Pressure drop during near-critical-pressure condensation of refrigerant blends

This paper presents the results of an experimental study on pressure drop during condensation of refrigerant blends R404A and R410A at near-critical pressures inside tubes of 0.76≤;D≤;9.4≤mm. Local frictional pressure gradients were measured at reduced pressures (P_r) of 0.8 and 0.9 for the mass flux range 200≤;G≤;800≤kg m^-2≤s^-1, in small quality increments. The data were compared with adiabatic and diabatic two-phase pressure drop correlations from the literature. These correlations were not able to adequately predict the pressure drop over the range of tube sizes and mass fluxes under consideration here at high reduced pressures. A new correlation for pressure drop is introduced, which accounts for property variations and microchannel effects. The correlation predicts 85% of the data within ±25%, with an average deviation between model predictions and data of ±14%.