Numerical Analysis of Condensation of R134a in a Single Microchannel

Abstract

The present work proposes a numerical, transient modeling approach for the simulation of condensation heat transfer in a single microchannel. The model was based on the volume of fluid approach, which governed the hydrodynamics of the two-phase flow. User-defined routines were implemented in order to simulate the effects of condensation, which included mass transfer at the liquid-vapor interface and the associated release of latent heat. A channel having hydraulic diameter of 100 micrometer was modeled using a two-dimensional computational domain. The working fluid was R134a and the vapor mass fluxes at the channel inlet ranged from 245 to 615 kg/m2s. The channel wall was maintained at a constant heat flux, ranging between 200 to 800 kW/m2. The predictive accuracy of the numerical model was assessed by comparing the two-phase frictional pressure drop and Nusselt number with the available empirical correlations in the literature. A reasonably good agreement was obtained for both parameters with mean absolute errors as low as ±7.5% for pressure drop and ±15.6% for Nusselt number. Further, a qualitative comparison of various flow patterns against experimental visualization data was performed. The predicted flow patterns were classified based on the relative dominance of surface tension and inertia forces, and the results were in close agreement with visualization data. On the whole, the newly developed approach was found to have a high predictive accuracy with respect to the simulation of condensation phenomena in microscale domains and was concluded to be a useful tool in support of the design and optimization of advanced microchannel-based heat exchangers.