Capillary tube selection for HCFC22 alternatives

In this paper, pressure drop through a capillary tube is modeled in an atte mpt to predict the size of capillary tubes used in residential air conditio ners and also to provide simple correlating equations for practicing engine ers. Stoecker's basic model was modified with the consideration of various effects due to subcooling, area contraction, different equations for viscos ity and friction factor, and finally mixture effect. McAdams' equation for the two-phase viscosity and Stoecker's equation for the friction factor yie lded the best results among various equations. With these equations, the mo dified model yielded the performance data that are comparable to those in t he ASHRAE handbook. After the model was validated with experimental data fo r CFC12, HFC134a, HCFC22, and R407C, performance data were generated for HC FC22 and its alternatives, HFC134a, R407C, and R407C under the following co nditions: condensing temperature; 40, 45, 50, 55 degrees C, subcooling; 0, 2.5, 5 degrees C, capillary tube diameter; 1.2-2.4 mm, mass flow rate; 5-50 g/s. These data showed that the capillary tube length varies uniformly wit h the changes in condensing temperature and subcooling. Finally, a regressi on analysis was performed to determine the dependence of mass flow rate on the length and diameter of a capillary tube, condensing temperature, and su bcooling. Thus determined simple practical equations yielded a mean deviati on of 2.4% for 1488 data obtained for two pure and two mixed refrigerants e xamined in this study. (C) 1999 Elsevier Science Ltd and IIR. All rights re served.