Does valve discharge coefficient vary?

[456LachTray]

Hi,

I am building a mathematical model for a two tanks system (as can be seen in the attachment)which can operate either as non-interacting (when h2 < H) or interacting system (when h2 > H).

In order to do so I need to determine the discharge coefficient of the valve connecting two vessels B1 and B2. This valve is fixed at a certain opening in any cases, be it non-interacting or interacting.

My question is whether the valve discharge coefficient in the above mentioned cases (non-interacting and interacting) are constant or different? In other words, does coupling effect between two tanks have impact on the discharge coefficient of the valve connecting two tanks ?

Can anyone help me?

Thank you very much in advance,

BR,

 

[gerhardl]

Your attachment is not popping up on my PC, but:

From the common definition of Kv (and Cv) for instance by link

http://www.duncanrogers.com/tools/valve-flow.asp,

you will see by definition that the valve discharge coefficient by definition is, and is meant to be a constant.

You could add to the definitions that this measured (not calculated) value is valid only for flow from port 1 to port 2.

Also note that Kvs (Cvs)is defined as a special case of Kv : the 'Kv' of the valve in a given (defined) position.

For 'non symmetric' valves (flowpath/valve have different form in opposite direction), the value have to be measured separately for flow from 2 to 1.

Same goes for the total flowpath: if non-symmetric (different length of piping before obstructions or different placement or form of other flow components than valves) you will, at least theoretically have some difference.

If the difference is large enough in both cases (valve and total flowpath) to influence your results, is quite another thing.

Hope this will help.