Instruments that are used for measuring the flow rate of a particular liquid, flowing through a pipe, are called flow meters. The measurements can be done based on either the mass flow rate or the volumetric flow rate and the units in which it is measured are kilogram per second and liters per second respectively. The standard liquid flowmeter is used in various fields and has significant utility. In the medical field, industrial sector, like food processing, semiconductor fabrication, water management, etc. There are various types of flow meters, depending on the principle that administers the application. Ultrasonic, Mechanical, Pressure, and Electromagnetic are the types of liquid flowmeters.
Open & Closed Channel Flow
The flow of any liquid can be classified into open or closed pipe flow. The open channel in the free-flowing stream is not restricted by any wall and the flow is controlled by the force of gravity. The fluid flow in the closed channel occurs due to the pressure difference in the pipeline.
Here are a few types of standard liquid flowmeters discussed:
- Ultrasonic Flowmeters
With the negligible use of the mechanical parts, the maintenance of these flowmeters is very low and has the advantage of measuring any kind of liquid with no hassle. The clamp-on version of these flowmeters is to be snapped outside the pipe, providing a non-intrusive installation. The output is of these meters is generally very accurate.
- Mechanical Flowmeters
These are the conventional devices, with either turbines or wheels inserted in the conduits to calculate the velocity and the volumetric flow with the help of the location of the pipe. They can be categorized into piston meter, single jet meter, and gear meter. Piston meter uses rotating pistons whereas gear meter uses two or more gears, which rotate perpendicular to each other and the single jet meter applies the impellers to measure the flow.
- Pressure Flowmeters
Either differential pressure or dynamic pressure determines the rate of the flow. While using the differential pressure, the pipe is constricted to decrease the pressure, as with the further introduction of liquid, the pressure hikes. The flow rate is concluded by the pressure difference between the inlet and outlet valve.
The dynamic pressure can be determined by finding the difference between the points where the pressure is stagnant and the point where the fluid viscosity is zero. Pilot tubes, dall tubes, cone meters are some examples of this flowmeter.
- Electromagnetic Flowmeters
As the name suggests, the flow rate is determined by the magnetic field created by the magnets in the pipe, which with the help of the conductive components of the fluid alters the voltage. This change in voltage is used to determine the flow rate. These are suitable for water, or water-based liquids like wastewaters. They can’t be used in oil, hydrocarbon, and distilled water.
Selection of the appropriate standard liquid flowmeter is essential to avoid any loss due to misapplication, as there are various kinds of flowmeters available. All the devices are not compatible with all types of liquids; the viscosity, quantity of impurity, material, and size of pipe, are some of factors to be considered.