Two-stage Water Desalination Equipment

Description

This project simulates a two-stage water desalination device, a system that purifies water through evaporation and condensation rather than filtration, removing even the smallest contaminants that other methods can miss. Water is heated to promote surface evaporation at the bottom of the device, and the resulting vapor rises and contacts cooler sloped surfaces where it condenses back into pure liquid water, directed toward the system outlet. The geometry is built in Design Modeler and meshed in ANSYS Meshing with an unstructured grid of 1,936,581 elements.

Methodology

The VOF multiphase model captures the liquid-vapor interface inside the desalination trays, and since surface evaporation isn't included in Fluent's base solver, a UDF is hooked into the source code to model this mass transfer mechanism directly. The device's bottom surface raises the bulk water temperature to around 353 K, increasing the water molecules' energy and accelerating the evaporation process. Turbulence is resolved with the realizable k-epsilon model, chosen for its accuracy in internal flows, and the energy equation is active given the heat transfer driving the process. The simulation runs transient and in 3D, with gravity enabled so the vapor's upward motion, a consequence of its lower density relative to liquid water, is captured correctly.

Analysis

The results show a stratified pressure distribution inside the system trays, consistent with the hydrostatic pressure of the standing water column in each tray. The temperature contour confirms elevated temperatures at the bottom surface, which increases the water molecules' motion and kinetic energy and in turn speeds up surface evaporation. The mass transfer rate contour quantifies how much vapor is generated at any point in the system, and this vapor generation rate matches the amount of water ultimately condensed at the cool sloped plates and collected as distillate, confirming that the vapor produced through evaporation is fully accounted for as clean water leaving through the outlet.