Grain Drying 101 Drying Conditions if the absolute humidity of the air inside the bin is greater than the absolute humidity of the outside air. Explain what absolute humidity is: amount of water in one cubic meter, explain how it is different from relative humidity, and that absolute humidity is calculated from the saturation curve and pro rated with the relative humidity. Diurnal cycle and the night drying and the yardlight rule.
Motor/Generator Set to make a portable system. Especially good for remote sites that have no power. Make use of the wasted heat from the motor.
Plenum design, show how we waste energy (pressure) in going across the screen. Better to use the electricity with a heater in front of a small fan. The pipe or plenum should be open on the bottom for the least resistance in getting the air into the grain.
Time Constant Tau. The time constant is the amount of time required for the outside air absolute humidity to get to 60% of the distance of the difference. A CFM/bu of 0.35 would be about 3 time contants and get us to over 90% of the way there. This blog would show that 0.35 CFM/bu is kind of the sweet spot for using as much of the grains energy as possible, while still drying in a relatively short time.
The argument for small fans: less capital cost, less power infrastructure required, more uniform drying, use more of the inherent grains heat to dry, more efficient — the downside is that it is a bit slower — but what is the hurry? How slow can you go. The ideal fan size. CFM/bu
More on condensation, and how to use the grain drying calculator to detect conditions for condensation.
More specifics on how to use the grain calculator.
Something for everybody, from the simplest strategy (yard light rule) to the most advanced (absolute humidity) and the pros and cons of each. Depending on what you have.
Long term storage, use whatever fan strategy until the end of January, in which you will get the grain frozen and cold as possible, and from January til the end of July keep the bin as sealed as possible.
Roof vents don’t do much, and can actually result in condensation on the top layer of grain in the spring when the grain is cold and it is swiped by warm moist air circulating through the vents.
Vertical in grain tubes.
top dries first, compression causes heat
comparison of control strategies, continuous, nite, temp differential, absolute humidity.
Flow from natural convection
Energy in the grain to dry
Motor HP as we drop the flow in half, top down drying, HP 5 to 1