Effect of heated wall inclination on natural convection heat transfer in water with near-wall injection of millimeter-sized bubbles
Effect of heated wall inclination on natural convection heat transfer in water with near-wall injection of millimeter-sized bubbles
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近壁注入毫米级气泡加热壁倾角对水中自然对流换热的影响
DOI：
10.1016/j.ijheatmasstransfer.2017.06.009
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发表时间：
2017
影响因子：
5.2
通讯作者：
Yuichi Murai
中科院分区：
文献类型：
--
作者：
Atsuhide Kitagawa;Petr Denissenko;Yuichi Murai
实验研究了近壁注入毫米级气泡的水中加热壁面自然对流换热。速度和温度测量是在近壁区域进行的。在受热壁垂直角0 ~ 40˚范围内，气泡注入使传热系数提高了一个数量级。注入气泡与未注入气泡的换热系数之比随着壁面倾角的增大而增大。根据实测的液体温度分布和液体流速分布，可以从两种机制来解释气泡注入强化换热的机理。首先，气泡驱动的流动增强了冷液体进入热边界层的壁面平行输运。其次，热液和冷液的壁向混合是由于气泡上升运动、气泡涡脱落和边界层内形成的非定常涡共同激活了液相的壁向速度波动。非定常涡流随气泡沿壁面运动，主要有助于壁面倾角增大时传热的增强。
Natural convection heat transfer from a heated wall in water with near-wall injection of millimeter-sized bubbles is studied experimentally. Velocity and temperature measurements are conducted in the near-wall region. In the range of the heated wall angles from 0 to 40˚ from the vertical, the heat transfer coefficient increases by up to an order of magnitude with bubble injection. The ratio of the heat transfer coefficient with bubble injection to that without injection increases with the wall inclination angle. Based upon measured liquid temperature distributions and liquid flow velocity profiles, enhancement of heat transfer by bubble injection is explained by two mechanisms. First, wall-parallel transport of cold liquid into the thermal boundary layer is enhanced by the bubble-driven flow. Second, wall-normal mixing of warm liquid and cold liquid occurs, as a result of wall-normal velocity fluctuations of the liquid phase activated by a combination of bubble rising motion, vortex shedding from the bubbles, and unsteady vortices formed within the boundary layer. The unsteady vortices travel along the wall together with the bubbles, primarily contributing to the enhancement of heat transfer at higher wall inclination angles.
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