Evaporation of refrigerant R134a, R404A and R407C with low mass flux in smooth vertical tube

Abstract

This experimental study analysis the low mass flux of refrigerant R134a, R404A, and R407C in the smooth vertical evaporator tube with an inner diameter of 32 mm. This downward-flow refrigerant with a mass flux of about 9 kg⋅m−2⋅s−1 in the parallel/counter flow of heating water shows suppressed heat transfer by convective boiling and dominant heat transfer by nucleate boiling. This dominant heat transfer by nucleate boiling is dependent on the superheated wall of evaporator tube. The experimentally obtained Nusselt number correlates 92.2 % for R134a, 92.4 % for R404A, and 83.2 % for R407C with the predicted Nusselt number for mass flux over 10 kg⋅m−2⋅s−1. In summary, the untypically low mass flux of refrigerant about 9 kg⋅m−2⋅s−1 is comparable with the current state of knowledge for low mass flux over 10 kg⋅m−2⋅s−1.