Effect of incident direction and droplet position on dynamic and heat transfer behaviors of droplet impacting on super-hydrophilic cylindrical surface

Abstract

Abnormal impact of droplet with different incident directions and positions can be found in evaporator, desalinator and nuclear engineering etc. The researches devoted to droplet abnormal impingement on a super-hydrophilic cylindrical surface are limited. In this paper, a numerical study of individual droplet impacting on super-hydrophilic cylindrical heated surface was conducted by applying VOF method. The incident direction and position of droplet were characterized by the impact angle φ and horizontal offset δx, the effect of which on dynamic and heat transfer behaviors was analyzed. Results show that there is an anisotropic spread during droplet impingement. Compared to no-offset vertical impact, the peaks of liquid film thickness for impact with an impact angle or horizontal offset are not the same at two edges of liquid film along circumferential direction. Impact angle or horizontal offset leads to a reduced contact area, a lower average temperature of liquid film and smaller total droplet input heat flow. For φ from 0° to 75° and δx from 0 mm to 5 mm, the maximum total droplet input heat flow decreases by 42.1% and 27.6% respectively. The local heat flux shows apparent fluctuations along the circumferential direction, and the high heat flux region is concentrated at a lower position in the circumferential direction of the cylinder for a larger φ or δx due to the auxiliary effect of gravity.