Boiling heat transfer mechanism of environmental-friendly refrigerants: A review

Abstract Due to the implementation of the climate change agreement, negative environmental impacts caused by some traditional refrigerants have been spotlighted. A large number of environmental- friendly refrigerants with near-zero ozone depleting potential (ODP) and low global warming potential (GWP), such as R1234yf, R1233zd(E), R1270, R600a, are synthesized and proposed to replace traditional ones. These refrigerants' boiling heat transfer characteristic plays a crucial role in evaporator design and refrigeration cycle configuration. Thus, this review aimed to bring the state-of-the-art literature review on the boiling heat transfer characteristics of environmental-friendly refrigerants with ODP close to 0 and GWP below 2000. In addition to describing the effects of heat flux, mass flow, saturation temperature, and mass transfer resistance on the heat transfer coefficient and pressure drop, this review also analyzed the heat transfer mechanism. Moreover, a detailed review of the correlation of boiling heat transfer and pressure drop was provided which might benefit practical applications. Furthermore, prospects and challenges to be addressed were also identified for future research. This paper benchmarks the recent progress on boiling heat transfer characteristics of single and mixed environmental-friendly refrigerants and presents insights into scientific research gaps that need to be addressed.