Numerical and Experimental Studies of Two-Phase Flow in Cooled / and Adiabatic Capillary Tubes


A numerical and experimental study was performed to predict the flow andthermal performance of a capillary tube that used in air conditioning andrefrigeration systems. In the numerical study, the (CFD) technique was employedto model the problem using the finite volume method for a two-phase, twodimensional flow in the pipe. In the experimental part, an experimental rig wasconstructed using a split unite to measure the temperature and pressure along thecapillary tube. These measurements were taken for (R-22) refrigerant withdifferent ambient temperatures. It was found that for a fixed length and diameterof capillary tube the mass flow rate of (R-22) increases as the inlet temperatureincreases. The numerical study was then applied to predict the flow and heattransfer along several types of capillary tube, i.e. several lengths, diameters, andrefrigerants, for cooled and non cooled tube. In the non cooled capillary results,the capillary tube length of R-407C (R-32/125/134a(23/25/52)) was found to beshorter than that required for (R-22). It was also found that (R-22) vaporized laterthan its corresponding (R-407C). The same condition was found for (R-12) and itsalternative R-134a (CF3CH2F). The numerical results show a large effect of thelength of capillary tube on the refrigeration system performance. When the lengthincreases, the drop in pressure, temperature, and density decreases, while thevelocity and dryness fraction increases.