Aeration ducts distribute air through the seed mass. In some storage facilities, the ducts are poured into the concrete floor and covered with a perforated plate. In others, perforated, half-round or round ducts are placed on top of the floor. Various types of homemade ducts are being successfully used for cottonseed aeration. Corrugated culvert material can be cut into half-circles with legs welded on to hold the half culvert above the floor, creating a pathway for the air. Wood framed ducts with hardware cloth to retain the seed can also be used.
|Duct Diameter (in)||Surface Area1(ff2/lin.ft)|
|1. Double surface area for round duct.|
Two important considerations for cottonseed aeration duct design are the duct open surface area and the duct cross-sectional area.
Open surface area is defined as the open area along the duct surface through which air can pass. It is generally described as a percent of the total area. Ducts should have at least 10% total open surface area; 15% is better. Pressure losses can be held to a minimum by limiting the velocity of the air into the duct (face velocity) from 10 to 15 ft/min.
The air velocity within an aeration duct should range from 1,500 to 2,000 ft/min. This will minimize static pressure losses and fan power requirements. Air velocities should be kept below 2,500 ft/min to avoid transporting seed within the duct.
Ducts should be evenly spaced on the floor of a seedhouse to keep the airflow path uniform within the seed mass. Duct spacing is determined by the depth of seed and the airflow rate used. For depths less than 20 ft a spacing no greater than the seed depth is preferred and should not exceed 1 1/2 times the cottonseed depth (Smith, 1975).
Ducts installed across the width of a rectangular building allow aeration to be started as soon as the first duct is covered with seed. The airflow can be concentrated in selected areas to remove hot spots that sometimes develop. For extra wide storage buildings, a central manifold pipe can be used to reduce duct length.