Droplet evaporation on a heated structured wall

Abstract

Evaporation of water droplets on a structured surface is studied experimentally. With an increase in the wall temperature Tw from 28 to 70 °C the exponent n increases from 1 to 1.37 in the evaporation law (j = dm/dt ~ R0n, where m is the droplet mass and R0 is the droplet radius). Usually, researchers simulating droplet evaporation consider a linear relationship between the evaporation rate j and the droplet radius R0 (n = 1). This paper shows an increase of the exponent n with a growth of the wall temperature Tw. The diffusion vapor layer on the droplet interface and the boundary air layer on the surface of the heated cylinder with a diameter exceeding the droplet's one are formed. A neglect of free convection more than 5 times underestimates calculation results compared with experimental data. At droplet evaporation it is necessary to take into account convection in a vapor-gas medium and wall roughness.