Pool Boiling Heat Transfer Characteristics of HFO-1234yf With and Without Microporous-Enhanced Surfaces

This fundamental study characterizes the pool boiling performance of a new refrigerant, HFO-1234yf (hydrofluoroolefin 2,3,3,3-tetrafluoropropene). The similarities in thermophysical properties with HFC-134a and low global warming potential make HFO-1234yf the prospective next generation refrigerant in automotive air-conditioning systems. This study examines the possibility of using this refrigerant for two-phase cooling of hybrid and electric vehicle power electronic components. Pool boiling experiments were conducted with HFO-1234yf and HFC-134a at system pressures ranging from 0.7 to 1.7 MPa using horizontally oriented 1 cm² heat sources. Results show that the boiling heat transfer coefficients of HFO-1234yf and HFC-134a are nearly identical at lower heat fluxes. HFO-1234yf yielded lower heat transfer coefficients at higher heat fluxes and lower critical heat flux (CHF) as compared with HFC-134a. To enhance boiling heat transfer, a copper microporous coating was applied to the test surfaces. The coating provided enhancement to both the boiling heat transfer coefficients and CHF, for both refrigerants, at all tested pressures. Increasing pressure decreases the level of heat transfer coefficient enhancements while increasing the level of CHF enhancements.