The impact of varying cold end diameter on the energy separation in Ranque-Hilsch vortex tube for different working gases: A CFD simulation and thermodynamic analysis

The vortex tube is a potential candidate for sustainable cooling due to its unique feature of energy separation without using any synthetic refrigerant. However, the investigation of energy separation and performance optimization always has been challenging due to its complex physics. In previous literature, the performance of vortex tube has been found affected by several parameters. In order to find the impact of varying cold end diameters with different gases, this paper investigates temperature separation in seven vortex tubes of different cold end diameters operating with three different working gases: He, N₂, and CO₂. A detailed thermodynamic analysis of their thermal separation performances at different cold mass fractions is presented for each working gas. Exergy analysis has also been conducted and discussed separately. As a result of this extensive investigation, it is found that the larger cold end diameter improves the performance of the vortex tube. The cold and hot temperature separation, cooling, and heating power at higher cold mass fractions are found to improve when operated with helium compared to other gas. However, the COP of cooling and COP of heating at higher cold mass fractions is found to be lower with helium. Improvements in the physical and kinetic exergies at the inlet and both outlets are observed with increasing cold end diameter, except for the kinetic exergy at the hot outlet. Helium gas is found to show more exergy at the inlet and both outlets among all three gases. The performance of vortex tube operating at higher cold mass fraction shows an improvement in exergies at outlets, except kinetic exergies at hot outlet. The total exergy efficiency decreases at cold outlet on increasing cold end diameter. However, the results of actual (physical) exergy efficiency shows an improvement at both outlet for larger cold end diameter. The actual exergy efficiency is calculated by considering the physical exergy alone because the kinetic exergy completely lost into the open atmosphere. Physical exergy efficiency at hot outlet is also found to increase on increasing cold mass fraction, while it decreases at cold outlet. Physical exergy efficiency of cooling and heating are found to more when operated with helium compared to nitrogen and carbon dioxide.