Pressure drop during condensation of R-134a inside parallel microchannels

• All pressure loss contributions were estimated in a microchannel arrangement during R-134a convective condensation.
• The influence of temperature, heat flux, and mass velocity on frictional pressure drop was evaluated.
• The model proposed by Cavallini et al. (2006) presented the best prediction performance.

In this study, we experimentally investigate the pressure losses during the convective condensation of R-134a inside eight circular (diameter D = 0.77 mm) horizontal and parallel microchannels. All pressure loss contributions, including the ones related to expansion, contraction, flow direction change, acceleration, and friction, are quantified for microchannel arrangement. The test conditions include the pressure, vapor quality, heat flux, and mass velocity, ranging from 7.3 to 9.7 bar, 0.55 to 1, 17 to 53 kW m−2, and 230 to 445 kg m−2 s−1, respectively. The frictional pressure drop roughly corresponds to 95% of the net pressure loss. The influence of temperature, heat flux, and mass velocity on the pressure drop is evaluated. The results show that the pressure drop increases with an increase in mass velocity and a decrease in saturation temperature, whereas it is not affected as much by the heat flux. The experimental results are compared with correlations and semi-empirical models described in the literature. Correlations based upon the adiabatic two-phase flows within bore pipes can reasonably predict the pressure drop for condensing microchannel flows. The model proposed by Cavallini et al. (2006) presents the best prediction performance.