Numerical Simulation of Condensation in a Minichannel

A steady-state Volume of Fluid (VOF) simulation of condensation of R134a inside a 1 mm i.d. minichannel is 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. The mass flux is G = 200 kg m⁻²s⁻¹ and it has been assumed that the flow was laminar inside the liquid phase and turbulent inside the vapour phase. Turbulence has been handled by a modified low-Re k-ω model. Numerical models adopted to handle such assumptions are presented and discussed. Computational results displaying the evolution of vapour-liquid interface, cross-sectional void fraction, vapour quality and heat transfer coefficient are reported and compared against some empirical correlations. In the simulation, the fluid is condensated till reaching around 0.5 vapour quality. At inlet, the liquid film is thin and evenly distributed all around the tube circumference, therefore high heat transfer coefficients are obtained. All the liquid condensated at the vapour-liquid interface is shown to be drained by gravity to the bottom of the minichannel. For this reason, moving downstream the channel, the film at the bottom of the pipe becomes thicker, while the film thickness keeps almost constant in the entire upper half of the minichannel.