微通道内流动沸腾不稳定性影响因素实验研究

Experimental Study on the Flow Boiling Instability Governing Parameters in Microchannels

微通道沸腾不稳定性降低设备运行性能及传热特性。设计入口集成种子汽泡发生器的三角形硅基微通道热沉。搭建同步光学可视化测量实验台。研究加热膜长度、质量流量及种子汽泡触发频率对微通道内沸腾不稳定性及传热影响。结果表明:加热膜长度和质量流量作为控制沸腾不稳定性的关键参数,加热膜长度越长或质量流量越低,沸腾起始点和临界热流密度越早发生。单相液体区域,热流密度增大,压降略微降低,温度线性升高。汽液两相区域,热流密度增大,压降迅速增大,温度呈指数式上升。触发种子汽泡作为一种主动式控制技术,沸腾不稳定性得到抑制或消除,换热得到显著增强,是一种值得推广的技术。

Flow boiling instabilities in microchannel can reduce the performance of equipment operation and disturb the heat transfer characteristic. The parallel triangle silicon microchannel heat sink was integrated with seed bubble generators in the microchannel upstream. The simultaneous optical visualization measurement experimental systems were set up. The flow boiling instability and heat transfer under different heater lengthes, mass fluxes and seed bubble frequencies were examined. The results show that, the heater length, heat and mass flux were identified as the key parameters to the boiling instability process. Longer heater length or lower flow rate induces earlier appearance of boiling incipience and critical heat flux. With heat flux increasing, the pressure drop decreases slightly and the temperature increases linearly in the single liquid phase region. However, the pressure drop increases sharply and the temperature increases exponentially in the vapor-liquid two phase flow region. Using triggering the generation of seed bubbles as the active controlling technic, the self-sustained boiling instability can be effectively controlled or fundamentally eliminated. Moreover, the heat transfer could be enhanced markedly. The seed bubble triggered technology is worth to be promoted.