Investigation of Characteristic Turbulent Coherent Structures in a Subcritical Carbon Dioxide Jet in a Multiphase Ejector*

Ejectors are heavily investigated to improve the performance of refrigeration systems. The efficiency of ejector devices depends on the physics of the entrainment, mixing and diffusing processes under multiphase operations. In this article, high-fidelity Large Eddy Simulation (LES) is employed to investigate a carbon dioxide (CO₂) ejector in a multi-evaporator vapor compression cycle. The experimental results utilized for this study are at Reynold’s number (Re) 1.2e5 at the high-pressure inlet (i.e. motive flow) maintaining CO₂ in subcritical state. The low-pressure inlet (i.e. suction flow) is maintained at Re 9.8e4 with CO₂ in vapor state, providing a pressure lift ratio of 1.2 at the diffuser outlet. A spatial-temporal representation of the flow topology revealed the actual jet morphology. Specifically, finger-like structures are key features to entrain more surrounding warm fluid into the colder dense core fluid at the cost of destabilizing and breaking up the jet by stretching the streamwise vortices and obstructing the increase in pressure-lift ratio. Furthermore, these finger-like turbulent coherent structures have been compared with well-known hairpin / horseshoe vortices structures formed by turbulent boundary layer bursting at the shear layer.