Stored-Grain Aeration Fan Airflow
The fan airflow to cool or dry stored grain: required_cfm = rate x bushels, with the ~15/rate cooling-front rule. Aeration cooling (0.1-0.25 cfm/bu) is a different job from natural-air drying (0.5-1.0). Static pressure rises steeply with depth and fan power grows ~fourfold when the rate or depth doubles, so a fan sized on cfm/bu alone stalls in a tall bin.
Formula and source
required_cfm = rate_cfm_per_bu x bushels; cooling_hours = 15 / rate_cfm_per_bu (per cooling front).
Stored-grain aeration fan airflow (MWPS / university extension; Shedd airflow-resistance curves), by name.
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