Experimental and numerical study on low-temperature supersonic ejector

Abstract

Ejectors have emerged as a viable solution for handling Boil-Off-Gas (BOG) generated by cryogenic storage tanks. The efficiency of ejector-based systems plays is highly dependent on the ejector's performance which is influenced by various factors including the geometry of the ejector and the boundary conditions. In this study, an axisymmetric supersonic ejector was designed, optimized, and evaluated for BOG removal. The baseline geometric dimensions design of the ejector was obtained via theoretical analysis. Subsequently, computational fluid dynamics (CFD) simulations were employed to optimize the boundary conditions and geometrical parameters. Experimental investigations were conducted to validate the design and evaluate the ejector's performance. The results highlighted the significant influence of two key parameters, namely, the mixing chamber diameter (Dm) and the nozzle exit position (NXP), on the ejector's performance. Optimized Dm showed an increase of about 12.5% compared with the baseline geometry. By operating the ejector within its on-design geometric and boundary conditions, the maximum entrainment ratio (ER) was achieved. The CFD models successfully identified and validated various flow phenomena, including double choke, single choke, and backflow, which were consistent with the experimental observations. Both the numerical models and experimental findings demonstrated that the modified ejector achieved an entrainment ratio of 1.06 under its design condition showing a 33.66% increase compared with that obtained using the baseline geometry. These results indicate the potential of the supersonic ejector as an alternative solution for BOG applications, emphasizing its efficacy in handling this industrial challenge.