Comparative study on a straight and helical capillary tube for CO2 transcritical system

Abstract

Abstract A comparative study on an adiabatic straight and helical capillary tube employing homogenous flow conditions for a CO2 refrigerant. The numerical model is based on the basic principles of conservation of mass, momentum, and energy. A result of the present model is validated with previously published test results. The properties of CO2 refrigerants are obtained from property code CO2PROP. Compared to the straight capillary tube, the percentage reduction in mass flow rate for various internal diameter, tube length, and coil diameter are evaluated. It is observed that percentage reduction in mass flow rate increases as the coil diameter, tube diameter, and length of helical capillary tube increases. Again comparison between straight and helical tube is done by calculating tube length at same working conditions. Compared to straight capillary, for similar operating and geometric conditions, the percentage reduction in length for coil diameter 50mm is 16.4%, for coil diameter 100mm is 14.2% and for coil diameter 150mm is 13.5%. This comparative study is useful for designing of compact refrigeration system using CO2 as a refrigerant.