Lecture 14
Determining System Sizing
Static Pressure - What is it?
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commonly used unit of pressure
pounds per square inch
commonly used when pressure drop is less
than 1 psi.
weight of 27.7 in column of water = 1 psi
positive or negative pressure
increases at an increasing rate
2 * air flow more than doubles pressure
20 - 40 cfm —> .18 - .525 (triples)
Heater Sizing & Fan sizing
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formula=Btu=(cfm*1.1*temp increase)*effic.
Fan sizing - Horsepower requirements
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formula= Hp = (cfm * Ps)/63.46 * efficiency)
cfm = airflow in cfm
Ps = static pressure in inches water
efficiency = fan efficiency
50 % efficiency, unless known
size of bin impact
depth of grain impacts
type of grain (soybeans -least; wheat -worst
"Approximate" Allowable Storage Time (Days) For Cereal Grains.
Temperature (°F)
M.C. -------------------------------------------(%) 30° 40° 50° 60° 70° 80°
---------------------------------------------------14
* * * *
200 140
15
* * * 240 125 70
16
* *
230 120 70 40
17
* 280 130 75 45 20
18
* 200 90 50 30 15
19
* 140 70 35 20 10
20
* 90 50 25 14 7
22 190 60 30 15
8
3
24 130 40 15 10
6
2
26
90 35 12 8
5
2
28
70 30 10 7
4
2
30
60 25 5 5
3
1
---------------------------------------------------Based on composite of 0.5 percent maximum dry matter
loss calculated on the basis of USDA research at Iowa
State University; Transactions of ASAE 333-337, 1972;
and "Unheated Air Drying," Manitoba Agriculture Agdex
732-1, rev. 1986.
*Approximate allowable storage time exceeds 300 days.
Perforating
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Perforated flooring
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1 square foot / 30 cubic feet (cfm) of air flow
1 square foot of exhaust flow for each 1000 cfm air flow
Perforated ducting
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maximum center line spacing
no greater than ½ the depth of grain
no greater than 1/4 the depth next to a wall
1 square foot cross sectional area for each 2000
cfm (Size of tube)
1 square foot perforated surface for each 30 cfm of air
flow.
if longer than 100 feet, fan on each end
Selecting a Heater
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BTU/hr = cfm * 1.10 * desired temp.
increase
• increase temp of 4364 cfm by 10 degrees F
• 4364 * 1.10 * 10 = 48,004 btu
• if anticipation 10% loss heating efficiency?
• 48,004 * 1.10 = 52,804
Determining Fan Horsepower
Considerations
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formula= Hp = (cfm * Ps)/63.46 *
efficiency)
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cfm = airflow in cfm
Ps = static pressure in inches water
efficiency = fan efficiency
50 % efficiency, unless known