Fluid movement in Two-stage Ejectors is more complex than in Single-stage types. High-pressure steam flows rapidly through the primary nozzle, creating a low-pressure area at the exit that pulls in the secondary fluid. As the primary flow slows down, the secondary flow speeds up. Both flows mix completely at the ejector’s end. In the current CFD study that relies on the reference paper “ Performance analysis of a two-stage ejector in an ejector refrigeration system using computational fluid dynamics”, a two-stage ejector refrigeration system is analyzed.

Figure 1: Schematic of two-stage ejector

Simulation Process

Due to the symmetrical design of the two-stage ejector, only half of it is drawn. The grids are composed of structured quadrilateral elements. The high-speed flow in each stage of ejector leads to compressibility of water vapor. This is why the ideal gas density approach is adopted. Avoiding backflow or reverse flow is very challenging because of separate ejectors. It is solved by employing suitable boundary conditions.

Figure 2: Designed Geometry model

Post-processing

The simulation of the two-stage ejector refrigeration system reveals interesting flow dynamics and thermal characteristics. The temperature contour shows a distinct thermal gradient, with the hottest regions (red) at the inlet and the coolest areas (blue) in the mixing chamber and diffuser. There’s a notable temperature drop across the primary nozzle, likely due to expansion. The velocity contour complements this, displaying high-velocity regions (red/orange) at the primary nozzle exit and in the mixing chamber, indicating effective momentum transfer. The secondary flow entrainment is visible in both contours, with cooler, lower-velocity fluid drawn in from the sides. The second stage shows a re-acceleration and mixing process, with another velocity peak and temperature adjustment. The diffuser section at the outlet exhibits gradual velocity decrease and temperature rise, suggesting pressure recovery. These patterns indicate effective two-stage mixing and compression, key for the ejector’s performance in the refrigeration cycle.