单气泡对层流自然对流传热影响的数值研究

Numerical simulation on effect of single bubble on natural convection heat transfer in laminar flow

在工业传热过程中,温度边界层的增厚严重降低了传热效率。研究发现在液相中加入气泡能提高相间的传热效率。采用VOF(流体体积法)研究单气泡注入对垂直管道内层流自然对流传热的影响,利用Boussinesq假设考虑自然对流的浮力项,分别研究相同气泡形状不同气泡尺寸以及相同气泡尺寸不同气泡形状对近壁流体自然对流传热的影响。结果表明:气泡直径越大,变形稳定后的上升速度和横向尺寸越大,对周围流场造成的扰动越剧烈,传热强化效果和传热强化影响区域增大;气泡直径相同时,随着Eo数的增大,气泡横向尺寸显著变大,传热增强效果变得明显。气泡注入影响传热增强的主要因素与气泡的横向尺寸和上升速度有关,横向尺寸和上升速度越大传热强化效果越好。

In the industrial process of heat transfer,an increase in temperature boundary layer seriously reduces heat transfer efficiency.The injection of bubbles in liquid can improve heat transfer between phases.The effect of single bubble injection on natural convection heat transfer in laminar flows near a vertical wall was investigated using VOF method,and the effect of the same bubble shape for different bubble sizes and the same bubble size for different bubble shapes on natural convection heat transfer in near-wall flows was studied,respectively.The buoyancy term of natural convection was considered using Boussinesq hypothesis.The results show that for the same bubble shape,the larger bubble diameter is,the lager bubble rise velocity and transverse dimension are after bubble deformation is stable.This leads to the stronger disturbance to the flow around a bubble and correspondingly the enhancement effect and influence area of heat transfer by a bubble increase.When bubble diameter is the same,with the increase of Eo number,the transverse dimension of a bubble becomes significantly larger and the enhancement effect of heat transfer becomes obvious.The main factors affecting heat transfer enhancement by bubble injection are related to bubble transverse size and rise velocity.The larger bubble transverse size and rise velocity are,the better the enhancement effect of heat transfer is.