Heat transfer coefficient during evaporation of R-1234yf, R-134a, and R-22 in horizontal circular small tubes

Choi, Kwang-Il ; Chien,Nguyen-Ba ; Oh, Jong-Taek;

Experimental data of heat transfer coefficient during evaporation of R-1234yf, R-134a, and R-22 in horizontal circular small tubes are compared. The local heat transfer coefficient is obtained for heat fluxes ranging from 10 to 35 kW [m.sup.-2], mass fluxes ranging from 100 to 650 kg [m.sup.-2] [s.sup.-1], saturation temperatures of 5,10, and 15[degrees]C, and quality up to 1.0. The test sections are made of stainless steel tubes with inner diameters of 1.5 and 3.0 mm, the lengths of 1000 and 2000. Effects of heat flux, inner tube diameter, and saturation temperature on heat transfer coefficient are reported in the present study. Nucleate boiling heat transfer contribution is predominant, especially at low quality region, and laminar flow appears in the evaporative small tubes. The experimental results are compared against four existing heat transfer coefficients, and the modified correlation of heat transfer coefficient is developed with good prediction.