Calculate orifice

[p3sx0s]

Hello,

I am a new designer and I was trying to figure out how to calculate the diameter of a restrictive orifice so that I get certain flow from a system.

Thanks

 

[Latexman]

What is your question? Please be specific.

Good luck,
Latexman

 

[p3sx0s]

I'll try to explain better,

To my understanding, an orifice can restrict the flow, therefore reduce the flow rate. I want to know what should the diameter of the orifice be compared to the pipe, to result the desired flow rate.

Hope it is clear now

Thanx

 

[Latexman]

I recommend you read your old fluid flow text book and Perry's Handbook, buy Crane's Technical Paper 410, and use Google to search the internet.

Good luck,
Latexman

 

[25362]

The Chemical Engineering issue of August 17, 1987, under the heading of Plant Notebook brings an article (with example) titled Quick sizing of restrictive orifices by Herman E. Waisvisz.

 

[chief]

Flow(gpm)=Fluid Velocity(ft/sec) x Orifice ID.inches (squared)/ 0.408

Offshore Engineering&Design

 

[mbeychok]

p3sx0s:

You didn't tell us if your flow is gas or liquid. That makes a big difference.

If it is a gas, then the upstream and downstream pressures define whether the flow rate is "choked" or "non-choked".

Read this Wikipedia article to learn how to determine if the flow is choked or non-choked, and how to calculate the choked flow rate for a given diameter of the hole in the orifice plate:

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

If the flow is non-choked, then read this Wikipedia article to learn how to calculate the non-choked flow rate for a given diameter of the hole in the orifice plate:

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

Equation 5 in the Orifice plate article is the final derived equation for non-choked flow.

Both article include references in the technical literature, if you are interested in them.



Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[JoeWong88]

p3sx0s:

General question like this can draw attention of many Jedies (Latexman, Milton, 25363). You are so lucky.

Read more in previous thread...Sizing of orifice?

and

Try FLOWSOLV out of many to back check your manual calculation.

JoeWong

 

[p3sx0s]

Guys, thanx for the support,

Seems that the problem is more complex than i thought, though i've reached to a methodology:

1. Look up pump’s head at existing flow rate (from the pump’s Head-Flow rate chart)

2. From the same chart, find pressure drop (which will be caused by the orifice) for the desired, reduced flow rate (from the requested flow, look up bigger head and calculate the difference from the first value)

3. Assume an orifice diameter

4. Check if differential at selected orifice agrees with the experimental from calculator (i.e.

http://www.pressure-drop.com)

Sounds ok to me,

Thanx again for the info

 

[Latexman]

On #4, be sure you calculate and use the "permanent pressure loss" of the orifice. A lot of references give flow coefficients for the differential pressure from 1 pipe diameter upstream to 1/2 pipe diameter downstream of the orifice, which is useful when sizing an orifice meter, but it's not the end result you need when sizing a restriction orifice. My Perry's 6th Ed. speaks to this on page 5-16.

Good luck,
Latexman