Heat transfer and pressure drop of R32 evaporating in one pass microchannel tube with parallel channels

This paper presents heat transfer coefficient and pressure drop of R32 measured in the same facility as introduced in Li and Hrnjak (2017). Experiments are conducted on a 24-port microchannel tube with a hydraulic diameter of 0.643 mm. The pressure drop of R32 is lower than R134a, and the heat transfer coefficient is higher at the same condition. The pressure drop increases with quality and mass flux but decreases with reduction of saturation pressure. R32 heat transfer coefficient increases when heat or mass flux rises. Heat transfer coefficient of R32 first increases when quality increases due to convective effects and then drops at moderate quality due to the absence of nucleate boiling and dry-out. A comparison of adiabatic pressure drop and heat transfer coefficient to correlations has been made. Based on the Blasius equation and homogeneous density, the viscosity model from Cicchitti et al. (1960) has the best fit to predict two-phase pressure drop. Kim and Mudawar (2012) has the smallest MAE to predict pressure drop. For heat transfer coefficient, Sun and Mishima (2009) is the best fit. Further research will be on expanding the database and understanding hydraulic and boiling behavior.