A GENERALIZED PERFORMANCE PREDICTION METHOD FOR ADIABATIC CAPILLARY TUBES

Generalized dimensionless correlations were developed to predict refri gerant mass flow rate in an adiabatic capillary tube, for both subcool ed and quality inlet conditions. Dimensionless parameters were created using the Buckingham Pi Theorem. These parameters were based on the e ffects of tube geometry, inlet conditions, and fluid properties. The c orrelations were based on experimental performance data with refrigera nts R-134a, R-22, and R-410A that encompass an extensive range of oper ating conditions, including: condensing temperatures from 79 degrees F to 127 degrees F (26 degrees C to 53 degrees C), capillary tube inner diameters from 0.026 to 0.090 in (0.66 to 2.29 mm), capillary tube le ngths from 20 to 200 in (508 to 5080 mm), and inlet conditions from 30 degrees F (16.7 degrees C) subcooled to 35% quality. Corresponding to this range of refrigerants, capillary tube geometry, and operating co nditions, the experimental mass flow rate range was between 3 and 375 lb(m)/h (1.4 to 170 kg/h). Independent assessments of both correlation s were made by comparing predictions to measured performance with R-15 2a. These data fell within the +/-6% and +/-13% prediction intervals f or the subcooled inlet and quality inlet correlations, respectively. T he accuracy of the subcooled inlet correlation was further assessed by comparing predicted performance to measured data reported by other in vestigators with refrigerants R-12, R-134a, and R-22. it was shown tha t the subcooled inlet correlation predicted the bulk of these flow dat a to within +/-10%. However, when compared to reported data with R-600 a (isobutane), however, the subcooled inlet correlation over-predicted mass flow rate by 0 to 20%.