Finding the diameter of the vena contracta in gas or vapor flows through orifice plates involves using the coefficient of contraction (Cc), typically around 0.62 for sharp edge orifices. Corrections may be necessary for fluid compressibility, often calculated by multiplying Cc by an expansion factor (Y). While approximations of Cc between 0.61 and 0.64 are common, they may not suffice for precise calculations. The discussion highlights concerns about how small variations in process variables can significantly impact noise calculations in orifice plates. Accurate determination of vena contracta velocity and area is crucial for reliable decibel values.