Experimental study of the flow of R-134a through an adiabatic helically coiled capillary tube

An experimental investigation was carried out to evaluate the flow characteristics of refrigerant R-134a through an adiabatic helically coiled capillary tube. The effect of various physical parameters like diameter and length of capillary tube, coil pitch, and inlet subcooling on the mass flow rate of R-134a was investigated. Moreover, the refrigerant mass flow rate through an instrumented capillary tube was also compared to that through a noninstrumented capillary tube. It was found that the provision of taps for pressure measurement on the capillary tube surface has a negligible effect on the mass flow rate of R-134a. Further, the coil pitch had a significant effect on the performance of the adiabatic helically coiled capillary tube. It was established that the coil pitch significantly influenced the mass flow rate through the adiabatic helically coiled capillary tube. It was concluded that the effect of coiling of the capillary tube reduces the mass flow rate by 5% to 15%, as compared to those of the straight capillary tube operating under similar conditions. The data obtained from the experiments were analyzed, and a semi-empirical correlation was developed. Almost 97% of the mass flow rate predicted by the proposed correlation lies in the error band of ±10%. © 2008 American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.