Modeling non-uniform airflow distribution in large grain silos using Fluent.

Computational fluid dynamics software (Fluent) was used to successfully model nonuniform airflow through large grain storage silos using Ergun’s equation, which can account for material properties of a grain mass such as porosity and fines concentration. Three example applications were investigated: a peaked grain mass, a grain mass with a high fines concentration core, and a grain mass aerated from a ring duct around the bottom of the silo wall. The velocity magnitude through a peaked grain mass decreased from 0.0163 m/s at the air inlet to less than 0.008 m/s at 1.0 m below the peak of the grain mass. The velocity magnitude in a core of high fine material concentration decreased from 0.0142 m/s at the air inlet to 0.008 m/s, which resulted in a 40 % lower effective airflow rate through the grain core versus the rest of the grain mass. This non-uniform airflow behavior confirmed the observation by practitioners that moving a cooling front through peaked grain or a core with high fines concentration takes substantially longer than through a leveled and/ or cored grain mass. Aerating grain from a ring along the bottom of the silo wall in order to target, for example, chilled air through warmer grain near the silo wall resulted in the spreading of the airflow throughout the grain mass. The airflow became more and more uniform as it moved upwards and no targeted cooling effect would be expected beyond about 1/10 of the grain depth.