Variable Area Flow Meters Working Principle – InstrumentationTools

Содержание
  1. Limitations of electromagnetic Flow Meters
  2. Advantages of Electromagnetic Flow Meter
  3. Disadvantages of Magnetic Flow Meter
  4. Applications of Magnetic Flow Meters
  5. How to Use Magnetic Flow Meters
  6. Articles You May Like :
  7. Share With Your Friends
  8. Principle
  9. St= f*d/V0 (without dimension)
  10. f=(St*V)/c*D
  11. Pmin=3.2*Pdel + 1.25*Pv
  12. Frequency Sensing Principle
  13. Performance of Vortex meters is influenced by
  14. Features
  15. Selection and Sizing :
  16. Vortex Meter Advantages
  17. Vortex Flow Meter Limitations
  18. Vortex Flow Meter Applications
  19. Share With Your Friends
  20. Rotameters
  21. Advantages
  22. Disadvantages
  23. Articles You May Like :
  24. Share With Your Friends
  25. Flow Meters; a beginners’ guide
  26. How to select the best flow meter for your application 
  27. Learn more about flow meters in 6 steps:
  28. 1. What is a flow meter?
  29. 2. How does a flow meter work?
  30. Mass flow measuring principles 
  31. Gas & liquid flow meters
  32. 3. How to select the best flow meter for your application?
  33. Phase of the fluid: gas/liquid/vapour 
  34. For which fluid do you use the flow meter?
  35. What is the flow rate?
  36. What is the inlet and outlet pressure?
  37. What is the ambient temperature and the temperature of the fluid?
  38. What is the location of the flow meter?
  39. 4. What do you want to achieve with your flow meter?
  40. Performance versus price  
  41. Flow Meter Accuracy versus Repeatability 
  42. Flow Meter Accuracy 
  43. Flow Meter Repeatability
  44. Flexible use
  45. 5. Which process conditions can be relevant?
  46. Cleaning
  47. Available space
  48. Mounting of the flow meter
  49. Type of communication
  50. Moisture
  51. Need help?
  52. Other (traditional) ultrasonic flow measuring principles
  53. Transit time principle
  54. Doppler effect principle
  55. Bronkhorst ultrasonic volumetric flow meter/controller
  56. Types of Flowmeters | Flowmeter Types
  57. Volumetric Flowmeters
  58. Mass Flowmeters
  59. Differential Head Type Flowmeters
  60. Types of Orifice plates (Fig. 1)
  61. Tappings for the Orifice plates:
  62. Features of Orifice Plates
  63. Advantages of Orifice Plates
  64. Disadvantages of Orifice Plates
  65. Venturi Meters
  66. Features of Venturimeters
  67. Advantages of Venturimeters
  68. Disadvantages of Venturimeters
  69. Annubar Flowmeter
  70. Features of Annubar Flowmeters
  71. Advantages of Annubar flowmeters
  72. Disadvantages of Annubar flow meters.
  73. Variable Area Flowmeters/ Rotameters
  74. Design Features of Rotameters
  75. Advantages of Rotameters
  76. Disadvantages of Rotameters
  77. Magnetic Flowmeters
  78. Design features of Magnetic Flowmeters
  79. Advantages of magnetic Flowmeters
  80. Disadvantages of Magnetic Flowmeters
  81. Vortex Flowmeters
  82. Design Features of Vortex Flowmeters
  83. Advantages of Vortex Flowmeters
  84. Disadvantages of Vortex Flowmeters
  85. Ultrasonic Flowmeters
  86. Design Features of Ultrasonic Flowmeters
  87. Advantages of Ultrasonic Flowmeters
  88. Disadvantages of Ultrasonic Flowmeters
  89. Turbine Flowmeters
  90. Features of Turbine Flowmeters
  91. Advantages of Turbine Flowmeter
  92. Disadvantages of Turbine Flowmeters
  93. Positive Displacement Flowmeters
  94. Features of Positive Displacement (PD) Flowmeters
  95. Advantages of PD Flowmeters
  96. Disadvantages of PD Flowmeters
  97. Thermal Mass Flowmeter
  98. Design Features of Thermal Mass Flowmeters
  99. Advantages Of Thermal Mass Flowmeter
  100. Disadvantages of Thermal Mass Flowmeters
  101. Coriolis Mass Flowmeter
  102. Coriolis Mass Flowmeter Characteristics
  103. Advantages of Coriolis Mass Flowmeters
  104. Disadvantages of Coriolis Mass Flowmeters
  105. Application of Flowmeters / Selection of Flowmeters
  106. Clean liquids/gases
  107. Dirty Liquids
  108. Dirty Gases
  109. Saturated Steam
  110. Super-heated Steam
  111. Parameters affecting Flow meter Selection
  112. Installation of Flow meters
  113. We are checking your browser… www.electrical4u.com
  114. Why do I have to complete a CAPTCHA?
  115. What can I do to prevent this in the future?

Limitations of electromagnetic Flow Meters

(i) The substance being measured must be conductive. Therefore, it can’t be employed for metering the flow rate of gases and steam, petroleum products and similar liquids having very low conductivity.

(ii) To render the meter insensitive to variations in the resistance of liquid, the effective resistance of the liquid between the electrodes should not exceed 1% of the impedance of the external circuit.

(iii) It is a very expensive device.

(iv) As the meter always measures the volume rate, the volume of any suspended matter in the liquid will be included.

(v) To avoid any trouble which would be caused by entrained air, when the flow tube is installed in a horizontal pipe-line, the electrodes should be on the horizontal diameter.

(vi) As a zero check on the installation can be performed only by stopping the flow, isolating valves are required and a bypass may also be necessary through which the flow may be directed during a zero check.

(vii) The pipe must run full, in case regulating valves are installed upstream of the meter.

Advantages of Electromagnetic Flow Meter

(i) The obstruction to the flow is almost nil and therefore this type of meters can be used for measuring heavy suspensions, including mud, sewage and wood pulp.

ii) There is no pressure head loss in this type of flow meter other than that of the length of straight pipe which the meter occupies.

(iii) They are not very much affected by upstream flow disturbances.

(iv) They are practically unaffected by variation in density, viscosity, pressure and temperature.

(v) Electric power requirements can be low (15 or 20 W), particularly with pulsed DC types.

(vi) These meters can be used as bidirectional meters.

(vii) The meters are suitable for most acids, bases, water and aqueous solutions because the lining materials selected are not only good electrical insulators but also are corrosion resistant.

(viii) The meters are widely used for slurry services not only because they are obstruction less but also because some of the liners such as polyurethane, neoprene and rubber have good abrasion or erosion resistance.

(ix) They are capable of handling extremely low flows.

Disadvantages of Magnetic Flow Meter

(i) These meters can be used only for fluids which have reasonable electrical conductivity.

(ii) Accuracy is only in the range of ± 1% over a flow rate range of 5%.

(iii) The size and cost of the field coils and circuitry do not increase in proportion to their size of pipe bore. Consequently small size meters are bulky and expensive.

Applications of Magnetic Flow Meters

This electromagnetic flow meter being non intrusive type, can be used in general for any fluid which is having a reasonable electrical conductivity above 10 microsiemens/cm.

Fluids like sand water slurry, coal powder, slurry, sewage, wood pulp, chemicals, water other than distilled water in large pipe lines, hot fluids, high viscous fluids specially in food processing industries, cryogenic fluids can be metered by the electromagnetic flow meter.

How to Use Magnetic Flow Meters

Magnetic flowmeters measure the velocity of conductive liquids in pipes, such as water, acids, caustic, and slurries. Magnetic flowmeters can measure properly when the electrical conductivity of the liquid is greater than approximately 5μS/cm. Be careful because using magnetic flowmeters on fluids with low conductivity, such as deionized water, boiler feed water, or hydrocarbons, can cause the flowmeter to turn off and measure zero flow.

This flowmeter does not obstruct flow, so it can be applied to clean, sanitary, dirty, corrosive and abrasive liquids. Magnetic flowmeters can be applied to the flow of liquids that are conductive, so hydrocarbons and gases cannot be measured with this technology due to their non-conductive nature and gaseous state, respectively.

Magnetic flowmeters do not require much upstream and downstream straight run so they can be installed in relatively short meter runs. Magnetic flowmeters typically require 3-5 diameters of upstream straight run and 0-3 diameters of downstream straight run measured from the plane of the magnetic flowmeter electrodes.

Applications for dirty liquids are found in the water, wastewater, mining, mineral processing, power, pulp and paper, and chemical industries. Water and wastewater applications include custody transfer of liquids in force mains between water/wastewater districts.

Magnetic flowmeters are used in water treatment plants to measure treated and untreated sewage, process water, water and chemicals. Mining and mineral process industry applications include process water and process slurry flows and heavy media flows.

With proper attention to materials of construction, the flow of highly corrosive liquids (such as acid and caustic) and abrasive slurries can be measured. Corrosive liquid applications are commonly found in the chemical industry processes, and in chemical feed systems used in most industries. Slurry applications are commonly found in the mining, mineral processing, pulp and paper, and wastewater industries.

Magnetic flowmeters are often used where the liquid is fed using gravity. Be sure that the orientation of the flowmeter is such that the flowmeter is completely filled with liquid. Failure to ensure that the flowmeter is completely filled with liquid can significantly affect the flow measurement.

Be especially careful when operating magnetic flowmeters in vacuum service because some magnetic flowmeter liners can collapse and be sucked into the pipeline in vacuum service, catastrophically damaging the flowmeter.

Note that vacuum conditions can occur in pipes that seemingly are not exposed to vacuum service such as pipes in which a gas can condense (often under abnormal conditions).

Similarly, excessive temperature in magnetic flowmeters (even briefly under abnormal conditions) can result in permanent flowmeter damage.

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Vortex Meters can be used for a wide range of fluids, i.e. liquids, gases and steam. They are to be seen as first choice, subject to verification to cover the requirements of a particular application. Vortex Flow Animation

Vortex meters are essentially frequency meters, since they measure the frequency of vortices generated by a “bluff body” or”shedder bar”.

Vortices will only occur from a certain velocity (Re-number) on-wards, consequently vortex meters will have an elevated zero referred to as the “cut-off” point. Before the velocity becomes nil, the meter output will be cut to zero.

At a certain back-flow (above cut off point) some vortex meters could produce an output signal, which could lead to a false interpretation.

Also See: Vortex Flow Meter Animation

Vortex meters are actual volume flow meters, like orifice meters. These being intrusive meters like orifice meters, will cause the pressure drop as flow is increased, resulting in a permanent loss. consequently, liquids near their boiling point, could introduce cavitation as the pressure across the meter drops below the vapour pressure of the liquid.

As soon as the pressure recovers above the vapour pressure the bubbles will impode. cavitation causes the meter to malfunction and should be avoided at all times.

Vortex Flow Meter Principle

Principle

A fluid flowing with a certain velocity and passing a fixed obstruction generates vortices. The generation of vortices is known as Karman’s Vortices and culmination point of vortices will be approx. 1.2D downstream of bluff body.

Strouhal discovered that as soon as a stretched wire starts vibrating in an air flow, frequency will be directly proportional to air velocity,Vortex Flow meter

St= f*d/V0 (without dimension)

St= Strouhal’s number

f=frequency of wire

d=diameter of wire

V0= Velocity

This phenomena is called “vortex shedding” and the train of vortices is known as “Karman’s Vortex street”.

The frequency of vortex shedding is a direct linear function of fluid velocity and frequency depends upon the shape and face width of bluff body. Since the width of obstruction and inner diameter of the pipe will be more or less constant, the frequency is given by the expression-

f=(St*V)/c*D

f= vortex frequency, Hz

St=strouhal’s number, dimention less

V=Fluid velocity at the sheddar bar, m/s

D=Inner diameter of the pipe, m

c=constant (ratio d/D)

d= Face width of sheddar bar, m

The pressure loss gradient across the vortex meter will have a similar shape to that of an orifice meter. the lowest point in pressure will be at the sheddar bar (comparable to vena contracta for orifice meter). downstream of this point of pressure will recover gradually, finally resulting in permanent pressure loss. To avoid cavitation, the pressure loss at vena-contracta is of interest.

The minimum back pressure required to ensure cavitation doesn’t occur is:

Pmin=3.2*Pdel + 1.25*Pv

Pmin= minimum required pressure at five pipe diameters downstream of the flow meter in bar

Pdel= calculated permanent pressure loss in bar

Pv= vapour pressure at operating temperature in bar

Remember- for most vortex meters d/D will have range, 0.22 – 0.26, & frequency od vortices will depend on sizre of meter, larger the meter, lower the frequency. So the maximum diameter of vortex meter is restricted, because resolution of meter could become a problem.for control purposes.

To overcome this problem, on-board digital multipliers are used which will multiply the vortex frequency without additional error.

Frequency Sensing Principle

Piezo-electrical Sensors- a pair of piezo-electrical crystals is built into the sheddar bar. as the sheddar bar will be subject to alternating forces caused by shedding frequency, so will the piezo-crystals.

Variable capacitance Sensors- a pair of variable capacitance sensors is built into the sheddar bar. As the sheddar bar will be subject to alternating micro movements caused by forces as a result of the shedding frequency, the capacitors will change their capacitance accordingly.

Performance of Vortex meters is influenced by

change in sheddar bar geometry owning to erosion

change in sheddar bar geometry owning to deposits, i.e. Wax

corrosion of upstream piping

change in position of sheddar bar if not properly secured

Hydraulic noise.

In-general votex meter will consist of following electonics part-

pick-up elements, AC-pre amplifiers, AC-amplifier with filters, Noise abatement features, Schmitt Trigger, Microprocessor

Features

The vortex shedding meter provides a linear digital (or analog) output signal without the use of separate transmitters or converters, simplifying equipment installation. Meter accuracy is good over a potentially wide flow range, although this range is dependent upon operating conditions.

The shedding frequency is a function of the dimensions of the bluff body and, being a natural phenomenon, ensures good long term stability of calibration and repeatability of better than ±0.15% of rate. There is no drift because this is a frequency system.

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The meter does have any moving or wearing components, providing improved reliability and reduced maintenance. Maintenance is further reduced by the fact that there are no valves or manifolds to cause leakage problems. The absence of valves or manifolds results in a particularly safe installation, an important consideration when the process fluid is hazardous or toxic.

The vortex shedding meter also offers a low installed cost, particularly in pipe sizes below 6 in. (152 mm) diameter, which compares competitively with the installed cost of an orifice plate and differential pressure transmitter.

The limitation include meter size range. Meters below 0.5 in. (12 mm) diameter are not practical, and meters above 12 in. (300 mm) have limited application due their high cost compared to an orifice system and their limited output pulse resolution.

Selection and Sizing :

 As the first step in the selection process, the operating conditions (process fluid temperature, ambient temperature, line pressure, and so on) should be compared with the meter specification.

The meter minimum flow rate is established by a Reynolds number of 10,000 to 10,500, the fluid density, and a minimum acceptable shedding frequency for the electronics. The maximum flow rate is governed by the meter pressure loss (typically two velocity heads), the onset of cavitation with liquids, and sonic velocity flow (choking) with gases.

Consequently, the flow range for any application depends totally upon the operating fluid viscosity, density, and the vapour pressure, and the applications maximum flow rate and line pressure.

On low viscosity products such as water, gasoline, and liquid ammonia, and with application maximum velocity of 15 ft/s (4.6 m/s), vortex shedding meters can have a rangeability of about 20:1 with a pressure loss of approximately 4 PSIG (27.4 kPa).

The meter’s good (“of rate”) accuracy and digital linear output signal make its application over wide flow ranges a practical proposition. The rangeability declines proportionally with increase in viscosity, decrease in density, or reductions in the maximum flow velocity of the process. Vortex shedding meters are therefore unsuitable for use on high viscosity liquids.

Vortex Meter Advantages

  • Vortex meters can be used for liquids, gases and steam
  • Low wear (relative to turbine flow meters)
  • Relatively low cost of installation and maintenance
  • Low sensitivity to variations in process conditions
  • Stable long term accuracy and repeatability
  • Applicable to a wide range of process temperatures
  • Available for a wide variety of pipe sizes

Vortex Flow Meter Limitations

  • Not suitable for very low flow rates
  • Minimum length of straight pipe is required upstream and downstream of the vortex meter

Vortex Flow Meter Applications

Vortex flow meters are suitable for a variety of applications and industries but work best with clean, low-viscosity, medium to high speed fluids.

Some of the main uses include:

  • Custody transfer of natural gas metering
  • Steam measurement
  • Flow of liquid suspensions
  • General water applications
  • Liquid chemicals & pharmaceuticals

Also Read: Turbine Flow Meter Working Principle

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Rotameters

The rotameter is an industrial flowmeter used to measure the flowrate of liquids and gases. Its operation is based on the variable area principle: fluid flow raises a float in a tapered tube, increasing the area for passage of the fluid. The greater the flow, the higher the float is raised.

The height of the float is directly proportional to the flowrate. With liquids, the float is raised by a combination of the buoyancy of the liquid and the velocity head of the fluid.

With gases, buoyancy is negligible, and the float responds to the velocity head alone. The float moves up or down in the tube in proportion to the fluid flowrate and the annular area between the float and the tube wall.

The float reaches a stable position in the tube when the upward force exerted by the flowing fluid equals the downward gravitational force exerted by the weight of the float. A change in flowrate upsets this balance of forces. The float then moves up or down, changing the annular area until it again reaches a position where the forces are in equilibrium.

Rotameter working principle

To satisfy the force equation, the rotameter float assumes a distinct position for every constant flowrate. However, it is important to note that because the float position is gravity dependent, rotameters must be vertically oriented and mounted.

The tapered tube’s gradually increasing diameter provides a related increase in the annular area around the float, and is designed in accordance with the basic equation for volumetric flow rate:

Rotameter formula

where:

Q = volumetric flow rate, e.g., gallons per minute
k = a constant
A = annular area between the float and the tube wall
g = force of gravity
h = pressure drop (head) across the float

With h being constant in a VA meter, we have A as a direct function of flow rate Q. Thus, the rotameter designer can determine the tube taper so that the height of the float in the tube is a measure of flow rate.

Variable area flowmeters are used primarily to set flowrates. The operator observes the meter, and adjusts the valve to bring the process flow to the proper flowrate. The meter’s ability to repeat or reproduce this flowrate is of primary importance. Rotameters are repeatable up to ±1 ⁄4% of the instantaneous flowrate. This feature enables the operator to reset or adjust the flow with confidence.

Advantages

  1. The rotameter is popular because it has a linear scale, a relatively long measurement range, and low pressure drop.
  2. It is simple to install and maintain.
  3. It can be manufactured in a variety of construction materials and designed to cover a wide range of pressures and temperatures.
  4. The rotameter can easily be sized or converted from one kind of service to another. In general, it owes its wide use to its versatility of construction and applications.
  5. Because of its functional advantages the rotameter is an exceptionally practical flow measurement device.
  6. The pressure drop across the float is low and remains essentially constant as the flowrate changes. Float response to flowrate changes is linear, and a 10-to-1 flow range or turndown is standard.
  7. Variable area flowmeters are commonly used to provide cost-effective local indication of small liquid or gas flows

Disadvantages

  1. Low accuracy – uncertainty on volumetric flowrate is ~2% of reading
  2. Generally small turndown
  3. Tendency of float to ‘stick’ at low flows
  4. Requirement for buoyancy correction in liquids
  5. Application Cautions for Variable Area Flowmeters

Do not apply variable area flowmeters to fluids that are opaque, dirty, or prone to coat the metering tube or float, because these may render the flowmeter inoperable.

Be sure to install variable area flowmeters with floats in the vertical orientation because their operation is dependent upon gravity. Variable area flowmeters that require upward flow may not suitable in many applications where the fluid flows using only gravity.

Variable Area Flow Meters Theory

A potential safety hazard can be created if a glass metering tube breaks, especially when dangerous fluids are present in the flowmeter. Be careful to install variable area flowmeters with glass metering tubes in locations where the glass cannot be damaged.

Also, the float can get stuck when flow turns on suddenly or when high flow rates cause the float to be reach its highest mechanical position.

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Flow Meters; a beginners’ guide

How to select the best flow meter for your application 

Do you need a flow meter for your application? Then you need to know what aspects you should take into consideration when selecting a flow meter for your application. We will guide you along your way of making the best selection.

But first, let’s explain a bit more about what flow meters are, how they work, what they are used for and the criteria to select the best flow meter for the application.

Flow Meter with ultrasonic and Coriolis measuring principle

Flow meters in calibration setup

Learn more about flow meters in 6 steps:

  1. What is a flow meter?
  2. How does a flow meter work?
  3. How to select the best flow meter?
    • Phase of the fluid: gas/liquid/vapour 
    • For which fluid do you use the flow meter?
    • What is the flow rate?
    • What is the inlet and outlet pressure?
    • What is the ambient temperature and the temperature of the fluid?
    • What is the location of the flow meter?
  4. What do you want to achieve with your flow meter?
    • Performance versus price  
    • Flow meter accuracy versus repeatability 
    • Flexible use  
  5. Which process conditions can be relevant?
  6. Examples of applications in which flow meters are used

1. What is a flow meter?

A flow meter is an instrument that measures a mass or volumetric flow rate of a gas or liquid. You might have come across a variety of terms when referring to a flow meter, such as flow sensor, mass flow meter, mass flow controller, flow regulator etc.

The purpose of a flow meter basically is measuring the flow of gas or liquid between two points in a process. Sometimes controlling or regulating the flow is necessary. This is done by combining a flow meter with a valve, creating a flow controller. In this case, besides measuring a flow, you can also control it to change the flow rate. The output can help you understand your process better to make decisions regarding product quality, speed of process and cost reduction.

2. How does a flow meter work?

There are two basic types of fluid measurement – mass and volume flow measurement. The volumetric flow measurement is temperature and pressure dependent and will be shown in units of volume such as ml/min or m3/h. When measuring mass flow, you see units of mass such as kg/h or g/min. Alternatively, mass flow can be expressed as standardized volumes e.g. mls/min or m3n/h. Therefore, you can either choose for a mass flow meter or a volumetric flow meter for your application.

Besides these two types of measurement, there are different measuring principles that all have their specific advantages and disadvantages:  

Mass flow measuring principles 

Coriolis mass flow measuring principle 

Thermal Mass Flow Meter/Controller for Gas (by-pass design).  

Gas & liquid flow meters

You can find a glossary page on our website, in which you will find a lot of terms and abbreviations that are common in the field of flow measurement. 

3. How to select the best flow meter for your application?

In this paragraph we will discuss some of the essential elements that go into the decision-making process of selecting a flow meter. Thereby, we consider the differences between various measurement principles. Read below what to think of when selecting a flow meter.

Phase of the fluid: gas/liquid/vapour 

Some flow meters can be easily eliminated because they simply will not work with the application. For instance, electromagnetic flow meters will not work with hydrocarbons and require a conductive liquid to function. Many flow meters cannot measure vapours or slurries.  

Listed below are some of the main flow meter categories paired with the fluid type the meters can handle: 

  • Gas – Coriolis Mass, Thermal Mass, Ultrasonic, Variable Area, Variable Differential Pressure, Positive Displacement, Turbine 
  • Liquid – Coriolis Mass, Thermal Mass, Ultrasonic, Variable Differential Pressure, Positive Displacement, Turbine, Electromagnetic 
  • Slurry – Coriolis Mass, some subsets of Variable Differential Pressure, Electromagnetic, Ultrasonic 
  • Vapour – Vortex, Ultrasonic, Diaphragm, Floating Element 

For which fluid do you use the flow meter?

Chemical and physical properties of the medium can influence the material of the flow meter and therefore the working of the instrument. Commonly, the following wetted parts (parts that are exposed to or in direct contact with the medium) may be offered:

  • aluminium
  • stainless steel
  • hastelloy and
  • monel in combination with Viton (FKM), Kalrez (FFKM) or EPDM elastomer seals

Please note that MEMS or CMOS (chip) sensors which are applied in some gas flow meters, are only suitable for a restricted number of non-aggressive gas types. 

Another aspect you must consider is the viscosity of the fluid, the density and dispersion (solid content). Not all measurement technologies can be used for all fluids, for example electromagnetic flow meters can only be applied for conductive liquids.  

What is the flow rate?

The flow rate is usually the most important specification to consider when selecting a flow meter. Fluid quantity can be displayed in volume, standardized volume and true mass units. The flow rate is the quantity of fluid per unit time flowing through a measuring device. 

Check out the blog to find out why it is important to know what reference conditions you are working with. A supplier usually indicates the minimum and maximum full scale range of a product series. This should meet your process requirements.  

BLOG: Reference conditions

What is the inlet and outlet pressure?

When selecting a flow meter, it is important to know if you need a low pressure drop or not. The pressure drop is defined as the difference between the inlet and the outlet pressure. Next to this, flow meters have a maximum operating pressure. If you have a high-pressure application, you need to take this pressure rating into consideration.

In case of mass flow control, the inlet pressure (P1) and outlet pressure (P2) are required for selection and dimensioning of the most appropriate control valve.

What is the ambient temperature and the temperature of the fluid?

The temperature of your fluid and of the instrument’s environment are the next topics on the list to check.

Variations in fluid temperature may affect the accuracy of your measurement. In case of temperature fluctuations, it could be interesting to select a flow meter with temperature compensation (e.g. the EL-FLOW Prestige flow meters).

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Too high or too low environment temperatures may also harm the electronic components of your flow meter during operation or storage. When you use a flow meter in a furnace of burner application, or in areas with very low temperatures, it is important to check whether the instrument can withstand these extreme temperatures. Therefore, check the temperature specifications as provided by the supplier before selecting your flow meter.

What is the location of the flow meter?

When selecting your flow meter, you must consider where you install it. Whether it is indoors, outdoors, in a laboratory or for a particular industry. For laboratories other specifications are applicable than for the oil and gas industry.

Flow meters used for fish farming

4. What do you want to achieve with your flow meter?

When selecting your flow meter, you need to think of what is important in your process. What do you want to achieve? 
 

Performance versus price  

The most common criteria to select a flow meter are price and performance. If you place price at the top of your criteria, you are likely to get a basic instrument, with less than average performance.  

 
Next to the price of the component, installation, maintenance, and repairs over time should be included in calculating the total cost of ownership. How much the meter costs to operate, like its electrical consumption, can also increase the overall cost of the flow meter. 

Flow Meter Accuracy versus Repeatability 

The specifications of the flow meter must be taken into consideration when selecting a flow meter. Accuracy and repeatability are important specs to look at.

Flow Meter Accuracy 

Accuracy is how close the measurement is to the true value. For flow meters, the measured deviations are often visualised on a calibration certificate. This is expressed as a percentage, e.g., ±1%.  Not all flow meters offer the same accuracy; however, not all applications require the highest possible accuracy. Nevertheless, absolute accuracy is important in quantitative research and development or catalytic applications.

Flow Meter accuracy

Flow Meter Repeatability

Repeatability is producing the same outcome given the same conditions. In other words, a flow meter should produce the same readings when operated under the same variables and conditions. This, too, is expressed as a ± percentage. This is, for example, especially important for burner applications. 

BLOG: Accuracy vs Repeatability

Flow Meter repeatability

Flexible use

Sometimes it makes sense to select a flow meter that can be used in multiple applications. For instance, when you need an instrument in a research project and you know that other projects will follow in the future, but you have no idea what fluids are used then. In cases like this, it can be beneficial to select a flow meter that is fluid independent and has a wide flow range as well.  

In case you have an application with high fluctuations in flow rate, you probably prefer a flow meter with a high turndown ratio. Turndown ratio is also commonly referred to as rangeability. It indicates the range in which a flow meter or controller can accurately measure the fluid. In other words, it’s simply the high end of a measurement range compared to the low end, expressed in a ratio and is calculated using a simple formula: Turndown Ratio = maximum flow / minimum flow. Read more about turndown ration in our FAQs.

5. Which process conditions can be relevant?

Cleaning

In the food and beverage and pharmaceutical industry, cleaning your instrumentation is important to avoid cross contamination. Clean-in-place (CIP) is a method of cleaning the interior surfaces of pipes, vessels, equipment, filters, and fittings. A typical CIP cycle consists of various steps including washing with a hot cleaning agent and hot acid with temperatures up to 95°C. Steam-in-place, also referred to as sterilization-in-place (SIP), consists of a phase in which the instrument is sterilized with saturated steam with a temperature up to 140 °C. Not all flow meters are suitable for these cleaning methods, so it’s an important factor to consider when applicable. Please also note that these markets often require the application of FDA approved seals as well.

Available space

Is space limited in your process? Then select a flow meter that is compact and does not require a straight run of pipe at the inlet or outlet. There are ultra compact flow meters on the market based on MEMS technology (e.g. the IQ+FLOW gas flow meter).

Flow Meters for gas and liquid flow measurement

Mounting of the flow meter

Before selecting a flow meter it is essential to check where to locate and how to position the instrument in your installation. The accuracy of some instruments is more affected by its mounting position than others. Other relevant aspects with respect to the mounting of flow meters may be disturbances caused by vibrations, crosstalk, pressure shocks and the effects of bends, valves and reductions of pipe diameters up- and downstream of the instruments. These effects may also vary per operating principle.

Type of communication

Check whether you need a digital or analog flow meter. Besides that, you need to know what type of communication is used in your process. Popular types of fieldbus communication are Profinet, EtherCAT, CANopen, Ethernet/IP and POWERLINK but also the more established versions such as Modbus, Profibus and DeviceNet can be integrated. There is also the possibility of using a manufacturer’s own fieldbus communication, such as Bronkhorst’s FLOW-BUS. This has the advantage of a simple and cost-effective network setup that can be transferred to common interfaces such as RS232, Profinet and Profibus. 

Moisture

Some flow meters are more sensitive to moisture or particles than others. Appropriate filtering to protect your instruments may be a good investment, saving costs for cleaning, repair, interruption of your process and possibly also the waste of raw material or finished product.

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Datasheet Ultrasonic Liquid Flow Measurement


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Bronkhorst ES-FLOW™ Ultrasonic Wave Technology

The operation of Bronkhorst® ES-FLOW™ flow meters is based on the propagation of ultrasound waves inside a very small, straight sensor tube, without obstructions or dead spaces. At the outer surface of the sensor tube multiple transducer discs are located which create ultrasonic sound waves by radial oscillation.

Every transducer can send and receive, therefore all up- and down-stream combinations are recorded and processed. By accurately measuring the time difference between the recordings (nanosecond range) the flow velocity and speed of sound is calculated. Knowing these parameters and the exact tube cross-section, the ES-FLOW™ is able to measure liquid volume flows in the range of 2 up to 1500 ml/min.

The distinctive character of this flowmeter is that it’s capable to measure the actual speed of sound, meaning that the technology is liquid independent and calibration per fluid is not necessary.

Find your ultrasonic flow meter/controller

Ultrasonic sensor ultrasonic wave principle

Other (traditional) ultrasonic flow measuring principles

(Source: Wikipedia. Note well, these techniques are completely different to the technology Bronkhorst applies in their ES-FLOW series and can therefore not be compared.)

Transit time principle

Product link: SONIC-VIEW

Transit time principle

Doppler effect principle

Another method in ultrasonic flow metering, also not suited for very low flowrates, is the use of the Doppler shift that results from the reflection of an ultrasonic beam off sonically reflective materials, such as solid particles or entrained air bubbles in a flowing fluid, or the turbulence of the fluid itself, if the liquid is clean.

Doppler effect principle

Bronkhorst ultrasonic volumetric flow meter/controller

Types of Flowmeters | Flowmeter Types

Broadly two types of flow meters are widely used in industries:

  • Volumetric Flow meters and
  • Mass 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. Volumetric flow meters provide an instantaneous analog, digital, or pulse output of the volumetric flow rate of the liquid or gas. Various types of Volumetric Flowmeters are available as listed below

  • Differential Head type
    • Orifice plates
    • Venturi meters
    • Annubar
  • Differential Area type (Rotameters)
  • Electromagnetic flowmeters
  • Ultrasonic flowmeters
  • Turbine flowmeters
  • Vortex flowmeters
  • Positive Displacement Meters

Mass Flowmeters

Mass flow meters measure the fluid mass flow rate that travels through a tube per unit of time. There are two types of mass flowmeters as mentioned below

  • Coriolis Mass flowmeter and
  • Thermal Mass flowmeters

Differential Head Type Flowmeters

  • The difference in pressure exists between the upstream & downstream sides of a restriction in a confined fluid stream, which related to the square of fluid velocity.
    • Q α √ ▲P

Where Q = Volume flow rate and ▲P = Differential pressure between taps

Differential head type flowmeters
Fig. 1: Differential head type flowmeters

Types of Orifice plates (Fig. 1)

  • Concentric orifice plate: Most commonly used
  • Segmental & Eccentric orifice plate: Used for fluids containing suspended solids.

Tappings for the Orifice plates:

  • Corner taps (< 1 inch)
  • D and D/2 taps ( 2 to 16 inch)
  • Flange taps (> 16 inch)

Features of Orifice Plates

  • Design Pressure: No limitation. Limited by DP transmitter
  • Design Temperature: No limitation. Limited by DP transmitter
  • Sizes: Maximum size is the pipe size
  • Flow range: limited only by pipe size.
  • Fluids/ Applications: Cryogenic / clean gases & liquids/ Steam (saturated/superheated)
  • MOC: No limitation (Steel/ monel/nickel/ haste alloy)
  • Accuracy : It varies from ±0.25% to ±0. 5% of actual flow. The accuracy of the DP transmitter varies from ±0.1% to ±0. 3% of full-scale error.
  • Rangeability is 3:1 to 5:1.
  • Upstream length/ Downstream straight length is 20 / 5

Advantages of Orifice Plates

  • Easily installed between flanges.
  • Fabrication simple and inexpensive.
  • No limitations on the materials of construction, line size and flow rate
  • Cost relatively independent of pipe diameter since the cost of DPT is fixed.
  • No process interruption for the exchange of DP transmitter.

Disadvantages of Orifice Plates

  • High permanent pressure loss & hence high energy consumption to overcome pressure loss.
  • Impractical for systems with low static pressure.
  • Measuring range to about 3:1 to 5:1.
  • Accuracies decrease with Beta ratios above approximately 0.7.
  • Subject to damage by water hammer and foreign objects.

Venturi Meters

A venturi tube (Fig. 2) measures flow rates by constricting fluids and measuring a differential pressure drop. In the upstream cone of the Venturi meter, velocity is increased, the pressure is decreased. Pressure drop in the upstream cone is utilized to measure the rate of flow through the instrument. Further details of the venturi meter are provided here

Figure showing Venturi meter and Annubar Flowmeter
Fig. 2: Figure showing Venturi meter and Annubar Flowmeter

Features of Venturimeters

  • Design Pressure: No limitation. Limited by DP transmitter/ pipe press.ratings.
  • Design Temperature: No limitation. Limited by DP transmitter/ pipe pressure ratings
  • Sizes: 25 mm to 3000 mm
  • Fluids/ Applications: Clean Liquids/ clean gases
  • Limited applications: Dirty /corrosive/viscous Liquids & Dirty gases
  • Flow range: limited only by pipe size and beta ratio.
  • MOC: No limitation (cast iron/ carbon steel/ SS/Monel, Titanium, Teflon, Hastelloy, Naval Bronze/haste alloy)
  • Accuracy : It varies from ±0.25% to ±0. 75% of actual flow. The accuracy of DP transmitter varies from ±0.1% to ±0. 3% of full-scale error.
  • Rangeability is 3:1 to 5:1.
  • Upstream length/ Downstream straight length is 20 / 5

Advantages of Venturimeters

  • Lower head losses than orifice plates reducing the capital expenditure on pumping eqpt. / save pump energy costs
  • No process interruption for the exchange of DP transmitter.
  • Can be used for temperature extremes
  • Cryogenics or High Temperatures

Disadvantages of Venturimeters

  • Highly expensive
  • Larger and heavier to handle.

Annubar Flowmeter

The Annubar flowmeter is a device to measure the fluid flow (liquid, vapor, or gas) in a pipeline. The flow is measured by creating a differential pressure. As per Bernoulli’s theorem, this differential pressure is proportional to the square of the fluid velocity in the pipeline. The annubar flowmeter measures this differential pressure which is then converted to flow rate using a secondary device.

  • The probe is installed in the media line as a pressure sensor.
  • With the flow, the probe records both the static and the dynamic pressure via the probe openings.
  • In the minus chamber of the annubar, lying on the opposite side, only the static pressure has any effect
  • The differential pressure corresponds to the dynamic pressure in the pipeline & the flow can is calculated directly.

Features of Annubar Flowmeters

  • Design Pressure: Upto 97 bars (38 Deg.C) / 55 bars (370 Deg.C)
  • Design Temperature: Upto 400 deg.C
  • Sizes: 50 mm to 3000 mm
  • Fluids : Clean Liquids, gases and steam
  • MOC: Brass / steel/ stainless steel/ Hastelloy
  • Accuracy : It varies from ±1% to ±2% of actual flow. The accuracy of the DP transmitter varies from ±0.1% to ±0. 3% of full-scale error.
  • Rangeability is 3:1 to 5:1.
  • Upstream length/ Downstream straight length is 20 / 5

Advantages of Annubar flowmeters

  • The integral manifold head allows direct mounting of DP transmitters
  • Hot tapping: Insertion/ installation without system shutdown
  • Very low-pressure drop

Disadvantages of Annubar flow meters.

  • Not suitable for viscous and slurry applications
  • Can be used for only for clean fluids.

Variable Area Flowmeters/ Rotameters

  • A free moving float is balanced inside a vertical tapered tube
  • As the fluid flows upward the float remains steady when the dynamic forces acting on it are zero.
  • The flow rate indicated by the position of the float relative to a calibrated scale.
Variable area flowmeters
Fig. 3: Variable area flowmeters

Design Features of Rotameters

  • Design Pressure: Upto 350 PSIG (GLASS TUBE) / 720 PSIG (METAL TUBE).
  • Design Temperature: Upto 400 deg.C (GLASS TUBE) / 538 Deg.C (METAL TUBE) .
  • Sizes: upto 75 mm
  • Fluids/ Applications : Clean liquids, gases and vapours
  • Flow range: upto 920 cub.m/hr for liquids & 2210 cub.m/hr for gases
  • MOC: Borosilicate glass/ brass / steel/ stainless steel/ Hastelloy
  • Accuracy : It varies from ±1% to ±2% of actual flow.
  • Rangeability is 10:1
  • Upstream length/ Downstream straight length is 10 / 5

Advantages of Rotameters

  • Simple, robust and linear output
  • It does not require external impulse or lead lines.
  • The pressure drop is minimal and fairly constant.

Disadvantages of Rotameters

  • Vertical installation only.
  • Glass tubes limit pressure & temperature and subject to breakage from hydraulic & thermal shock
  • Glass tubes eroded by undissolved solids & unsuitable for metering alkaline solutions
  • Metal tube meters more expensive.
  • Foreign particles can accumulate around the float & block the flow

Magnetic Flowmeters

  • Operate on Faraday’s Law of magnetic induction.
  • When a conductive fluid moves in a magnetic field, a voltage is generated between two electrodes at right angles to the fluid velocity and field orientation.
  • The flow tube has a fixed area & field intensity so the developed voltage is linearly proportional to the volumetric flow rate.
Figure showing Magnetic Flowmeters
Fig. 4: Figure showing Magnetic Flowmeters

Design features of Magnetic Flowmeters

  • Design Pressure: 20 BARS to 172 BARS
  • Design Temperature: Upto 120 deg.C with teflon liners / 180 Deg.C with ceramic liners
  • Sizes: 2.5 mm to 3000 mm
  • Fluids : Liquids (clean/ corrosive/dirty/viscous/ slurry)
  • Velocity range: 0.1 to 10 m/s
  • MOC: Liners: ceramic/ teflon/rubber : Electrodes: Platinum/ hastelloy/SS
  • Accuracy: It varies from ±0.5% to ±1% of actual flow.
  • Rangeability is 10:1
  • Upstream length/ Downstream straight length is 10 / 5

Advantages of magnetic Flowmeters

  • Flow rate unaffected by fluid density, consistency, viscosity, turbulence, or piping configuration.
  • Highly accurate due to the absence of moving parts/ external sensing lines
  • Corrosion-resistant using Teflon liner and platinum electrodes
  • Wide flow measuring ranges & no pressure drop

Disadvantages of Magnetic Flowmeters

  • Costly, relative to other flowmeter types.
  • Temperature of the fluids being metered limited by the liner material rating.
  • Cannot be used for gas flow measurements

Vortex Flowmeters

  • An obstruction is placed across the pipe bore at right angle to fluid flow.
  • As fluid flows, vortices are shed from alternating sides of the body & this shedding frequency is directly proportional to fluid velocity.
  • Detection of the vortices by means of pressure changes in the vortex stream.
  • Rate of creation of vortices directly proportional to the flow rate.

Design Features of Vortex Flowmeters

  • Design Pressure: 138 bars
  • Design Temperature: -200 Deg. C to 400 Deg.C
  • Sizes: 15 mm to 300 mm
  • Fluids : Gases (clean/ dirty) and clean liquids
  • Velocity range: 0.3 to 10 m/s (liquids) and 6 to 80 m/s (gases)
  • MOC: mostly in stainless steel, some in plastic
  • Accuracy : It varies from ±0.5% to ±1% of actual flow for liquids and ±1% to ±1.5%  for gases
  • Rangeability is 20: 1
  • Upstream length/ Downstream straight length is 20 / 5

Advantages of Vortex Flowmeters

  • Minimal maintenance, no moving parts.
  • Calibration using fluid flow not required & unaffected by viscosity, density, pressure, and temperature within operating specification.
  • Digital or analog output.

Disadvantages of Vortex Flowmeters

  • At low flows, pulses are not generated and the flowmeter can read low or even zero.
  • Reynolds number should be greater than 10000.
  • Vibration can cause errors in accuracy.
  • Correct installation is critical as a protruding gasket or weld beads can cause vortices to form, leading to inaccuracy.
  • Long, clear lengths of upstream pipework must be provided, as for orifice plate flowmeters.
Figure showing Vortex Flowmeter, Ultrasonic flowmeter and Turbine Flowmeter
Fig. 5: Figure showing Vortex Flowmeter, Ultrasonic flowmeter and Turbine Flowmeter

Ultrasonic Flowmeters

  • A pair (or pairs) of transducers, each having its own transmitter and receiver, are placed on the pipe wall, one (set) on the upstream and the other (set) on the downstream.
  • The time for acoustic waves to travel from the upstream transducer to the downstream transducer (td) is shorter than the time it requires for the same waves to travel from the downstream to the upstream (tu).
  • The larger the difference, the higher the flow velocity.

Design Features of Ultrasonic Flowmeters

  • Design Pressure: 207 bars (insertion type)/ unlimited (clamp on type)
  • Design Temperature: -180 Deg. C to 260 Deg.C
  • Sizes: 3 mm to 3000 mm
  • Fluids : clean gases, clean/corrosive liquids (with little/no solids/ bubbles)
  • Velocity range: 0.3 to 15 m/s
  • MOC: mostly in stainless steel/ alloyic
  • Accuracy is: +0.5% of flowrate for insertion type/+1% to +3% of flowrate for clamp on type
  • Range ability is 10 : 1 to 300 : 1
  • Upstream length/ Downstream straight length is 10 / 5
  • Bidirectional flow measurement
  • For insertion type, hot tapping in pressurised pipelines possible

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 wider ranges of Reynolds number
  • Can be used in corrosive fluid flow
  • Portable models available for field analysis and diagnosis

Disadvantages of Ultrasonic Flowmeters

  • Only clean liquids and gases can be measured
  • Higher initial set up cost

Turbine Flowmeters

  • Consists of a multi-bladed rotor mounted at right angles to the flow & suspended in the fluid stream on a free-running bearing.
  • The diameter of the rotor is slightly less than the inside diameter of the flow metering chamber.
  • Speed of rotation of rotor proportional to the volumetric flow rate.

Features of Turbine Flowmeters

  • Design Pressure: 1500 PSIG
  • Design Temperature: 150 Deg. C
  • Sizes: 5 mm to 600 mm (Full bore type)/ > 75 mm for insertion type
  • Fluids : Clean liquids/ gases and vapours
  • Velocity range: 0.3 to 15 m/s
  • MOC: mostly in stainless steel/ hastelloy
  • Accuracy is: +0.25% to + 0.5% of flowrate for full bore type/+1% to +3% of flowrate for insertion type
  • Range ability is 10 : 1
  • Upstream length/ Downstream straight length is 15/ 5
  • Bidirectional flow measurement
  • For insertion type, hot tapping in pressurized pipelines possible

Advantages of Turbine Flowmeter

  • Very accurate. Commonly used to prove other meters.
  • Digital output provides for direct totalizing, batching, or digital blending without reducing accuracy.
  • There is less tendency to read high in pulsating flow than in head or variable-area type meters.

Disadvantages of Turbine Flowmeters

  • Not usable in dirty streams or with corrosive materials.
  • Subject to fouling by foreign materials -fibers, tars, etc.
  • Bearings subject to wear or damage. Shift in calibration if bearings replaced
  • It can be damaged by overspeeding (over 150 percent) or by hydraulic shock.
  • Pressure loss at rated flow varies & can be high.

Positive Displacement Flowmeters

  • This meter repeatedly entraps the fluid into a known quantity and then passes it out.
  • The quantity of the fluid that has passed is based on the number of entrapments.
  • The volume flow rate can be calculated from the revolution rate of the mechanical device.

Features of Positive Displacement (PD) Flowmeters

  • Design Pressure: 1500 PSIG (liquids)/ : 100 psig (gases)
  • Design Temperature : 293 Deg. C (liquids)/ : -34 to 60 Deg. C (gases)
  • Sizes: 6 mm to 400 mm
  • Fluids : Clean Liquids/ gases
  • Flow range: 0 – 20000 GPM (liquids)/ : 0 – 3000 cub.m/hr (gases)
  • MOC: mostly in aluminum, stainless steel, plastics, hastelloy
  • Accuracy is + 0.5% to + 1% of flowrate
  • Range ability is 15 : 1
Positive Displacement Flowmeters and Thermal mass flowmeters
Fig. 6: Positive Displacement Flowmeters and Thermal mass flowmeters

Advantages of PD Flowmeters

  • Good accuracy and high range ability
  • Can be used in viscous liquid flow
  • Low to medium initial set up cost
  • Require no power supply and available in wide variety of read out devices

Disadvantages of PD Flowmeters

  • Maintenance required at frequent intervals because of the `moving parts.
  • High pressure drop due to obstruction
  • Not suitable for low flow rate
  • Not suitable for fluids with suspended solids
  • Gas (bubbles) in liquid could significantly decrease the accuracy

Thermal Mass Flowmeter

  • Operates by monitoring the cooling effect of a gas stream as it passes over a heated transducer.
  • Gas flow passes over two PT100 RTD transducers.
  • The temperature transducer monitors the actual gas process temperature, whilst the self-heated transducer is maintained at a constant differential temperature by varying the current through it.
  • The greater the mass flow passing over the heated transducer, the greater the current required to keep a constant differential temperature.
  • The measured heater current is, therefore, a measure of the gas mass flow rate.

Design Features of Thermal Mass Flowmeters

  • Design Pressure: 1200 PSIG
  • Design Temperature: 176 Deg. C
  • Sizes: 15 mm to 1000 mm
  • Fluids : Clean gases
  • Flow range: 0 – 2500 SCFM
  • MOC: mostly in stainless steel/ glass, teflon, monel
  • Accuracy is +1% to + 2% of flowrate
  • Range ability is 10 : 1 to 100:1
  • Upstream length/ Downstream straight length is 5/ 3

Advantages Of Thermal Mass Flowmeter

  • No temperature or pressure compensation required
  • Linear output (as temperature differential is proportional to mass flow)
  • Can be used on corrosive process streams if proper materials are specified
  • DC voltage or 4 to 20 mA dc outputs available

Disadvantages of Thermal Mass Flowmeters

  • Practical for gas flow only
  • Subject to blockage by foreign particles or precipitated deposits due to small openings in flowmeter
  • Power requirements excessive in larger pipe sizes
  • Has to taken out of process line for servicing
  • Accurate field calibration is difficult

Coriolis Mass Flowmeter

  • When a moving mass is subjected to an oscillation perpendicular to its direction of movement, Coriolis forces occur depending on the mass flow.
  • When the tube is moving upward during the first half of a cycle, the fluid flowing into the meter resists being forced up by pushing down on the tube.
  • On the opposite side, the liquid flowing out of the meter resists having its vertical motion decreased by pushing up on the tube. This action causes the tube to twist.
  • This twisting movement is sensed by a pick-up and is directly related to the mass flow rate

Coriolis Mass Flowmeter Characteristics

  • Design Pressure: 345 bar
  • Design Temperature: 200 to 426 Deg. C
  • Sizes: 1.5 mm to 150 mm
  • Fluids/ Applications : Liquids (clean/ dirty/viscous/ slurries) clean /liquified gases
  • Flow range: 0 – 25000 lb/m
  • MOC: mostly in stainless steel, hastelloy/titanium
  • Accuracy is + 0.15% to + 0.5% of flowrate
  • Range ability is 20 : 1
  • Bidirectional flow measurement
Coriolis Mass Flowmeter
Fig. 7: Coriolis Mass Flowmeter

Advantages of Coriolis Mass Flowmeters

  • Capable of measuring difficult handling fluids
  • Independent of density changes, flow profile and flow turbulence. Hence straight lengths are not required.
  • No routine maintenance required since no moving parts
  • High accuracy

Disadvantages of Coriolis Mass Flowmeters

  • Not available for large pipes (upto 150 mm only)
  • High flow velocities required for detection resulting in high pressure drop
  • Expensive compared to other flowmeters
  • Difficulty in measuring low pressure gases.

Application of Flowmeters / Selection of Flowmeters

Clean liquids/gases

  • Orifices
  • Venturi
  • Annubar
  • Variable Area
  • Magnetic (only liquids)
  • Ultrasonic
  • Vortex
  • Coriolis Mass Flowmeters
  • Thermal mass flowmeter (only gases)
  • PD meters

Dirty Liquids

  • Most suited: Magnetic/Coriolis Mass Flowmeters
  • Limited applications: Venturi meters

Dirty Gases

  • Most suited: Vortex meters
  • Limited applications: Venturi meters/Thermal mass flowmeter/Variable area flowmeter

CORROSIVE LIQUIDS: Magneticflowmeters/Ultrasonic flowmeters

NON-NEWTONIAN LIQUIDS: Coriolis Mass Flowmeters

VISCUOUS LIQUIDS: Coriolis/Magnetic/Positive Displacement Meters

ABRASIVE SLURRIES: Magnetic flowmeters/Coriolis Mass Flowmeters

FIBROUS SLURRIES: Magnetic flowmeters/Coriolis Mass Flowmeters (limited applications)

Saturated Steam

  • Most suited: Orifice DP meters/ Vortex flowmeters
  • Limited applications: Venturi meters/Variable area meters

Super-heated Steam

  • Most suited: Orifice DP meters
  • Limited applications: Venturi meters

Cryogenic Applications: Venturi-meters/Orifice plates

Parameters affecting Flow meter Selection

There are various factors that influence the flowmeter selection for a specific industrial process. Some of those factors are:

  • The fluid phase; for example: gas, liquid, steam
  • Flow conditions and flow range; for example: clean, dirty, abrasive, or viscous fluid.
  • Process design parameters; for example, pressure, temperature ranges, density.
  • Pipe size
  • Accuracy desired.
  • Material of Construction (corrosive or non-corrosive fluid).
  • Repeatability and cost-effectiveness.
  • Environmental considerations, if any.

Installation of Flow meters

Flow measurement using flowmeters is an essential activity for any industry. So, it must provide reliable and accurate data. The accuracy and repeatability of measured data, to a large extent, depend on the correct installation of the flowmeter. Some of the critical steps that must be followed during flowmeter installation are listed below:

  • It must be installed in the proper location.
  • It should not be installed where there are vibrations or magnetic fields.
  • The flow direction must be known before installing.
  • Flowmeters should be installed on a straight pipe.
  • Some flowmeters may need straight length upstream and downstream of the flowmeter. It should be maintained for accurate results.
  • For liquid flow applications, the downward flow should be avoided.
  • Ensure that the flowmeter is completely filled with fluid.
  • Vapor or air in liquid lines and liquid droplets in gas lines should be avoided.
  • It’s preferable to install a filter upstream of the flowmeter to remove solids.
  • If repair is required, a by-pass line should be provided.

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