Steam Ejector

Steam Ejector ANSYS Fluent CFD Simulation Tutorial

Description

This project simulates a steam ejector using ANSYS Fluent — a mechanical device with no moving parts that uses a primary (motive) steam jet to entrain and mix with a secondary fluid. Ejectors perform two essential jobs in process industries: creating vacuum for suction and mixing two fluid streams. They achieve both through continuous conversion between kinetic and pressure energy as the flow passes through a convergent-divergent nozzle.

In this simulation, water vapor serves as the motive fluid driving the suction of a secondary stream. The flow accelerates beyond the speed of sound inside the device, making this a fully compressible, supersonic problem — and an ideal gateway into compressible flow modeling. Ejectors are found throughout the gas and petrochemical industries and beyond: refrigeration, vacuum systems, desalination, chemical processing, and power plants all rely on them.

Methodology

The 2-D ejector geometry, built around a convergent-divergent (de Laval) nozzle, is designed in Design Modeler, and a structured mesh of approximately 52,000 elements is generated — an efficient grid well suited to internal compressible flow.

Because the flow is supersonic and density varies strongly with pressure, the simulation uses the density-based solver — the correct choice for compressible flows where the pressure and density fields are tightly coupled. The pressure difference between the primary and secondary inlets is defined so that the motive jet naturally generates the low-pressure region that drives the suction of the secondary fluid, rather than imposing the entrainment artificially. The Mach number governs the behavior throughout the device, with the flow passing through subsonic, sonic, and supersonic regimes as it traverses the nozzle.

Analysis

At the end of the solution process, contours of pressure, velocity, and Mach number are extracted to trace the complete energy conversion cycle inside the ejector: the motive steam accelerates through the converging section, reaches sonic conditions at the throat, and expands to supersonic speed in the diverging section, creating the low-pressure zone that draws in the secondary fluid.

Downstream of the nozzle, the results show the mixing of the motive and secondary streams and their subsequent compression as the combined flow decelerates — the mechanism by which the ejector delivers its pumping effect without any moving parts. By completing this project, you will learn to set up the density-based solver for compressible flow, design and mesh a convergent-divergent nozzle, configure the inlet pressure difference that drives entrainment, and interpret Mach number fields to identify subsonic, sonic, and supersonic regions — skills that carry directly into nozzles, diffusers, supersonic airfoils, and any flow where compressibility matters.