Orifice Plate Design Formula Needed

Are we talking human breath measurement or oil delivery pipeline?

The two are rather different...!

Hi ,

It is gas flow line , for measurement of Natural gas flow.

Regards ,

Voltamps

Right...you will see from that Wiki reference that the relationship between flow and pressure drop isn't simple and certainly not linear.

If you want a simple linear pressure flow relationship you need to look at a variable orifice. e.g Imagine a circular disc with a slits in it forming a cross this will give 4 'flaps' which will open up progressively with flow giving a more linear relationship.

There is also the fleisch tube which gives a more linear relationship by inducing laminar flow, these are used extensively in pulmonary function measurement.

Dunno if they make 'em in the size/flows you would need.....not hard to make.

Basically you have a choice..Simple orifice complex maths. or complex orifice simple maths.

Making your own variable orifice is fun (if you are getting paid for it!)

Have fun...

Del

http://en.wikipedia.org/wiki/Orifice_plate

Wikipedia spoils all the fun of having accumulated reference material over years(books, notes etc).

Technology deprived persons like myself usually forget about the wonders of wikipedia as a source of information.

In this case it would have been a big task to retype the formula in an correct and understandable format - the √ is a bit limited.

There are a few parameters for orifice plates that need to be defined first.

The following link will work for an orifice inside a pipe.

http://www.efunda.com/formulae/fluids/calc_orifice_flowmeter.cfm

If the orifice is a hole in a tank then the coefficients are different.

If the fluid is compressible then there's a whole new set.

You will need a text book or handbook to look up the coefficients for your case.

Thanks alot.

The software site given is excellent and will help me alot with selecting orifices for flow measurements for steam/gas/water.

Thanks again.

I would recommend the Crane formula (pg. 3-24) from Tech. paper 410. It usually takes a few iterations to get the diameter correct. Remember that the turndown of an orifice isn't that great (I have seen that greater than 4:1 will start to read inaccurately). Also, to convert into mass or molar flows, you will need an accurate flowing density that you can either calculate or measure with a densitometer. Since you probably know the general composition of the fluid (natural gas), the density is a function of pressure and temperature that you can probably get close enough to with an ideal gas ratio. Unless this is a billing quality meter, that should get you pretty close to accurate.

"Flow measurement" by Spink. Go to this book. It is a very good source for the subject. There is not an easy formula, as I know.

SaC.