# How to Calculate Air Flow Rate for a Cylindrical Vessel with Perimeter Holes?

• naboulsi
In summary, the conversation discusses the difficulty in calculating the required air flow for a cylindrical drum used to measure the accuracy of a vacuum machine. The vessel is made of steel and has a diameter of 22.5 inches and a height of 34.5 inches, with 50 holes measuring 13mm in diameter. The air flow rate is needed for a vacuum of 1" of H20 at a temperature of 70 degrees Fahrenheit and relative humidity of 26%. Based on the assumptions of steady state and a discharge coefficient of 0.7, the estimated flow rate is 280 SCFM, calculated using Bernoulli's equation. The use of this vessel as a calibration standard is questioned.
naboulsi
We are having trouble calculating a required ft^3 per minute air flow for a particular vessel which was constructed to measure the accuracy of a vacuum machine.
Our vessel is a steel cylindrical drum 1mm thick with a diameter of 22.5" and a height of 34.5". It has 50 holes around the lower perimeter measuring 13 mm in diameter. What is the air flow rate if we pull a vacuum of 1" of H20 at a temp of 70 deg. F and Relative Humidity of 26%. Can anyone help us out?

Hi naboulsi,
This probably belongs in the mechanical engineering forum. Anyway, assuming your system is maintaining 1" water vacuum, steady state, and assuming a discharge coefficient for your drilled holes of roughly 0.7 (from experience) I'd estimate your flow rate to be 280 SCFM.

The way to calculate it is to use Bernoulli's equation: assuming perfect nozzles, that 1" of static pressure becomes your velocity pressure.

That is a pretty poor sounding calibration standard.

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