Selecting the Right Aeration Fan for Your Bin

Selecting the Right Aeration Fan for Your Bin

October 3, 2008

 

Table 1. Static pressures for airflow resistance data for shelled corn at various air flows and grain depths.
 
Grain Depth
Airflow (cfm/bu)
(ft)
0.5 0.75 1.0 1.25 1.5 2.0

 
Expected Static Pressure (inch of water)

8
0.2 0.3 0.5 0.6 0.8 1.2
10
0.3 0.5 0.8 1.1 1.4 2.0
12
0.5 0.8 1.2 1.6 2.1 3.2
14
0.7 1.2 1.7 2.3 3.0 4.6
16
0.9 1.6 2.4 3.2 4.2 6.4
18
1.2 2.1 3.1 4.3 5.6 8.7
20
1.6 2.7 4.0 5.6 7.3 11.3

Farmer Question: I want to build a 27-foot diameter drying bin that is 21 feet to the eave. I am planning to install a full mesh drying floor (leaving 20 feet of bin space for corn storage) and would like to design for 1.25 cfm/bu airflow when the bin is full. Should I buy an axial flow or centrifugal aeration fan?

See Table 1 for the estimated static pressure to push a range of airflows through various depths of shelled corn. We recommend axial flow fans for installations requiring static pressures of less than 3.0 inches of water, either axial flow or centrifugal fans for static pressures of 3.0-4.0 inches, and centrifugal fans for installations requiring static pressures of greater than 4.0 inches of water, and Table 1 shows that the static pressure needed to push 1.25 cfm/bu through 20 feet of corn is 5.6 inches of water. A centrifugal fan will work as well as an axial flow fan from a 16-foot to 18-foot grain depth and is recommended for depths greater than 18 feet. To achieve the recommended airflow with the lowest possible input horsepower at full depth, a centrifugal fan is required in this installation.

Tom Dorn
Extension Educator, Lancaster County