from the Automation List department...
Orifice beta ratio
 Posted by surendar on 19 September, 2007 - 1:03 am
Can anybody tell what is the practical significance of orifice beta ratio between 0.3 to 0.7? What will happen if beta ration goes below 0.3 or goes above 0.7?

 Posted by Rohit Chandak on 19 September, 2007 - 10:38 pm
Beta Ratio is the ratio between the line inner diameter to bore size of the orifice. The flow coefficient is found to be stable between beta ratio of 0.2 to 0.7 below which the uncertainity in flow measurement increases.

 Posted by A.K.Hait on 20 September, 2007 - 10:39 pm
Interesting question. I don't have all the books and material at hand now to give a very detailed answer. However, I will try to throw some light on it off my head.
1. Orifice plate flow calculation formula is basically based on empirical formulas based on actual testing. Most of the results are available for beta ratio 0.3 to 0.7.
2. Low beta ratio means the plate has a smaller hole i.e pressure loss will be higher. This may cause higher size of pump and more money.
3. Higher beta ratio increases the discharge coefficient uncertainty. Higher beta ratio means low differential pressure across your orifice and some times may be difficult to measure.
4. Higher beta ratio needs longer staright length.

I remember long time back when we used to do manual calculations of orifice plate bore as per BS 1042, we always tried to keep the beta ratio approx. 0.6. Because near to o.6 beta ratio the discharge point curve is almost flat, so that even if there is some mistakes in your manual calculation, overall accuracy is not affected.

Hope this helps a little!

 Posted by surendar on 23 September, 2007 - 7:34 pm

 Posted by Jeff on 14 October, 2010 - 9:56 am
How do you carry out a manual calculation?

 Posted by David on 16 October, 2010 - 11:18 am
>How do you carry out a manual calculation?

pencil and paper; sliderule.

It's almost a lost art :')

 Posted by Steve Myres on 16 October, 2010 - 1:00 pm
"How do you carry out a manual calculation"

Well, when the manual calculation has had too much to drink, you and a buddy each place one of the calc's arms over your shoulders and lift....

 Posted by Mr Scott on 17 November, 2010 - 11:27 pm
> How do you carry out a manual calculation? <

A useful device, (also inexpensive, about 20 bucks) called a "Sonny" can be purchased from a few online vendors. It is a circular chart with 4 or 5 rotating discs printed on flat plastic discs. Each disc you turn has measured indicators on it and you basically plug in your data by turning the corresponding disc. Once you've used it for a while, it'll become second nature, but please note your flow rate won't come out to pinpoint accuracy, 1 or 2 psi off because of the circle chart getting smaller in the centre making it slightly more difficult to be accurate. Anyhow, this manual calculation will take you 50 seconds to complete, and you'll be the only one who can save the day.

 Posted by Mr. Zack on 17 February, 2011 - 6:31 am
> How do you carry out a manual calculation?

What should I do If my Restriction orifice calculation result is low beta ratio (i.e. 0.1) based on required dP. Note: pressure loss required is fixed. please help.

 Posted by ken on 13 September, 2011 - 5:34 pm
I am having the same problem.I am using miller to calculate and got beta ratio 0.08.

What will happen if i still design my RO with 0.08 beta ratio result?

 Posted by Syukri on 28 December, 2011 - 10:32 pm
Ken & Zack,

For restriction orifice the limit is the noise generated and vibrations.

We can go to 0.1 beta ratio if the noise is less than 85 dB

 Posted by Austin on 6 June, 2012 - 5:00 pm
> Can anybody tell what is the practical significance of orifice beta ratio
> between 0.3 to 0.7? What will happen if beta ration goes below 0.3 or goes above 0.7?

Any higher or lower results in too much uncertainty in measurement. For complete calculations and maximum allowable errors, consult the American Gas Association Report No.3 Part 2 "Orifice Metering of Natural Gas and other Related Hydrocarbon Fluids-Specification and Installation Requirements". That is, assuming this is in relation to a hydrocarbon orifice meter.

 Posted by David Todd on 8 June, 2012 - 12:35 pm
The Beta ratio which you refer to is probably for a Square Edge plate wih flange taps and refers to the allowable Beta limits for the calculation of the orifice size. The Beta limits for the square edge flange taps plate are 0.2 to 0.7 (this may vary slightly depending upon which standard calculation method which you are using). The empirical sizing calculation formulae were determined for the above range of beta. Outside of this limit the formulae are inaccurate and unknown with any certainty. There are a number of different types of orifice plate types available and each type has its own beta limits.
For example square edge corner taps (beta limits are 0.23 to 0.8), Square edge radius taps (beta limits 0.2 to 0.75), Quarter Circle (beta limits 0.25 to 0.6), Conical Entrance (beta limits 0.1 to 0.316).
For Restriction Orifice sizing minimum beta is 0.1 and the maximum beta is not critical.

 Posted by Ray on 10 October, 2012 - 6:33 am
Nice job man

 Posted by Bill on 19 October, 2012 - 2:58 pm
Typically, with an orifice computer program designed for sharp edge orifice plates. I play around with the flow and pressure differential to give me a beta ratio of ~.61. Given a fixed pipe size that you are installing the orifice plate in, determine a maximum flowrate that won't be exceeded. then play around with the differential (usually in inches of water, "WC) to give you a beta between .55 and .70. Typical differentials used are 100 inches and 200 inches.

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