Thermodynamic Modelling of Supersonic Gas Ejector with Droplets

Abstract

This study presents a thermodynamic model for determining the entrainment ratio and double choke limiting pressure of supersonic ejectors within the context of heat driven refrigeration cycles, with and without droplet injection, at the constant area section of the device. Input data include the inlet operating conditions and key geometry parameters (primary throat, mixing section and diffuser outlet diameter), whereas output information includes the ejector entrainment ratio, maximum double choke compression ratio, ejector efficiency, exergy efficiency and exergy destruction index. In single-phase operation, the ejector entrainment ratio and double choke limiting pressure are determined with a mean accuracy of 18% and 2.5%, respectively. In two-phase operation, the choked mass flow rate across convergent-divergent nozzles is estimated with a deviation of 10%. An analysis on the effect of droplet injection confirms the hypothesis that droplet injection reduces by 8% the pressure and Mach number jumps associated with shock waves occuring at the end of the constant area section. Nonetheless, other factors such as the mixing of the droplets with the main flow are introduced, resulting in an overall reduction by 11% of the ejector efficiency and by 15% of the exergy efficiency.

Current Advances in Ejector Modeling, Experimentation and Applications for Refrigeration and Heat Pumps. Part 1: Single-Phase Ejectors

“…Two very recent studies by [102,191], based on analytic models are worth mentioning. Chen et al [102] proposed a two-dimensional model to assess the performance of a VGE, accounting for the nozzle configuration.…”

“…Validation of this model was performed with R134a data generated by the authors as well as additional data from the literature which were generally better represented than by using conventional 1D modeling. Croquer et al [191] developed a new thermodynamic model of supersonic ejectors with the capacity to handle liquid droplet injection in the mainstream flow. The authors assessed the effect of droplet injection on operation and performance of the device in terms of efficiency, exergy destruction and compression ratio.…”

Phenomenological Thermodynamics of Irreversible Processes

“…S. Croquet, S. Pocet & Z. Aidoun [ 39 ] present in “ Thermodynamic Modelling of Supersonic Gas Ejector with Droplets ”, a study of determination of the entrainment ratio and double choke limiting pressure of supersonic ejectors within heat driven refrigeration cycles with and without droplet injection at the constant area section of the device. The aim is to compare the computational performance of the device with experimental data.…”

Analytical and Numerical Study on the Performance of ‎Supersonic Ejector at Different Operating Conditions ‎and Working Fluids

“…Though, the performance of the supersonic ejector is a function of geometrical and operating parameters. Plenty of literature has been proposed to understand the impact, including design approaches (Seehanam et al 2007;Kumar et al 2019), geometrical parameters (Li et al 2019;Zhu et al 2009;Wu et al 2018;Lin et al 2013), and operating parameters (Huang et al 1985;Shestopalov et al 2015;Aidoun and Ouzzane 2004;Vereda et al 2012) in different fields of applications for various working fluids (Croquer et al 2017;Cardemil and Colle 2012;Zhu and Jiang 2014) at on/off design conditions. The computational fluid dynamics (CFD) tools play an essential job in ejector design optimization and performance evaluation.…”