Influence of Coil Diameter and Axial Pitch on Flow Characteristic of Adiabatic Helical Capillary Tube

Capillary tube is an expansion device with small bore used in the refrigeration system, to connect the condenser and evaporator. The capillary tube may be straight or helical or spiral in shape. This paper presents effect of coil diameter and axial pitch of the helical capillary tube on the pressure distribution along it by using the mathematical model on the refrigerant R134a. The model is based on the recommendation from the literature published. Three different equations for friction factor were also examined for this model in this study. The model is validated by comparison made with the experimental data available in the literature for various cases by using three equations of friction factor. A good agreement was obtained with available experimental data with all equations for friction factor. The results show that the predicted length and the pressure distribution along the helical capillary tube are affected by the axial pitch and helix diameter. This mathematical model is enough precise and valuable to provide an effective means in analysis of the capillary tube performance.