Innovative hot valve design for improved energy efficiency in Ranque-Hilsch vortex tube separators: Experimental and numerical analysis

The vortex tube (VT) is a device that uses thermodynamic processes and the interaction of vortices to create a strong temperature separation. Previous studies have shown that spherical and truncated cone control valves offer higher thermal efficiency than flat and cone types. This study introduces a dimensionless structural parameter, defined as Curvature Radius/Tube Radius (NCR), to characterize the curvature of a spherical hot control valve. The study examines how NCR influences the energy separation phenomenon and efficiency through both experimental tests and numerical simulations, using the k-ε and SST k-ω turbulence models. The experiments were conducted at ambient temperatures of 294.2, 298.2, and 302.2 K, with inlet pressures set at 0.7, 0.8, and 0.9 MPa. Under these conditions, four spherical valves were tested, with corresponding NCR values of 1, 1.14, 1.28, and 1.42. The experimental results show that the highest temperature drop (ΔTc), isentropic efficiency (η), cooling power separation (Q̇c), heating power separation (Q̇h: Cold Mass Fraction≤0.64) and COPCM belong to NCR = 1.28 (optimum). Additionally, the increasing pressure does not weaken the superior cooling/heating performance of the optimum model compared to other models. The optimized spherical valve performs better than the traditional truncated cone control valve for cooling and heating applications. The results indicate that for NCR = 1.28, the stagnation point is positioned at the closest distance from the spherical valve. Also, when the swirl and axial velocities in the beginning of the separation and the swirl velocity drops along the tube reach their peak values the system's efficiency is maximized.