Numerical investigation of convective dropwise condensation flow by a hybrid thermal lattice Boltzmann method

Abstract

The present paper, convective dropwise condensation flow over a cold spot is numerically investigated using a 2D hybrid thermal lattice Boltzmann (LB) model with vapor-liquid phase change. After validating the present LB model, dropwise condensation on a cold spot as the nucleation region is simulated so as to study the nucleation and growth of the isolated droplet. The well-known power law for the growth of a single condensing droplet is demonstrated. And then, both simulations of dropwise condensation and convective dropwise condensation are carried out to study the effect of forced convective flow on dropwise condensation. Aiming to consider the effect of contact angle, the droplet is growing in the constant contact radius (CCR) mode. The results indicate that the forced convectional flow complicates the internal flow of the droplet and the vapor flow. The detouring flow (including the lee-side vortex) around the droplet in an isothermal system is replaced by the suction flow owing to condensation. The interaction between the dragging force of the vapor flow and the surface tension gradient changes the size of two symmetric vortices within the droplet in dropwise condensation. The size of these two vortices inside the droplet depends on the velocity and direction of convective flow. By comparison, the heat transfer enhancement of the superimposed flow is not worth mentioning in spite of different flow mode. Not affected by the vapor flow, the heat transfer is weakened by increasing of the contact angle owing to the change of conduction resistance. The present study illustrates the mechanisms of convective dropwise condensation flow in detail.