A liquid flow meter is an instrument that you can use to measure the mass, volumetric, linear, and nonlinear liquids’ flow rate. You need to measure the velocity of the fluid to calculate its flow rate. There are various liquid flow meter types. The type of liquid and your application will determine which liquid flow meter to use. Also, the installation and the fluid nature determine which liquid flow meter to use.
Types, functions, and applications of liquid flow meters
As we have mentioned overhead, there are five major liquid flow meter types available in the market. We will discuss each of them, their function, and the type of application. The liquid flow meter types include:
Differential pressure flow meters
Examples of the differential pressure flow meters are; flow nozzles, venturi tubes, orifice plates, variable area meters, pilot tubes, etc. They are usually essential for measuring the flow rate of a liquid.
The principle of operation states that when there is a drop in pressure across the flow meter, it will always be proportional to the flow rate square value. To determine the flow rate, you need to measure the differential pressure and find its square root.
The primary parts of a differential pressure flow meter cause a movement energy change. In contrast, the secondary parts help calculate the pressure differential and give out the signal readout, which you can convert to the flow value.
Mass flowmeters
Good examples of mass flow meters are thermal and Coriolis. Many people usually use Coriolis flow liquid flow metering rather than a thermal mass flow meter. They came due to the need to get high accurate measurement results on the processes based on mass. For instance, chemical reactions and heat transfers.
Applications of mass flow meters include wastewater industries, pharmaceutical industries, power industries, and mining industries.
Velocity flowmeters
These liquid flow meter types determine the flow by measuring the speed higher than one flow point and integrating the rate in the whole flow area. Examples include; vortex shedding, turbine, electromagnetic, ultrasonic flow meter, momentum change, etc.
Turbine flow meters are essential in petroleum pipelines. Where you can use them to detect leakage in the pipes, they are also applicable in metering fuel, chemicals, and water, which helps in drilling the oil. Another critical application is that turbine meters help load light hydrocarbon products in road tankers and rail cars.
Open channel flowmeters
Open channel flow meters come in two types: flume and Weir. The definition of an open area is a region within which the liquid moves or flows. The regions may be like; rivers, tunnels, streams, canals, non-pressurized sewers, etc. You need to use depth-related methods in monitoring open channel flows frequently. You can then measure the water depth to calculate the instantaneous flow rate.
Positive displacement flow meters
The positive displacement flow meter is a fluid flow meter that measures the fluid flow using fitted rotors. There is always the shifting of fixed and known rotor volumes. The spinning of the rotors is always proportional to the displaced liquid volume.
The integral electronic pulse transmitter will count the number of rotations of the rotor. You can then convert this information into the volume and flow rate. Examples of positive displacement flow meters include; oval gear, reciprocating piston, rotary vane, and nutating disk.
Positive displacement flow meters are applicable in measuring the flow rate of fluids like lubrication oils, polymer additives, heating oils, vegetables and animal fats, etc.
Venturi Meters
By restricting fluids and monitoring a differential pressure drop, a venturi tube monitors flow rates. The velocity of the Venturi meter increases as it moves upstream, but the pressure decreases. The rate of flow through the instrument is measured by measuring the pressure drop in the upstream cone.
Venturimeter Characteristics
- There is no restriction on design pressure. The DP transmitter/pipe press. Ratings have a limit.
- Design Temperature: There are no restrictions. Pressure ratings on DP transmitters and pipes limit what can be done.
- Sizes range from 25 mm to 3000 mm.
- Clean Liquids/Clean Gases Fluids/Applications
- Liquids that are dirty, caustic, or viscous, as well as dirty gases, have limited applicability.
- Only pipe size and beta ratio limit the flow range.
- MOC: No restrictions (cast iron, carbon steel, stainless steel, Monel, titanium, Teflon, Hastelloy, naval bronze/haste alloy)
- The accuracy ranges from 0.25 percent to 0.75 percent of the actual flow rate. The DP transmitter’s accuracy ranges from 0.1 percent to 0.3% of full-scale inaccuracy.
- The ratio of rangeability is 3:1 to 5:1.
- Upstream and downstream straight lengths are 20 and 5, respectively.
Final words
A liquid flow meter has an essential role in different industrial applications. However, they usually come in different types, enabling you to choose the best type depending on your type of application. If you find it challenging to choose a suitable flow meter for your application, you may consult an industrial engineer to help you choose one. Also, you can purchase these devices at a reasonable cost.