Multi hole orifice plate calculations

Hi, The pressure drop across a plate with 1 or more orifices will not be a linerar function of flow, unless the orifices are a bundle of tubes which will induce laminar flow (or something aproaching it).

More background information would be usefull...

What fluid, velocity, cross sectional area, plate thickness?

Why multi orifice. what application etc.

My guess is you can arive at a ball park figure, but you will need to make adjustments.

Hi, THanks for the prompt response.

The plate is to be used with 12" and 18" flanges; with a carbonate solutions flowing across it. The flow rate is of the order of 1030 m3/h. The DP to be obtained is about 45.4 barg and the vapor pressure is 10.1 barg. The operating temperature is 115 degc and specific gravity 1.2; with a viscosity of 0.548 cP.

I would need some reference in order for me to calculate the number of holes required, orifice dia, the pitch distance and element thickness. THe references I have are all for single orifice plates; and so far I am unable to find some design criteria for multihole orifices.

Appreciate the help on the matter.

Hi, getting outside my sphere of expertise here. (I used to design respiratory flow meters)

But the info will doubtless help others, I'd guess that as the flow will not be laminar you can treat a multi-hole plate as a bunch of individual holes, like resistors in parallel.

(I reserve the right to be wrong)

Del

Del, You are right the flow wont be linear across the plate since the flow profile will no doubt be parabolic unless the rate is so low that a flat front is possible. Then of course you would get boundry layer formation and the outer holes would be usless.

I think...

Exactly which parameter do you want to measure?Flow?Differential pressure?

In a single orifice plate, the differential pressure has a square root function to flow:ie:

50 percent DP equals 70.70 percent flow, etc.

The total DP and flow are derived from standard orifice plate calculations.

Why do you require multiple orifices?I have never seen this before.

Please explain your required need.

Thanks,

HTRN

Rosemount 1595 series conditioning orifice plate is a multibore device. The advantage of this plate is the short straight pipe requirements. See the Emerson Process Management / Rosemount catalog Flow Products 1595 for details.

Hope this helps.

Using multiple holes presents very little problem. Just treat each hole individually. The minor differences in the upstream and downstream conditions due to velocity because of the varying location of each orifice really won't matter all that much. If you can place them all at the same elevation (to keep the head the same on all orifices) you will cut down on the number of calculations you need.

You can have these orifices fabricated in any size you desire. Have a nicely rounded entrance to lower pressure loss. Setting up a spreadsheet to crunch numbers will eliminate the tedious repetition of finding "the perfect" size.

Ah, this implies single orifices in series each on it's own plate..

I was assuming 1 plate with many holes! ?

Which is the correct assumption?

Contrary to intuition, the orifice plates I have seen have a very sharp entry facing upstream to maximize the D/P across the orifice at a specific distance .The total pressure drop overall is very minimal.

I am curious as to why an orifice plate is the element of choice in this application. Have you considered other means , such as magnetic,vortex shedding,turbine,elbow, doppler, or segmented wedge?

The placement of the taps is somewhat important. I can see using a common upstream tap, but each of the holes may require it's own downstream tap, making for a much more complicated setup. What are your thoughts on this? Mike P.S. Why multiple holes?

Hi Amsats:

Go to CU Services LLC

Ramsey Cronfel can design these devices very quickly, provide CAD drawings and all calculations. His prices are great as well.

Hank

I have tested multi hole orifices in the laboratory. If you design the holes such that there is no separation at the inlet and the jet exiting the hole is the same diameter as the hole (no vena contracta) then the design is quite simple. Calculate the area of the vena contracta of the single hole orifice using its contraction coefficient and make the area of all holes equal to that area. To make this work the orifice plate needs to be something like 3/4" thick with 1 inch holes rounded at a 1" radius on the inlet side. If you use sharp edged holes and make the area of the many holes equal to the single hole the flow will be greater through the multi hole plate by about 20%, depending on the design.

See Idelchik's Handbook of Hydraulic Resistance for the full answer.

Now i am dealing with a multistage restriction orifice order for 3 different refineries. Proposals from many vendor companies are received but few of them calculate the RO properly. In our project CCR net gas pressure will drop from 30.3 kgf/cm2-g to 6 kgf/cm2 at flow of 941 kg/h ( 30º, 5.83 kg/m3, 2" 80 sch, 0.009 cp, 3.633 mol. mass, cp/cv:1.39 ), pipeline is 2" 80 sch. When we calculate it as different orifice plates, as you know in every plate density is changing but companies doesnt consider that. Mine and basic engineering companies calculation for the orifices are like that [ 14.142mm,18.822mm, 23.253mm ] and [ 11.45mm, 15.52mm, 20.54mm ] . Only a company from italy calculated it similar to our results.

hi i also agree with you...

Do you have experience with multihole orifice sizing calculation and noise level caluclation...

Currently i'm using flow consultant software, which has provision for single hole only..

Kindly advice me

Multi hole orifice plate Sieve

Here is a source for info you always wanted to know about multiple hole orifices but did not know where to start:

Start here:

https://www.wika.com/media/Data-sheets/Flow/Primary-flow-elements/ds_fl1015_en_co.pdf

This company can also design orifice plates to your specs and answer all of your questions about design.

Apart from it being unlikely the OP is still around, some of the data in #2 is very suspect.

As he says "The DP to be obtained..." presumably DP is differential pressure, ΔP. ΔP is in bar, not barg, and 45.4 bar is a huge figure, and unlikely.

Water at 115°C has vapour pressure about 1.7 bara, lower for a solution, so what is the 10.1 barg?

To give any help we'd need a lot more information on what he's trying to do.