I need few practical ideas to measure the pressure drop across each .04 inch diameter hole.
Hello Sir,
I need few practical ideas to measure the pressure drop across each .04 inch diameter hole which is arranged in a honeycomb structure on a 300mm diameter aluminum (6061-T6) plate which is 10mm thick. The hole profile is a bit complex as shown in the attachment.
The requirement is to measrue pressure drop across each hole in shortest time possible.
Thanks,
Paul.
How many holes are there and what is spacing on the holes?
Interesting you have mixed your units. Are you sure that the holes are 0.040″ diameter and not 0.03937″ or 1mm diameter? (Sorry had to ask that question – Beware of crashing into Mars)
Is there are specific reason why you need to measure the individual pressure drop across each of the holes and not simply look at the pressure drop across the entire orifice plate?
Niel
Jerome:
Yes, a U-tube or other manometer system would allow you to measure the net pressure drip across the entire plate, but as I understand the challenge as posted Paul believes that he needs to measure the pressure drop across each of the holes.
If the holes are very close to each other this may be impossible and as you stated all you need to do is use a single point on each side of the orifice plate to determine what is happening.
If the holes are widely space. I am thinking tens of diameters then you may be able to get some information about how the individual orifices are performing.
Niel
hey paul, is this a test fixture for random or one time use? or a product to be sold and used regularly? eg. quick connect and removal….
what is the base or sustaining pressure?
is this above or below ATM? which leads into; gage units or absolute?
if you are checking vacuum, you may need to be more concerned with how to seal the unit adequately, as this can be very important in your readings.
what kind of resolution is required?
how much time is allowed for the test or cycle?
you can perform a pressure decay test which could compare the differential pressures involved. it would probably yield the fastest indication of leakage and might have more useful info resulting from the test.
Right you are Neil. I didn’t read the whole question and still can’t find the attachment showing the structure in more detail.
Still I’ll have another go at it. I’ll assume that the plate is installed in a pipe and that air or some other gas is made to flow through the pipe and also that the holes are all the same diameter. The holes themselves act as pipes because of the large length to diameter ratio, 10 to .04 mm. In that case If the flow rate is low enough for laminar flow, poiseuille’s equation holds,
P2-P1=F*L*128*n/Pi*D^4,
where F is the flow rate in cc per second, L is the length of the hole in cm, D is the diameter of the hole in cm and n is the viscosity in CGS units and P2-P1 is the pressure drop across the hole in dynes per square cm. (from a dated book which doesn’t use MKS units) The restriction to flow of the large pipe itself is negligible compared to that of the holes because of the 4th power dependence on diameter, so the pressure profile across the large pipe is nearly constant and the pressure drops across each of the small holes are equal. Now all that is needed is a measurement of the flow rate through the large pipe. Divide that measurement by the number of holes and insert it in F in poiseuille’s formula and solve for the pressure drop. The large pipe flow rate can be measured with various commercial flowmeters and might not be too easy to implement without affecting the flow through the large pipe. How is the flow measured now? That determines the pressure drop.
If the flow through the holes is not laminar but turbulent the pressure will vary greatly in the discharge region of the holes and the “pressure drop across the hole” is probably not meaningful. I’ve used this formula before with mixed results. The flow rate has to be very small to get valid results. There is a large transition region between laminar and turbulent flow. Well that’s my best shot.
If the orifice plate is installed in a tube with gas or air flowing through it, a simple way of measuring the pressure drop across it is to connect a U tube manometer (a piece of glass tubing bent into the shape of a U) filled with dyed water (or mercury depending on the pressure drop) to nipples on either side of the orifice so that the pressure on each side is communicated to each leg on the manometer. If the pressure drop is greater than a few feet of water or mercury a commercial differential pressure gauge based on a capsule or bourdon tube would be needed instead of the manometer. To convert inches of water or mercury to PSI, measure the height difference between the two legs calculate the weight of liquid corresponding to that difference and divide by the cross sectional area of the manometer tube.
