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

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 trans-fer 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 refrig-erant 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). (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This experimental study focuses on the low mass flux of refrigerants R134a, R404A, and R407C in a smooth vertical evaporator tube with an inner diameter of 32 mm. The results indicate that nucleate boiling dominates the heat transfer in the downward-flow refrigerant, and its effectiveness is dependent on the superheated wall of the evaporator tube. The experimentally obtained Nusselt number correlates well with the predicted Nusselt number for mass flux over 10 kg.m(-2).s(-1).