Influence of geometric and operating parameters on the performance of the helical capillary tube for the R744 refrigerant

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This paper reveals the numerical investigation of the helical capillary tube. The study is carried out for an adiabatic, homogenous capillary tube with the R744 refrigerant. The basic principles of conservation of mass, momentum, and energy are used to develop the mathematical model. The results of the present coiled capillary tube model are verified with previously published test results. The refrigerant properties of R744 are employed from CO2PROP. The influence of various geometric parameters of the capillary tube-like tube diameter, roughness, and coil diameter on the performance of the tube been computed. The consequence of the tube diameter on the tube performance is larger than other geometric parameters. As the tube diameter increase by 18%, the mass flow rate increase by nearly 55%. Similarly, as an increment in the coil diameter took place by 10%, the mass flow rate increase by 5%. The negligible change is observed owing to the change in surface roughness. While the surface roughness increases by 18%, the mass increases by 1%. Moreover, the influence of various operating factors is evaluated. A significant variation in the tube and system performance is seen owing to the change in gas cooler temperature. As the gas cooler temperature rises by 5%, the drop in mass flow rate is about 18%. Comparatively, less effect is recorded due to an evaporator temperature. As the evaporator temperature rises by 15%, the mass flow decreases by nearly 11%. The considerable impact is perceived owing to the change in pressure of the gas cooler. As the gas cooler pressure increases by 4%, the mass flow rate increases by nearly 7%. Similarly, the influence of operating and geometric parameters on the coefficient of performance and cooling capacity of the transcritical R744 system is evaluated. For optimum performance of the R744 cycle, the selection of proper gas cooler temperature and gas cooler pressure is a key factor. This work is useful to design the helical capillary tube with R744 refrigerant.