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ISSN Online: 2688-7231

ISBN Online: 978-1-56700-524-0

Proceedings of the 26thNational and 4th International ISHMT-ASTFE Heat and Mass Transfer Conference December 17-20, 2021, IIT Madras, Chennai-600036, Tamil Nadu, India
December, 17-20, 2021, IIT Madras, Chennai, India

Numerical analysis of supercritical CO2 nozzle on the ejector performance

Get access (open in a dialog) DOI: 10.1615/IHMTC-2021.1050
pages 703-708

Abstract

An ejector compresses low-enthalpy secondary flow by momentum and energy augmentation using a co-flowing high-enthalpy primary flow in a varying area duct. The majority of studies on the ejector were carried out in the ideal gas domain. Significant real gas effects and the thermophysical properties variation occur in a supercritical CO2 (s-CO2) nozzle. CO2 is modelled as real gas with Refrigerant Gas Property tables generated over the appropriate pressure and temperature ranges using the NIST REFPROP database. 1-D model of the ejector is implemented to determine the area ratio of the operating condition. The mixing phenomena between the primary and secondary flow influence the ejector performance. Geometrical parameters influence the mixing characteristics. Thus, this work focuses on the nozzle geometry that affects the primary flow expansion characteristics that impact the ejector's performance. The pressure-coupled FLUENT solver using the K-ω SST model is used to simulate an axis-symmetric ejector to understand the effect of different nozzle geometry on the ejector performance. The static pressure along the ejector axis for the converging-diverging nozzle (nozzle-II) indicates the primary flow is overexpanded, and the pressure profile of the converging nozzle (nozzle-I) indicates that primary flow is under expanded. The nozzle-II was designed for isentropic expansion since the property variation of the fluid is drastic, unlike ideal gas; thus, shock is observed at the diverging part, which affects the performance of the ejector. The entrainment ratio of nozzle-I is 10% higher than that of the nozzle-II.