Comparative Study on a Straight and Helical Capillary Tube for CO₂ and R22 Refrigerant

A comparative study has been carried out on the adiabatic straight and helical capillary tube, using a CO₂ and R22 refrigerant. The numerical model for CO₂ and R22 is developed using the basic principles of conservation of mass, momentum, and energy. The effect of coiling in the helical capillary tube is compared with a straight capillary tube for CO₂ and R22 refrigerant. Compared with the straight capillary tube, the percentage reduction in mass flowrate in the helical capillary tube is calculated with a change in coil diameter, tube diameter, and length. As the coil diameter increases from 30 mm to 150 mm, the percentage reduction in mass is from 5.8% to 2.2% in CO₂, and 5% to 1.6% in R22. For helical capillary tube with 50 mm coil diameter, as the tube diameter increases from 1 to 1.5 mm, the percentage reduction in mass flowrate with CO₂ refrigerant is from 2.65% to 4.96%, however, for R22 it is from 2.43% to 4.24%. Similarly, as the capillary tube length increases from 1.3 m to 1.8 m, the percentage reduction in mass with CO₂, with 50 mm coil diameter is 4.44–4.55%. However, the percentage reduction in mass with R22 is 3.71–3.85%. Moreover, compared with the straight capillary tube, the percentage reduction in length in a helical capillary tube with coil diameter 50 mm is 16% for CO₂ and 9% for R22 refrigerant.