Flow characteristics of two phase flow of oil and refrigerant studied to evaluate the oil return performance in refrigerant lines. Minimum required velocity
of refrigerant to move oil upward in the vertical refrigerant pipelines was estimated by theory and numerical calculations. Annular flow model used study
two phase flow of refrigerant and oil. Refrigerants R134a and R410A were considered because of their increasing popularity in HVAC industry,
refrigerant R22 as well considered to validate the results. A hypothesis claimed to correlate oil film velocity to the turbulent shear stress of vapor core, in
addition numerical simulation carried out to determine relation of oil film velocity profile with vapor velocity, oil film thickness and refrigerant properties.
Results of proposed theory and numerical simulation were in reasonable agreement with existing experimental data.