Suction velocity of different vacuum heads

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SUMMARY

The discussion focuses on calculating the suction velocity of a dust collection system featuring four vacuum slots, each measuring 27 inches by 1 inch. Pressure measurements taken with a manometer at two points indicated a pressure of 1.1 inwc, translating to a velocity of approximately 4250 ft/min. The user seeks to understand how changes in cross-sectional area affect suction velocity, specifically whether reducing the area from a rectangular slot to a circular opening increases suction velocity or decreases flow. The conclusion drawn is that while velocity remains constant across ducts, the relationship between area and velocity must be carefully analyzed using the flow rate equation Q = A*V.

PREREQUISITES
  • Understanding of fluid dynamics principles, particularly Bernoulli's equation.
  • Familiarity with manometer usage for pressure measurement.
  • Knowledge of flow rate calculations using the equation Q = A*V.
  • Basic concepts of duct design and airflow characteristics.
NEXT STEPS
  • Research the impact of cross-sectional area changes on airflow using the Continuity Equation.
  • Learn about the principles of suction and pressure drop in duct systems.
  • Explore the effects of different vacuum head designs on suction performance.
  • Investigate the use of Computational Fluid Dynamics (CFD) software for simulating airflow in duct systems.
USEFUL FOR

This discussion is beneficial for mechanical engineers, HVAC professionals, and anyone involved in designing or optimizing dust collection systems and airflow dynamics.

APalmer80
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I've been trying calculate the capacity of one of our dust collection systems. It features four vacuum slots lined up (27 inches by 1 inch each) shown as #3 on the diagram attached.

Using a manometer, I took pressure measurements at points #1 and #2. Both were around 1.1 inwc, which translates to about 4250 ft/min. The pipe diameter at #1 is one foot, the pipe diameter at #2 is 8 inches.

I am trying to calculate the suction velocity at a distance x from the vacuum heads. I've been trying to wrap my head around finding this value. I know that my flow rate is: Q = A*V, and that the capacity Q1 in the #1 pipe should be the summation of the capacity of the four openings.

Is velocity going to change as you decrease the cross sectional area of the pipe? According to my measurements, it looks like velocity is staying constant in all ducts. Then the question becomes, is the air velocity at point #1 equal to the velocity at the opening at #3? Or are you increasing the air suction in ft/min as you decrease the area of the opening?

I appreciate any help in advance, thanks.
 

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So to clarify, if I change the vacuum opening from a long rectangle slot of a single 1 inch circle, does the suction velocity increase, or does the flow decrease?
 

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