Lecture 16

1. Lecture 16 Aeration

2. Aeration • Natural air movement issues - moisture, temp • Management Issues •    keep center of bin within 10 degrees F of ambient temp •    .1 cfm / bushel for bins •    .2 cfm / bushel for flat storage •    not any lower than 32 degrees F •    not any higher than 60 degrees F •  Table 5.1

3. Positive vs. Negative Pressure • pushing adds 2 degrees F •    negative prevents condensation •    uses solar heat from top of bin •    bottom last to cool, difficult to determine when dry •    positive requires smaller duct diameters

4. Air Flow rates • .1 cfm is adequate •    if larger fan, then less time •   160 hrs @ .1  — 32 hrs @ .5 •    caution - can overdry &/or add moisture

5. Caution w/Automatic controls •   humidistat not enough •    thermostat & humidistat required •    best if computer controlled •     saves energy •     less likely to damage grain •     record information (temp, etc.)

6. Duct types Used • plastic, steel •    6" - 36" •    round & ½ round •    plastic - perforations not as much •    plastic - cheaper

7. Sizing • Assume level surface •    Depends on:   1. Cross sectional Area   2. Surface area exposed to grain minimum cross sectional area     =    total volume (cfm)                                         Allowable duct velocity (fpm)

8. Sizing • Total air volume depends on: •    fan •    bin •    grain type Exit velocity for escaping air Min. total surface area =  Total air volume (cfm)      Maximum velocity of duct exit air (fpm)