An experimental analysis of adiabatic capillary tubes

This paper presents an experimental study on capillary tubes commonly used as expansion devices in household refrigerators and freezers. The paper discusses the details of the experimental facility that has been developed and used to generate reliable experimental data within an acceptable level of uncertainty. The investigations include the effect of capillary length, capillary diameter, refrigerant subcooling, condensing pressure and type of refrigerant or? the mass flow-rates through the capillaries. The experiments were performed with three refrigerants, namely CFC-12, HFC-134a and HC-600a, and at different condensing pressures and levels of subcooling under choked flow conditions. Eight capillaries with different combinations of:lengths, diameters and tube roughnesses were used, and extensive data (exceeding 1000 sets) were collected. A conventional, dimensional analysis was performed to derive correlations to predict the mass flow rates for different refrigerants. The predictions from the developed correlations are found to be in good agreement with the measured data and other studies in the literature. The correlations would be very valuable in the design exercise of capillary tubes for alternative refrigerants in future. (C) 1999 Elsevier Science Ltd. All rights reserved.