Refrigerant charge minimization as well as the use of eco-friendly fluids can be considered two of the most important targets for the next generation of air conditioning and refrigerating systems to cope with the new environmental regulations. Traditional microfin tubes are widely used in air and water heat exchangers for heat pump and refrigerating applications during either condensation or evaporation. The enhancement potential of microfin tubes can lead to more efficient and compact heat exchangers and thus to a reduction of the refrigerant charge of the systems. This paper explores the heat transfer and fluid flow characteristics of the new low-GWP refrigerant R1234yf during flow boiling inside a mini microfin tube with internal diameter at the fin tip of 3.4 mm. The microfin tube is brazed inside a copper plate and electrically heated from the bottom. Several T-type thermocouples are inserted in the wall to measure the temperature distribution during the phase change process. In particular, the experimental measurements were carried out at constant saturation temperature of 30 °C, by varying the refrigerant mass velocity between 190 kg m~(-2) s~(-1) and 940 kg m~(-2) s~(-1), the vapor quality from 0.2 to 0.99, at three different heat fluxes: 10, 25, and 50 kW m~(-2). The experimental results are presented in terms of the two-phase heat transfer coefficient, onset of dryout vapor quality, and frictional pressure drop as a function of the operating test conditions.
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