Condensation heat transfer of HFO-1234yf and HFC-134a in small tube

High global warming potential of the conventional HFC and HCFC refrigerants, leads the industry of the automobile air-conditions system to find a better replacement for them. New developed refrigerant, HFO-1234yf, with the GWP as low as 4, is going to be a good candidate for replacing with HFC-134a, which has GWP as high as 1430. In this research, experimental single-phase liquid and two-phase condensation heat transfer coefficient of the HFC-134a with HFO-1234yf inside a double pipe combination with 4 mm inner tube diameter, measured and compared. Vapor quality inside the tube approximately increased by 0.2, therefore condensation heat transfer coefficient measured based on the average vapor qualities though the test section at different mass fluxes. Test results of HFC-134a and HFO-1234yf for single-phase heat transfer and liquid were agree with Gnielinski [1], and Blasius [2] correlation. Experimental results for HFC-134a and HFO-1234yf showed that by increasing the vapor qualities from 0.1 to 0.8 and mass fluxes from 200 to 1200 kg/m²s heat transfer coefficient increase. Heat transfer coefficients of these two refrigerants were analyzed by flow pattern of them inside the tube. HFO-1234yf showed similar heat transfer in slug flow with HFC-134a, by increasing the mass and vapor quality, flow pattern of these two refrigerants moved to annular, and heat transfer coefficient of HFO-1234yf in annular flow slight reduced. Gravity and vapor shear stress are the two main forces on film condensation and also effect on flow pattern. Conventional correlations include the gravity and shear effects in the forced condensation inside the tube. In order to evaluate the experimental results, two well-known correlations, Akers [3] and Shah [4], were implied.