Theoretical investigation on convective condensation annular flow of R410a inside rectangular microchannel

Abstract

A three-dimensional theoretical model of the annular flow for R410a convective condensation in a rectangular microchannel with the hydraulic diameter of 0.67 mm is established in this investigation. The concurrent vapor-liquid two-phase flow field is divided into three regions: the liquid flow in the thin film region on the sidewall, the condensate liquid flow in the meniscus region at corners, and the vapor flow in the vapor core region. This model takes into account the effects of surface tension at the corner, the interfacial shear stress induced by the vapor flow, the momentum transfer on the vapor-liquid interface, and the turbulence of condensate liquid flow in meniscus region. Uniform wall temperature is adopted as a boundary condition in this analytical model, and the computational results are validated against experimental data. The mass fluxes ranging from 100 kg/(m2 s) up to 1000 kg/(m2 s) are considered in a rectangular microchannel with the aspect ratio of 0.5. The distribution of the liquid film thickness, the mass flow rate along the sidewall induced by the surface tension, the condensate liquid flow velocity in the meniscus region, the local heat transfer coefficient at each cross section and the average heat transfer coefficient are obtained to analyze the mechanism of condensation flow and heat transfer in a microchannel. Remarkably, the importance of condensate liquid turbulence in the meniscus region is validated by the great agreement between computational results and experimental data.