Porosity: Drying Seed Process Using Porous Medium

Drying Seed Behavior in a Porous Medium — ANSYS Fluent CFD Simulation

This project investigates the drying process of seeds within a semi-cylindrical domain packed with seed particles, using ANSYS Fluent to capture the coupled heat and mass transfer occurring as hot air flows through the seed bed. The simulation tracks temperature, moisture distribution, and velocity fields within the porous seed zone to evaluate how the drying process evolves over time under given thermal and flow conditions, offering insight into drying efficiency, local heat transfer, and vapor concentration patterns.

Geometry and Mesh

The geometry was built using ANSYS SpaceClaim and DesignModeler. Taking advantage of symmetry, only half of the physical domain was modeled, with the bottom surface defined as a symmetry boundary to reduce computational cost. Two zones were defined: a fluid zone representing the drying air, and a seed zone treated as a porous medium with a porosity of 0.418, reflecting the physical packing of the seeds. The domain was discretized in ANSYS Meshing using a tetrahedral mesh of approximately 4.5 million cells, providing sufficient resolution to resolve the temperature and velocity gradients around the seed particles.

Model and Solver Settings

A pressure-based transient solver was used to capture the time-dependent heat and mass transfer behavior, with gravity set to -9.81 m/s² in the Y-direction to correctly account for buoyancy. The energy equation was activated to model heat exchange between the hot air and the seed surfaces, and the RNG k-ε turbulence model was selected for its accuracy in capturing recirculating and swirling flows within porous media. The species transport model was enabled to track water vapor (H₂O) concentration, with air, H₂O, and wheat defined as the working materials. Pressure-velocity coupling was handled using the SIMPLEC algorithm, with a velocity inlet for the incoming hot air and a pressure outlet for the exiting flow. The transient formulation allowed the temperature and moisture fields within the seed zone to be monitored over time.

Results

The temperature contours show a gradual rise across the seed bed, with values ranging from approximately 302.6 K to 303.1 K, indicating a gentle but effective drying process. The H₂O mass fraction contours show a progressive decrease in vapor concentration along the airflow path, confirming that moisture is being removed from the seed surfaces. Velocity streamlines show the air accelerating as it passes through the porous region, enhancing convective heat and mass transfer. Together, the flow, temperature, and species fields indicate that the airflow is well distributed through the porous bed, promoting uniform drying conditions throughout the domain. These results can help guide the optimization of airflow velocity, porosity, and inlet temperature for improved drying performance in industrial applications.