Turbine flowmeter is velocity type flowmeter which shows a linear relationship with the flow of fluid in the stream. As it shows a linear relationship, there is no need of using square root extractor.
The turbine flowmeter uses a free spinning turbine wheel, which rotates as the fluid flow through the pipeline. The angular velocity of the turbine is directly proportional to the flow velocity of the fluid.
Construction & Working:
A turbine flowmeter consists of a free spinning multibladed rotor installed perpendicular to the flow of the fluid. The fundamental design goal of a turbine flowmeter is to make the turbine element as free-spinning as possible, so no torque will be required to sustain the turbine’s rotation.
As fluid got pass through the sharp edges of the blades the velocity of the fluid increases and pressure drops. As a result, the rotor floats in a balance between upstream and downstream cones, pushed forward by the pressure difference across the blades and pushed backwards by the flow impingement. Thus the rotor rotates.
Above figure is the cross-section of the turbine flowmeter. The blades start rotating at an angular speed, inside the pipeline. The magnetic pickoffs placed in the pipe body is the sensing element. As the paramagnetic blades cuts through the magnetic pickoff coil, its magnetic properties cause the magnetic field to deflect to accommodate its presence. This deflection causes to generate an irregular shaped voltage in the coil.
The frequency of the pulse generated is directly proportional to the angular velocity of the turbine and thus proportional to the flow speed of the stream.
Used in oil and gas wastewater, gas utility, chemical, power, food and beverage, aerospace, pharmaceutical, metals and mining, and pulp and paper industries.
The turbine flowmeter cannot be used in higher magnitude flow because premature bearing wear and/or damage can occur.Also cannot be used to measure very low flow rates due to rotor/bearing drag that slows the rotor.
Each electrical pulse generated is also proportional to a small incremental volume of flow.
Can operate in wide range of temperature and pressure
Easy to install, maintain and to calibrate
Only a low pressure is dropped across the turbine.
Require constant back pressure to prevent cavitation
Can not used to measure corrosive fluid, which will affect the blades
May does not work properly for laminar flow measurement, which has higher viscosity.
Very sensitive to fluid viscosity.