Ejector: Two-Phase Flow

Description

This project simulates two-phase ejector flow using ANSYS Fluent, modeling liquid and vapor ammonia moving through a device that functions as a fluid-dynamic pump with no moving parts other than an inlet control valve. An ejector works by directing a high-pressure primary fluid through a nozzle so that its jet entrains a lower-pressure secondary fluid and carries it into a region of higher discharge pressure, the same principle behind steam ejectors that deliver water to a boiler using the boiler's own steam instead of a mechanical pump. In this case, liquid ammonia enters the primary inlet at 9 MPa and 393 K, and this high-pressure jet induces vapor ammonia to be drawn through and exit the ejector alongside the liquid. The geometry is designed and meshed in Gambit with a structured grid of 11,808 elements.

Methodology

Turbulence is resolved with the realizable k-epsilon model and standard wall functions, and the energy equation is active to capture the thermal effects tied to the phase change and high operating pressure. The VOF multiphase model tracks the interface between ammonia vapor and ammonia liquid so their interaction can be resolved directly. The simulation is steady, uses a pressure-based solver, and neglects gravity. The outlet is a pressure outlet at 0 Pa gauge and 312 K, walls are stationary with zero heat flux except for a coupled wall segment, and the solution uses SIMPLE for pressure-velocity coupling, PRESTO! for pressure discretization, a compressive scheme for volume fraction, second-order upwind for momentum and energy, and first-order upwind for the turbulence quantities, with hybrid initialization.

Analysis

The results include contours of pressure, temperature, and velocity throughout the ejector. These fields characterize how the high-pressure primary ammonia jet entrains and accelerates the secondary vapor stream, and how the two phases interact as they move through the nozzle and mixing sections toward the discharge, the core behavior that determines an ejector's effectiveness as a passive pumping device in ammonia-handling process systems.