Modelling of Condensation in a Circular Minichannel by Means of the VOF Method

Abstract

3D steady-state Volume of Fluid (VOF) simulations of condensation of R134a inside a 1 mm i.d. circular minichannel are proposed. The minichannel is horizontally oriented and both the effects of gravity and surface tension are taken into account. A uniform interface temperature, as well as a uniform wall temperature, were fixed as boundary conditions in order to model the phase change process. Simulations were performed at mass fluxes G = 100 kg m−2s−1 and G = 400 kg m−2s−1. It has been assumed that the flow was turbulent inside the vapour core, while for the condensate film two different computational approaches have been considered. The first approach (i.e. “laminar liquid film”) corresponds to the assumption that the flow is laminar inside the liquid phase and turbulent inside the vapour phase. For the second approach (i.e. “turbulent liquid film”), instead, a low Reynolds form of a turbulence model has been used through both phases. The aforementioned approaches are compared to each other and the computed heat transfer coefficients are compared against experimental data by Matkovic et al.: data at low mass flux is well predicted by the “laminar liquid film” approach and overpredicted by “turbulent liquid film” approach, while data at high mass flux is underpredicted by the former approach and well predicted by the latter. The evolution of the vapour-liquid interface along the minichannel, as well as the velocity field, are reported. Besides, the computed cross sectional void fraction is compared against empirical correlations available in the literature.