Introduction to Flowmeter Selection - Advanced (1)

Introduction to Flowmeter Selection - Advanced (1)

Types of Fluid Flow Meters/Type of flowmeter

Different types of liquid flow meters are introduced - Orifice, Venturies, Nozzles, Rotameters, Pitot Tubes, Calorimetrics, Turbine, Vortex, Electromagnetic, Doppler, Ultrasonic, Thermal Mass, Mass, Coriolis

The most common calibration fluid flow measurements are:

• Differential pressure flowmeter
• Orifice Flow Meter
• Venturi Tube Flow Meter
• flow nozzle flow meter
• Variable area - Rotameter - Rotameter
• Velocity Flow Meter
• Pitot tube flowmeter
• Turbine flowmeter
• Vortex flowmeter
• Electromagnetic Flowmeter
• Ultrasonic flowmeter
• Positive Displacement Flowmeter
• Mass flowmeter
• Thermal Mass Flow Meter
• Coriolis flowmeter
• Open Channel Flow Meter

Differential pressure flowmeter

The differential pressure flow in the drop device is calculated by measuring the pressure drop over the flow rate inserted by an obstruction.

Differential pressure flow meters are based on the Bernoullis equation, where the pressure drop and further the measured signal is a function of the square of the flow velocity.

The most common types of differential pressure flow meters are:

• orifice plate
• flow nozzle
• Venturi tube
• Variable Area - Rotameter

orifice plate

With the orifice, fluid flow is measured by varying pressures from upstream to downstream side of a section of blocked pipe.

.Accurate measurement of the choke provides a duct blocking, narrowing and force constriction of the flowing liquid.

Orifice plates are simple, inexpensive, and available in any material for almost any application.

The precision conversion efficiency of the orifice plate is less than 5:1. Its accuracy is poor at low flow rates.

High accuracy depends on the orifice plate in good condition, with a sharp edge on the upstream side.

Reduced wear accuracy.

• Orifice Plates, Nozzles and Venturi Meters

Venturi tube

Because of simplicity and reliability, venturi flowmeters are often used in applications where the need for a higher range rate, or lower pressure drop, than an orifice plate can provide.

In the flow path, a pressure differential is created in the flow path, where the flow of the fluid is reduced in the interception area measured by the venturi.

In the post-constriction zone, the fluid passes through a pressure recovery outlet section, with up to 80% of the pressure differential generated in the constriction zone being recovered.

With proper instrumentation and flow calibration, venturi flow can be reduced by approximately 10% full scale with proper accuracy.

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This provides a precision conversion efficiency of 10:1.

• Orifice Plates, Nozzles and Venturi Meters

flow nozzle

Flow nozzles are often used as measuring elements for air and gas flow in industrial applications.

Nozzle flow is relatively simple and inexpensive and can be used for many applications on many materials.

The conversion efficiency and precision are available with orifice plates.

• Orifice Plates, Nozzles and Venturi Meters

In Sonic Nozzles - Severe (Choke) Flow Nozzles

As the gas accelerates through the nozzle, the velocity increases and the pressure and gas density decrease.

The highest speed is achieved in the throat, the smallest area, where it rests at Mach 1 or sonic.

At this point it is not possible to increase the flow and reduce the downstream pressure.

Flow is choking.

. This condition is used in many control regimes to maintain a fixed, accurate, repeatable gas flow independent of downstream pressure.

Recovery Pressure Drop Orifices, Nozzles and Venturi Meters

After the differential pressure has been generated, the fluid passes through the pressure recovery outlet section, where the resulting pressure differential is partially recovered in the constriction zone.

As we can see, the pressure drop of the orifice is significantly higher than that of the venturi.

Variable Area Flowmeter or Rotameter

The rotameter consists of a vertically oriented glass (or plastic) tube with the larger end on top, which is a freely moving tube within the metering float range.

Fluid flow causes an upward pressure differential in the floating riser and the buoyant fluid overcomes the effects of gravity.

The float rises to the area between the annular tube and the float rises enough to allow a dynamic equilibrium state between the pressure difference and the buoyancy factor upward and the gravity factor downward.

The float in height is the displayed flow.

The tube is available in properly calibrated and graduated flow units.

Typical rotameter meters have turndown ratios as high as 12:1.

The accuracy may not be as good as the 1% full scale rating.

Magnetic floats for alarm and signaling functions.

Velocity Flow Meter

The flow calculation method in a velocity flow meter is to measure the flow rate at one or more points of velocity, flow velocity and integrate the flow area.

Pitot tube

Pitot tubes are one of the most common (cheapest) methods to measure the flow of fluids, especially in applications in air, ventilation and air conditioning systems, even when used in aircraft velocity

Pitot tubes measure the flow rate of a fluid by converting kinetic energy into potential energy.

Limit point measurement using pitot tubes.

With an "Au", or multi-port pitot probe, dynamic pressure can be measured over the entire velocity profile, and an average effect is obtained with Au.

Calorimetric mass flow meter

The flow measurement principle of calorimetric fluids is based on the close connection of two temperature sensors with the thermal insulation of the fluid, but each other.

. Two of the sensors are continuously heated and the effect of the coolant flow is used to monitor the flow.

In a fixed (no flow) fluid state there is a constant temperature difference between the two temperature sensors.

As the fluid flow increases, the thermal energy from the heated temperature sensor and the difference between the sensor decreases.

This reduction is proportional to the flow rate of the fluid.

 

Response time will vary due to heat transfer fluid.

Generally lower thermal conductivity requires higher speed for proper measurement.

Calorimetric flow meters can achieve high accuracy at low flow rates.

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Turbine flowmeter

There are many different designs of turbine flow meters, but in general they are all based on the same simple principle:

If the fluid moves through the pipe and behaves on the turbine blades, the turbine starts to spin and spin.

The rate of rotation is measured to calculate flow.

The turndown ratio may exceed 100:1 if the turbine flowmeter is calibrated for single flow and with fixed conditions.

Accuracy may be better than +/- 0,1%.

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Vortex flowmeter

A swirling downstream flow is created in the obstruction fluid flow.

Every time there is a critical fluid blocking flow velocity, a vortex street occurs.

An example of vortex shedding, where alternating low-pressure regions are created downstream.

These alternating low pressure areas cause blockages towards the low pressure areas.

The strength of the eddy current can be measured with the sensor.

• Principles of Vortex Flowmeters - It brings the principles of Vortex Flowmeters.

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Electromagnetic Flowmeter

Electromagnetic flowmeters operate on Faraday's law of electromagnetic induction, which states that a voltage conductor is caused to move through a magnetic field.

The liquid acts as a conductor and the magnetic field coil is energized to create a flow outside the tube.

. The generated voltage is proportional to the flow rate.

Two electrodes are installed on the inner wall of the pipeline to detect the voltage, which is a secondary factor to measure.

.Magnetic flow meters can measure difficult and corrosive liquids and slurries, they can measure flow in both directions with equal accuracy.

Electromagnetic flow meters have a relatively high power consumption and can only be used for conductive liquid water.

• The principle of electromagnetic flowmeter - it brings the principle of electromagnetic flowmeter

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Ultrasonic Doppler Flowmeter

The effect of motion on the sound source, its frequency on the sound, was observed and described by Christian John Doppler.

The frequency of the reflected signal is modified by the velocity and direction of the flowing fluid

If the liquid is moving towards a sensor, the frequency of the signal's election will increase.

As the hydraulics move away from the transducer, the frequency of the return signal decreases.

The frequency difference is equal to the reflected frequency minus the original frequency and can be used to calculate the velocity of fluid flow.

• Ultrasonic Doppler Flowmeter and Time of Flight
• .Ultrasonic Flowmeter Tutorial - Basic tutorial about ultrasonic flowmeters.

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Positive Displacement Flowmeter

Positive displacement flowmeters measure the flow of fluids during accurate flow measurement devices with rotor elements.

Known and fixed numbers are displaced between rotors.

The fluid is displaced proportional to the amount of rotation of the rotor.

. The number of rotations of the rotor is calculated by a complete electronic pulse transmitter and converted to volume and flow.

The construction of positive displacement rotors can be done in the following ways:

• Reciprocating Piston Flow MeterThere are single and multiple piston types.
• The oval has two rotating gear meters, and the oval gear is synchronised with the teeth that are close to each other.
• A fixed amount of liquid flows through the meter per revolution.
• . Shaft rotation can be monitored for specific flow rates.
• removablediskMeterNutatingThe disk is mounted in a chamber with concentric spheres located on the side walls of the sphere.
• The pressurized liquid passing through the measuring chamber causes the disk rock circulation path to have no axis of rotation of its own.
• This is the only moving part in the measuring chamber.
• Depend onrotary vaneMeter equal, rotating impeller, two or more compartments, inside the housing of the meter.
• In continuous impeller contact with the casing.
• A fixed volume of liquid is swept to the outlet of the meter from the rotating impeller of each compartment.
• The revolution of the impeller is counted and registered in volume units.

The positive displacement flowmeter can be used for all relatively non-abrasive fluids such as heating oils, lubricating oils, polymer additives, animal and vegetable oils, inks, freons, and more.

Accuracy up to0.1%The ratio of full scale is more than 70:1.

Mass flowmeter

directMeasure mass flow.

Also known as thermal diffusion or immersion mass flow meters, include a family of instruments used to measure the total mass flow of fluids (mainly gases) flowing through closed pipes. The second type is the capillary type thermal mass flow meter. Many mass flow controllers (MFCs) that combine mass flow meters, electronics, and valves are based on this design. In addition, thermal mass flow meters can be constructed by measuring temperature differences on a silicon-based MEMS chip.

Both types measure fluid mass flow by convecting heat from a heated surface into a flowing fluid. In the case of thermal diffusion or immersion flow meters, heat is transferred to the boundary layer of the fluid flowing over the heated surface. In the case of the capillary type, heat is transferred to most of the fluid flowing through the small heated capillary. The principles of operation of both types are thermal in nature, but differ so much that two different standards are required. Also, their applications are quite different. Thermal diffusion meters are typically used for general industrial gas flow applications in pipes and conduits, while capillary types are primarily used for smaller flow rates of clean gases or liquids in pipes. This type is most widely used in industry for thermal mass flow meters. However, capillary types are not the subject of this discussion.

Thermal Mass Flow Meter

Thermal mass flow meters operate independently of density, pressure and viscosity.

Isolating the fluid flow path with a warm water thermal sensing element conducts the sensing element in the hot air flow.

The heat carried out is proportional to the mass flow rate and the temperature difference, he calculates the mass flow rate.

The reliability of the accuracy of the heat flow calibration device depends on the actual process and changes in temperature, pressure, flow rate, heat capacity and viscosity of the fluid.

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Coriolis flowmeter

The direct mass measurement Coriolis flowmeter integrates in addition to other technologies.

Insensitive to changes in mass measurements, pressure, temperature, viscosity and density.

Due to the ability to measure liquids, slurries and gases,

Coriolis flowmeter.

Coriolis mass flow meters use the Coriolis effect to measure the amount of mass moving through an element.

The fluid to be measured flows through a U-shaped tube and is an angular harmonic oscillation that causes vibration.

. Due to the Coriolis force, the tube will deform and an additional vibration component will be added to the oscillation.

This extra component will cause the phase shift to some places where the tube can measure the sensor.

Coriolis flowmeters are generally very accurate, better than +/-0,1% with a bed ratio of over 100:1.

Coriolis meters can also be used to measure liquid density.

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Open Channel Flow Meter

A common method of measuring flow through an open channel is to measure the height of a liquid as it passes through a multi-obstructed flume or weir channel.

Commonly used are the Sharp top weir, the V-notch weir, the Cipolletti weir, the rectangular apex weir, the Parshall flume or the Venturi flume.

• Weir Flow Measurement Standards - Important and Commonly Used Standards in Weir Flow Measurement
• Flow Measurements and Weirs - Weirs are commonly used to measure flow velocity in open channels and connect river water supplies and sewage treatment plants
• Weir Flow Measurement Standards - Important and Commonly Used Standards in Weir Flow Measurement

Flow meter principle

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