Design and CFD analysis of a CRMC steam ejector for geothermal heat-powered cooling using non-equilibrium wet steam modelling

Geothermal steam is an abundant but impure heat source, carrying dissolved salts and particulates. Steam ejectors, which use the motive fluid directly in a simple supersonic nozzle, are uniquely suited to this application and represent the core technology of the EU-funded Geosyn geothermal cooling project. This study presents a novel integrated design framework for a geothermal heat-powered ejector chiller delivering 20 kW of cooling. The Constant Rate of Momentum Change (CRMC) design procedure is combined with parametric Bézier curve profiles to obtain a continuous curve aimed at minimizing irreversibility. The numerical framework employs the SST k-omega turbulence model and a non-equilibrium wet steam model accounting for spontaneous nucleation, droplet growth, and latent heat release within the motive nozzle. The CFD model is validated against an experimental dataset available in the literature, establishing confidence in its predictive capability for condensing supersonic flows. A parametric CFD study varying nozzle throat diameter, area ratio, nozzle exit position, and body diameter identifies two seasonal configurations sharing a common 62 mm ejector body, allowing seasonal adaptation solely by nozzle substitution. The summer design achieves an entrainment ratio of 0.40, a secondary mass flow of 8.65 g/s and a critical condenser pressure of 5.2 kPa, meeting the design target. The winter design achieves an entrainment ratio of 0.412 at 7.79 g/s with reduced motive consumption.