Vena contracta in orifice plates

[DaiG]

Hi, does anybody know how to find the diameter of the vena contracta in gas/vapour flows in orifice plates?

 

[edgepflow]

This is given by the coefficient of contraction Cc = Area vena contracta / Area Orifice. The value is usually about 0.62 for a sharp edge orifice. These results may need correction for the compressibility of the fluid. To a first approximation, multiply Cc X Y where Y is the expansion factor.

 

[DaiG]

Yea, I am aware of this method but concern is with the coefficeint Cc. Usually an approximation would be good enough and 0.61 to 0.64 usually does the trick. My issue is I am trying to develop a method for calculating a value of noise in orifice plates. approximating Cc isn't a reliable method for me because my final decibel value is thrown substantially if certain process variable differ by 0.01 decimal places and the vena contracta velocity and area are troubled areas for me. Thanks anyway though.