Comparative analysis of microfin vs smooth tubes in R32 and R410A boiling

Abstract

• This paper investigates R32 and R410A boiling inside a 4.2 mm microfin tube. • The microfin tube exhibits a maximum heat transfer enhancement around 1.8 − 1.9. • In general the heat transfer enhancement is lower than the mere surface area increase. • R32 exhibits heat transfer coefficients and pressure drops higher than R410A. • R32 is a very promising low GWP substitute for R410A. This study performs the comparative analysis of R32 and R410A boiling inside a 4.2 mm ID microfin tube. The experimental tests were carried out at different saturation temperatures, different vapour qualities, heat fluxes and mass velocities to evaluate the specific contribution of each operating parameter. The boiling heat transfer coefficients show a great sensitivity to heat flux and vapour quality and no sensitivity to refrigerant mass velocity. The microfin tube exhibits a maximum heat transfer enhancement with respect to the smooth tube around 1.8 − 1.9 at a heat flux of 12 kW m −2 and a vapour quality of 0.8, and in general the heat transfer enhancement is lower than the mere surface area increase over the smooth tube (Rx = 1.65). R32 exhibits boiling heat transfer coefficients and frictional pressure drops 10 − 20% higher than those of R410A and it seems a valuable low GWP substitute for R410A.