Lecture 16 Aeration

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

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

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

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.)

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

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)  

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