Lagrangian modeling of intermittent flow condensation in circular micro- and mini-channels

•First principles modeling of the intermittent flow regime in microchannels.•Lagrangian bubble tracking scheme to couple the overall bubble train.•Development of a numerical solver for the coupled differential algebraic equations.•Model includes local parameters (bubble and slug velocity, film dynamics).•Predicted heat transfer coefficient agrees with experiments (AAD = 11%). Very few models exist in the literature for predicting phase-change heat transfer in the intermittent flow regime during condensation in microchannels. Intermittent flow is characterized by a transient bubble-slug train, which is modeled here using a transient Lagrangian bubble tracking scheme. The compressibility of the bubbles and local parameters, such as the film thickness, bubble velocity and slug velocity are taken into account. The model also accounts for the phase change due to condensation of vapor in the bubbles into the surrounding liquid. Heat transfer is assumed to occur through conduction in the thin film around the bubble and through convection in the slug. The model is applied to the condensation of R134a in a circular microchannel of hydraulic diameter 1.55 mm at a saturation temperature of 30°C and a wall subcooling of 2.5 K. Hydrodynamic parameters show good agreement with studies in the literature, and condensation heat transfer coefficients are in good agreement with experimental results (AAD = 11%).