A flowmeter is a device that measures fluid flow. Flowmeters are flow meters used to measure the linear, nonlinear, mass, or volumetric flow rate of a gas or liquid. Flowmeters are also known as flow meters or flow measuring instruments. Accurate measurement of gas and liquid flows is required for better control and quality of industrial processes.
This article summarizes the following information:
Types of flowmeters
The principle of operation of any type of flowmeter
Design features of each flowmeter
Advantages and disadvantages of each type of flowmeter
Selection and application of flowmeters
Types of flowmeters
Two types of flowmeters are widely used in industry:
Volumetric flowmeter
Mass flowmeter
Volumetric flowmeter
Volumetric flowmeters are so named because they measure the volume of fluid passing through a specific location over a period of time. Volumetric flowmeters provide an analog, digital, or instantaneous output of the volume flow rate of a liquid or gas. There are several types of volumetric flowmeters:
Flowmeter pressure difference
Orifis Pages
Venturi meter
Side flowmeter (rotameter)
Electromagnetic flowmeter
Ultrasonic flowmeter
Turbine flowmeters
Vortex flowmeters
Positive displacement flowmeter
Mass flowmeter
Mass flowmeter measures the mass of a fluid moving in a tube per unit time. There are two types of mass flowmeters listed below:
Coriolis mass flowmeter
Thermal mass flowmeters (copper thermal flowmeters)
Compression difference flowmeters
The pressure difference between the upstream and downstream sides is a constraint on a fluid flow that is directly related to the square of the fluid velocity.
Q α √ ▲ P
Where Q = volumetric flow velocity and ▲ P = differential pressure between two points
Turbine flowmeter
The turbine flowmeter consists of a multi-blade rotor mounted at right angles to the flow and suspended in a fluid flow on a free bearing. The rotor diameter is slightly less than the inside diameter of the flow measuring chamber. is.
Features of turbine flowmeters
Design pressure: 1500 PSIG
Design temperature: 150 degrees Celsius
Size: 5 mm to 600 mm (full hole type) /> 75 mm for insert type
Fluids: Clean liquids / gases and vapors
Speed range: 0.3 to 15 meters per second
Material: mostly in stainless steel / core
Accuracy: + 0.25% to + 0.5% of the flow rate for the all-hole type / + 1% to + 3% of the flow rate for the insert type
Repeatability is 10: 1
Upstream / downstream straight length is 15.5
Two-way flow measurement
For insertion type, hot tapping is possible in pressurized pipelines
Advantages of using a turbine flowmeter
very precise. Usually used to prove other meters.
Digital output provides a direct, categorized, or direct digital combination without compromising accuracy.
There is less tendency to read high in pulsed flow than head type or variable area meters.
Disadvantages of turbine flowmeters
Cannot be used in dirty or corrosive streams.
Exposed to fouling by foreign materials – fibers, tar, etc.
Bearings are subject to wear or damage. If the bearing is replaced, change the calibration
May be damaged at high speed (more than 150%) or hydraulic shock.
The pressure drop in the rated current is different and can be high.
Magnetic flowmeter
Follow Faraday’s law of magnetic induction.
When a conductive fluid moves in a magnetic field, a voltage is generated between the two electrodes at angles perpendicular to the velocity of the fluid and the direction of the field.
The flow tube has a constant area and field strength, so the voltage developed is linearly proportional to the volumetric flow rate.
Design features of magnetic flowmeters
Design pressure: 20 BARS to 172 BARS
Design temperature: up to 120 ° C with Teflon liner / 180 ° C with ceramic liner
Size: 2.5 mm to 3000 mm
Liquids: Liquids (clean / corrosive / dirty / viscous / slurry)
Speed range: 0.1 to 10 meters per second
Material: Lining: Ceramic / Teflon / Rubber: Electrodes: Platinum / hastelloy / SS
Accuracy: The actual current varies from 0.05% to 1.1%.
Repeatability is 10: 1
Upstream / downstream straight length is 10.5
Advantages of magnetic flowmeters
Flow rate is not affected by fluid density, consistency, viscosity, turbulence, or piping configuration.
Lack of moving parts
Corrosion resistant using Teflon liner and platinum electrodes
Wide flow measurement range without pressure drop
Disadvantages of magnetic flowmeter
Expensive, compared to other types of flowmeters.
The measured fluid temperature is limited by the grading of the liner material.
Cannot be used to measure gas flow
Vertex flowmeter
An obstruction is placed across the pipe hole at a right angle to the fluid flow.
As the fluid flows, the vortices come out alternately, and this frequency is directly proportional to the velocity of the fluid.
Vortex detection using pressure changes in vortex flow.
The rate at which vortices are generated is directly proportional to the velocity of the flow.
Vertex flowmeter design features
Design pressure: 138 bar
Design temperature: -200 degrees C to 400 degrees Celsius
Size: 15 mm to 300 mm
Liquids: Gases (clean / dirty) and clean liquids
Speed range: 0.3 to 10 meters per second (liquids) and 6 to 80 meters per second (gases)
Material: Mostly in stainless steel, some plastic
Accuracy: varies from 0.5% to 1% of the actual flow for liquids and from 1.5% to 1.5% for gases.
Repeatability is 20: 1
Upstream / downstream length is 20.5
Advantages of Vertex Flowmeter
Minimal maintenance, no moving parts.
Calibration using fluid flow is not required and is not affected by viscosity, density, pressure and temperature in the operating specifications.
Digital or analog output
Disadvantages of Vertex Flowmeters
At low currents, no pulse is generated and the flowmeter can read low or even zero.
Reynolds number must be greater than 10,000.
Vibration can cause accuracy errors.
Proper installation of the vortex flowmeter is very important because a protruding washer or welded nuts can cause a vortex and lead to inaccuracies.
Like perforated plate flowmeters, the upstream pipes must provide long, clear lengths.
Coriolis mass flowmeter
When a moving object is subjected to an oscillation perpendicular to its direction of motion, Coriolis forces occur depending on the mass flow.
When the pipe moves upwards in the first half of a cycle, the fluid that pours into the meter resists pressing the pipe downwards.
On the other hand, the liquid that comes out of the meter resists the reduction of its vertical movement by pressing on the pipe. This causes the pipe to twist.
This torsional motion is sensed by a pickup and is directly related to the mass flow velocity
Features of Coriolis mass flowmeter
Design pressure: 345 bar
Design temperature: 200 to 426 degrees Celsius
Size: 1.5 mm to 150 mm
Fluids / Applications: Liquids (clean / dirty / viscous / slurry) Clean gases / Liquids
Flow range: 0 to 25,000 pounds per meter
Material: Mostly in stainless steel, hastelloy / titanium
Accuracy is + 0.15% to + 0.5% flow rate
Repeatability is 20: 1
Two-way flow measurement
Advantages of Coriolis mass flowmeters
Able to measure difficult fluids
Independent of changes in density, flow profile and flow turbulence. So there is no need for straight length.
No need for regular maintenance because there are no moving parts
High accuracy
Coriuls flowmeter not available for large pipes (only up to 150 mm)
High flow rate required to detect and thus high pressure drop
Expensive compared to other flowmeters
Difficulty measuring low pressure gases.
Types of Orifice pages
Concentric hole plate: The most used
Segmental & Eccentric aperture plate: Used for fluids containing suspended solids.
Tapping for Orifice pages:
Corner valves (<1 inch)
Valves D and D / 2 (2 to 16 inches)
Flange valves (> 16 inches)
Features of Orifis pages
Design pressure: no restrictions. Limited by DP transmitter
Design temperature: No limitation limited by DP transmitter
Sizes: The maximum size is the size of the pipe
Flow range: limited by pipe size only.
Fluids / Applications: Refrigeration / Gases and clean liquids / Steam (saturated / superheated)
MOC: Unbound (Steel / Monel / Nickel / Hasty Alloy)
Accuracy: varies from 0.25 to 0%. 5% actual current DP transmitter accuracy varies from ± 0.1% to ± 0. 3% full scale error
Range is 3: 1 to 5: 1.
Upstream / downstream length is 20.5
Benefits of Orifis Plate
Easily installed between flanges.
Simple and cheap construction.
No restrictions on construction materials, line size and flow velocity
The cost is relatively independent of the pipe diameter because the DPT cost is fixed.
No interruption in the process for exchanging DP transmitters.
Disadvantages of Orifice Plate
High permanent pressure drop resulting in high energy consumption to overcome pressure drop.
It is impractical for systems with low static pressure.
Measurement range around 3: 1 to 5: 1.
Accuracy decreases with beta ratios of about 0.7.
Exposed to damage by water hammers and foreign objects.
Venturi Flowmeter
A venturi tube (Figure 2) measures the flow rate by contracting fluids and measuring the differential pressure drop. In the upstream cone of the flowmeter, the pressure increases rapidly, the pressure decreases. The pressure drop in the upstream cone is used to measure the flow velocity through the device. More details on the Venturi Flowmeter are provided here.
Venturi Flowmeter Features
Design pressure: no restrictions. Limited by DP transmitter / pressure tube rating.
Design temperature: No restrictions, restrictions on pressure difference transmitter / and pressure rating tube
Size: 25 mm to 3000 mm
Fluids / Applications: Clean liquids / clean gases
Limited applications: Dirty / corrosive / viscous liquids and dirty gases
Flow range: Only limited by pipe size and beta ratio.
MOC: Unbound (Cast Iron / Carbon Steel / SS / Monel, Titanium, Teflon, Hostel, Marine Bronze / Accelerated Alloy)
Accuracy: varies from ± 0.25 ٪ to ± 0. 75% of the actual current The accuracy of the DP transmitter varies from ± 0.1 ٪ to ± 0. 3% full scale error.
Range is 3: 1 to 5: 1.
Upstream / downstream length is 20.5
Advantages of Venturi Flowmeter
Head losses are less than aperture plates, which reduces capital costs for pumping Eqpt. / Save pump energy costs
No interruption in the DP transmitter exchange process.
Can be used for high temperature
Cryogenic or high temperatures
Disadvantages of Venturi Flowmeter
it is very expensive
It is bigger and heavier.
Anubar flowmeter
Anubar flowmeter is a device for measuring the flow of fluid (liquid, vapor or gas) in a pipeline. Flow is measured by creating differential pressure. According to Bernoulli’s theorem, this differential pressure is proportional to the square of the velocity of the fluid in the pipeline. The Anubar flowmeter measures this differential pressure, which is then converted to flow using a secondary device.
The probe is installed as a pressure sensor in the media line.
With flow, the probe records both static and dynamic pressures through the probe openings.
In the negative chamber of the probe, located on the opposite side, only the static pressure is affected
The differential pressure is related to the dynamic pressure in the pipeline and the flow can is calculated directly.
Features of Anubar Flowmeter
Design pressure: up to 97 bar (38 ° C) / 55 bar (370 ° C)
Design temperature: up to 400 degrees Celsius
Size: 50 mm to 3000 mm
Liquids: Clean liquids, gases and vapors
MOC: Brass / Steel / Stainless Steel / Hastelloy
Accuracy: varies from 1% to 2% of the actual current. The accuracy of the DP transmitter varies from ± 0.1 ٪ to ± 0. 3% full scale error.
Range is 3: 1 to 5: 1.
Upstream / downstream length is 20.5
Advantages of Anubar Flowmeters
The integrated manifold head allows direct installation of DP transmitters
Hot Tap: Log in and install without shutting down the system
Very low pressure drop
Disadvantages of Anubar flowmeters
Not suitable for viscose and slurry applications
Can only be used for clean liquids.
Side flowmeter (rotameter)
Side flowmeters or rotameters are one of the most common types of flowmeters. It consists of a vertical glass or plastic tube. The size of the pipe varies from top to bottom. That’s why it got its name from the side of the Apple Flowmeter. Inside the tube, there is a free-floating measuring float.
A free moving vessel is balanced inside a vertical conical tube
When the fluid flows upwards, the float remains constant when the dynamic forces on it are zero.
The flow rate is indicated by the floating position relative to the calibrated scale.
Design features of Able Flowmeter (Rotameter)
Design pressure: up to 350 PSIG (glass tube) / 720 PSIG (metal tube).
Design temperature: up to 400 ° C (glass tube) / 538 ° C (metal tube).
Size: up to 75 mm
Fluids / Applications: Clean liquids, gases and vapors
Flow range: Maximum 920 cubic meters per hour for liquids and 2210 cubic meters per hour for gases
MOC: Borosilicate Glass / Brass / Steel / Stainless Steel / Hastelloy
Accuracy: varies from 1% to 2.% of the actual current.
Winability is 10: 1
Upstream / downstream length is 10.5
Advantages of Rotameters
Simple, strong and linear output
No need for external impact or lead lines.
The pressure drop is minimal and relatively constant.
Disadvantages of rotameters
Vertical installation only
Glass tubes limit pressure and temperature and are prone to breakage due to hydraulic and thermal shocks.
Glass tubes eroded by insoluble solids and unsuitable for measuring alkaline solutions
Metal tube flowmeter is more expensive.
External particles can accumulate around the float and block the flow
Ultrasonic flowmeter
A pair of transducers, each with its own transmitter and receiver, are mounted on the tube wall, one (set) upstream and the other (set) downstream.
The time it takes for sound waves to travel from the upstream to the downstream converter (td) is shorter than the time it takes for the same waves to travel from the downstream to the upstream (tu).
The larger the difference, the faster the flow.
We describe the ultrasonic flowmeter along with its features, advantages and disadvantages in this section. Stay with us…
Ultrasonic flowmeter design features
Design pressure: 207 bar (insert type) / unlimited (depending on the type)
Design temperature: -180 degrees C to 260 degrees Celsius
Size: 3 mm to 3000 mm
Fluids: Clean gases, clean liquids / corrosive (low / no solid / bubble)
Speed range: 0.3 to 15 meters per second
Material: Mostly in stainless steel / alloy
Accuracy: + 0.5% flow rate for insert type / + 1% to 3% flow rate for type clamp
Repeatability is 10: 1 to 300: 1
Upstream / downstream length is 10.5
Two-way flow measurement
For insertion type, hot tapping is possible in pressurized pipelines
Advantages of Ultrasonic Flowmeters
No obstruction / moving parts in the flow path
No pressure drop
Low maintenance cost
Multi-path models have higher accuracy for a wider range of Reynolds numbers
Can be used in corrosive fluid flow
Portable models are available for field analysis and detection
Disadvantages of Ultrasonic Flowmeters
Only clean liquids and gases can be measured
Higher initial startup cost
Positive displacement flowmeters
The meter repeatedly traps the liquid in a certain amount and then removes it.
The amount of fluid that has passed is trapped based on the number.
Volumetric flow can be calculated from the rotational speed of the mechanical device.
Characteristics of positive displacement flowmeters (PD).
Design pressure: 1500 PSIG (liquid) /: 100 psig (gas)
Design temperature: 293 degrees C (liquids) /: -34 to 60 degrees. C (gases)
Size: 6 mm to 400 mm
Fluids: Clean liquids / gases
Flow range: 0 – 20000 GPM (liquids) /: 0 – 3000 cubic meters per hour (gas)
Material: mostly in aluminum, stainless steel, plastic, hastelloy
Accuracy is + 0.5% to +1 ٪ Dubai
Repeatability is 15: 1
Advantages of PD Flowmeters
Good accuracy and high repeatability
Can be used in viscous liquid flow
Low to medium initial start-up costs
No power supply required and available on a wide range of reading devices
Disadvantages of PD flowmeters
Due to the “moving parts” need to be repaired at frequent intervals.
High pressure drop due to obstruction
Not suitable for low flow
Not suitable for fluids with suspended solids
Gas (bubbles) in the liquid can significantly reduce the accuracy
Thermal mass flowmeter
It works by monitoring the cooling effect of the gas flow as it passes over the heated exchanger.
Gas flow passes through two PT100 RTD converters.
The temperature transducer controls the actual temperature of the gas process, while the self-heated transducer is kept constant by changing the flow current at differential temperature.
The higher the mass current that passes through the heated exchanger, the higher the current required to maintain the differential temperature.
Therefore, the measured heater flow is a measure of the mass flow rate of the gas.
Design features of thermal mass flowmeters
Design pressure: 1200 PSIG
Design temperature: 176 ° C
Size: 15 mm to 1000 mm
Fluids: Clean gases
Flow range: 0 – 2500 SCFM
Material: mostly in stainless steel / glass, Teflon, monel
Accuracy is 1% to + 2% flow rate
Repeatability is 10: 1 to 100: 1
Upstream / downstream length is 3.5
Advantages of thermal mass flowmeter
There is no need to compensate for temperature or pressure
Linear output (since the temperature difference is proportional to the mass flow)
It can be used on corrosive process streams if suitable materials are identified
DC voltage or 4 to 20 mA dc outputs are available
Disadvantages of thermal mass flowmeters
Practical for gas flow only
Prone to blockage by foreign particles or sediments due to small pores in the flowmeter
Excessive electricity needs in larger pipe sizes
Must be out of process line for service
Accurate field calibration is difficult
Application of flowmeters / selection of flowmeters
Clean liquids / gases
What is the most suitable flowmeter?
Orifis
Venturi
Side Flowmeter
Magnetic (liquids only)
Ultrasonic
Vertex
Coriolis mass flowmeters
Thermal mass flowmeter (gases only)
PD meter
Dirty liquids
What is the most suitable flowmeter? Magnetic flowmeter / Coriolis
Limited applications: flowmeter and lighting
Dirty gases
Most suitable: Vertex flowmeter
Limited Applications: Venturi Flowmeter / Thermal Mass Flowmeter / Double Able Flowmeter
Corrosive liquids: Magnetic flowmeter / Ultrasonic flowmeter
Non-Newtonian fluids: Coriolis mass flowmeter
Viscous liquids: Coriolis / magnetic / positive displacement gauge
Abrasive slurries: Magnetic flowmeters / Coriolis mass flowmeter
Fibrous slurries: Magnetic flowmeters / Coriolis mass flowmeter (limited applications)
Saturated steam
Most suitable: Orifice DP / Vortex flow meters
Limited applications: Venturi meter / variable area meter
Super hot steam
Most suitable: Orifice DP meter
Limited applications: Venturi meter
Refrigeration applications: Venturi meter / Orifis plates
Parameters affecting the flowmeter selection
Various factors affect the choice of flowmeter for a particular industrial process. Some of those factors are:
Fluid phase; For example: gas, liquid, steam
Flow conditions and flow range; For example: clean, dirty, abrasive or sticky liquid.
Process design parameters; For example, pressure, temperature range, density.
Tube size
Desired accuracy
Construction materials (corrosive or non-corrosive fluid).
Reproducibility and cost-effectiveness
Environmental considerations, if any.
Install the flowmeter
Flow measurement using flowmeters is an essential activity for any industry. Therefore, it must provide reliable and accurate data. The accuracy and repeatability of the measured data largely depends on the correct installation of the flowmeter. Here are some vital steps to take when installing a flowmeter:
– Must be installed in a suitable place.
– Should not be installed in places where there is vibration or magnetic field.
– The direction of flow must be clear before installation.
– Flowmeters should be installed on a straight pipe.
Some flowmeters may require a straight length upstream and downstream of the flowmeter. Must be maintained for accurate results.
For liquid flow applications, downstream flow should be avoided.
Make sure the flowmeter is completely filled with liquid.
Vapor or air in liquid lines and liquid droplets in gas lines should be avoided.
– It is preferable to install a filter above the flowmeter to remove solids.
– If a repair needs to be provided, a crossing line must be provided.
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