Pressure Drop Across Multi-Orifice Plate in Turbulent Airflow

[robram]

I wish to simulate the pressure drop of air going through a filter by the use of a multi-orifice plate. There are a number of flow rates that can exist but the pressure drop must stay the same for each of the flow rates. I need to know what total area of holes in the plate, is required for the different flow rates in order to achieve the same pressure drop. It is has been proven by test, that a plate with a certain area of holes, achieves the correct pressure drop for one particular flow rate. If the flow rate is doubled, is it likely that doubling the area of holes in the plate will achieve the same pressure drop?

I just need to gain a feel for what is going on, a rough rule of thumb or something, as the plates are going to be tested anyway. Is it likely that in assuming the above question (If the flow rate is doubled, is it likely that… etc. ) is true, I will have to close off some of the holes (decrease the hole area) or make new holes (increase the hole area)

The flow is turbulent air. To give you a rough idea of the figures; the pressure drop required is 1350Pa (plus or minus 100 or so), the flow rate is multiples of 0.25 m3/s. A hole area of 0.00573 sq.m has achieved the pressure drop of 1350 Pa with 0.25 m3/s proven by test.

I apologise for the long-winded nature of this question.
Many thanks for taking the time to read.

 

[fredt]

Pressure drop is proportional to the square of the volumetric flow and inversely proportional to the square of the area. This means that if you double the flow you will need to approximately double the open area for the same pressure drop.

Depending on the scale of the device, the best way to go is to use commercially available perforated plate that comes in different area ratios. These can also be stacked together to tune the resistance for different flows.

 

[robram]

Thank you very much for your answer.

 

[ShaunE]

robram

wouldn't it be easier to fit a damper in the line to give easily controllable pressure drop? You could put a pressure tapping either side of the valve / damper to attach a manometer or similar.

 

[arto]

Look in the Industrial Perforators Handbook, page 26:

http://www.iperf.org/IPRF_DES.pdf

 

[robram]

Thanks very much for all your replies,

ShaunE,

I'm not totally familiar with the problem, and am asking the question on behalf of someone else; but I know that the pressure drop doesn't need to be controlled, as the different flow rates occur in discrete situations.

Cheers for your advice, though.

 

[siretb]

You may consider the following equation
pressure drop (Pa) = rho*u^2*[0.707*sqrt(1-vf)+(1-vf)]^2/vf^2/2
wher u is the front velocity (m/s) before the mesh or plate and vf is the void fraction
rho is the gas density kg/m3
It applies for high Reynolds Number

 

[packdad]

I agree with ShaunE. If all you care about is simulating the flow and pressure drop across the element, why not instrument a damper/valve? Seems like that would make life much easier. Is that really all you are trying to do? Or are you (or whoever) going to be using these plates somewhere else after the test?