Condensation and evaporation heat transfer of R32 and R410A in reversible shell-and-tube and brazed plate heat exchangers

The heat pump market is faced with the problem of replacing R410A, a mixture with 1924 GWP(100) (global warming potential over 100 years). A proposed midterm substitute is R32 (GWP(100) 677) which, although mildly flammable, has some advantages over other alternatives: it is a pure fluid, relatively cheap, already available on the market, with different suppliers due to the absence of patents. This work compares the two-phase heat transfer performance of R410A and R32 in two different types of heat exchangers commonly used both as evaporators and condensers in reversible heat pumps: brazed plate and shell and tube. As regards the brazed plate, the tests are conducted with one and thirty-four refrigerant channels respectively; for shell-and-tubes, the study concerns a heat exchanger with refrigerant flowing inside the tubes in two different passes. Water is used as secondary fluid. During condensation, the refrigerant enters from above as superheated vapor, and it exits from below as subcooled liquid. As it evaporates, it enters from below as liquid/vapor mixture, and exits from above as superheated vapor. The experimental analysis shows that in condensation the performance of R32, as compared to R410A, is much better, both for the brazed plate and the shell-and tube. During evaporation, on the other hand, while for the shell-and-tube a slightly better behaviour of R32 is found, for the brazed plate there are almost no differences between the two fluids. This last result agrees with recent works in literature.