The standard single-stage ejector-diffuser (SSED) system consists of a diffuser, a mixing chamber, a mainstream inlet, and an entrained stream intake. It uses a high-pressure primary stream to drive the low-pressure entrained stream through pure shear movements free from mechanical energy input. Many industrial uses, including jet refrigeration systems, have taken great advantage of it for mass transport and heat exchange. According to the reference paper entitled “ Analytical and computational studies on the performance of a two-stage ejector–diffuser system”, the current numerical study over a single-stage ejector-diffuser system is conducted.

Figure 1: Schematic of SSED from reference paper

Simulation Process

The ejector–diffuser flows are numerically studied by using the axisymmetric domains. The schematic of it is given in the reference paper and illustrated below. 586192 polyhedral cells are produced. A mixture of air, nitrogen and water vapor modeled by the Species Transport model enters SSED system. The compressibility is inevitable in ejectors, so the ideal-gas approach is adopted.

Figure 2: Schematic of SSED system with an axisymmetric view

Post-processing

Complex fluid dynamics of a compressible gas mix (air, water vapor, and nitrogen) handled as an ideal gas are revealed by the simulation of this single-stage ejector-diffuser. Indicating a shock wave, the pressure distribution shows low pressure in most of the devices, with a sharp spike at the nozzle throat. Whereas the speed field shows acceleration to supersonic speeds at the throat, followed by fast deceleration, the temperature profile shows cooling at the throat followed by heating downstream. These patterns show the creation of a shock wave in which the flow moves from supersonic to subsonic, therefore stressing the important part the converging-diverging nozzle geometry performs in regulating the gas dynamics. Pressure, temperature, and velocity interact to emphasize the extremely compressible character of the flow in this ejector-diffuser system.