寸为2mm时测得最高换热系数为1.1×10^5 W/m^2，在间隙尺寸为5mm时测得最高换热系数为7.8× 10^4 W/m^2。研究了利用沸腾现象选择高性能热力系统工质的方法。对1-丙醇/水、2-丙醇/水和水/乙二醇的混合物进行了核沸腾换热特性研究。由于“马兰戈尼效应”，酒精水溶液可以预期传热增强。在低酒精浓度区，随着酒精浓度的增加，CHF急剧下降。在中等酒精浓度区域，CHF在达到最小值后，随着酒精浓度的增加逐渐增大，直至共沸浓度。少