Flow boiling of R134a and R134a/propane mixtures at low saturation temperatures inside a plain horizontal tube

Local heat transfer coefficients for flow boiling of pure 1,1,1,2-tetrafluoroethane (R134a) and binary mixtures of propane (R290) and R134a were measured. The experimental setup employed a vapor heated plain horizontal tube (d(i) = 10 mm, d(o)= 12 mm, L = 500 mm). The measurements covered a wide range of saturation temperatures (233 <= T(s) <= 278 K), mass fluxes (100 <= (m) over dot <= 5300 kg/m(2) s), qualities (0 <= (x) over dot <= 1), and concentrations (0 <= (z) over tilde <= 0.65). In the zeotropic region of R134a/R290 mixtures, the measured local heat transfer coefficient was found to show a maximum decrease by a factor of 2 relative to that for pure R134a. At the azeotropic point (65% R290), it was found to increase by a factor of 1.2. The measured local heat transfer coefficients for both R134a and R134a/R290 were compared with a number of correlations.