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

[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?

 

[Q_Goest]

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.

 

[russ_watters]

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

 

[FredGarvin]

That is a pretty poor sounding calibration standard.