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.

The term airflow is defined as the volume of air 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.

Drying Front

The drying front is the level in the stored crop at which point 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.