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Lecture 14

Lecture 14. Determining System Sizing. Static Pressure - What is it?. 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

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Lecture 14

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  1. Lecture 14 Determining System Sizing

  2. Static Pressure - What is it? • 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)

  3. Heater Sizing & Fan sizing •  formula=Btu=(cfm*1.1*temp increase)*effic. • Fan sizing - Horsepower requirements • 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

  4. "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.

  5. Perforating • Perforated flooring •  1 square foot / 30 cubic feet (cfm) of air flow •  1 square foot of exhaust flow for each 1000 cfm air flow • Perforated ducting •  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

  6. Selecting a Heater • 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

  7. Determining Fan Horsepower Considerations • formula= Hp = (cfm * Ps)/63.46 * efficiency) •    cfm = airflow in cfm •    Ps = static pressure in inches water •    efficiency = fan efficiency •  50 % efficiency, unless known

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