Falling film boiling of a salt droplet on a slightly inclined plane: Flow, heat transfer, and crystallization

Abstract

Droplet crystallization greatly reduces heat transfer efficiency in the falling film boiling. The flowing and heating transfer on the heating surface play an important role in droplet crystallization position. An experimental platform is designed for NaCl-H2O droplet boiling with a slight inclination angle (θ). When the θ is less than 4°, the increase of salt concentration shortens the distance from the dryout point to the starting point, and the increase of θ increases the evaporation rate and the distance. The viscous force (Fv) values of the droplet during the pre and post braking periods are calculated, and the critical point of the droplet flow and the calculation equation of critical shear stress are proposed. The result finds that Fv decreases sharply at the critical point. In addition, as the ΔT increases by 25 °C, the Weber number increases by at least ten times. The influence of surface tension (concentration) on the droplet flow decreases remarkably with the increase of the ΔT.