Water is essential for life, but clean water is scarce in many places. A Solar Still is a green technology that cleans dirty water using the sun. It mimics the natural rain cycle. Dirty water evaporates, leaves the salt behind, and then condenses as clean water. To improve these devices without building expensive prototypes, engineers use Solar Still CFD simulation.

This project is a Solar Distiller fluent simulation designed to teach you how to model this phase change process. We use ANSYS Fluent to visualize the invisible movement of vapor and heat. By using the mass transfer fluent capabilities, we can see exactly how water turns to steam and back again. For more examples of sustainable technology, please visit our Renewable energy tutorials.

Figure 1: 3D Geometry of the Solar Distiller showing the basin and sloped glass cover.

Simulation Process: Multiphase and Radiation Setup in Fluent

To start this Solar Still ANSYS fluent tutorial, we created a 3D model of the distiller. The most important part of the setup is choosing the right physics models. Since we have liquid water, water vapor, and air all mixing together, we selected the Mixture Multiphase Model. This allows the software to track where the water is and where the air is.

To simulate the sun, we activated two specific tools: the Solar Ray Tracing model and the Rosseland Radiation model. The Solar Ray Tracing calculates the path of the sunbeams as they pass through the glass cover and hit the water basin. The Rosseland model helps calculate how that heat spreads. Finally, to make the water actually boil and condense, we used the Lee Model. The Lee Model is the standard tool for evaporation in solar still CFD. It tells the program to turn liquid into gas when it gets hot (evaporation) and gas into liquid when it gets cold (condensation). We ran the simulation in Transient mode to watch the process happen over time.

Post-Processing: Analysis of the Evaporation-Condensation Cycle

A real and deep analysis of the Solar Still CFD simulation results explains the physics of the water cycle inside the box. The process starts at the bottom basin. The Solar Ray Tracing model simulates the sunbeams passing through the glass cover. These beams hit the dark bottom of the basin and heat the dirty water. As the water temperature rises, the Lee Model for mass transfer becomes active. It calculates exactly how much liquid turns into gas. We can see this in the Volume Fraction contour. Right above the water surface, the blue color shows that the air is being pushed away by the rising hot steam. This proves that evaporation in solar still CFD is happening fast because of the solar heat. The steam is lighter than the air, so it naturally floats upward.

The second part of the analysis focuses on the condensation at the top. The hot vapor travels up until it touches the sloped glass cover. The simulation setup defines this glass as a cooler surface because it touches the outside air. When the hot vapor hits the cold glass, the Lee Model works in reverse. It turns the gas back into liquid droplets. The Solar Distiller fluent results show this clearly. The contours show a thin layer of liquid water forming on the inside of the glass. Because the glass is tilted, gravity pulls these clean drops down into the collection trough. This separates the fresh water from the salty water at the bottom. The simulation proves that the mass transfer fluent settings correctly balance the evaporation rate at the bottom with the condensation rate at the top, resulting in a continuous production of clean water.

Figure 2: Volume fraction contours of Air and Water showing the separation of phases.

Key Takeaways & FAQ

• Q: What is the Lee Model in Fluent?
  • A: The Lee Model is a mathematical formula used in ANSYS Fluent to simulate phase change. It controls how fast liquid turns to vapor (evaporation) and vapor to liquid (condensation) based on temperature.
• Q: Why do we use Solar Ray Tracing?
  • A: In a Solar Still CFD simulation, the heat source is the sun. Solar Ray Tracing calculates exactly how much solar energy enters the glass and heats the water basin.
• Q: What does the Mixture Model do?
  • A: The Mixture Multiphase Model is used when different fluids (like water, vapor, and air) move together. It helps us calculate the “Volume Fraction,” which tells us how much of each fluid is in a specific cell.