Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Agricultural and Biosystems Engineering


The first stage of this investigation involved two years of field tests in three 5.5-m diameter drying bins, two of which were equipped with single-auger grain stirrers. The first year, 24% moisture (wet basis) corn was dried using 3.7- to 5.2-kW fans. One bin was unstirred and another was stirred 48 h per week. The third bin was stirred at bin filling, when average moisture reached 20%, and again when average moisture fell below 15.5%. Both stirred bins used less energy and had less overdrying than the unstirred bin, with least energy use in the bin stirred three times;In the second field test, 20% moisture corn was dried. One bin was unstirred and the other two were stirred at the beginning and end of drying. The 3.7- to 5.2-kW fan on one stirred bin was replaced with a 2.2-kW model. Again, the stirred bins used less energy and had less overdrying. The stirred bin with the small fan used the least Oil, Gas, and Energy;The initial stirring was found to decrease bulk density and airflow resistance and greatly increase airflow. Subsequent stirring had unpredictable effects on bulk density and generally increased airflow resistance. Stirring shifted fines toward the drying floors and produced a small quantity of fines;In the second stage of the investigation, field test results were used to modify and calibrate a computer model to simulate natural-air stir drying. It was found that airflow had to be reduced to 74% of the input value and only 57.5% of the input electrical power could be used to calculate air temperature rise or the model would overpredict drying. Simulated natural-air drying of 20 and 24% moisture corn harvested mid-October in central Iowa showed that stirring reduced required fan size, electric-energy use, and overdrying;In the final stage, an economic analysis was conducted using corn physical properties from the field studies, average energy use and overdrying from the simulations, and local equipment and operating costs. The analysis showed that stirring increased net revenues for natural-air drying of 24% moisture corn and did for 20% moisture corn when electricity prices were high.



Digital Repository @ Iowa State University,

Copyright Owner

William Floyd Wilcke



Proquest ID


File Format


File Size

162 pages