Abstract
Flow characteristics of an adiabatic spiral and a helical capillary tube in a CO2 transcritical system are numerically simulated. A homogeneous two-phase flow model is developed using the mass, energy and momentum conservation equations, taking into consideration the helical and spiral coiling effects of the capillary tubes. Friction factor and viscosity correlations are used from the available literature. Results are compared with conventional subcritical refrigerant R22. Reduction in a mass flow rate of refrigerant is more pronounced in the spiral capillary tube than helical capillary tube effect; about 18% and 11% with CO2 and R22, respectively. Length requirement with a spiral capillary tube is relatively less compared to other chosen configurations for the given mass flow rate and operating conditions.
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