Flow meters are devices for measuring the flow of liquids and gases, based on the determination of the flow rate at specific time intervals. There are many types of flow meter, which differ, among other things, in the physical phenomenon used for their operation, the method of installation, size or construction.
Flowmeters are based on measurement methods using various physical phenomena. Most are based on measuring
volumetric flow (i.e. the volume of a substance flowing through a pipeline in a given time), but there are also technologies that measuremass flow (i.e. the mass of a substance flowing through a pipeline per unit time).
Due to their different designs, flowmeters can be divided into groups such as:
Operation of electromagnetic flowmeters are based on the fluid's ability to excite an electric current during movement. They allow highly accurate measurements of fluid flow, but, which can be a limitation in some applications, they can be only be used with conductive liquids. Consequently, they are not suitable for gases and in applications where the fluid being measured is, for example, oil or ultrapure water.
Ultrasonic flowmeters are high-tech devices that use the transit time of sound waves from source to receiver to measure the flow of liquids.
These devices measure flow in a non-contact manner, so they are ideal for aggressive liquids and high-pressure conditions. They can be used with clean and slightly contaminated and even viscous liquids, but are not recommended for highly viscous liquids.
Differential pressure flowmeters can be used to measure the flow of liquids, gases or steam. They use a basic body (primary element) which, when installed inside a pipe, causes a narrowing of the flow path and, consequently, a drop in pressure. Used in conjunction with a differential pressure transducer, it determines the flow rate based on a function of the differential pressure at the obstruction.
These flowmeters are standardised and have low maintenance requirements. However, pressure drops are higher compared to other types of flowmeters, resulting in increased energy costs to maintain flow in the process.
Turbine flowmeters consist of a housing with a vane impeller installed in it, which rotates under the influence of water movement and transmits the number of rotations made to a reading device. They are distinguished by their simplicity and low price. They will prove useful for measuring the flow of inert or low-aggressive media that contain traces of solid particles.
Calorimetric flowmeters make use of the thermal conductivity of the medium. They heat the flowing fluid stream and then, using a temperature sensor, measure how quickly the medium dissipates this heat.
These flowmeters will work well for measurements in cooling circuits, pumps and heat exchangers, as well as for monitoring leaks and lubrication systems.
Depending on the installation method, a distinction is made between contact and non-contact flowmeters. The advantage of non-contact portable flowmeters is that they can be installed on pipelines without disturbing their continuity. They are rarely permanently installed and are more often used for verification measurements at various points.
The selection of flow measurement device for large water-using organisations, wastewater treatment plants, thermal power plants and other industrial facilities depends on a number of factors. Among other things, application characteristics such as the degree of contamination of the flow, installation conditions, flow velocity, pressure and temperature, etc.
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