Study of helically coiled adiabatic capillary tubes for transcritical CO2 expansion

Abstract

Transcritical expansion through coiled adiabatic capillary tubes having CO 2 as the refrigerant is numerically simulated and the performance is compared with R22 flow through such tubes. Mori and Nakayama friction factor correlation in combination with Churchill equation, which is fitted into Blasius type equation, is used to calculate the friction factor. Results indicate that reduction in mass flow rate with a coiled capillary tube compared to a straight one is more pronounced in case of CO 2 in comparison to R22. Mass flow rate of refrigerant increases as the coil diameter increases, but changes little beyond a coil diameter (D) of 180 mm. A shorter capillary tube will be required to match the requisite system mass flow rate when coiled capillary tubes are employed. Subscripts 1 -4 state points con condenser ev evaporator tp two-phase