From the foregoing historical review, many flowmeter technologies and designs have evolved in order to cover the vast number of applications. These range from flow of blood in small arteries to the flow in rivers and canals, from cryogenic liquids up to high temperature gases, and from below atmospheric pressure to conditions inside high-pressure industrial reactors. The operating conditions and applications often dictate the choice of technology. The table below summarizes the enormous range of operating parameters. These have been conveniently split into closed pipe and open channel applications.

“operating conditions” for flowmeters

In closed pipe lines

Flow rates                                                                           0.1 g/h to 5000 t/s (0.0002 lb/h to 5500 t/s)

Nominal diameters (pipe diameters)                      0.1 mm to 15 m (0.004 in to 50 ft)

Pressures                                                                            vaccum to 3000 bar (43500 psi)

Temperatures                                                                   -250 to +800 °C (-418 to 1470 °F)

Fluids (medium)                                                               liquids, gases, steam, fluid mixtures

In Open channels (channels, rivers, etc.)

Line sizes                                                                             50 mm (2 inch) to “river size”, ocean current and

point measurements

Temperatures                                                  normal ambient temperature

The two following illustrations give some indications of the flowmeters and metering methods in common use today. As indicated, most meters measure the volume of flow of the fluid velocity. Flowmeters in closed pipes – as opposed to open channels – constitute the majority of applications.

Flow measurement (in closed pipes) 70%

Fluids 65%, Gases/ mixtures 35%

Volume Flow Measurements

Direct method                   Positive Displacement

Indirect method               Differential Pressure, Variable area, Turbine, Vortex, Electromagneti,    Ultrasonic, Pitot tube, others

Mass Flow Measurements

Direct method                   Coriolis principle, Thermal principal, Weighing systems, Solid type meters

Indirect method               Multivariable type

Flow measurement (in open lines) 30%

Fluids 95%, Solids/slurries 5%

Flumes                 Parshall, Palmer-Bowlus,  Khafagi,  rectangular/ Trapezoidal ( with/without restrictions), Special flumes

Weirs                    Triangular (V shaped), rectangular/ Trapezoidal ( with/without restrictions)

Other methods Velocity- area method (current meter, ultrasonic), Level Measurement (Ultrasonic, DP, Float, etc..), Solid type meters.