Solar Indirect Dryer

Solar Indirect Dryer CFD Simulation, ANSYS Fluent

Description

A solar indirect dryer is a passive ventilation system driven purely by solar energy, consisting of two main components: a collector that absorbs solar radiant heat, and a drying chamber where food or fruit is arranged on trays, with air flowing through them to remove moisture. As the collector walls absorb solar radiation, their temperature rises, warming the air inside — this heated air becomes less dense and begins to rise naturally due to buoyancy, driving airflow through the system without any mechanical assistance.

This project simulates an indirect solar dryer located in Egypt, modeled at 12:00 PM on July 1st. The collector has a surface area of 8 m², with the drying chamber sized to accommodate four trays. The geometry was designed in SpaceClaim and meshed in ANSYS Meshing, totaling 1,330,000 elements.

Methodology

Since capturing the temperature-driven density difference responsible for buoyancy is central to this problem, the material's density model was set to incompressible ideal gas, with an operating density of 1.225 kg/m³. The energy equation was activated alongside a radiation model — the Discrete Ordinates (DO) model was selected specifically because air participates directly in radiative heat exchange within this domain — with solar ray tracing enabled to account for incoming solar radiation.

To capture the flow resistance and pressure drop introduced by the trays and food items without explicitly modeling their intricate geometry, a porous medium was used to represent their combined effect on the surrounding airflow.

Conclusion

Results include velocity and temperature contours throughout the dryer. Temperature and density contours show that air near the collector wall absorbs heat and correspondingly decreases in density: air entering at 314 K rises to 322 K after passing through the collector, with density dropping from 1.225 kg/m³ at the inlet to 1.095851 kg/m³ at the collector exit — this density reduction is precisely what drives the air's upward buoyant motion through the system.

The pressure contour further shows a clear pressure drop as air passes through the trays, consistent with the porous resistance applied there. Altogether, heat transfer from the collector walls to the air establishes a natural, self-sustaining airflow through the dryer, reaching a mass flow rate of 0.0908 kg/s — confirming that the passive, buoyancy-driven design successfully generates sufficient airflow for effective drying without any external power input.