Simulation of Steady Flow Condensation of R134a Inside a Square Minichannel Using Vof Model

A minichannel based cooling system is highly effective in designing the thermal management devices for the cooling of electronic components due to its high heat transfer performance and miniaturization. Minichannel can dissipate more amount of heat under two phase flow with sharp cornered edges. The flow condensation in minichannel is a complex phenomenon and hence numerical simulation can be adopted for investigating the effect of geometric and flow parameters. A three-dimensional steady flow condensation of R134a inside a 0.972mm square cross-section minichannel with a constant heat flux condition is numerically simulated in ANSYS FLUENT platform using the phase change model and analysed in this study. The liquid-vapor interface is tracked by VOF (Volume of Fluid) model and the effects of turbulence, surface tension, gravity and vapor-liquid interfacial shear stress are also taken into account for the present study. The numerical model treating liquid film and vapor core as both laminar and turbulent are validated against experimental data at mass fluxes in the range of 100-600 kg/m2s. The study reveals that influence of gravity reduces the average heat transfer coefficient in minichannel for lower mass flux, whereas, it increases at higher mass fluxes as confirmed by the investigation on cross-sectional average heat transfer coefficient under normal and zero gravity conditions for stated mass fluxes. The distribution of heat transfer coefficient at the corner, side and bottom surfaces are investigated separately. The condensation heat transfer coefficient is lower at the corner and maximum at the side surface for both the mass fluxes 100 and 600 kg/m2s considered in this study except at the initial stage. Also, the effects of angular cross-sectional orientation of the minichannel on the heat transfer coefficient and pressure gradient are investigated and observed an enhancement in the average heat transfer coefficient by 2.38% as a result of a 45o shift in the angular cross-sectional orientation with a reduction of pressure drop by 9.23% for a mass flux of 100 kg/m2s