Flow pattern map, heat transfer and pressure drops during evaporation of R-1234ze(E) and R134a in a horizontal, circular smooth tube: Experiments and assessment of predictive methods

This paper presents experimental results for local heat transfer coefficients, adiabatic frictional pressure gradients and two-phase flow regimes with the low-GWP refrigerant R-1234ze(E), compared to Hydro-Fluoro-Carbon refrigerant R-134a in the same conditions.In particular the results refer to an experimental investigation carried out in a circular smooth tube of 6.00 mm of inner diameter, for saturation temperatures between −2.9 °C and 12.1 °C, mass fluxes between 146 and 520 kg m−2 s−1 and heat fluxes between 5.0 and 20.4 kW m−2. These experimental results are compared to those for R-134a at the same operating conditions.Moreover, an assessment of predictive methods is provided for local heat transfer coefficients and frictional pressure gradients; also a direct comparison of flow regimes visualizations for R-1234ze(E) with a flow pattern map available in literature is presented.