Types of flow meters can be divided into two functional groups on the basis of measurement of quantity & flow rate. The flow meter that measures the quantity is the positive displacement type flow meter. On the other hand, the flow meter that measures the rate of flow is the inferential type flow meter.
Types of Flow Meters
Broadly two types of flow meters are widely used in industries:
- Volumetric Flow meters and
- Mass Flow meters
The primary element of the flow meter has its contact with the fluid, this causes some interaction between the fluid & primary element. The interaction of the primary element with the fluid may acceleration of the fluid flow.
The secondary element of the flow meter converts flows into an electrical signal. Further, we can display the electrical signal in terms of volume, weights, or rates of flow.
For example, the orifice plate along with the pressure pipe & its connection form a primary element. The differential pressure devices such as pressure gauge & transmitter form the secondary element. The secondary element converts the pressure into an electrical signal or in some sort of mechanical indication.
Almost all types of flow meters have the same type of primary and secondary elements.
Positive Displacement Type Flow Meter (Quantity Meters)
A positive displacement flow meter requires mechanical displacement of the fluid to measure the flow. Thus, the positive displacement (PD) flow meters measure the quantity of a moving fluid.
The positive displacement meters are as follows.
- Oval Gear meter
- Nutating disc meter
- Spur gear meter
- Variable area flow meter
- Screw meter
- Oscillating piston meters
- Helical gear meter
- Rotary Vane meter
Inferential Type Flow Meters-Volumetric Flowmeters
Volumetric flow meters got their name because these flow meters measure the fluid volume passing through a specific location in a set period of time. Thus, it provides an instantaneous analog, digital, or pulse output of the volumetric flow rate of the liquid or gas. The followings are the various types of Volumetric Flowmeters.
- Orifice Plate
- Flow Nozzles & Venturi tubes
- Pitot Tubes
- Turbine flow meter
- Vortex shedding Flow meter
- Ultrosonic flow meter
Thin-plate & concentric orifice flow meters are Inferential type flow meters. They have their widespread use in industries.
Flow Nozzles & Venturi Tubes
Flow nozzles & venturi tubes types flow meters are the primary flow rate devices. These devices are suitable for measuring more flow than an orifice plate under the same conditions. Therefore, they are suitable for flow measurement at high velocity. A smaller bore nozzle or Venturi is suitable for measuring the same flow if we choose a differential limit.
The pitot tube is a type of flow meter most suitable for measuring fluid flow velocity. The open endpoints upstream so the fluid rams into the opening and increases the pressure inside. That pressure is called the stagnation pressure because the flow stagnates – comes to rest – inside the tube.
Generally, it is used in the combination with a measurement of the static pressure – the undisturbed pressure in the fluid. The difference between the stagnation pressure and the static pressure is called dynamic pressure.
Turbine Type Flow Meters
A turbine meter has a primary element that rotates by a linear velocity of the fluid stream on immersion of the element in the fluid. The revolution of the primary element is proportional to the rate of fluid flow. The more the revolution, the more the flow.
We can use it for the pressure ranges from sub-atmospheric to 6000 psi. They function well for clean fluid.
Swirlmeters Flow Meter
Swirlmeters have their widespread application for flow rate measurement because they have a simple structure, stable operation stability, and accurate measuring precision.
Vortex Shedding Meters
Vortex shedding is caused when a fluid flows past a blunt object. The fluid flow past the object creates alternating low-pressure vortices downstream of the object. Finally, the object will tend to move towards a low-pressure zone.
In the cyclone, the fluid moves in a circular/ spiral motion because of pressure difference. The flow is a type of vortex flow.
Mass flow meters measure the fluid mass flow rate. There are two types of mass flowmeters.
- Coriolis Mass flowmeter and
- Thermal Mass flowmeters