A liquid flow meter is a device used to measure the volumetric, mass, nonlinear and linear flow rate of a liquid. The flow rate is calculated by measuring the liquid’s velocity. There are many types of liquid flow meters. The type selected will depend on the application and type of liquid. The nature of the fluid and the installation will impact the type of liquid flow meter selected.
Applications of Liquid Flow Meters
There are five types of liquid flow meters: Differential Pressure, Velocity, Positive Displacement, Mass and Open Channel.
Differential Pressure Flow Meters
Examples of differential pressure flow meters include venture tubes, orifice plates, flow nozzles, elbow-tap meters, pilot tubes, variable area meters and target meters.
Differential pressure flow meters are most commonly used to determine a liquid’s flow rate. Nearly 50% of the world’s flow meters consist of this type. They operate on the principle that when the pressure drops across the flow meter, it proportional to the square number of the flow rate. To determine the flow rate, the pressure differential is measured and then the square root is taken.
Differential pressure flow meters have a primary and secondary part. The primary part causes a change in movement energy, adding to the differential pressure within the pipe. The secondary part calculates the pressure differential and gives the signal read-out which is converted to the flow value.
Velocity Flow Meters
Examples of velocity flow meters include turbine, vortex shedding, swirl, Conada Effect & Momentum Exchange, electromagnetic, ultrasonic, Doppler and Transit time.
In a velocity flow meter, flow is determined by measuring the speed at more than one flow point and then integrating the speed over the entire flow area.
Turbine flow meters are used in petroleum pipelines. They detect leaks along the pipeline. Turbine meters are also used to load light hydrocarbon products into rail cars and road tankers. They also meter chemicals, fuel and water used in oil drilling processes.
Positive Displacement Flow Meters
Examples of positive displacement flow meters include reciprocating piston, oval gear, nutatingdisk and rotary vane.
In a positive displacement flow meter, fluid flow is measured by precisely fitted rotors. Fixed and known volumes are shifted between the rotors. The spinning of the rotors is proportional to the volume of the displaced fluid. The amount of rotations is counted by an integral electronic pulse transmitter. This information is then converted into flow rate and volume.
Positive displacement flow meter are used to measure the flow rate of fluids such as polymer additives, lubrication oils, heating oils, vegetable and animal fat, printing ink and dichlorodifluoromethane R-12.
Mass Flow Meters
Examples of mass flow meters include Coriolis and thermal. Of the two types, the Coriolis meter is the most used. They were developed in response to the need for higher accuracy levels in flow measurement of mass related processes such as heat transfers and chemical reactions.
Mass flow meters are used in pharmaceuticals, mining, power industries and in waste water.
Open Channel Flow Meters
The Weir and Flume are two types of open channel flow meters.
Open channel refers to any area within which the liquid flows. Examples include non-pressurized sewers, tunnels, canals, rivers and streams. To monitor open-channel flows, depth-related methods are frequently used. The instantaneous flow rate can be calculated by measuring the depth of the water.
Liquid flow meters play an integral role in industrial applications. The type chosen will depend on the application.