How to distinguish orifice flowmeters, nozzle flowmeters and Venturi tube?
Measurement of the flow rates of liquids, gases and vapors with orifice meters has found wide use both in industrial and in scientific measurements. A restriction fulfilling the function of a primary converter, is installed in a pipeline and produces in it a local change of a flow section. The method depends upon the fact that an increase in velocity and kinetic energy of the flow behind the restriction as compared with the parameters upstream of it, brings about a decrease in a static pressure pout downstream of the restriction with respect to the pressure pin upstream of it.
The most widely used standard restrictions are orifice flowmeters, nozzle flowmeters and Venturi tube. The orifice flowmeter is a thin disk with a hole with diameter d and area S, located in line with the pipeline whose diameter is D. The nozzle flowmeter is made in the form of an insert with an orifice smoothly contracting at the inlet and ending with a cylindrical part. The nozzle flowmeter profile allows us to realize a smooth compression of a jet up to its minimum section, which ensures less overall loss of pressure than in the case of the orifice plate. The Venturi tube has losses of pressure of all the restrictions due to the installation of a diffusor at the outlet, which recovers the pressure.