Theoretical and Numerical Study of Oil Return in Vertical Tubes in Refrigeration Systems

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. 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.