Chapter 178 - Design of vortex tubes and experimental program on LOX separation using cryogenic vortex tubes

Abstract

This chapter describes the use of computational fluid dynamics (CFD) techniques to arrive at optimum design parameters of vortex tubes to fabricate them. Ranque-Hilsch vortex tubes are well known devices having no moving mechanical parts in which, compressed gas injected through tangential nozzles into a vortex chamber results in the separation of inlet flow into two streams, one of which is warmer than the inlet gas while the other is colder. Vortex tubes for mixture separation are finding increased use for drying and purification of gas mixtures as well as separation of liquid oxygen (LOX) from pre-cooled air stream. Experimental studies have shown that for a 12 mm diameter straight vortex tube with six conical nozzles, maximum temperature difference of ≈109 K between hot and cold end flows was obtained for length to diameter ratio (L/D) > 25 and with optimum cold end diameter (dc) of 7 mm. Studies of LOX separation from pre-cooled air flow show that conical vortex tube gives highest LOX purity of ≈96% and the higher separation efficiency of ≈61% compared to straight vortex tubes. Experiments were conducted to study LOX purity and separation efficiency of straight and conical vortex tubes. The maximum LOX purity of 96% was obtained for conical vortex tube along with 14% separation efficiency. A maximum of 61% separation efficiency was obtained for conical vortex tube when the LOX purity was controlled at ≈66%. Straight vortex tubes give inferior performance in LOX separation compared to conical tubes. For straight tubes, the studies show that the purity and separation efficiency are dependent on L/D ratios.