A generalized correlation for refrigerant mass flow rate through adiabatic capillary tubes

A capillary tube is a common expansion device used in small sized refrigeration and air-conditioning systems. A generalized correlation for refrigerant flow rate in adiabatic capillary tubes is developed by implementing dimensionless parameters based on extensive experimental data for R-22, R-290, and R-407C measured in this study. Dimensionless parameters are derived from the Buckingham Pi theorem, considering the effects of tube inlet conditions, capillary tube geometry, and refrigerant properties on mass flow rate. The generalized correlation yields good agreement with the present data for R-22, R-290, and R-407C with average and standard deviations of 0.9 and 5.0%, respectively. Approximately 97% of the present data are correlated within a relative deviation of ±10%. Further assessments of the correlation are made by comparing the predictions with measured data for R-12, R-134a, R-152a, R-410A, and R-600a in the open literature. The correlation predicts the data for those five refrigerants with average and standard deviations of −0.73 and 6.16%, respectively.