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Different type flow meter, which is used to measure the flow. There are many types of flow meters; each flow meter has a different range and specification. Each flow meter is used for a specific application. The working principal of all flow meters is different, based on which application they are to be used for is decided.
Flow meter type
Flow meter type or Different type flow meter is mainly divided into three functional segments.
- Positive Displacement Flow Meter
- Mass flowmeter
- volumetric flow meter
Positive Displacement Flowmeter: –
The positive displacement flow meter is the only flow measuring technology to directly measure the amount of fluid passing through a flow meter. It is a best technology for measurement of clean liquid, ‘PD’ or Positive Displacement flowmeter is a versatile and cost effective option for a wide range of application. It obtains this by trapping pockets of fluid among rotating components housed within a high precision chamber. This can be compared to repeatedly filling the beaker with fluid and pouring the contents down the aisle, while counting the number of times the beaker is filled.
Example of PD flowmeter.
- Oscillating Piston Flow Meters
- Nutating Disc Flow Meters
- Oval Gear Flow Meters
- Roots Flow Meters
- Multi-Piston Flow Meters
- Bi-Rotor Flow Meters
The output signal of mass flow meter is directly related to the mass passing through the flowmeter. Mass flow meter measures the mass of the fluid flowing in the line. The types of mass flow meters are given below.
Coriolis Mass Flow Meter :-
The Coriolis principle is very basic but extremely effective. It consists of a tube that is activated by a certain vibration. When a fluid passes through the tube, the speed of the mass flow changes the vibration of the tube, which is a phase shift. With a phase shift, a linear output is obtained that is proportional to the flux. The Coriolis method for measuring mass flow is independent of the type of material in the tube and can be applied to any gas or liquid.
Thermal Mass Flowmeter :-
Thermal mass flow meters are precision instruments that are direct measurement instruments for gas mass flow measurement for various forms of gas. They measure gas flow using convective heat transfer by inserting a probe into the gas stream of a pipe, stack, or duct.
Two resistance temperature detector (RTD) sensors are placed at the tip of a thermal mass flow meter, measuring heat transfer as a fluid passes through a heated surface. One of the RTDs is heated by an integrated circuit, while the other, the reference RTD, sets the temperature of the gas.
As the current passes through the hot sensor, the molecules carry the heat away, causing the sensor to cool as energy is released. The heat loss creates a temperature difference between the heated sensor and the reference sensor. The enclosed integrated circuit restores the energy lost to the heated sensor within a short time to accommodate overheating. The power required to maintain overheating is the mass flow signal.
Volumetric flow meter
A volumetric flow meter is a device that measures the amount of material passing, directly or indirectly, through a certain place, in a given time.
Many volumetric flow meters do not actually measure the volumetric flow rate directly but measure the speed of the flow. The measurement of flow speed is converted to a volumetric flow rate by multiplying the flow velocity by the cross-sectional area of the flow pipe where the volumetric flow meter is installed,
Q = V *A
Volumetric flow meters provide live analog, digital or pulse output of the volumetric flow rate. A volumetric flow meter may also include additional electronics such as a recorder, totalizer, etc.
Volumetric flow can be measured either directly using a volumetric flow meter or indirectly by measuring flow speed or by measuring the pressure drop created by a shape barrier. The volumetric flow rate can then be obtained using mathematical formulas and other fixed parameters such as cross-sectional area, density, etc.
Volumetric flow meter Type:-
- Electromagnetic flow meter
- Ultrasonic flow meter
- Turbine, Propeller and Pedal Wheel
- vortex shedding flow meter
- target flow meter
- Variable Area and Rotameter flow meter
- Orifice plate, open channel, flow nozzle, laminar, venturi and pitot tube
Electromagnetic flow meter
Electromagnetic flow meter works on Faraday’s law of electromagnetic induction “When a conducting material is passed through a stationary transverse magnetic field, an E.M.F is produced which is induced between the ends of the coil. This E.M.F. is proportional to relative velocity.
Ultrasonic Flow meter
In ultrasonic flow meters, the measurement flow rate is determined by the variation in the parameters of the ultrasonic oscillations. There are currently two types of ultrasonic flow meters in use. They are time difference type and Doppler flow meter.
Time difference type Ultrasonic Flow meter:-
This instrument measures flow by measuring the time it takes for an ultrasonic wave to cross a pipe section and against the flow of liquid within the pipe.
Doppler flow meter
In a Doppler flow meter, an ultrasonic wave is projected at an angle though the pipe wall into the liquid by a transmitting crystal in a transducer mounted on the outside of the pipe.
When the flowing fluid hits the turbine rotor blades, a force is applied to the blade surface which spins the rotor. The rotor speed is directly proportional to the fluid velocity. Measures volumetric flow rate when it is at a constant rotational speed. The rotation speed is monitored in most meters by a magnetic pickup coil, which is fitted to the exterior of the meter housing.
Vortex flow meter
Vortex flow meters work under the vortex shedding principle, where an oscillating vortex occurs when a fluid such as water flows through a bluff (as opposed to streamlined) body. The frequency of falling vortices depends on the size and shape of the body. It is ideal for applications where low maintenance cost is important. Industrial sized vortex meters are custom manufactured and sized appropriately for specific applications.
Target flow meter
The target flow meter measures flow by measuring the force on the target concentrated in the pipe at right angles to the direction of liquid flow. The fluid flow develops a force on the target which is proportional to the square of the flow.
Rotameter flow meter
A rotameter is used to measure the volume flow rate of a fluid in a closed tube. It is a direct current measuring device that does not require an external power source. The rotameter can only be installed in the vertical position. It belongs to a class of meters called variable-area flow meters, which measure flow rates by allowing the cross-sectional area from which the fluid is separated, thereby having a measurable effect.
Orifice plates are circular plates with holes of a certain size. It is fitted between two flanges in the line to measure volumetric flow through the orifice. The pressure drop caused by this is measured by a differential pressure transmitter.
A flow nozzle is also called a half venturi.The flow nozzles are used for flow measurement at high fluid velocities & the more rugged ,more resistant to erosion than the sharp edged orifice plate
Different type flow meters are generally described in three functional categories, whose function is to measure the flow using a different principle. We tell you the above mentioned three categories in simple language.
In a positive displacement flowmeter, the flowing material is in direct contact with the flowmeter. In this, assume that you have a bowl (in which you eat food), whose size you know. Suppose one kilo of flowing material will come in this bowl. Now you are measuring the material from that bowl and pouring it in another vessel. Exactly the same happens in the positive display main flow meter. It consists of a chamber of a known dimension that rotates due to flow and the reading is displayed on a calibrated scale.
A mass flow meter uses the Coriolis principle to measure the flow rate of a flowing material directly at the rate of mass. Such as Kg / Hr , Ton / Min etc.
There are many types of volumetric flowmeters and their principles are also different. They measure volumetric flow directly. The value taken by them can be converted into mass by mathematical calculation.