Condensation heat transfer in rectangular microscale geometries

•Condensation heat transfer at microscales (100 < Dh < 160 μm; 1 < AR < 4) measured.•Unified model for intermittent and annular flow heat transfer developed.•Effects of saturation temperature, hydraulic diameter, and aspect ratio elucidated.•The model predicts 94% of the data within ±25%.

Heat transfer coefficients during condensation of refrigerant R134a in small hydraulic diameter (100 < Dh < 160 μm) rectangular (1 < AR < 4) channels are presented. A novel technique to accurately determine condensation heat duty and heat transfer coefficient in such microscale geometries at small Δx is used. Models in the literature that were developed for larger tubes are shown to under predict the data. A new model that accounts for the flow mechanisms during condensation at such small scales, and takes into account the effect of G, x, Tsat, Dh and AR, is developed. The model predicts 94% of the data in the intermittent, transition and annular flow regimes within ±25%.