Experimental and numerical study of the gas–gas separation efficiency in a Ranque–Hilsch vortex tube

• Experimental investigation of the performance of a vortex tube (VT).
• Effects of the inlet pressure, cold fraction and working medium are investigated.
• CFD simulations are performed and the results are compared with experimental data.
• Economic comparison between VTs as a separation unit and a distillation column.

A brass vortex tube is used to carry out a series of experiments. The main objective of the present research is to investigate the separation performances of a vortex tube (VT) for a hydrocarbon mixture. Examination is also applied to study the effects of nozzle intakes number and cold fraction on the gas species separation at specific inlet pressure 236.37 kPa in a VT with two gas mixtures (LPG as a hydrocarbon mixture and LPG–N2). A two-dimensional computational fluid dynamic (CFD) model simulation of a VT is presented. CFD code after validation is also applied to investigate the role of cold fraction and nozzle intakes number on the gas species separation. The highly rotating flow field structure and its characteristic are simulated and analyzed with respect to various operating inlet pressure and different cold fractions. Numerical results of compressible and turbulent flows are derived by the use of a standard k–ε turbulence model, while the VT was taken as a computational domain. Finally the results are extrapolated for investigating the effect of inlet pressures (up to 850 kPa) on VT separation performance. A comparison between a distillation column and a cascade of 7 VTs providing similar separation is presented. Stage efficiencies for both distillation column and cascaded VTs, along with respective capital and operational expenditures are calculated and compared. It is shown that a VT cascade is quite more advantageous.