R134a And Its Low GWP Substitutes R1234yf And R1234ze(E) Flow Boiling Inside A 4mm Horizontal Smooth Tube

This paper presents some new experimental data on R1234yf saturated flow boiling inside a 4 mm horizontal smooth tube: the effects of heat flux, refrigerant mass flux, and mean vapor quality are investigated separately to point out the different heat transfer mechanism contributions (i.e., nucleate boiling or/and forced convection boiling). The experimental tests were carried out at a saturation temperature equal to 10 °C, refrigerant mass flux from 200 to 600 kg m-2 s-1, heat flux from 15 to 30 kW m-2, and at increasing vapor quality up to incipient dryout. The measurements are here reported in terms of boiling heat transfer coefficient and frictional pressure drop. Furthermore, the R1234yf performance is compared against R1234ze(E) and R134a, since the substitution of R134a with low GWP refrigerants is one of the most important actual challenge for refrigeration and air conditioning, and R1234ze(E) and R1234yf seem to be very promising substitutes of it. Finally, the experimental heat transfer and frictional pressure drop data are used to assess some classical literature correlations.