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Pressure Vessel StressCalculations

Brian

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Stress calculations for a 5 foot Long 2 foot indiameter cylindrical pressure vessel during

normal operation pressure of 150 psi Hoop Stress or Stress in the Circumferential

Direction = Pr/t With P = 150 psi, r = 12 in, and t = .25 in

Hoop Stress = 7200 psi

Axial Stress = Pr/2t With P = 150 psi, r = 12 in, and t = .25 in

Axial Stress = 3600 psi

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Max pressure calculations for a 5 foot Long2 foot in diameter cylindrical pressure

vessel Calculations based on Grade B pipe with a

Minimum Yield Strength: 35000 psit = .25 inr = 12 in

Max Pressure based on Hoop Stress = 35000 psiPressure = 729.17 psi

Max Pressure based on Axial Stress = 35000 psiPressure = 1458.3 psi

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Stress calculations for 12 in diameterspherical end caps during normal operation

pressure of 150 psi.

Hoop Stress = Axial Stress = Pr/2t With P = 150 psi, r = 6 in, and t = .25 in

Hoop Stress = 1800 psi

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Max pressure calculations for 12 indiameter end caps

Calculations based on Grade b pipe with aMinimum Yield Strength: 35000 psit = .25 inr = 6 in

Max Pressure based on Hoop Stress = 35000 psiMax Pressure = 2916.7 psi

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Results

Based on the previous calculations we havedetermined that the limiting factor in regardto max pressure within the pressure vessel isthe Hoop Stress for the cylindrical pressurechamber. But it is still 3.86 times the intendedoperation pressure of 150 psi.

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Heating System Selection

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Convection Incoloy Tubular Heating selected Is most common in commercial autoclaves Easily obtained used in home appliances

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Insulation of Vessel Prevent heat from escaping (minimize power required to

heat) Keep surface temperature low to prevent burning danger Can also add outer covering, i.e. sheet metal (extra cost)

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Insulation Thickness

0.4 m O.D. corresponds to a 3.5 insulation layer Common (R13)

No real gains if any thicker

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Heating of Vessel

Surface temp. at 3.5 thickness is 80F Heat loss also levels off at 3.5

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Total power to maintain max. temp: ~470W Total power to heat up air at 15F/min (total 27

min): ~1.5kW Allowing for thermal mass of

parts/molds/pipe, ~4-5 kW needed Can easily be run on 240V power Elements can be obtained to provide this Blowers inside vessel will help maintain

uniform temp.

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Estimated Heating System Costs

63 ft^2 R13 fiberglass ($20) 4-5kW incoloy tubular heating element ($250)

Potential sheet metal covering ($125) Shipping, fittings, etc ($125 est.) Subsystem estimated total: $400-$500