垂直圓柱體置於混合對流中熱泳效應對氣膠粒子沉積之影響

THE EFFECT OF THERMOPHORESIS ON AEROSOL PARTICLE DEPOSITION FROM MIXED CONVECTION FLOW OVER A VERTICAL CYLINDER

本文利用邊界層理論分析二維穩態、層性和不可壓縮性氣流中的粒子，在同時受到混合對流、擴散、圓柱曲率、熱泳力等作用下，計算流經一個被加熱或冷卻垂直圓柱體之速度、溫度和濃度分佈，以及氣膠粒子於璧面上的沉積率。利用非相似方程式求解邊界層方程式，發現氣膠粒子在非均勻溫度場裡，其熱泳作用和對流效應對璧面沉積速率有很大的影響，結果顯示被冷卻的圓柱體，粒子有被吸附的現象，而被加熱的圓柱體則有被驅離的情形。另一方面，當粒子直徑大於0.1μm時，其沉積通量會趨近於一定值，且熱泳效應尤其顯著。當圓柱曲率參數變大時，其璧面則有較高的沉積速率，另外在助流情形下，浮力增強對冷卻璧的粒子沉積速率有絕對提升效果。

This study concerns the analysis of the particle deposition rate of a two-dimensional, laminar, steady, and incompressible mixed convective flow over a vertical hot or cold cylinder subjected to the effects of convection, diffusion, geometric curvature and thermopheoresis. Employing non-similar equations to solve the boundary layer equation, the distributions of velocity, temperature, and mass and the deposition rate are shown. The results show that, within the non-uniform temperature field, the aerosol particle deposition rate is largely influenced by thermopherosis and convection. The particles are attracted to move toward the cold cylinder, and are blown away from the hot cylinder. On the other hand, as the particle diameter becomes larger than 0.1 μm, the deposition rate is shown to approach a constant value. This result is more obvious under the effect of thermophoresis. The larger the surface cylinder curvature, the higher the deposition rate. Buoyancy enhances the particle deposition rate onto a cold cylinder.