To determine if viscous effects lead to significantly increased oil concentrations in two-phase flow regions, experiments were run that determined the quantity of oil in smooth and micro-fin test sections during evaporation and condensation of R-22 and oil mixtures. The quantity of oil in the tubes was proportional to, but higher than, the flowing oil concentration. For example, the average oil concentration in the evaporator was approximately three times the system average, while the condenser concentration was about double that of the system.

KEYWORDS: measuring, oils, smooth tube heat exchangers, viscosity, experiment, condensation, evaporation, refrigerants, R22, mixtures, tubes, heat transfer fluids, extended surfaces heat exchangers.