R1234yf Flow Boiling Heat Transfer Inside a 2.4-mm Microfin Tube

ABSTRACT

This paper presents an experimental study on R1234yf flow boiling inside a mini microfin tube with an inner diameter at the fin tip of 2.4 mm. R1234yf is a new refrigerant with an extremely low global warming potential (GWP <1), proposed as a possible substitute for the common R134a, whose GWP is about 1300. The mass flux was varied between 375 and 940 kg m⁻² s⁻¹, heat flux from 10 to 50 kW m⁻², and vapor quality from 0.1 to 1. The saturation temperature at the inlet of the test section was kept constant and equal to 30°C. The wide range of operative test conditions permitted highlighting the effects of mass flux, heat flux, and vapor quality on the thermal and hydraulic behavior during the flow boiling mechanism inside such a mini microfin tube. The results show that at low heat flux the phase-change process is mainly controlled by two-phase forced convection, and at high heat flux by nucleate boiling. The two-phase frictional pressure drop increases with increasing both mass velocity and vapor quality. Dry-out was observed only at the highest heat flux, at vapor qualities of around 0.94–0.95.

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Notes on contributors

Andrea Diani

Andrea Diani received his master's and Ph.D. degrees in energy engineering at the University of Padova. Currently, he is a postdoctoral researcher at the Department of Industrial Engineering of the same university. His research activity is focused on experimental and numerical analysis of microstructured surfaces for refrigeration, air conditioning, and electronics cooling applications. .

Alberto Cavallini

Alberto Cavallini is professor emeritus and a former full professor of energy science with the Engineering School of the University of Padova. He is a former president of the Scientific Council of the International Institute of Refrigeration and now honorary president of the same Institution. He is a fellow of ASHRAE. He is a member of the advisory board of the International Journal of Refrigeration, one of the European editors of the International Journal of Transport Phenomena, and former associate editor of the International Journal of HVAC&R Research. He has been president of AICARR, the Italian Society of Air Conditioning, Heating and Refrigerating Engineers (1996–1998). His research activity regards the fields of energy management, heat transfer (with special emphasis on boiling and condensation heat transfer with refrigerants), and refrigeration and air conditioning with particular reference to problems related with the refrigerant substitution issue. He is author or co-author of about 300 scientific and technical publications, most of which appeared in the international scientific literature, and of five university textbooks. He is the 2002 recipient of the J&E Hall Gold Medal of the UK Institute of Refrigeration and of the Medal of Merit of the IIR. .

Luisa Rossetto

Luisa Rossetto is a full professor at the University of Padova. She teaches advanced heat transfer and applied thermodynamics to the engineering students of the University of Padova. Her research activity concerns the field of enhanced heat transfer, particularly during single-phase flow of air or liquids in metallic foams or through finned surfaces and during condensation and vaporization of refrigerants inside or on the outside of tubes with enhanced surfaces. She is member of the following associations: ASHRAE, IIR, UIT, and ATI. She is member of Commission B1 (Thermodynamics & Transfer Processes) of IIR. She is the author or co-author of more than 170 papers, most published in the international scientific press. .