Description

A solar indirect dryer is a passive method of ventilation that operates based on solar energy. In fact, it consists of two parts: The first is a collector that absorbs heat radiation from the Sun, and the second is a chamber where food or fruit is arranged in trays. Air flows through these trays and removes moisture from them.

The temperature of the collector walls increases as they absorb solar radiation, which causes the air inside the collector to warm up. As the temperature of the air increases, its density decreases, and the air starts to flow upward due to the buoyancy effect.

In this project, an indirect solar dryer was simulated in Egypt on July 1 at 12:00 PM. The collector has a surface area of 8 m², and the chamber can accommodate four trays.

The geometry was designed in SpaceClaim, and a mesh with 1,330,000 elements was generated in Ansys Meshing.

Methodology

According to the physics of this problem, we need to capture the density difference with temperature for the buoyancy effect. Therefore, the density model in the material is chosen as "incompressible ideal gas," and the operating density is specified at 1.225 kg/m^3.

The energy model is activated, as well as the radiation model, and DO is chosen for the radiation model because the air participates in the radiation. Solar ray tracing is used to take solar radiation into account.

To show the effect of the trays and foods on the flow and pressure drop in the simulation without explicitly meshing their intricate geometry, a porous medium has been utilized.

Conclusion

As a result, the velocity and temperature contours are reported. The temperature and density contours indicate that air near the wall absorbs heat, leading to a decrease in its density. At the inlet, the air temperature is 314 K, and after passing through the collector, its temperature reaches 322 K. Concurrently, its density decreases from 1.225 at the inlet to 1.095851 at the exit of the collector. Therefore, due to buoyancy, the air rises.

The pressure contour indicates a pressure drop as air passes through the trays. Heat transfer from the collector walls to the air causes a natural airflow with a mass flow rate of 0.0908 kg/m³ in the dryer.