Abstract:

The increasing demand for efficient and compact methods of heat transfer has generated interest in the utilization of a narrow channel with a significant velocity gradient along its height, thus presenting substantial potential. This research study focused on investigating the heat transfer phenomena in a flow boiling system that employs a narrow slot channel made of titanium under negative pressure conditions. The experimental analysis employed a designated working fluid, namely an ethylene glycol aqueous solution with a mass concentration of 55%. The experimentation was conducted under specific operational parameters, encompassing a mass flow rate spanning from 750kg/(m²·s) to 2000kg/(m²·s), a saturation temperature within the range of 80℃ to 90℃, and an inlet temperature ranging from 60℃ to 70℃. The findings of the study revealed that the activation of a substantial quantity of nucleation sites in titanium necessitated an elevated heat flux. Consequently, this phenomenon maintained the average heat transfer coefficient (h) in a state of relative constancy both prior to and subsequent to the onset of nucleate boiling (ONB). The heat flux required to start of ONB and the mean heat transfer coefficient during the phase of fully developed boiling were subject to influence from alterations in the mass flow rate. Notably, in instances where a considerable degree of subcooling was present, the thermal performance within the confines of a titanium narrow-slit channel displayed reduced sensitivity to variations in inlet temperature during the fully developed boiling stage. Elevating the inlet temperature while concurrently reducing the subcooling degree markedly enhanced the average heat transfer coefficient by as much as 65%. The perturbation of back pressure on heat transfer performance manifested primarily during the fully developed boiling stage, wherein diminished back pressure corresponds to augmented average heat transfer coefficients.

Key words: microchannels, ethylene glycol aqueous solution, negative pressure, gas-liquid flow, flow boiling, heat transfer

摘要：

高效、紧凑的换热方式需求日益增大，具有高度方向速度梯度大的窄缝通道成为最有前景的方式之一。本文以质量分数为55%的乙二醇水溶液为工质，针对钛窄缝通道在负压工况进行流动沸腾换热实验。实验在质量流率750~2000kg/(m²·s)、饱和温度为80~90℃、入口温度60~70℃的条件下进行。结果表明，钛需要更高的热流密度激活大量成核点，从而其过冷沸腾起始点（ONB）前后平均换热系数h基本不变；质量流量对于ONB和沸腾充分发展阶段的平均换热系数影响很大；在高过冷度时，沸腾充分发展阶段，钛窄缝通道换热性能对于入口温度不敏感；提高进口温度降低过冷度可以极大提高平均换热系数，70℃条件下平均换热系数在沸腾充分发展阶段可以提高65%；背压对于换热性能的影响主要在沸腾充分发展阶段，背压越低平均换热系数越大。

关键词: 微通道, 乙二醇水溶液, 负压, 气液两相流, 流动沸腾, 传热