Orifice (2P) Parametrization and Control

Modeling option: Vapor operating condition

Orifice type: Variable

Opening characteristic: Linear

Problem: I do not know how to reconcile the concepts of physical signal S, control member travel, maximum orifice area, in order to understand the actual fraction of orifice area that is open given a value for S.

Questions:

1. Is S a physical signal between 0 and 1, no units (unit = 1)?
2. Is S = 0 associated with control member position at closed orifice and S = 1 to the fully open orifice?
3. Is the orifice assumed of "rectangular" cross section, thus orifice width = maximum orifice area / (control member travel + control member position at closed orifice)?

[Walter Roberson]

(Orfice 2P is documented at https://www.mathworks.com/help/hydro/ref/orifice2p.html )

Answer 1

[Yifeng Tang]

Hi @Rinaldo

Is S a physical signal between 0 and 1, no units (unit = 1)?

S is a position input, with a length unit (m, cm, mm, inch, etc.). Together with the travel between open and close, this S value defines an opening fraction of the maximum opening area or max nominal flowrate.

Is S = 0 associated with control member position at closed orifice and S = 1 to the fully open orifice?

That'll depend on the values in the highlighted boxes below. You may define where “closed” is and which direction of S changes will open the orifice. Again, it's usually not 0 and 1. The actual extreme values depends on the control member travel parameter.

Is the orifice assumed of "rectangular" cross section, thus orifice width = maximum orifice area / (control member travel + control member position at closed orifice)?

I don't think there is a "width" here. You may view it as a mapping between the control member (spool?) position to the orifice area.

Hope this helps.

Yifeng