Numerical study on the impact of fluid distribution on a counter-current direct contact evaporator

Humidification-Dehumidification (HDH) desalination units have been extensively studied during the past decades using macro-scale modeling, which relies on empirical closure correlations. Nonetheless, the HDH process remains relatively inefficient in terms of total energy requirements when compared with other desalination technologies such as Reverse Osmosis (RO) or Multi-Stage Flash (MSF). To improve the performance of direct contact evaporation, modeling of the transport phenomena at the small local scale is required. The objective of the present paper is to accurately model the hydrodynamic as well as heat and mass transfer as it typically occurs in a HDH counter-current direct contact evaporator. The numerical model is based on the Volume-of-Fluid (VOF) method included in ANSYS Fluent v19.2, which is modified to properly model diffusion driven evaporation. The study with multiple fluid distribution patterns shows a high increase in liquid hold-up and evaporated mass with an increase in water spray density, while the gas distribution does not have a noticeable impact on the performance of the evaporator column. The insight provided by the CFD model highlights the importance of considering the water distributor in conjunction with the packed column design for improving the performance. (C) 2020 Elsevier Ltd. All rights reserved.