Cooling Grain With Night Air: Why Bin Diameter Drops Out of the Aeration Time and Airflow Rate Does Not

Aeration with cool night air is the standard low-cost defence of stored grain against weevils and other stored-grain insects, which largely stop developing below about 15 C. This study sizes the operation for cylindrical wheat bins 2.4 m deep using a cooling-front energy balance. At an airflow of 5 m3/h per tonne, the cooling front advances at 0.0085 m/h regardless of bin diameter, and the bulk mean reaches 15 C after 230.2 hours of suitable air — 28.8 nights at eight usable hours per night — whether the bin holds 5.8 tonnes (2 m diameter) or 52.3 tonnes (6 m). Total fan energy is 10.13 kWh for the 23.2-tonne, 4 m bin at every airflow rate examined, because a faster fan simply finishes proportionally sooner; what the rate buys is calendar time, falling from 460.4 hours at 2.5 m3/h/t to 115.1 hours at 10 m3/h/t. The originated sizing rule is to choose the airflow rate from the nights available before warm weather, not from the bin size, and to budget roughly 29 nights of cool air at the common 5 m3/h/t rate. This study is simulated, not measured. SIMULATED, NOT MEASURED.