Two-phase adiabatic frictional pressure gradients for R410A and CO2 in a macro channel: Experiments and a simplified predictive method for annular flow from low to medium reduced pressures

In this work the effect of reduced pressure is experimentally investigated for two-phase adiabatic frictional pressure gradients for CO2 and R410A in a wide range of reduced pressure (0.19-0.52 for R410A and 0.57-0.64 for CO2) and mass flux (150-500 kg m−2 s−1) in a adiabatic horizontal smooth tube of 6.00 mm of inner diameter, collecting 1214 new data points. A simplified phenomenological method for annular flow was proposed and validated with the present and existing databases by the same authors and independent databases for several fluids (CO2, R410A, R134a and also the new fluid R1234ze(E)).