Experimental and analytical investigation on flow condensation heat transfer of zeotropic mixtures of tetrafluoromethane/ethane

Tetrafluoromethane (R14) and ethane (R170) are important components to improve the recuperation process in the middle and low temperature regions of a mixed-refrigerant Joule-Thomson (MRJT) refrigeration system. In this paper, an experimental investigation on flow condensation heat transfer characteristics of R14/R170 mixtures (0.193/0.807, 0.437/0.563, 0.632/0.368 and 0.799/0.201 by mole) in a horizontal smooth tube was carried out. Experiments were implemented at mass fluxes from 100 to 350 kg m⁻² s⁻¹ and saturation pressures from 1.5 to 2.5 MPa over the entire range of vapor quality. The effects of concentration, mass flux, saturation pressure and vapor quality were analyzed and discussed. Compared with linear interpolation values of pure fluids, heat transfer degradation of mixtures increases with the rise of vapor quality. In addition, all experimental data were compared with sixteen well-known correlations combined with equilibrium method. It is found that all models underestimate the current experimental data. This should be due to the neglect of the intensifying effect of vapour-liquid interface fluctuation. Finally, an improved heat transfer correlation for zeotropic mixtures was proposed and predicted the experimental results well with a mean absolute relative deviation of 13.91%.