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Module 2: Characteristics of Gases - Velocity - Practice Problems

Instructions:
Work these problems on a sheet of paper and check your answers against those provided below.
Helpful Calculators:
The following calculators may be useful in solving these problems. You can access them either from the "Calculators" button on the screen or from the links below.
Temperature Converter
Pressure Converter
Gas Flow Rate Converter (Actual Standard Conditions)
Gas Flow Rate Converter (Wet Dry Basis)

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Q icon #1
What is the velocity of a 50,000 ACFM gas stream moving through a duct having a height of 4 ft and a width of 3.5 ft?

A icon
Answer: 3,571 ft/min
Solution:
Calculate the gas velocity (v) using the following equation:
practice equation 1
  1. Calculate the area of the duct through which the gas stream is flowing.
    practice equation 1(1)

  2. Calculate the gas velocity (v).
    practice equation 1(2)

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Q icon #2
What is the velocity of a 1,650 m3/min gas stream moving through a duct having a height of 4 ft and a width of 3.5 ft?

A icon
Answer: 1,269 m/min
Solution:
Calculate the gas velocity (v) using the following equation:
practice equation 2
  1. Calculate the area of the duct through which the gas stream is flowing and convert to Cgs units.
    practice equation 2(1)

  2. Calculate the gas velocity (v).
    practice equation 2(2)

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Q icon #3
What is the velocity of a 35,000 SCFM gas stream moving through a duct having a height of 5 ft and a width of 3.5 ft? If necessary use a gas temperature of 250°F, a gas pressure of -10 in. W.C. and a barometric pressure of 397 in. W.C.

A icon
Answer: 2,828 ft/min
Solution:
  1. Convert the gas flow rate in standard conditions to actual conditions.
    practice equation 3(1)

  2. Calculate the area of the duct through which the gas stream is flowing.
    practice equation 3(2)

  3. Calculate the gas velocity (v) using the following equation:
    practice equation 3(3)

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Q icon #4
What is the velocity of a 31,500 DSCFM gas stream moving through a duct having a height of 4.2 ft and a width of 4.8 ft? If necessary use the following information to solve the problem:
practice equation 4

A icon
Answer: 2,676 ft/min
Solution:
  1. Convert the gas flow rate in standard dry conditions to standard wet conditions.
    practice equation 4(1)

  2. Convert the gas flow rate in standard conditions to actual conditions.
    practice equation 4(2)

  3. Calculate the area of the duct through which the gas stream is flowing.
    practice equation 4(3)

  4. Calculate the gas velocity (v) using the following equation:
    practice equation 4(4)

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Q icon #5
Calculate the stack exit velocity based on the emission test data and information provided below.
practice equation 5

A icon
Answer: 1,790 ft/min or 29.8 ft/sec
Solution:
Since the gas flow rate is already expressed in ACFM, there is no need to correct the flow rate for the absolute pressure or absolute temperature.
Calculate the gas velocity based on the following equation:
practice equation 5(a)
  1. Calculate the cross-sectional area of stack (at exit).
    practice equation 5(1)

  2. Calculate the gas velocity.
    practice equation 5(2)

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Q icon #6
Calculate the stack exit velocity based on the emission test data and information provided below.
practice equation 6

A icon
Answer: 1,974 ft/min or 32.9 ft/sec
Solution:
Calculate the gas velocity based on the following equation:
practice equation 6(a)
  1. Convert the gas flow rate from ACFM to SCFM.
    practice equation 6(1)

  2. Calculate the cross-sectional area of stack (at exit).
    practice equation 6(2)

  3. Calculate the gas velocity.
    practice equation 6(3)

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Q icon #7
What is the average gas velocity in a duct based on the data provided below?
practice equation 7

A icon
Answer: 58.5 ft/sec
Solution:

practice equation 7(a)

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Velocity
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