A study of the application of wet steam modeling for thermocompressor simulation in TVC desalination

Abstract

Recently, the wet steam model, grounded in classical nucleation theory, has been utilized for computational fluid dynamics (CFD) simulations of thermocompressors and steam ejectors. However, this model, which accounts for the formation of liquid droplets in a homogeneous non-equilibrium condensation process, presents computational challenges due to its complexity. Unlike the ideal gas model, it involves solving multiple equations concurrently with the Navier-Stokes equations, rendering it computationally intensive and difficult to converge. The primary objective of this study is to evaluate the feasibility and efficacy of employing this intricate wet-steam model for modeling steam thermocompressors, specifically analyzing its impact on pressure, temperature, and Mach number contours. This paper aims to investigate the influence of modeling non-equilibrium condensation on various parameters affecting ejector performance. Utilizing numerical simulations conducted via ANSYS Fluent software, employing both 2-D axisymmetric wet steam and ideal gas models, our study reveals that non-equilibrium condensation leads to a higher entrainment ratio and critical back pressure. Additionally, our findings indicate that while the wet steam model notably affects temperature contours, its effect on pressure and velocity contours is comparatively minimal. The CFD analysis found that pathline trajectories were similar with both ideal gas and wet steam models. Droplet formation and evaporation within the thermocompressor revealed a gradual evaporation up to the midpoint of the constant area section, followed by a rise in liquid mass fraction due to droplet formation. However, after the constant area section, a shock wave led to a sudden pressure increase and decrease in liquid mass fraction of wet steam. These changes persist through the diffuser section of the ejector.Furthermore, to enhance the reliability of our results, this research integrates a robust validation methodology. We compare experimental results obtained from ejector studies in the literature with our simulations. Moreover, we introduce an experimental section in our research, specifically addressing zero suction mass flow rate conditions, thereby offering a practical validation approach.