Clean Water: Domestic Water Distiller

Home Water Distiller CFD Simulation

Description

This project simulates a small-scale home water distiller using ANSYS Fluent, investigating one of the more accessible approaches to water desalination. The system relies entirely on heat transfer and phase change to produce clean water: a floor heater warms water until it evaporates, and because this steam carries none of the original salt, bacteria, or contaminants, cooling it back into liquid form yields pure freshwater. The steam travels through a spiral tube, where a fan cools the surrounding pipe walls, driving the vapor to condense back into fresh water on the other side.

The device is built from three functional sections: an evaporator at the bottom where water turns to steam, a condenser at the top where that steam is cooled, and a spiral tube connecting the two that serves as the pathway for vapor transfer and the site where condensation actually occurs. To keep the model manageable, the heater and fan themselves weren't explicitly modeled; instead, fixed temperatures were assigned directly to represent their effects; the evaporator was held at 373 K, matching the saturation temperature of water, while the condenser was set to 363 K. The patch tool was used to define the initial water level inside the evaporator tank.

Because the process unfolds over time as water evaporates and vapor condenses, the simulation was run as a time-dependent, unsteady case, allowing the rate of phase change and the resulting freshwater output to be tracked as the system evolves. The three-dimensional geometry was built in Design Modeler, and the model was meshed in ANSYS Meshing using an unstructured grid of 478,805 cells.

Methodology

Three phases coexist in this system: liquid water, water vapor, and air, which serves as the coolant inside the condenser. Since these phases need to be tracked with distinct, clearly defined boundaries, the Volume of Fluid (VOF) model was used, with air set as the primary phase and both liquid water and water vapor treated as secondary phases. The Sharp interface option was applied to keep the boundary between phases crisp rather than smeared across a transition layer.

The evaporation-condensation process between the water and vapor phases was captured through a mass transfer mechanism based on Lee's equations, which calculate phase-change rates based on the saturation temperature and the evaporation/condensation frequency coefficients. With the saturation temperature set at 373.15 K, any fluid temperature above this threshold triggers evaporation, while any temperature below it triggers condensation.

Conclusion

The simulation produced contours of temperature, phase-change rate, and volume fraction for both water and vapor, captured on a mid-plane cross-section at the final second of the 10-second simulation, along with animations tracking how these quantities evolve over time. Plots of freshwater output — both the volume-averaged water fraction inside the system and the mass flow rate of freshwater leaving the condenser — were also generated.

The temperature and mass transfer contours line up closely: wherever the fluid temperature drops below the saturation point, condensation occurs, shown by a negative phase-change rate. Inside the evaporator, water evaporates from its surface and rises as steam; once that steam reaches the cooler condenser tube, it condenses back into liquid, producing usable freshwater. The output plots confirm that freshwater production increases steadily over time as more condensation occurs, demonstrating that the desalination system's core evaporation-condensation cycle works as intended.