Condensation two-phase flow patterns for zeotropic mixtures of tetrafluoromethane/ethane in a horizontal smooth tube

Mixed-refrigerant Joule-Thomson refrigeration (MJTR) systems have distinct advantages in the temperature range from 80 to 230 K. Tetrafluoromethane (R14) and ethane (R170) are essential components of mixed-refrigerants. In this paper, the adiabatic flow pattern map for R14/R170 mixtures was firstly developed based on previous flow pattern data. Then an experimental investigation on condensation two-phase flow patterns for R14/R170 mixtures (0.193/0.0.807, 0.437/0.563, 0.632/0.368 and 0.799/0.201 by mole) in a horizontal smooth tube with inner diameter of 4 mm was presented. Experiments were carried out at mass fluxes from 100 to 350 kg m⁻²s⁻¹, saturation pressures from 1.5 to 2.5 MPa and heat fluxes from 8.4 to 42.2 kW m⁻² over the entire range of vapor quality. The effects of mass flux, saturation pressure, heat flux and concentration on flow pattern evolutions were discussed and presented. Analysis results indicated that mass transfer resistance and heat flux account for the nonequilibrium effects of zeotropic mixture condensation, which leads to the different evolutionary trends between condensation and adiabatic two-phase flow. Finally, a new condensation flow pattern map was deduced by containing nonequilibrium effects into adiabatic flow pattern map.