Compressible Flow: Steam Ejector

What You'll Build

This lesson walks you through a CFD simulation of a steam ejector — a mechanical device with no moving parts that uses a primary (motive) steam jet to suck in and mix with a secondary fluid. Ejectors perform two essential jobs: creating vacuum for suction and mixing two fluid streams, and they do it by continuously converting between kinetic and pressure energy as the flow passes through a convergent-divergent nozzle.

In this project, you'll model water vapor as the motive fluid driving the suction of a secondary fluid, watching the flow accelerate beyond the speed of sound and observing how the vacuum-driven suction physically arises.

What You'll Learn

• How an ejector works — the physics of vacuum generation, fluid entrainment, and mixing through energy conversion

• Why supersonic flow is fundamentally compressible, and how Mach number governs the behavior inside the device

• How to design a 2-D convergent-divergent (de Laval) nozzle ejector geometry in Design Modeler

• How to generate an efficient structured mesh (~52,000 elements) suited to internal compressible flow

• How to set up the density-based solver — the correct choice for compressible and supersonic flows where density varies strongly with pressure

• How to handle the pressure difference between primary and secondary inlets that drives the suction phenomenon

• How to post-process pressure, velocity, and Mach number contours to trace where the flow goes subsonic, sonic, and supersonic

• How to interpret the mixing and compression of the motive and secondary streams downstream of the nozzle throat

Why It Matters

Ejectors are everywhere — refrigeration, vacuum systems, desalination, chemical processing, and power plants. This lesson is your gateway to compressible flow modeling and the density-based solver, skills that carry directly into nozzles, diffusers, supersonic airfoils, and any flow where Mach number matters.