Oil quantity measurements in smooth and micro-fin tubes during evaporation and condensation of refrigerant-oil mixtures
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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. Parameters whose effects were investigated included mass flux (74,000 to 221,000 lb/h·ft2 [100 to 300 kg/m2·s]), oil concentration (1.2% to 5.0%), viscosity (150 and 300 SUS), evaporation exit conditions (80% to 85% quality; 18° to 27°F [10° to 15°C] above the saturation temperature of pure refrigerant), and evaporation pressure (73 and 116 psi [0.5 and 0.8 MPa]). 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.
author list (cited authors)
Schlager, L. M., Pate, M. B., & Bergles, A. E.