梯形微通道气液分相强化换热实验研究

针对微通道换热器强化沸腾换热,提出分段式梯形换热结构,该结构可实现气泡在表面张力驱动下间断性流向通道两侧,保持中间加热区为液体,实现气液分相流动,进而强化沸腾换热性能。采用无水乙醇为工质,实验研究直肋和梯形结构铜基表面在热流密度为160~320 kW/m²和工质流量为0.4~2.0 g/s时壁温、换热系数等参数变化规律。结果表明：在饱和沸腾区,梯形分相结构可有效实现气液分离,进而降低壁面温度,大幅提高换热系数；如在25 mm位置处,5段结构换热系数比平行结构换热系数提高了60.4%；在单相加热区,换热面积为主要影响因素,直肋结构换热系数略大,但换热系数比饱和沸腾时小一个数量级。平均换热系数分析得到5段结构微通道比平行结构微通道提高了53.8%,可见分段式结构可实现气液分相流动,有效提高沸腾换热的平均换热系数,增强整体换热能力。

Experimental Study on Enhanced Heat Transfer of Gas-liquid Phase Separation in Trapezoidal Microchannel

In order to enhance the boiling heat transfer in microchannel heat exchanger, a segmented trapezoidal heat transfer structure is proposed, which can achieve gas-liquid separated phase flow and so enhance the boiling heat transfer. The bubbles flow to sides of the microchannel driven by surface tension, and liquid keep in the middle heating zone. The variation of copper temperature and heat transfer coefficient of rib and trapezoid structures with heat flux of 160~320 kW/m² and ethanol flow rate of 0.4~2.0 g/s were studied experimentally. The results show that in the saturated boiling region, the trapezoidal phase separation structure can effectively achieve gas-liquid separation, thus reducing the copper temperature and greatly improving the heat transfer coefficient. For example, at the position of 25 mm, the heat transfer coefficient of 5-section trapezoidal structure is 60.4% higher than that of parallel structure. In the single-phase heating zone, the heat transfer area is the main factor, so the heat transfer coefficient of straight rib structure is slightly larger, but the heat transfer coefficient in the single-phase region is one order of magnitude smaller than that in the saturated boiling region. The average heat transfer coefficient of the 5-section trapezoidal microchannel is 53.8% higher than that of the parallel microchannel. It can be seen that the segmented structure can realize the liquid-gas phase separation flow, effectively improve the average heat transfer coefficient of boiling heat transfer and enhance the overall heat transfer ability.