The point where the fluid flow profile constricts to a minimum cross-sectional area after flowing
through the orifice is called the vena contracta, and it is the area of minimum fluid pressure. The
vena contracta corresponds to the narrow throat of a venturi tube. The precise location of the vena
contracta for an orifice plate installation will vary with flow rate, and also with the beta ratio (β) of
the orifice plate, defined as the ratio of bore diameter (d) to inside pipe diameter (D)