Perforated Pipe Calculations

[frogzlife]

Hi there, I would like to know how to show the flow distribution across a perforated pipe. The pipe is as follows:

____ __ __ __ __ __ __ ____

--> <--
___________________________

The flow enters at both ends at different pressures and the holes vary in size (i.e. larger in the middle and smaller towards the ends to obtain an even flow distribution)

My problem is looking to find the flow rates through the holes as they feed gas to a combustion system. The pressure of gas at both ends is known and the inlet flow rate is known.
any guidance is greatly appreciated.
Thanks!

 

[JStephen]

For starters, I'd use the flow rate in the pipe and calculate pressure drop along the length. If it's not significant, then just assume all the pipe is at the same pressure and make all the holes the same size.

If that won't hold, you could work up a spreadsheet for the case. If you know the pressure at a hole, calculate outflow from that hole, deduct it from total flow rate, and that's the flow remaining in the pipe. Use that flow rate to calculate pressure drop down to the next hole and repeat. You might have to adjust flow rates back and forth to make it zero at the center.

This would still be approximate for various reasons- the cross flow out the holes isn't the flow pattern assumed in the pipe friction tabulations, for example.