铝基微通道内纳米流体饱和沸腾及可视化研究

Saturated boiling and visualization of nanofluids in aluminum-based microchannels

分别以去离子水及质量分数为0.3%,0.6%和0.9%Al2O3纳米流体为工质,在截面宽×高为0.3 mm×2.0 mm矩形铝基微通道内进行沸腾换热实验,并利用高速摄像仪进行可视化研究,分析热流密度、雷诺数、壁面粗糙度对流体传热系数的影响,探究流体流型变化与气泡生长规律。研究结果表明:纳米流体与去离子水的饱和沸腾传热系数随热流密度的增加而快速增大,努塞尔数Nu随雷诺数Re增大而增大但增幅不同,质量分数为0.3%,0.6%和0.9%的3种纳米流体的Nu比去离子水的Nu分别提高约8%,13%和16%;在相同热流密度及质量流速条件下,纳米流体与去离子水的传热系数均随传热壁面粗糙度的增加而增大;流体流型的变化呈现周期性,增大热流密度,可缩短气泡生长周期,泡状流比例增加。

The boiling heat transfer characteristics were experimentally investigated through aluminum-based rectangular microchannels with the size of 0.3 mm×2.0 mm, using Al2O3-H2 O nanofluids with particle of 0, 0.3%, 0.6%, 0.9%（mass fraction） as the working fluids, and the visualization was studied by using high speed camera device. The influence of heat flux, Re and wall roughness on the fluid heat transfer coefficients was discussed, and the variations of stream pattern and the bubbles＇ growth were investigated. The results show that the saturated boiling heat transfer coefficients of nanofluids and deionized water both increase significantly with the increase of mass flow rate. The values of Nu increase with the increase of Re. But the amount of increase is different. The Nu of nanofluids with particle of 0.3%, 0.6% and 0.9% are 8%, 13% and 16% higher than those of deionized water. With the same heat flux density and mass velocity, the heat transfer coefficient of two working fluids both increase with the increase of roughness of the channels. The stream pattern changes periodically, and the growth cycle of the bubbles will be shorter when heat flux density increases.