Venturi flow nozzle

There is another modification of the variable differential pressure technique for flowrate measurements. This technique employs a Venturi flow nozzle, which is shown schematically in Fig. 6.4. 


The Venturi flow nozzle is installed in pipes with internal diameter varying from 65 to 500 mm. It produces a large differential pressure with a minimum loss of static pressure. This nozzle is able to measure flowrates of fluids with suspended solids. However, Venturi flow nozzles are very expensive. It consists of three parts: a profiled inlet 1, a cylindrical throat 2, and a conical outlet 3. A pipes 4 and 5 are connected to the inlet and outlet of the Venturi flow nozzle. The nozzle may be long and short. In the first case the biggest diameter of the outlet cone D_c^max is equal to the internal diameter of the pipe  D_p, in the second case it is less than D_p. The restriction diameter of Venturi flow nozzles D_n ³ 15 mm. The differential pressure is measured as in the case for orifice flowmeters with the only difference, that the downstream pressure in the cylindrical throat is sensed through radially drilled holes 6.

Figure 6.4. Venturi flow nozzle.

Article Source:: Dr. Alexander Badalyan, University of South Australia