Novel classification of multistage flash desalination via finite and infinite flashing: Investigating thermofluid dynamics under varying inlet flow rates employing validated multiphase CFD simulations

Abstract

This research presents a comprehensive investigation into the flashing process within the evaporation zone of a multistage flashing (MSF) desalination chamber. It introduces a novel classification of the flashing process as ideal, finite, and infinite, aiming to advance the understanding of this critical phenomenon. A validated volume-of-fluid (VOF) multiphase computational model is employed to accurately predict the shape of the free surface and elucidate the complex phase change phenomena occurring within the MSF chambers. By systematically varying the inlet brine velocities and rigorously analysing the thermofluid behaviour in the flashing chamber under both finite and infinite flashing conditions, this study provides a comparative analysis of design factors, including flashing rate and maximum bubble nucleation. Additionally, non-equilibrium losses and flashing efficiency are examined as pivotal metrics for evaluating the flashing process. The findings reveal distinct behaviours of the evaporation zone for finite and infinite flashing processes. Intriguingly, alterations in the flow rate lead to simultaneous enhancements and detriments in thermal efficiency due to the intricate interplay of turbulence promotion, improved mixing, and reduced residence time. Furthermore, the study highlights the significant impact of the inlet flow rate on phase change size, flashing rate, and bubble nucleation frequency within the bubble formation region. This investigation emphasizes the critical importance of comprehending the flashing phenomena and its consequential effect on the thermal efficiency of MSF systems. Leveraging advanced computational models, this study provides a solid foundation for identifying innovative methodologies to optimize the flashing process and enhance the overall performance of MSF systems. The ground-breaking insights presented in this research contribute significantly to the scientific understanding of the field and pave the way for future advancements in MSF desalination technology.