Flow Boiling Characteristics for R1234ze in 1.0 and 2.2 mm Circular Channels

Experimental flow boiling heat transfer results are presented for horizontal 1.0 and 2.2 mm I.D. (internal diameter) stainless steel tubes for tests with R1234ze, a new refrigerant developed as a substitute for R134a with a much lower GWP (Global Warming Potential). These two tube diameters were chosen due the necessity to a better investigation the macro to microchannel transition boundary. The experimental campaign includes mass velocities ranging from 50 to 1500 kg m⁻²s⁻¹, heat fluxes from 10 to 300 kW m⁻², exit saturation temperatures of 25, 31 and 35 °C, vapor qualities from 0.05 to 0.99 and heated lengths of 180 mm and 361 mm. Flow pattern characterization was performed using high-speed videos. Data for heat transfer coefficients, critical heat fluxes and flow pattern transitions were obtained. R1234ze demonstrated similar thermal performance to R134a data when running at similar conditions. For critical heat flux the correlation of Katto and Ohno (1984) best predicted the database with a mean absolute error of 6.3%. For the heat transfer coefficients, the Thome et al. (2004) three-zone model predicted the data for slug flow with 15.9% and Saitoh et al. (2007) predicted data for other flow regimes with mean absolute error of 19.4%.