A flow meter is a device that measures the volume of material passing through time. In most industries, including oil and petrochemical industries, it is important to know the exact amount of flow or fluid flow, such as gas or oil. Note that the total flow rate, which represents the mass of the consumable material, is used in many cases, such as industrial processes. Also, accurate flow measurement is of special importance due to financial considerations in the sale and purchase of a certain volume of materials and goods, such as household gas meters and oil exchanges, etc.
Various techniques are used to measure the flow, some of the most common of which are as follows:
Flow measurement by Positive Displacement method
Flow measurement by Orifice Plate method
Flow measurement by Turbine method
Flow measurement by rotametric method (variable area)
Ultrasonic flow measurement with Doppler phenomenon Ultrasonic: Doppler
Flow measurement by ultrasonic method with transfer time method and …. Ultrasonic: Transit Time, Time of Travel, Time of Flight
Flow measurement by Venturi Orifice Plate method
Magnetic flow measurement
Flow measurement by Vortex Shedder method
Flow measurement by Rotameter (Variable Area) method
Flow measurement by flowmeter method for Weir and Flume Open channel
Flow measurement by Coriolis method
Thermal flow measurement
Flow measurement by pitot method
Turbine flowmeters have a simple mechanism and consist of a turbine with specific blades that along with a sensor, for example, a proximity switch with each turbine rotation to produce a number of pulses due to the passage of flow and flow, which is calibrated by the device based on flow amount and number The generated pulse is obtained from the flowmeter range.
Mass Flowmeters or Copper Flowmeters Mass Flowmeter
Another method of measuring flow by weight is known as mass flowmeters or copper flowmeters. In the previous conventional methods, to measure the mass of the passing fluid, it was necessary to measure the density of the material, which in practice was a very erroneous calculation of the mass. At present, all types of mass flowmeters with Corylias and copper thermal technologies perform this measurement with high accuracy. In these flowmeters, the fluid flow can be measured independently of pressure and you will be free from measurement errors of gaseous fluid flow due to temperature changes. And keeps the pressure safe.
Flow switches simply output the switch or ON / OFF with different mechanisms to feel the fluid flow in the set point or set point and allow you to control the flow of the line. Usually, the simplest methods are the most widely used, and in very common flow switches, they use a metal blade that is attached to a lever, cut the length of this blade, or so-called trim, according to the set point. When the flow reaches your set value, the lever is tilted to one side and the switch is actuated. In more advanced examples, this switch is used non-contact, for example, with the help of the magnetic property of the end of the lever, which stimulates the output relay reed.
Pitot Tube Pitot Tube
In the measurement of gaseous fluids, especially air in low range, the Pivot tube method is usually used.
Positive displacement flowmeter
Positive displacement flowmeters are used for accurate measurement of fluids, especially viscous liquids, and are divided into the following types:
Ovale gear flowmeter
Helical gear flowmeter (used for high viscosity materials)
Axial Nutating disk model
Diaphragm or jumper flowmeter (used for city gases)
The vortex flowmeter is based on a phenomenon in fluid dynamics discovered by a scientist named Theodore von Karman. In practice, the vortex flowmeter operates with a mechanism based on measuring the oscillations created behind a barrier in the fluid. Vertex flowmeter is used in many industries to measure liquids, gases and vapors. In chemical and petrochemical industries, for example in electricity generation … In fluids such as saturated steam, very hot steam, compressed air, nitrogen, biphasic gases, flue gas, carbon dioxide, demineral water, solvents, heat transfer oil, water Boiler power supply, etc. This flowmeter can be used.
Flow measurement in vortex flowmeter is volumetric, but for mass measurement in cases such as steam, you must use a separate pressure transmitter as well as temperature sensor and connect them to the flow computer to calculate the mass or amount of energy transferred.
Electromagnetic flowmeters can measure the amount of flow with acceptable accuracy using Faraday’s law of electromagnetic induction and measuring changes in magnetic flux due to the velocity of the flowing fluid. In fact, by creating a magnetic flux in the fluid passing through the flowmeter and measuring it, an electromagnetic flowmeter can be achieved.
Due to the mechanism of magnetic flowmeter, water or fluid must have electrical and conductive properties to some extent, otherwise the measurement will be disturbed and flowmeters with different mechanisms such as vortex flowmeter or turbine flowmeter must be used, for example, magnetic flowmeter. Demineral or distilled water cannot be used to measure flow.
Electromagnetic flowmeters usually work at temperatures up to 80 degrees and according to the liner inside the flowmeter in different applications, the liner is made of Teflon or hard rubber, etc.
The following is a simple illustration of the measuring mechanism of this electromagnetic flowmeter.
Nowadays, ultrasonic methods have become one of the most practical instruments for measuring instrumentation, especially non-contact samples. The source is generated and on the other hand a receiver checks this frequency moment by moment. If the fluid flow changes, this reciprocating frequency will change significantly due to the fluid velocity. Measuring and calibrating these changes in terms of flow will allow you to measure flow by ultrasonic method. In practice, the flow measurement technique by ultrasonic method will have its complexities, but the basis for measuring most ultrasonic flowmeters is the Doppler mechanism.
Open channel Flowmeter
Open channel flowmeters are used to measure the volume of fluid passing through a channel. The basis of work in measuring the flow in this method is water conduction in predefined sections and measuring changes in water level or sewage and its calibration in terms of flow.
Orifice Plate flowmeter
Orifice plate flowmeters are one of the oldest flow measurement methods that offer relatively simple design, high efficiency, and acceptable reliability and repeatability. The orifice is a flat plate in which a hole, depending on the design calculations Orpheus has been created. The work is based on the principle that creating an obstacle in the flow path causes a pressure drop in the line and creates a pressure difference on both sides of the orifice. By measuring this pressure difference with the help of a pressure difference transmitter or pressure difference gauge and with the formulas used in fluids, this value can be calibrated in terms of flow.
The rotameter uses the variable area technique in measuring the flow as an instantaneous flow indicator or flow indicator. A common example of a rotameter consists of a glass cylinder that is calibrated according to the flow of the material over time and a piece of metal cone that moves upward as the flow in the glass increases.
You should have seen rotameters like these in oxygen capsules in hospitals. In industry, the rotameter is calibrated according to the temperature of the fluid in question, as well as the density or viscosity of the material, as well as its pressure.