Hello,

I was wondering if someone could point me at a good website or article compering the affect that the Beta Value of an orifice plate or flow nozzle has on the % output of the instrument signal. it is for a lab report for my process instrumentation class.

Thanks alot,

Lee

 

Hello Lee,
First some clarifation:- Comparing the three devices that you talked about;provided that the orifice plate, the flow nozzle and the venturi all have the same beta ratio then the orifice will produce the highest differential pressure followed by the nozzle and then the venturi. This assumes that they are all subjected to the exact same conditions.

As far as the orifice goes; the ones will the smallest beta value will produce the highest differential pressure and the larger beta produces the smaller differential pressure (assuming the flowrate for the two is the same). This is because the smaller the orifice the greater the velocity of the fluid must be to pass through it...this in turn gives you the higher differential pressure (bernoulli's equation).

Suggested sources for information; "The americal society of mechanical engineers handbook", Omega.com "Flow & level handbook", Bela Liptak "Flow measurement" CRC press, ISA publications.

Hope this helps,
M.E.

> Hello,
>
> I was wondering if someone could point me at a good website or article compering the affect that the Beta Value of an orifice plate or flow nozzle has on the % output of the instrument signal. it is for a lab report for my process instrumentation class.
>
> Thanks alot,
>
> Lee

 

I can't vouch for the accuracy of the calculations but here's a web site that I've used for preliminary / ballpark orifice sizing.

http://www.fastlink.com.au/~jeffdare/calc/orifice.html

I think you can view the source for the page and figure out the algorithm being used. I don't know how well it does at extreme values of beta.

Caveats:
-there is no direct input of beta
-it only gives you flow at a specified pressure drop, or possibly pressure drop at a specified flow. I haven't tried to create a curve of values across a flow range to see how it performs.

~Steve