Session: Research Posters

Paper Number: 172183

Regimes of a Decelerating Wall-Bounded Multiphase Jet Inside Ejectors 

Transcritical carbon dioxide refrigeration systems with ejectors rely on the interactions between the high-pressure liquid supplied from the condenser and the low-pressure vapor supplied from the evaporator to enable efficient pressure recovery. The liquid is accelerated through a convergent nozzle (motive), which develops a jet. The jet drags the vapor (suction) using shear interactions. A deeper understanding of the interface physics and turbulent flow during the entrainment process is needed to guide internal shape optimizations. Study investigated the flow regimes and turbulence mechanisms of such jets using Large Eddy Simulation for a CO₂ ejector in a subcritical vapor compression cycle. Also, another study focuses on the evolution of coherent structures and their effects on the entrainment of vapor into the liquid jet. The Reynolds number (Re) of the liquid jet is maintained at 1.2e5, whereas the Reynolds number (Re) of the induced vapor flow is 9.8e4. The pressure difference between the vapor inlet and the ejector outlet is -4.92 bar. Large Eddy Simulation is used to understand the physics. The jet inside the ejector is categorized into different regimes based on the dominant physics in the regime. The jet initially expands due to the pressure drop between the high-pressure nozzle and the low-pressure suction chamber in response to the isothermal expansivity of CO₂(l) [Regime 1], and thereafter behaves as an incompressible flow with an interface affected by Kelvin-Helmholtz instabilities [Regime 2]. Near the nozzle throat, the flow is strongly two-phase. The developing region of the jet [Regime 3] is characterized by an adverse pressure gradient with reverse flow outside, similar to a negatively buoyant turbulent jet. The fully developed turbulent jet [Regime 4] is a wall-bounded turbulent flow filling the mixing chamber. The primary physics is shown to be shear interactions at the liquid-gas interface, triggering a Kelvin-Helmholtz instability and the formation of "Ring" vortices. Subsequent development of flow structures are associated with deformations of the "Ring" vortices by shear and the formation of turbulence. As turbulence develops, the two-phase character of the flow diminishes, and the concept of interface disappears. The maximum kinetic energy transfer from the liquid jet to the gas is shown to occur in the strongly two-phase regime, showing that shear interactions are more efficient than turbulence entrainment and phase change for mobilizing the vapor flow. The design intent is to entrain vapor from the suction inlet. Our insight is that entrainment is maximized by design changes that extend Regime 3, where entrainment occurs. This study advances the development of a reduced-order mixing zone model for an ejector, offering strategies to optimize ejector efficiency for any fluid and operating conditions. The first part of the work is accepted in the Physics of Fluids, and the second part of the work is under consideration.

Presenting Author: Sreetam Bhaduri Purdue University

Presenting Author Biography: Sreetam joined Purdue University in Spring 2022. Prior to coming to Purdue, he pursued a Master of Science (by Research) in Mechanical Engineering from the Indian Institute of Technology Madras, Chennai, India in Fall 2021. Previous to his master's degree, he pursued a Bachelor of Technology (B.Tech) in Mechanical Engineering from Vel Tech University, Chennai, India back in Fall 2018. During his undergraduate and graduate studies, he engaged himself researching internal combustion engines, with both experiments and numerical simulations. His primary research interests are in Computational Combustion Modeling and Computational Fluid Dynamics (CFD).

Authors:

Sreetam Bhaduri Purdue University
Leonard J. Peltier Bechtel Nuclear, Security, & Environmental
David Ladd Bechtel Manufacturing & Technology
Eckhard A. Groll Ray W. Herrick Laboratories, School of Mechanical Engineering, Purdue University
Davide Ziviani Ray W. Herrick Laboratories, School of Mechanical Engineering, Purdue University