The 3D Solar Still (Distiller) advances sustainable water purifying technologies. This unique solar distillation system uses a three-dimensional structural design to increase sunshine exposure and efficiency. Evaporating water leaves contaminants and condenses into clean, drinkable water on the colder still surfaces. This design boosts distilled water production and lowers processing time compared to flat solar stills. In our recent investigation, a valuable numerical paper is validated. You can check it here. Now, we are allowed to take a step further and conduct a CFD study about Evaporation/Condensation in a Solar Still (Distiller) and study the process unsteadily and in 3D configuration.

Figure 1: Schematic of Solar distiller

Simulation Process

The geometry and mesh grid are primarily generated. Due to the presence of three phases, including pure water liquid, water vapor and air, a Mixture multiphase module is utilized. The Rosseland radiation module and Solar Ray Tracing sub-model are coupled to simulate the radiative effects of the sun. It is a closed system and there isn`t any mass transfer through the boundaries. The evaporation and condensation process are solved according to Lee’s model.

Post-Processing

The transient CFD modeling of our 3D solar still shows interesting phase interactions which drive the water purification process. If you look at the air volume fraction contour, you can see that there is a natural gradient: there is more air at the top and less air near the water’s surface. The colors aren’t just pretty; they show us how the evaporation-condensation cycle makes different areas inside the still. The sloped glass cover shape is very important in this case. As the sun’s rays heat the water at the bottom, vapor rises and makes this stacked pattern. The amazing thing about our mixed multiphase model is that it can show small changes in air concentration that simpler models would miss. These gradients have a direct effect on how well water vapor goes through the system, which in turn affects how much freshwater you can make.

Figure 2: Water and air volume fraction contour – Solar still distiller

Part of the volume that is liquid water tells the other side of the story. The concentration slowly drops from the bottom to the top  (almost zero). This is what you want in a successful still design. The sloped shape of the solar still makes it easy for the water to evaporate from the bottom and condense on the cooler glass surfaces. Our simulation that changes over time shows that this isn’t a static process; the phase change dynamics change as the sun’s strength changes throughout the day. Lee’s model correctly shows how water molecules change from a liquid to a vapor, which creates a cycle of continuous purification. The most useful thing about this 3D simulation is seeing how the distribution of the liquid changes in all directions. This shows that corner regions do play a big role in overall production. These insights simply couldn’t be gathered using standard 2D analysis. This ANSYS Fluent method is therefore very useful for improving the designs of next-generation solar stills so that they produce the most water.