Theoretical analysis for flow condensation heat and mass transfer of zeotropic mixtures in a horizontal smooth tube

As the increasingly serious impact of CFCs and HFCs on the environment, research on zeotropic mixtures plays an indispensable role in many industries. Especially, the study of zeotropic mixtures is essential for optimizing Liquefied Natural Gas system design. As primary constituents of natural gas, methane (R50) and ethane (R170) are equally vital in mixed-refrigerant Joule-Thomson cycles. This work experimentally examines flow condensation heat transfer for R50/R170 blends in horizontal smooth tubes across wide-ranging conditions. A non-equilibrium film theory-based analytical model was proposed to examine heat and mass transfer during binary zeotropic mixture condensation, incorporating vapor-liquid interfacial mass transfer resistances. Rigorous examination quantified impacts of mass flux, saturation pressure, heat flux, and vapor quality on temperature and concentration gradients. The results revealed substantial heat transfer degradation from temperature/mass fraction gradients, exhibiting strong dependency on volatile component concentration and mixture vapor quality. Model predictions demonstrated good agreement with measured condensation heat transfer coefficients for binary refrigerants.