Orifice Plate for Flow Measuring

Orifice plates are sooooo 1973. Go for a vortex-shedding unit instead from a reputable manufacturer (names withheld).

Selection is best done over the telephone with a Sales Engineer.

I wonder if someone could explain why a vortex shedding meter might be better than an orifice plate for the OP's situation.

Sales Engineers can, certainly, and they are on the other end of a phone.

Sorry, I should have mentioned that I am not the OP and I am not in the market for a device, but merely wishing to add to my general knowledge.

This website has something to say about vortex meters:

Vortex Meter Advantages
• Vortex meters can be used for liquids, gases and steam
• Low wear (relative to turbine flow meters)
• Relatively low cost of installation and maintenance
• Low sensitivity to variations in process conditions
• Stable long term accuracy and repeatability
• Applicable to a wide range of process temperatures
• Available for a wide variety of pipe sizes
Vortex Flow Meter Limitations
• Not suitable for very low flow rates

• Minimum length of straight pipe is required upstream and downstream of the vortex meter

So how does that list distinguish vortex flow meters from orifice flow meters?

As cited by PWslack, the following youtube video of Endress-Hausser might help you

• Vortex shedding
• Differential flow meter by orifice

See application

Orifice Plates are sized according to flow rate range being measured and type of fluid being measured.

You must go to your vendor of choice and review their offerings based on the application requirements.

If you have difficulty understanding all of the information and/or the requirements contact the applications group of your preferred vendor and they will be more than happy to help you so that you purchase their equipment.

If they are not willing to do so, simply go to a different vendor.

I have never experienced anything but good advice from any major instrument suppliers such as ABB, Siemens, Emerson-Rosemount, Endrus-Hauser, Vega.

Very good answer!

Thanks ,if I think there is an Equation by it that we can know size of orfice plate .

Yes, there is, and it can be looked up in any Process Engineering textbook [try "The Chemical Engineer's Handbook" by Perry, any edition]. However, it is not necessarily the optimal measuring technique for every situation, which is why a telephone discussion with equipment suppliers is essential before selecting the technique.

Technology moves on. Orifice plates don't.

There isn't just one equation. It depends on the flow regime (Reynolds No. etc) and can get quite complicated when dealing with compressible flow or steam. If you haven't got a feel for fluid properties, flow, energy etc you're likely to find it hard going.

One drawback of OP (or any DP generating meter) is DP varies as square of flow, so accuracy suffers if you have a big turndown. Another option for gas flow is thermal mass type, which also gives negligible pressure loss, and reads directly in normal, std etc flow units, no need to correct for actual pressure and temperature.

Not quite any DP meter. The Fleisch pneumotachograph (used in medicine and physiology to measure respiratory airflows) has a resistance element consisting of multiple small parallel tubes. The flow is almost laminar and the pressure-flow calibration curve is almost linear.

OK, but I doubt he had such a low-flow application in mind!