Numerical comparisons of the thermal behaviour of air and refrigerants in the vortex tube

Abstract

Vortex tubes (VT), as a temperature separation device, have been widely used in open systems in which air is commonly used. When a VT is employed in a closed system, other working fluids could be considered. This paper numerically compares the thermal behaviour of air and two refrigerants (R134a and R600) in a VT under a range of operating conditions. It analyses their cooling and heating effect, the shear stress, flow streamlines patterns and temperature distributions. The results show that the refrigerants share certain similar trends with air: a higher VT inlet pressure leads to an increase in cooling effect that would reach a peak value when the chamber inlet/nozzle outlet velocity gets chocked. However, a larger VT pressure drop (between VT inlet and hot end) may result in a lower heating effect for refrigerants but not for air. A higher VT inlet pressure produces a larger pressure drop and this leads to a bigger temperature drop associated with the expansion process to partially or wholly cancel the temperature increase from the rotating process.

An investigation into the influences of refrigerants’ thermal-physical properties on temperature separation effect of a vortex tube

“…The axial, tangential and radial components at the inlet can be specified to achieve the desired entry angle. As in [17], five turbulence models (k-ε standard, k-ε RNG, k-ε RNG (swirl), k-ω SST, k-ω standard) are chosen for this study. The preliminary iteration using the first order upwind method [18] is employed to obtain quickly the initial approximated results, based on the defaulted under-relax factors.…”

“…There is a "slight" mis-match between the ranking orders of α and ΔT h , especially for refrigerants with weak heating effects. It is believed that the heating effect (temperature rise) created from the rotational process could be cancelled out by the temperature drop resulted from the adiabatic expansion through the vortex tube [17]. As the latter could be related to Joule-Thomson (J-T) effect, the author is to assess whether J-T coefficient [28,29] could be used to help us to understand better the relative ranking of the heating effect.…”

“…R32 has 78.11 o C [16], air has -140.31 o C). This may bring a non-ideal gas behaviour in vortex tube than air [17]. So, the observations of properties' influence mainly based on air from previous research may be not suitable to assess the temperature separation effect of different refrigerants.…”

Fluid properties impact on energy separation in Ranque–Hilsch vortex tube

“…When it comes to the assimilation of the energy separation phenomenon, it is beneficial to understand the significance of the working fluid in the vortex tube, which has been examined by different research groups [10,25,29,31,[36][37][38]. Khazaei et al [29] has studied the effect of utilizing various fluids on the radial temperature distribution.…”

“…It has been reported [25] that thermal diffusivity, kinematic viscosity and thermal conductivity are considered as main factors affect gas energy separation. The amount of energy separation depends on type of fluid used [38]. Liang [31] used numerical tool to investigate the coefficient of performance (COP) of a vortex tube working with binary gas mixture CH 4 − CO 2 .…”