液滴撞击圆柱外表面蒸发换热的数值模拟

Numerical simulation of evaporation and heat transfer of droplet impacting on cylindrical outer surface

为进一步研究液滴撞击加热壁面过程中的破裂现象及不同参数对液滴蒸发换热的影响,采用CLSVOF方法和相变模型对液滴撞击加热圆柱外表面进行三维数值模拟.模拟过程中考虑了壁面温度、接触角以及撞击速度对液滴蒸发换热的影响.结果表明:液滴产生破裂的位置与液滴撞击壁面时的速度有关,当撞击速度较小时,破裂产生于液滴中心处;当撞击速度较大时,破裂处位于中间和边缘两部分液体之间.液滴撞击壁面后,在三相接触线和液滴破裂处附近产生了蒸汽旋涡,强化了液滴与壁面间的换热,增加了液滴侧的壁面热流密度.短时间内壁面温度对液滴蒸发量的影响较小,但撞击速度与接触角对其蒸发量的影响较大,且接触角越小,撞击速度越大,壁面平均热流密度越大,液滴蒸发量越大,有利于液滴与壁面间的换热.

To further study the rupture of droplet after its impacting and the influence of different parameters on the droplet evaporation and heat transfer,three dimensional numerical simulation is performed by using CLSVOF method and phase transformation model. The effect of wall temperature,contact angle and impact velocity on the evaporation and heat transfer of droplet are considered in the simulation and the results show that the rupture position is related to the impact velocity of the droplet. When the impact velocity is small,the rupture occurs at the center of the droplet. When the impact velocity is large,the rupture position deviates from the center of the droplet.It is also found that vapor vortexes are generated near the three-phase contact line and the rupture,which strengthen the heat transfer between the droplet and the wall,and increase the heat flux density of droplet side as well. In a short time,the wall temperature has little effect on droplet evaporation,but the impact velocity and contact angle have great effect on droplet evaporation. The smaller the contact angle and the greater the impact velocity,the greater the average heat flux density and the greater the droplet evaporation,which is beneficial to heat transfer between the droplet and the wall.