Experimental study of R1234yf flow boiling in small tubes at saturation temperature of 5 C and low mass flux

Low GWP fluid R1234yf in refrigeration and air conditioning systems could reduce the global warming effect of the application. Previous experimental studies of flow boiling of R1234yf in the small tubes lacked low temperature and low mass flux. In this study, a new test facility was built to measure the heat transfer coefficient and pressure gradient during flow boiling in small tubes. Heat transfer coefficient and pressure gradient of R1234yf flow boiling from vapor quality 0 to 1 in 1, 2, and 3 mm tubes were investigated. The tested mass flux covered from 25 to 200 kg m(-2) s(-1), heat flux from 2 to 16 kW m(-2), and saturation temperature at 5 degrees C. The effect of mass flux and heat flux was discussed. It was found that the impact of mass flux on HTC was strongly affected by vapor quality and the mass flux. The convective heat transfer seemed only important at moderate and high vapor quality. When the flow had a low mass flux and laminar velocity profile, the effect of mass flux was week. The effect of heat flux was stronger when the mass velocity was lower. When the low mass flux (<100 kg m(-2) s(-1)), Muller-Steinhagen and Heck [30] and Liu and Winterton [39] were recommended for predicting dP/dz and HTC, respectively.