Investigation of the two-phase convective boiling of HFO-1234yf in a 3.9Â mm diameter tube

In this study, the influences of heat flux and mass flux on the two-phase convective boiling heat transfer performance are reported for refrigerants HFO-1234yf and HFC-134a in a 3.9 mm smooth diameter tube. Tests are performed with a saturation temperature of 10 °C. It is found that at lower vapor quality region the nucleate boiling is the dominant heat transfer mechanism while the convective evaporation mechanism takes control at the higher vapor quality region. Both HFC-134a and HFO-1234yf shows similar trend and the difference in heat transfer coefficient between HFO-1234 and HFC-134a is quite small. The comparable heat transfer performance between HFC-134a and HFO-1234yf is attributed to similar physical properties and nucleate boiling contribution. The present test results are in line with some existing reports but are inconsistent with one other study having a tube diameter of 1.1 mm. It is found that the departure of heat transfer coefficients between the available publications is mainly attributed to the different flow phenomena caused by the difference of the channel size and channel geometry. A noticeable deterioration of the heat transfer coefficient for HFO-1234yf is encountered in the microchannel. The pressure drops for HFC-134a is about 5-15% higher than that of HFO-1234yf.