Dropwise Condensation: Simulation Results

Abstract

Simulations have been performed for water vapor condensation underneath a horizontal and an inclined textured substrate. A horizontal surface having unidirectional wettability gradient has also been considered. Here, the effect of thermophysical properties, physicochemical properties of the substrate, promoter layer thickness, nucleation site density, saturation temperature, degree of subcooling, effect of wettability gradient and angle of inclination are parametrically explored. Quantities such as the contact angle and contact angle hysteresis play an important role. We have used a nucleation site density of 10⁶ cm⁻² in most simulations reported. The simulation data is presented in the form of condensation patterns, area coverage as a function of time, and area-averaged heat transfer coefficient as a function of time. The cycle time and the maximum drop size at instability are tabulated. On the basis of numerical data, heat transfer coefficients of water vapor condensation are expressed as correlations. In order, the horizontal, inclined, and the graded surface experience (a) larger to smaller drop sizes, (b) longer to shorter cycle times, and (c) lower to higher heat transfer coefficients.