MKultistage Orifice Assembly

[zdarlight]

Hi all,

Currently reviewing a design of a multistage orifice assembly before we manufacture it.

We have always used a typical configuration which looks a little something like this.
concentric plate / eccentric plates with differing bore locations down the line / concentric plate.

The reason we have always done this is to prevent a jet from skipping a stage.
We are now about to manufature a three plate assembly which looks like this:
eccentric/concentric/eccentric
I myself see no problem with this configuration but some of my collegues are showing concern simply because this is not the way we have done it before.
I'm just after any thoughts or input that might be of use to me. Are there any implications with this design? etc.

 

[Latexman]

What's the separation between plates?

Good luck,
Latexman

 

[zdarlight]

42.85mm. 42.85mm pipe ID also.

 

[Latexman]

Our standard is 5 pipe IDs separation between plates. That allows the flow to mostly recover and you can use the same type plate side-by-side.

1 pipe ID does not allow for much recovery. Are you maintaining the different bore locations down the line? If you are, I think it should work as good as the previous configuration. If you are not, I'd do some testing.

Good luck,
Latexman

 

[zdarlight]

Hmm strange. Our understanding has always been to limit pressure recovery between stages hence the 1D plate spacings. Anyway thanks. I didn't think the new configuration would make any difference at all but try telling that to people who are set in thier ways!

 

[ione]

zdarlight,
I’m with you on your last post. The purpose of using multistage restrictions is that of getting considerable pressure drop without inducing cavitation or flashing phenomena. If each element is properly sized, why look for pressure recovery between plates?

Is your multistage orifice to be used with single-phase fluid?

 

[Latexman]

ione,

In the limit of that thinking, why not use zero separation, i.e. a 3X thick orice plate?

I would think if the vena contracta does not have time/separation to contract and expand, contract and expand, and contract and expand there will be less pressure drop, thus it'll be less efficient and more plates may be needed compared to more separation. This is probably like zdarlight explained as a jet skipping a stage (or not having to go through as torturous a path).

Does anyone know of some research on this?

Good luck,
Latexman

 

[zdarlight]

Yep, Hydrocarbon gas.

Sorry Latexman, what do you mean by a 3X thick orifice plate?

 

[Latexman]

Three 1X thick orifice plates with L/d=1 separation between them - the separation (no pressure recovery) = one 3X thick orice plate.

Not!

Good luck,
Latexman

 

[ione]

I start from the assumption that such a configuration, I do mean multistage orifices, is used to get a given pressure drop and not for metering purposes. Said that, I'd apply to multistage orifices in those cases where the pressure drop were too "demanding" to be reached in just one step. With the term "demanding" I do mean such a pressure drop that would lead to cavitation. If the same pressure drop could be attained in one stage without any drawback, this would be the way I'd go.
Latexman, with a 3x thick plate the fluid would anyway experience a pressure recovery, since the permanent pressure drop attainable is always lower than the peak pressure drop at the vena contracta, as the fluid expands thus reducing its velocity and increasing its pressure.