A flow nozzle consists of a restriction with an elliptical contour approach section that terminates in a cylindrical throat section. Pressure drop between the locations one pipe diameter upstream and one-half pipe diameter downstream is measured.
Flow nozzles provide an intermediate pressure drop between orifice plates and venturi tubes; also, they are applicable to some slurry systems that would be otherwise difficult to measure.
The flow calculations for the long radius nozzle are similar to that of the orifice plate, with the exception of the values of the discharge coefficient.
The following table shows some standard values for this value.
Credits - Mitchell Cottrell