Numerical Simulation of Laminar Liquid Film Condensation in a Horizontal Circular Minichannel

Abstract

A three-dimensional volume of fluid (VOF) simulation of condensation of R134a inside a 1 mm i.d. minichannel is presented. The minichannel is horizontally oriented and the effect of gravity is taken into account. Simulations have been run both with and without taking into account surface tension. A uniform interface temperature and a uniform wall temperature have been fixed as boundary conditions. The mass flux is G = 100 kg m−2 s−1 and it has been assumed that the flow is laminar inside the liquid phase while turbulence inside the vapor phase has been handled by a modified low Reynolds form of the k–ω model. The fluid is condensed till reaching 0.45 vapor quality. The flow is expected to be annular without the presence of waves, therefore the problem was treated as steady state. Computational results displaying the evolution of vapor–liquid interface and heat transfer coefficient are reported and validated against experimental data. The condensation process is found to be gravity dominated, while the global effect of surface tension is found to be negligible. At inlet, the liquid film is thin and evenly distributed all around the tube circumference. Moving downstream the channel, the film thickness remains almost constant in the upper half of the minichannel, while the film at the bottom of the pipe becomes thicker because the liquid condensed at the top is drained by gravity to the bottom.