Development of a continuous empirical correlation for refrigerant mass flow rate through non-adiabatic capillary tubes

Capillary tube, suction line heat exchangers (CT-SLHX) are widely used as expansion devices in small-capacity refrigeration and air-conditioning systems to enhance the refrigeration capacity and ensure that superheated refrigerant vapor enters the compressor. To calculate the mass flow rate through a capillary tube, a reliable non-adiabatic capillary tube model is necessary. Most previous correlations were developed separately for subcooled liquid inlet conditions and for saturated two-phase inlet conditions; so the models are not continuous at the saturated liquid point. An empirical model that is continuous at the saturated liquid point was developed and is introduced herein with a new dimensionless π parameter. This new empirical model is validated using experimental measurements available in the literature for the refrigerants R-134a, R-600a, R-410A, R-152a, and R-22. The new correlation shows good agreement with the experimental data.