Vortex Flow Meters

Question 1

Explain the principle of operation of vortex shedding flow meters.

Answer 1

Vortex meters use turbulence of flow that is created when the process passes through a solid object (bluff body) in the body of the flow meter. The bluff body creates vortices which are detected and are reported as flow.

Question 2

What is the approximate Strouhal’s number for fluids with an Re greater than 20000.

Answer 2

0.17 St

Question 3

What parameter sets the minimum flow rate for vortex flow meters? What parameter sets the
maximum flow rate?

Answer 3

Minimum flowrate: depends on the Reynold’s number (has to be greater than 10 000)

Maximum flowrate: depends on maximum allowable pressure loss

Question 4

List the vortex detector methods that are used by Vortex Flow Devices.

Answer 4

1) Differential Pressure sensor downstream of the bluff body: the frequency of the alternating pressure signal is directly proportional to the fluid velocity
2) Ultrasonic transmitter downstream of bluff body
3) Thermistor sensors: as velocity increases on one side of the shedder bar the heated thermistor cools, the change in temperature is recognized as a vortex
4) Cantilevered strut: detects force generated by passing vortices

Question 5

List the advantages of vortex meters.

Answer 5

1) Frequency output is linear to flow rate
2) No moving or wearing components
3) Can safely handle hazardous or toxic processes
4) Measurement does not rely on pressure, density, or temperature as long as Reynold’s number is above 20 000
5) Pressure loss is a function of the shedder bar size

Question 6

List the disadvantages of vortex meters.

Answer 6

1) Low K-factor creates a lower resolution than turbine flow meters
2) Can not measure low flows or high viscosity fluids
3) Not bi-directional
4) Has to be constructed in a pipe more than 1/2 inch and less than 16 inch in diameter to work properly

Question 7

What are some applications of vortex meters?

Answer 7

1) Clean liquids or gasses including superheated steam
2) Slightly dirty fluids

Question 8

Explain how to reduce the amount of straight pipe required before a vortex shedding flow
meter and how this reduction tool works

Answer 8

Install a flow conditioner which will develop the flow profile.