| Key Concepts
Static Pressure
Static Pressure is a measure of the amount
of air pressure a blower must provide in order to force air
through the crop stored in a bin. Static pressure is affected
by the depth of the stored crop, the size and moisture content
of the crop kernels, impurities (trash) in the stored crop
and airflow.
Static pressure increases with:
- an increase of depth
- smaller sized kernels
- more impurities
- an increase of airflow
Proper airflow is essential for successful
Aeration, Natural Air Drying and Pressure Curing. It is
moving air that absorbs moisture and carries it out of the
bin.
Airflow is the volume of airflow that is
generated by a blower and is usually measured in terms
of cubic feet per minute (CFM) or liters per second (L/S).
One CFM = 0.47 L/S, or 1 L/S = 2.1 CFM. The volume of air
generated by a blower depends on its design, motor speed
and horsepower.
Airflow is affected by static pressure. Airflow
rates drop off quickly as static pressure increases. KEHO's
blowers and air pumps are designed to produce optimum airflow
at the higher static pressure ranges often encountered in crop
drying.
Equilibrium Moisture Content
The equilibrium moisture content is the point
at which the combination of temperature and humidity in
the stored crop is equal to the air consistently moving
through it. At equilibrium, a crop will not be dried or
moistened.
The following sample table shows the effect
of temperature and relative humidity. Remember that Equilibrium
Moisture Content varies with the type of crop.
Hard Wheat
Equilibrium Moisture Content
|
Temperature |
Relative Humidity (%) |
| °C |
°F |
35 |
40 |
45 |
50 |
55 |
60 |
65 |
70 |
75 |
80 |
85 |
|
-2 |
30 |
11.6 |
12.2 |
12.8 |
13.4 |
14.0 |
14.7 |
15.4 |
16.2 |
17.0 |
18.0 |
19.2 |
| 2 |
35 |
11.4 |
12.0 |
12.6 |
13.2 |
13.8 |
14.5 |
15.2 |
15.9 |
16.8 |
17.8 |
19.0 |
|
5 |
40 |
11.1 |
11.8 |
12.4 |
13.0 |
13.6 |
14.3 |
15.0 |
15.7 |
16.6 |
17.6 |
18.8 |
| 8 |
45 |
10.9 |
11.5 |
12.1 |
12.8 |
13.4 |
14.1 |
14.8 |
15.5 |
16.4 |
17.4 |
18.6 |
|
10 |
50 |
10.7 |
11.3 |
11.9 |
12.6 |
13.2 |
13.9 |
14.6 |
15.3 |
16.2 |
17.2 |
18.4 |
| 13 |
55 |
10.5 |
11.1 |
11.7 |
12.4 |
13.0 |
13.7 |
14.4 |
15.2 |
16.0 |
17.0 |
18.3 |
|
15 |
60 |
10.3 |
10.9 |
11.6 |
12.2 |
12.8 |
13.5 |
14.2 |
15.0 |
15.9 |
16.9 |
18.1 |
| 18 |
65 |
10.1 |
10.8 |
11.4 |
12.0 |
12.6 |
13.3 |
14.0 |
14.8 |
15.7 |
16.7 |
17.9 |
|
22 |
70 |
10.0 |
10.6 |
11.2 |
11.8 |
12.5 |
13.2 |
13.9 |
14.7 |
15.5 |
16.6 |
17.8 |
| 26 |
75 |
9.8 |
10.4 |
11.0 |
11.7 |
12.3 |
13.0 |
13.7 |
14.5 |
15.4 |
16.4 |
17.6 |
|
28 |
80 |
9.6 |
10.2 |
10.9 |
11.5 |
12.1 |
12.8 |
13.6 |
14.4 |
15.2 |
16.3 |
17.5 |
Drying Front
The drying front is the level in the stored
crop at which point below, the crop is basically dry. The
drying front starts in the bottom of the bin (where airflow
is the greatest) and moves to the top. A stored crop is not
considered dry until the drying front moves completely through
the stored crop. Blowers must not be turned off until the
drying front has moved through the entire bin.
An understanding of the drying front and how
moisture and air move in a bin will assist you in operating
your system for the best results.
(For more information see
our animation).
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