Menu
Measuring liquid move is a critical requirement for many industrial plants. In some operations, the power to make accurate flow measurements is so important that it could make the distinction between a profit or a loss. In different circumstances, inaccurate circulate measurements or failure to make them can result in severe (or even catastrophic) outcomes.
For most liquid move measurement instruments, circulate is set inferentially by measuring the change in velocity or kinetic vitality of the liquid. The velocity is determined by the strain difference that forces the liquid via the pipe or conduit. Since the cross-sectional area of the pipe is known and remains fixed, the average circulate price is an indicator of the flow price. In this case, the fundamental relationship for figuring out the move rate of a liquid is
Q = V x A
Q = Flow price of liquid through the pipe
V = Average move price
A = Cross-sectional area of the pipe
Other factors that have an result on the move price of a liquid embody the viscosity and density of the liquid, and the friction of the liquid involved with the pipe.
Liquid move could be measured immediately using positive displacement move meters. These units divide the liquid into particular increments and continue to maneuver. The total move fee is the accumulation of the measured increments and could be counted mechanically or electronically.
Table of Contents
Reynolds number
Types of liquid flow meters
Differential Pressure flow meters
Orifice plate circulate meters
Venturi circulate meters
Flow tubes
Flow nozzle
Pitot tube flowmeter
Elbow flowmeter
Target meter
Variable area move meter
Positive displacement flow meter
Reciprocating piston flowmeter
Oval Gear Flow Meters
Disc type meter
Rotary vane gauges
Spiral move meter
Velocity meters
Turbine flow meters
Vortex flowmeters
Electromagnetic circulate meters
Ultrasonic circulate meters
Mass move meter
Coriolis circulate meters
Thermal mass move meters
Open channel move meter
Select a right liquid circulate meter
Using flow meters
Calibration
Maintenance
Reynolds number
The performance of a move meter can additionally be influenced by the dimensionless unit called Reynolds quantity. It is defined as the ratio of the inertial drive of a liquid to its resistance.
The formula is
R = 3160 x Q x Gt
D x ต
R = Reynolds number
Q = Flow fee of the liquid, gpm
Gt = Specific gravity of the liquid
D = Internal diameter of the pipe, in.
ต = Viscosity of the liquid, cp
Flow fee and particular gravity are the inertial forces, pipe diameter and viscosity are the resistance. For most liquid applications, the pipe diameter and particular gravity stay constant. At very low velocities or high viscosities, R may be very low and the liquid flows in a smooth layer with the best velocity at the heart of the pipe, where viscous forces at the pipe wall limit it to very low velocities. This kind of move known as laminar flow. the R worth is under about 2000. a characteristic of laminar flow is the parabolic form of its velocity distribution.
However, most functions contain turbulent flow with R-values above 3000. turbulent circulate occurs at high speeds or low viscosities. The flow breaks down into turbulent eddies that flow via the pipe with the identical average velocity. The fluid velocity is less important and the velocity distribution is more uniform in shape. A transition zone exists between turbulent and laminar move. Depending on the pipe configuration and other set up circumstances, the circulate on this zone could also be turbulent or laminar.
Types of liquid flow meters
Many types of move meters are available to be used in closed pipe methods. In basic, units could be classified as differential strain meters, constructive displacement meters, velocity meters, and mass meters. Differential stress units (also known as head gauges) embody orifice plates, venturi, move tubes, circulate nozzles, pitot tubes, elbow type move meters, target type circulate meters and variable area move meters.
Positive displacement circulate meters embrace piston, elliptical-gear, chapter-actuated disk and rotary vane sorts. Velocity meters include turbine, vortex shedding, electromagnetic, and acoustic designs. Mass meters include Coriolis and thermal sorts. Measurement of liquid circulate in open channels usually includes weirs and flumes.
Differential Pressure flow meters
The use of differential pressure as an inferred measurement of the move price of a liquid is well known. By far, differential pressure circulate meters are the most commonly used unit today. It is estimated that more than 50% of all liquid move measurement applications use this sort of unit.
The primary working precept of differential stress move meters relies on the premise that the strain drop across the meter is proportional to the square of the flow fee. The circulate fee is obtained by measuring the differential stress and extracting the sq. root.
Like most move meters, differential pressure circulate meters have a main element and a secondary factor. The major element causes a change in kinetic energy, which creates a differential strain within the pipe. The device must be properly matched to the pipe measurement, move conditions and liquid traits. And, the accuracy of the factor measurement must stay good within affordable limits. The secondary element measures the differential pressure and supplies a sign or reading that is converted to an actual circulate worth.
Orifice plate move meters
Orifice plates are the preferred liquid flow meters in use right now. An orifice is just a flat piece of metallic with a specific measurement gap drilled in it. Most orifices are concentric, but eccentric, conical (quadrant) and segmented designs are also out there.
In follow, the orifice is installed in the pipe between two flanges. As the first system, the orifice restricts the circulate of fluid, thereby making a differential strain throughout the plate. Pressure measurement ports on both sides of the plate are used to detect the difference. The main benefits of orifice plates are that they haven’t any transferring elements and that their price doesn’t improve considerably with the scale of the pipe.
Tapered and quadrant orifices are comparatively new. These units have been developed primarily for measuring liquids with low Reynolds numbers. An primarily constant circulate coefficient can be maintained at an R-value below 5000. Tapered orifice plates have an upstream bevel, the depth and angle of which have to be calculated and machined for every application.
The section wedge is a variant of the section orifice. It is a throttle orifice designed primarily to measure the flow of liquids containing solids. The system is able to measuring flow at low Reynolds numbers and nonetheless sustaining the required square root relationship. Its design is easy and the wedge hole has only one important dimension. The stress drop via the gadget is simply about half that of a conventional orifice plate.
The one-piece wedge meeting combines the wedge element and stress measurement fitting into a one-piece pipe fitting bolted to a conventional stress transmitter. No special piping or fittings are required to install the system within the pipeline.
The metering accuracy of all orifice circulate meters is determined by the installation conditions, the orifice plate space ratio, and the bodily traits of the liquid being measured.
Venturi move meters
The advantage of a venturi is its capacity to deal with giant flows at low strain drops. A venturi is basically a bit of pipe with a conical inlet and a straight throat. As the liquid passes through the throat, it will increase in velocity, resulting in a strain distinction between the inlet and outlet areas.
Flow meters don’t have any transferring elements. They may be put in in giant diameter pipes using flanged, welded or threaded end connections. The unit is often fitted with four or more strain measuring ports to common the measured pressure. Venturi tubes can be used for most liquids, including these with excessive solids content material.
Flow tubes
Flow tubes are somewhat just like venturi, except that they do not have an entrance cone. They have a tapered throat, however the outlet is elongated and easy. The distance between the front and the tip is about one-half the diameter of the tube. The strain measurement port is located about one-half the diameter of the tube downstream and one diameter upstream.
Flow nozzle
At high velocities, the flow nozzle can deal with roughly 60% of the liquid flow compared to an orifice plate with the identical stress drop. Liquids containing suspended solids can additionally be metered. However, these units aren’t recommended for high viscosity liquids or liquids containing large quantities of viscous solids.
Pitot tube flowmeter
The Pitot tube senses two types of strain simultaneously, shock stress and static stress. The shock system consists of a tube with one finish of the tube bent at proper angles to the direction of move. The end of the static tube is closed, but has a small slot within the facet of the gadget. These tubes can be put in individually within the pipe or combined in a housing.
Pitot tubes are typically installed by welding a coupling to the pipe and inserting the probe by way of the coupling. The use of most Pitot tubes is limited to single level measurements. These gadgets are prone to clogging by overseas matter within the liquid. The advantages of Pitot tubes are low cost, no shifting parts, straightforward installation and minimal stress drop.
Elbow flowmeter
Elbow circulate meters work on the precept that centrifugal forces are exerted along the outer edges as the liquid strikes alongside a round path. Thus, because the liquid flows by way of the pipe elbow, the force on the internal floor of the elbow is proportional to the density of the liquid multiplied by the sq. of its velocity. In addition, the drive is inversely proportional to the radius of the elbow.
Arbitrary 90 levels. Elbows can be used as liquid circulate meters. All that is required are two small holes placed at the midpoint of the elbow (45 degree point) for the manometer faucet. A pressure sensing line can be linked to the faucet using any convenient methodology.
Target meter
The target meter senses and measures the force attributable to the liquid putting the goal or a drag disk suspended in the liquid stream. By measuring the pressure utilized to the target the liquid circulate rate can be immediately indicated. In its simplest kind, the meter consists only of an articulated oscillating plate that strikes outward with the liquid circulate. In this case, the device is used as a move indicator.
More subtle versions use refined low-level force sensor sensing components. The goal drive brought on by the liquid circulate is sensed by a strain gauge. The output signal of the meter signifies the flow fee. The goal meter can be utilized to measure the flow fee of dirty or corrosive liquids.
Variable space flow meter
Variable space meters consist primarily of a conical tube and a float. Although classified as differential pressure devices, they’re truly fixed stress devices. Flange end connections provide a easy approach to set up them in the pipe. Working precept of rotameter is when there is not any liquid flow, the float is free to relaxation at the backside of the pipe. When the liquid enters the bottom of the pipe, the float begins to rise. The place of the float varies immediately with the circulate fee. Its actual place is on the point where the strain distinction between the upper and decrease surfaces balances the weight of the float.
Because the move price can be learn immediately on a scale mounted next to the tube, there is no want for an auxiliary flow reading device. However, if desired, an automated sensing gadget can be used to sense the float level and transmit the flow sign. Variable space move meter tubes are made of glass, metallic or plastic. Tube diameters vary from 1/4 to larger than 6 inches.
Positive displacement circulate meter
The operation of those items consists of separating the liquid into exactly measured increments and persevering with to move. Each segment is counted by a connection register. Because each increment represents a discrete quantity, optimistic displacement models are popular in automated dosing and accounting functions. Volumetric circulate meters are perfect for measuring the flow of viscous liquids or where a simple mechanical flow meter system is required.
Reciprocating piston flowmeter
Reciprocating piston move meters are available in single and multi-piston versions. The particular selection is decided by the range of circulate rates required in a selected utility. Piston circulate meters can be used to handle a variety of liquids. The fluid by no means is out there in contact with gears or other parts that could clog or corrode.
Oval Gear Flow Meters
Oval gear flowmeters have two rotating oval gears with intently synchronized enamel. A fixed amount of fluid passes via the meter with every revolution. The shaft rotation can be monitored to obtain a specific circulate fee.
Disc type meter
Chapter shifting disc kind meters have a movable disc mounted on a concentric sphere that is located in a spherical sidewall chamber. The pressure of the fluid passing by way of the measurement chamber causes the disc to oscillate in its circulation path with out rotating about its own axis. It is the only transferring part within the measurement chamber.
A pin extending vertically from the disk is connected to a mechanical counter, which displays the oscillating motion of the disk. Each cycle is proportional to a selected move fee. As with all optimistic displacement meters, adjustments in viscosity below a given threshold will affect the measurement accuracy. A big selection of sizes and capacities are available. These units may be produced from a wide selection of building materials.
Rotary vane gauges
Rotary vane meters are available in a wide range of designs, however all of them function on the identical principle. The fundamental unit consists of an equally divided rotating impeller (containing two or more compartments) mounted contained in the instrument housing. The impeller is in fixed contact with the housing. As the impeller rotates, a hard and fast volume of liquid is swept from each compartment to the outlet of the meter. The number of impeller revolutions is calculated and recorded in quantity units.
Spiral move meter
The helical move meter consists of two radially inclined helical rotors which are gear driven along with minimal clearance between the rotors and the housing. The two rotors switch the liquid from one finish of the chamber to the opposite along the axial course.
Velocity meters
These devices function linearly with respect to the volumetric circulate fee. Because there is not any sq. root relationship (as with differential strain devices), they’ve a a lot larger vary. Velocity meters are least sensitive to modifications in viscosity when the Reynolds number exceeds 10,000. Most velocity meter housings are equipped with flanges or fittings to allow them to be related immediately into the piping.
Turbine circulate meters
Turbine move meters have been extensively used for precise liquid measurement applications. The gadget consists of a multi-bladed rotor mounted in a pipe, perpendicular to the circulate of the liquid. The rotor rotates because the liquid passes by way of the vanes. Rotational pace is a direct perform of move fee and may be sensed by magnetic sensors, photocells or gears. Electrical pulses could be counted and totalized.
The variety of electrical pulses counted in a given time period is proportional to the move price. A tachometer may be added to measure the turbine speed and determine the liquid move price. A properly specified and put in turbine flow meter has good accuracy, especially for low viscosity liquids.
A main drawback with turbine flowmeters is bearing put on. A “bearingless” design has been developed to keep away from this downside. The liquid entering the circulate meter passes through the spiral vanes of the stator, causing the liquid circulate to rotate. The move acts on the spheres, inflicting them to travel in the space between the primary stator and the spiral-like second stator. The orbital movement of the sphere is detected electronically. The frequency of the generated pulse output is proportional to the circulate fee.
Vortex flowmeters
Vortex circulate meters benefit from the natural phenomenon that occurs when a liquid flows via a blunt object. Vortex or vortex flow alternates downstream of the thing. The frequency of the vortex shedding is proportional to the speed of the liquid flowing through the flowmeter.
The three major parts of the circulate meter are the blunt object strut mounted on the meter bore, the sensor that detects the presence of vortices and generates an electrical pulse, and the sign amplification and conditioning transmitter whose output is proportional to the flow price.
Electromagnetic circulate meters
Magnetic circulate meters can handle most liquids and slurries, supplied that the fabric to be metered is electrically conductive. The major part is the circulate tube (primary element), which is installed immediately within the pipe. The stress drop across the meter is similar as the strain drop by way of the equivalent size of pipe, since there aren’t any transferring components or flow obstructions. The voltmeter may be related on to the circulate tube or remotely mounted and connected to the circulate tube via a shielded cable.
Electromagnetic flow meters work according to Faraday’s law of electromagnetic induction, which states that a voltage is induced when a conductor passes by way of a magnetic subject. The liquid acts as the conductor; the magnetic area is generated by an energized coil exterior the circulate tube. The amount of voltage generated is proportional to the circulate fee. Two electrodes mounted on the wall of the tube detect the voltage measured by the secondary component.
Electromagnetic flowmeters provide main advantages: they will measure tough and corrosive liquids and slurries; they’ll measure ahead and reverse move with equal accuracy. The disadvantages of early designs have been high energy consumption and the necessity to get hold of a full tube with no flow to set the meter to zero initially. Recent enhancements have eliminated these problems. The pulse-type excitation approach reduces energy consumption because excitation occurs solely half the time in the unit. A zero setting is not required.
Ultrasonic flow meters
Ultrasonic flowmeters can be divided into doppler meters and journey time (or transverse) meters. Doppler meters measure the frequency shift caused by the circulate of a liquid. Two sensors are mounted in a housing related to 1 side of the pipe. A sign of known frequency is sent to the liquid to be measured. Solids, bubbles or any discontinuities within the liquid trigger the heart beat to be reflected to the receiver component. Since the liquid causing the reflection is moving, the frequency of the returned pulse is shifted. The frequency shift is proportional to the velocity of the liquid.
There can also be a conveyable doppler meter that might be run on AC energy or a chargeable power pack. The instrument can be used by merely clamping the sensing head to the skin of the pipe. A set of 4 to 20 mA output terminals allows the unit to be linked to a strip chart recorder or other remote gadget.
The travel time meter’s sensors are mounted on each side of the pipe. The configuration permits the sound waves to travel between the units at an angle of 45 levels. angle to the direction of fluid flow. The speed of the signal propagating between the sensors will increase or decreases with the direction of transmission and the velocity of the liquid being measured. By transmitting the sign in both directions alternately, a time-differential relationship proportional to the flow price can be obtained. A limitation of the journey time meter is that the liquid being measured must be relatively free of entrained gases or solids to reduce sign scattering and absorption.
Mass circulate meter
Mass flowmeters the continued need for more correct flow measurement in mass related processes (chemical reactions, warmth transfer, and so on.) has led to the event of mass circulate meters. A variety of designs are available, however essentially the most generally used for liquid move purposes is the Coriolis meter. It operates on the premise of a pure phenomenon generally recognized as the Coriolis force, hence the name.
Coriolis move meters
Coriolis meters are true mass meters that instantly measure mass flow as a substitute of quantity flow. Since the mass is fixed, the meter is linear and does not have to be adjusted for modifications in liquid characteristics. It also eliminates the need to compensate for changing temperature and stress situations. The meter is particularly suitable for measuring liquids whose viscosity varies with velocity at a given temperature and strain.
Coriolis meters are additionally available in a wide selection of designs. A well-liked unit consists of a U-shaped flow tube encapsulated in a sensor housing connected to an digital unit. The sensing unit may be mounted immediately into any process. The electronics unit could be situated as much as 500 feet away from the sensor.
Thermal mass circulate meters
Thermal mass flowmeters are traditionally used for gas measurements, however are additionally out there in designs for liquid move measurements. These mass meters additionally function unbiased of density, strain and viscosity. Thermal mass meters use a heated sensing component that’s isolated from the fluid flow path. The flowing stream conducts heat from the sensing element. The warmth transferred is proportional to the mass circulate rate. The sensor is never in direct contact with the fluid. The digital assembly features a flow analyzer, temperature compensator, and signal conditioner that gives a linear output proportional to the mass circulate price.
Open channel circulate meter
An “open channel” is any pipe during which liquids circulate on a free surface. This contains tunnels, unpressurized sewers, partially stuffed pipes, canals, streams and rivers. Of the various strategies that can be used to monitor circulate in open channels, depth-related strategies are the most typical. These strategies assume that instantaneous flow can be decided from a measurement of water depth or head. Weirs and flumes are the oldest and most generally used main gadgets used to measure move in open channels.
Weirs work on the principle that an obstruction in a channel causes water to move backwards, making a excessive water stage (head) behind the obstruction. The head is a function of the move fee, and due to this fact the flow price through the device. The weir consists of a vertical plate with a pointed high. The high of the plate can be straight or notched. Weirs are categorised by the shape of the notch. The primary types are V-notched, rectangular and trapezoidal.
The discharge by way of the weir and flume is a operate of the liquid stage, so the device must use degree measurement techniques to find out the flow rate. Staff gauges and floating operating units are the simplest gadgets to use for this objective. Various digital sensing, totalizing and recording systems are also available.
A current improvement includes using ultrasonic pulses to measure liquid stage. Measurements are made by sending an acoustic pulse from the sensor to the surface of the liquid and timing the return echo. Linearized circuitry converts the height of the liquid to a move rate. A bar graph recorder records the flow price and a digital totalizer records the whole variety of gallons. Another lately introduced microprocessor-based system uses ultrasonic or float sensors. A keypad with an interactive LCD show simplifies programming, management and calibration tasks.
Select a proper liquid flow meter
Data exhibits that more than 75% of the circulate meters put in in industry don’t perform nicely. And poor selection accounts for 90 percent of those problems. Clearly, flowmeter choice isn’t a job for amateurs.
The most important requirement is to know exactly what the instrument should do. There are a number of issues to consider here. Will the measurement be used for course of control (repeatability is the primary concern) or for accounting or commerce handover (high accuracy is important)? Is a local indication or a distant signal required? If a distant output is required, is it a proportional sign or a contact closure to start out or cease one other device? Is the fluid viscous, clean or slurry? Is it electrically conductive? What is its specific gravity or density? What flow charges are concerned in the application? What is the working temperature and strain of the process? Accuracy (see glossary), vary, linearity, repeatability, and piping requirements must also be considered.
It is equally important to grasp what a flow meter can not do in addition to what it can do earlier than making a last alternative. Every instrument has strengths and weaknesses, and the diploma of efficiency satisfaction is instantly associated to how properly the instrument’s features and weaknesses match the application requirements. Often, the user’s expectations of flowmeter performance do not match these offered by the provider. Most suppliers are eager to assist prospects choose the best flowmeter for a particular job. Many present questionnaires, checklists and specification sheets designed to acquire the important info essential to match the right flowmeter to the job.
Technical improvements to the flowmeter should even be considered. For instance, a common mistake is to select the design that was hottest for a given utility a number of years in the past and assume that it’s still one of the best software for the job. In recent years, many modifications and improvements might have occurred within the improvement of flowmeters for particular applications, leading to a wider vary of decisions.
Flow meters are available in a variety of prices. Variable area flowmeters are often the least expensive, with some smaller models costing less than $90. Mass circulate meters are the costliest. They start at about $3000. However, the entire system value should all the time be thought-about when deciding on a flowmeter. Installation, operation and maintenance costs are additionally important economic elements. For a few of the extra complex designs, maintenance costs can be high.
As with many different products, the plant engineer usually gets what he pays for when he buys a flow meter. But his satisfaction with the product will depend on the care he makes use of in choosing and putting in the instrument. It comes again to understanding the method, the product and the move metering necessities. It isn’t unusual to “overbuy”. Plant engineers shouldn’t purchase extra highly effective or complicated flowmeters than they need.
Using flow meters
Although suppliers are at all times ready to provide flowmeter installation providers, it’s estimated that about 75% of users set up their own equipment. But set up errors can occur. One of the most common conditions isn’t allowing adequate upstream and downstream straight pipe for the flowmeter.
Each design has some tolerance for erratic velocity situations within the piping, but all installations require correct piping configurations to operate successfully. Proper piping provides the correct circulate sample for the gadget. Without it, accuracy and performance may be adversely affected. Flow meters are typically put in backwards (especially orifice plates). Pressure sensing traces may additionally be reversed.
For electrical parts, intrinsic safety is an important consideration in hazardous areas. Most flowmeter suppliers supply intrinsically protected designs for this sort of use.
Stray magnetic fields are present in most industrial vegetation. Power traces, relays, solenoids, transformers, motors and mills all contribute their share of interference. Users must ensure that the flowmeter they select is not topic to such disturbances. The downside happens primarily with the electronics within the secondary parts that have to be protected. Strict adherence to the manufacturer’s recommended set up practices can often prevent such issues.
Calibration
All move meters require an initial calibration. In most circumstances, the instrument is calibrated by the producer for the desired circumstances of use. However, if certified personnel can be found on the factory, the person can perform his personal calibration.
The need for recalibration depends significantly on how properly the meter is matched to the appliance. Certain fluids that cross by way of the meter are typically abrasive, aggressive or corrosive. Over time, some components of the system will degrade sufficient to affect efficiency. Some designs are extra prone to break than others. For instance, wear on particular person turbine blades may cause performance modifications. If the applying is critical, the accuracy of the flow meter ought to be checked incessantly. In different circumstances, recalibration may not be required for a couple of years as a end result of the application just isn’t critical and wouldn’t in any other case change the meter’s efficiency. Some flowmeters require special tools for calibration. Most manufacturers will provide such companies at their vegetation or consumer services, and they’ll bring the equipment with them for on-site calibration.
Maintenance
Many components can have an effect on upkeep necessities and the expected lifetime of a circulate meter. The primary issue, in fact, is matching the correct instrument to the particular application. Poorly chosen tools will all the time trigger problems early on. Flowmeters with out transferring components often require much less consideration than devices with transferring parts. But all flowmeters will eventually require some type of upkeep.
The major factor in a differential strain flowmeter requires plenty of piping, valves and fittings when related to the secondary element, so upkeep could be a recurring process in such installations. Pulse traces can turn out to be clogged or corroded and have to be cleaned or changed. And, improperly positioned secondary parts can lead to measurement errors. Repositioning components can be costly.
Flow meters with shifting elements require periodic internal inspection, particularly if the liquid being measured is soiled or viscous. Installing a filter before such gadgets will help cut back fouling and put on. Accessible instruments similar to ultrasonic or electromagnetic meters may have problems with the electronics of their secondary elements. Pressure transducers related to secondary elements ought to be eliminated and inspected periodically.
Applications where coatings might happen are also potential problems for accessible instruments corresponding to magnetic or ultrasonic units. If the coating is insulated, the operation of the magnetic flow meter can eventually be impaired if the electrodes are insulated from the liquid. This scenario could be avoided by regular cleansing. With ultrasonic flow meters, the refraction angle may change and the acoustic vitality absorbed by the coating may cause the circulate meter to not work.
More articles on circulate meters:
Relation between flow and strain
Difference between flow meter and circulate transmitter
Water level sensor types and works
Solution of water air pollutionn
Handling #keyword# isn’t really easy to do, and your objectives might not be met. If they aren’t, you shouldn’t be frustrated, since this is par for the course. Any individual that really wants to succeed has got to take it a step at a time or else things will become extremely confusing. It is all about taking that initial step, and accomplishing your objectives, and you could accomplish that, what these tactics that you now know. Reading this article can readily give you more information on this subject, but #links# can provide you with a lot more relevant information that goes into quite some depth.
Measuring liquid circulate is a critical requirement for lots of industrial vegetation. In some operations, the ability to make accurate circulate measurements is so important that it could possibly make the difference between a profit or a loss. In different circumstances, inaccurate move measurements or failure to make them can lead to serious (or even catastrophic) outcomes.
For most liquid flow measurement instruments, move is determined inferentially by measuring the change in velocity or kinetic power of the liquid. The velocity is decided by the stress distinction that forces the liquid via the pipe or conduit. Since the cross-sectional space of the pipe is thought and remains fixed, the common flow rate is an indicator of the circulate price. In this case, the basic relationship for determining the flow fee of a liquid is
Q = V x A
Q = Flow fee of liquid by way of the pipe
V = Average move rate
A = Cross-sectional area of the pipe
Other components that have an effect on the flow price of a liquid embody the viscosity and density of the liquid, and the friction of the liquid involved with the pipe.
Liquid move may be measured immediately using optimistic displacement circulate meters. These models divide the liquid into specific increments and continue to maneuver. The complete circulate rate is the buildup of the measured increments and could be counted mechanically or electronically.
Table of Contents
Reynolds number
Types of liquid flow meters
Differential Pressure circulate meters
Orifice plate move meters
Venturi move meters
Flow tubes
Flow nozzle
Pitot tube flowmeter
Elbow flowmeter
Target meter
Variable area flow meter
Positive displacement move meter
Reciprocating piston flowmeter
Oval Gear Flow Meters
Disc sort meter
Rotary vane gauges
Spiral circulate meter
Velocity meters
Turbine flow meters
Vortex flowmeters
Electromagnetic circulate meters
Ultrasonic circulate meters
Mass circulate meter
Coriolis circulate meters
Thermal mass move meters
Open channel move meter
Select a proper liquid move meter
Using circulate meters
Calibration
Maintenance
Reynolds number
The performance of a circulate meter is also influenced by the dimensionless unit called Reynolds number. It is defined as the ratio of the inertial force of a liquid to its resistance.
The formulation is
R = 3160 x Q x Gt
D x ต
R = Reynolds number
Q = Flow rate of the liquid, gpm
Gt = Specific gravity of the liquid
D = Internal diameter of the pipe, in.
ต = Viscosity of the liquid, cp
Flow fee and specific gravity are the inertial forces, pipe diameter and viscosity are the resistance. For most liquid functions, the pipe diameter and specific gravity remain fixed. At very low velocities or excessive viscosities, R is very low and the liquid flows in a clean layer with the very best velocity at the middle of the pipe, where viscous forces at the pipe wall limit it to very low velocities. This sort of flow known as laminar circulate. the R worth is beneath about 2000. a attribute of laminar move is the parabolic shape of its velocity distribution.
However, most functions involve turbulent circulate with R-values above 3000. turbulent move happens at high speeds or low viscosities. The circulate breaks down into turbulent eddies that flow via the pipe with the same average velocity. The fluid velocity is much less important and the rate distribution is extra uniform in shape. A transition zone exists between turbulent and laminar flow. Depending on the pipe configuration and other set up conditions, the circulate in this zone could also be turbulent or laminar.
Types of liquid move meters
Many forms of circulate meters are available to be used in closed pipe systems. In basic, devices could be classified as differential strain meters, positive displacement meters, velocity meters, and mass meters. Differential stress units (also known as head gauges) embody orifice plates, venturi, flow tubes, flow nozzles, pitot tubes, elbow kind move meters, goal sort circulate meters and variable area flow meters.
Positive displacement flow meters embrace piston, elliptical-gear, chapter-actuated disk and rotary vane sorts. Velocity meters embrace turbine, vortex shedding, electromagnetic, and acoustic designs. Mass meters embody Coriolis and thermal sorts. Measurement of liquid flow in open channels usually involves weirs and flumes.
Differential Pressure flow meters
The use of differential strain as an inferred measurement of the move price of a liquid is well known. By far, differential pressure flow meters are the most generally used unit right now. It is estimated that greater than 50% of all liquid circulate measurement purposes use this type of unit.
The primary working principle of differential strain circulate meters is based on the premise that the strain drop across the meter is proportional to the sq. of the circulate fee. The circulate fee is obtained by measuring the differential stress and extracting the sq. root.
Like most flow meters, differential stress flow meters have a main component and a secondary factor. The major factor causes a change in kinetic energy, which creates a differential pressure in the pipe. The system should be properly matched to the pipe measurement, move conditions and liquid characteristics. And, the accuracy of the element measurement must stay good within cheap limits. The secondary element measures the differential strain and offers a signal or studying that is converted to an precise move worth.
Orifice plate circulate meters
Orifice plates are the preferred liquid circulate meters in use right now. An orifice is simply a flat piece of metal with a selected measurement hole drilled in it. Most orifices are concentric, however eccentric, conical (quadrant) and segmented designs are also available.
In follow, the orifice is put in in the pipe between two flanges. As the first device, the orifice restricts the move of fluid, thereby making a differential strain throughout the plate. Pressure measurement ports on each side of the plate are used to detect the difference. The main advantages of orifice plates are that they don’t have any shifting elements and that their price doesn’t improve considerably with the dimensions of the pipe.
Tapered and quadrant orifices are relatively new. These units were developed primarily for measuring liquids with low Reynolds numbers. An essentially fixed circulate coefficient can be maintained at an R-value below 5000. Tapered orifice plates have an upstream bevel, the depth and angle of which must be calculated and machined for every utility.
The segment wedge is a variant of the phase orifice. It is a throttle orifice designed primarily to measure the flow of liquids containing solids. The gadget is able to measuring flow at low Reynolds numbers and still maintaining the required sq. root relationship. Its design is simple and the wedge gap has just one important dimension. The stress drop through the gadget is simply about half that of a conventional orifice plate.
The one-piece wedge meeting combines the wedge factor and stress measurement fitting into a one-piece pipe becoming bolted to a conventional pressure transmitter. No special piping or fittings are required to install the system in the pipeline.
The metering accuracy of all orifice flow meters is dependent upon the installation conditions, the orifice plate area ratio, and the bodily traits of the liquid being measured.
Venturi circulate meters
The benefit of a venturi is its capability to handle massive flows at low strain drops. A venturi is essentially a section of pipe with a conical inlet and a straight throat. As the liquid passes by way of the throat, it will increase in velocity, resulting in a strain distinction between the inlet and outlet regions.
Flow meters haven’t any transferring parts. They may be put in in massive diameter pipes using flanged, welded or threaded end connections. The unit is usually fitted with four or extra stress measuring ports to common the measured stress. Venturi tubes can be utilized for most liquids, including these with high solids content.
Flow tubes
Flow tubes are considerably much like venturi, besides that they don’t have an entrance cone. They have a tapered throat, but the outlet is elongated and clean. The distance between the entrance and the tip is about one-half the diameter of the tube. The strain measurement port is positioned about one-half the diameter of the tube downstream and one diameter upstream.
Flow nozzle
At excessive velocities, the move nozzle can deal with roughly 60% of the liquid flow compared to an orifice plate with the identical stress drop. Liquids containing suspended solids may also be metered. However, these gadgets usually are not beneficial for prime viscosity liquids or liquids containing giant quantities of viscous solids.
Pitot tube flowmeter
The Pitot tube senses two kinds of stress concurrently, shock strain and static pressure. The shock device consists of a tube with one finish of the tube bent at proper angles to the course of flow. The end of the static tube is closed, however has a small slot in the aspect of the gadget. These tubes could be installed individually within the pipe or mixed in a housing.
Pitot tubes are sometimes put in by welding a coupling to the pipe and inserting the probe by way of the coupling. The use of most Pitot tubes is proscribed to single point measurements. These gadgets are prone to clogging by foreign matter in the liquid. The advantages of Pitot tubes are low price, no moving components, easy installation and minimal pressure drop.
Elbow flowmeter
Elbow circulate meters work on the principle that centrifugal forces are exerted alongside the outer edges because the liquid moves along a round path. Thus, as the liquid flows by way of the pipe elbow, the pressure on the inside floor of the elbow is proportional to the density of the liquid multiplied by the sq. of its velocity. In addition, the drive is inversely proportional to the radius of the elbow.
Arbitrary ninety levels. Elbows can be used as liquid circulate meters. All that is required are two small holes placed on the midpoint of the elbow (45 diploma point) for the manometer faucet. A strain sensing line can be linked to the tap using any handy technique.
Target meter
The target meter senses and measures the pressure attributable to the liquid striking the goal or a drag disk suspended within the liquid stream. By measuring the pressure applied to the target the liquid circulate rate can be directly indicated. In its simplest kind, the meter consists only of an articulated oscillating plate that moves outward with the liquid circulate. In this case, the device is used as a circulate indicator.
More refined versions use sophisticated low-level force sensor sensing parts. The goal drive attributable to the liquid flow is sensed by a pressure gauge. The output sign of the meter indicates the circulate price. The goal meter can be utilized to measure the move price of dirty or corrosive liquids.
Variable space circulate meter
Variable area meters consist primarily of a conical tube and a float. Although classified as differential strain units, they’re truly fixed stress units. Flange finish connections present a easy method to set up them in the pipe. Working precept of rotameter is when there is not any liquid flow, the float is free to relaxation at the backside of the pipe. When the liquid enters the underside of the pipe, the float begins to rise. The place of the float varies instantly with the move rate. Its exact position is at the level the place the strain distinction between the higher and decrease surfaces balances the load of the float.
Because the circulate fee may be read immediately on a scale mounted subsequent to the tube, there is no want for an auxiliary move studying gadget. However, if desired, an automatic sensing system can be utilized to sense the float stage and transmit the flow sign. Variable space move meter tubes are made from glass, metal or plastic. Tube diameters vary from 1/4 to higher than 6 inches.
Positive displacement flow meter
The operation of those models consists of separating the liquid into precisely measured increments and persevering with to move. Each section is counted by a connection register. Because every increment represents a discrete volume, constructive displacement units are in style in computerized dosing and accounting purposes. Volumetric flow meters are ideal for measuring the flow of viscous liquids or where a simple mechanical flow meter system is required.
Reciprocating piston flowmeter
Reciprocating piston flow meters are available in single and multi-piston variations. The particular choice is determined by the range of move charges required in a selected software. Piston flow meters can be used to deal with a wide range of liquids. The fluid never comes in contact with gears or different parts that might clog or corrode.
Oval Gear Flow Meters
Oval gear flowmeters have two rotating oval gears with carefully synchronized tooth. A fastened quantity of fluid passes through the meter with every revolution. The shaft rotation could be monitored to acquire a selected circulate fee.
Disc sort meter
Chapter transferring disc sort meters have a movable disc mounted on a concentric sphere that’s positioned in a spherical sidewall chamber. The strain of the fluid passing via the measurement chamber causes the disc to oscillate in its circulation path with out rotating about its personal axis. It is the only transferring half within the measurement chamber.
A pin extending vertically from the disk is connected to a mechanical counter, which screens the oscillating motion of the disk. Each cycle is proportional to a specific circulate rate. As with all positive displacement meters, changes in viscosity beneath a given threshold will affect the measurement accuracy. A wide selection of sizes and capacities can be found. These items could be produced from a big selection of construction supplies.
Rotary vane gauges
Rotary vane meters can be found in a big selection of designs, but all of them function on the same precept. The basic unit consists of an equally divided rotating impeller (containing two or extra compartments) mounted contained in the instrument housing. The impeller is in constant contact with the housing. As the impeller rotates, a onerous and fast quantity of liquid is swept from each compartment to the outlet of the meter. The variety of impeller revolutions is calculated and recorded in quantity models.
Spiral move meter
The helical circulate meter consists of two radially inclined helical rotors which are gear driven together with minimal clearance between the rotors and the housing. The two rotors switch the liquid from one end of the chamber to the opposite along the axial course.
Velocity meters
These devices function linearly with respect to the volumetric flow price. Because there isn’t a square root relationship (as with differential strain devices), they have a a lot larger vary. Velocity meters are least sensitive to adjustments in viscosity when the Reynolds number exceeds 10,000. Most velocity meter housings are equipped with flanges or fittings to permit them to be related immediately into the piping.
Turbine move meters
Turbine circulate meters have been extensively used for exact liquid measurement functions. The gadget consists of a multi-bladed rotor mounted in a pipe, perpendicular to the flow of the liquid. The rotor rotates because the liquid passes by way of the vanes. Rotational speed is a direct function of move rate and may be sensed by magnetic sensors, photocells or gears. Electrical pulses could be counted and totalized.
The number of electrical pulses counted in a given time interval is proportional to the flow rate. A tachometer may be added to measure the turbine speed and determine the liquid flow rate. A correctly specified and installed turbine circulate meter has good accuracy, especially for low viscosity liquids.
A major problem with turbine flowmeters is bearing put on. A “bearingless” design has been developed to avoid this problem. The liquid getting into the circulate meter passes via the spiral vanes of the stator, inflicting the liquid circulate to rotate. The move acts on the spheres, inflicting them to travel within the house between the primary stator and the spiral-like second stator. The orbital movement of the sphere is detected electronically. The frequency of the generated pulse output is proportional to the circulate price.
Vortex flowmeters
Vortex flow meters take advantage of the pure phenomenon that occurs when a liquid flows via a blunt object. Vortex or vortex move alternates downstream of the object. The frequency of the vortex shedding is proportional to the rate of the liquid flowing through the flowmeter.
The three major components of the circulate meter are the blunt object strut mounted on the meter bore, the sensor that detects the presence of vortices and generates an electrical pulse, and the sign amplification and conditioning transmitter whose output is proportional to the circulate price.
Electromagnetic flow meters
Magnetic circulate meters can deal with most liquids and slurries, supplied that the material to be metered is electrically conductive. The main component is the move tube (primary element), which is installed immediately within the pipe. The stress drop throughout the meter is identical because the pressure drop through the equal length of pipe, since there are not any shifting components or move obstructions. The voltmeter could be linked directly to the flow tube or remotely mounted and related to the flow tube via a shielded cable.
Electromagnetic move meters work based on Faraday’s law of electromagnetic induction, which states that a voltage is induced when a conductor passes by way of a magnetic area. The liquid acts because the conductor; the magnetic area is generated by an energized coil exterior the flow tube. The quantity of voltage generated is proportional to the flow price. Two electrodes mounted on the wall of the tube detect the voltage measured by the secondary factor.
Electromagnetic flowmeters supply major advantages: they will measure difficult and corrosive liquids and slurries; they’ll measure ahead and reverse flow with equal accuracy. The disadvantages of early designs have been high energy consumption and the want to obtain a full tube with no circulate to set the meter to zero initially. Recent enhancements have eliminated these issues. The pulse-type excitation technique reduces power consumption because excitation happens only half the time within the unit. A zero setting is now not required.
Ultrasonic flow meters
Ultrasonic flowmeters could be divided into doppler meters and journey time (or transverse) meters. Doppler meters measure the frequency shift attributable to the flow of a liquid. Two sensors are mounted in a housing connected to one side of the pipe. A sign of known frequency is sent to the liquid to be measured. Solids, bubbles or any discontinuities within the liquid cause the heart beat to be reflected to the receiver element. Since the liquid causing the reflection is moving, the frequency of the returned pulse is shifted. The frequency shift is proportional to the velocity of the liquid.
There can also be a portable doppler meter that can be run on AC power or a rechargeable power pack. The instrument can be used by simply clamping the sensing head to the skin of the pipe. A set of four to twenty mA output terminals allows the unit to be connected to a strip chart recorder or other distant device.
The journey time meter’s sensors are mounted on all sides of the pipe. The configuration permits the sound waves to journey between the gadgets at an angle of forty five degrees. angle to the path of fluid circulate. The pace of the signal propagating between the sensors increases or decreases with the course of transmission and the pace of the liquid being measured. By transmitting the sign in both directions alternately, a time-differential relationship proportional to the move price may be obtained. A limitation of the journey time meter is that the liquid being measured should be comparatively freed from entrained gases or solids to attenuate signal scattering and absorption.
Mass move meter
Mass flowmeters the continued need for extra correct move measurement in mass related processes (chemical reactions, heat switch, and so forth.) has led to the event of mass flow meters. A variety of designs can be found, however the most generally used for liquid flow applications is the Coriolis meter. It operates on the basis of a pure phenomenon generally known as the Coriolis drive, hence the title.
Coriolis move meters
Coriolis meters are true mass meters that directly measure mass flow as a substitute of volume flow. Since the mass is fixed, the meter is linear and does not need to be adjusted for adjustments in liquid traits. It additionally eliminates the necessity to compensate for altering temperature and stress situations. The meter is particularly appropriate for measuring liquids whose viscosity varies with velocity at a given temperature and strain.
Coriolis meters are also out there in a wide selection of designs. A well-liked unit consists of a U-shaped move tube encapsulated in a sensor housing related to an digital unit. The sensing unit can be mounted instantly into any course of. The electronics unit can be situated as much as 500 toes away from the sensor.
Thermal mass flow meters
Thermal mass flowmeters are historically used for gasoline measurements, but are additionally available in designs for liquid move measurements. These mass meters additionally function unbiased of density, strain and viscosity. Thermal mass meters use a heated sensing component that’s isolated from the fluid flow path. The flowing stream conducts heat from the sensing element. The warmth transferred is proportional to the mass move rate. The sensor isn’t in direct contact with the fluid. The electronic meeting features a flow analyzer, temperature compensator, and signal conditioner that gives a linear output proportional to the mass flow fee.
Open channel move meter
An “open channel” is any pipe during which liquids move on a free floor. This includes tunnels, unpressurized sewers, partially filled pipes, canals, streams and rivers. Of the many techniques that can be utilized to watch flow in open channels, depth-related strategies are the most typical. These techniques assume that instantaneous flow could be decided from a measurement of water depth or head. Weirs and flumes are the oldest and most generally used main gadgets used to measure circulate in open channels.
Weirs work on the principle that an obstruction in a channel causes water to circulate backwards, making a high water degree (head) behind the obstruction. The head is a operate of the flow rate, and due to this fact the flow rate by way of the device. The weir consists of a vertical plate with a pointed high. The top of the plate could be straight or notched. Weirs are classified by the form of the notch. The fundamental types are V-notched, rectangular and trapezoidal.
The discharge via the weir and flume is a perform of the liquid level, so the device should use stage measurement techniques to find out the circulate fee. Staff gauges and floating working items are the simplest units to make use of for this function. Various digital sensing, totalizing and recording systems are also available.
A current improvement consists of using ultrasonic pulses to measure liquid stage. Measurements are made by sending an acoustic pulse from the sensor to the surface of the liquid and timing the return echo. Linearized circuitry converts the peak of the liquid to a move fee. A bar graph recorder data the flow rate and a digital totalizer data the whole number of gallons. Another recently launched microprocessor-based system makes use of ultrasonic or float sensors. A keypad with an interactive LCD display simplifies programming, management and calibration duties.
Select a right liquid flow meter
Data shows that more than 75% of the move meters installed in trade don’t perform nicely. And poor selection accounts for ninety p.c of these problems. Clearly, flowmeter selection just isn’t a job for amateurs.
The most important requirement is to know precisely what the instrument ought to do. There are numerous issues to suppose about right here. Will the measurement be used for course of control (repeatability is the primary concern) or for accounting or trade handover (high accuracy is important)? Is an area indication or a remote signal required? If a distant output is required, is it a proportional sign or a contact closure to begin out or cease another device? Is the fluid viscous, clear or slurry? Is it electrically conductive? What is its particular gravity or density? What move rates are involved within the application? What is the working temperature and stress of the process? Accuracy (see glossary), vary, linearity, repeatability, and piping necessities should also be thought of.
It is equally essential to know what a circulate meter can’t do as properly as what it could do before making a final selection. Every instrument has strengths and weaknesses, and the diploma of efficiency satisfaction is immediately associated to how well the instrument’s options and weaknesses match the appliance necessities. Often, the user’s expectations of flowmeter performance don’t match those provided by the supplier. Most suppliers are eager to assist clients choose the best flowmeter for a specific job. Many present questionnaires, checklists and specification sheets designed to acquire the crucial data necessary to match the right flowmeter to the job.
Technical improvements to the flowmeter should also be thought of. For instance, a standard mistake is to pick the design that was most popular for a given software a quantity of years in the past and assume that it’s still the best tool for the job. In current years, many changes and innovations might have occurred within the growth of flowmeters for specific applications, leading to a wider range of choices.
Flow meters can be found in a wide range of costs. Variable space flowmeters are normally the least expensive, with some smaller items costing lower than $90. Mass move meters are the most expensive. They start at about $3000. However, the entire system cost should always be thought of when deciding on a flowmeter. Installation, operation and maintenance prices are additionally important economic components. For some of the more complicated designs, maintenance prices may be excessive.
As with many other products, the plant engineer often gets what he pays for when he buys a flow meter. But his satisfaction with the product will depend on the care he makes use of in choosing and installing the instrument. It comes again to understanding the process, the product and the move metering necessities. It is not unusual to “overbuy”. Plant engineers should not buy extra highly effective or advanced flowmeters than they need.
Using move meters
Although suppliers are always ready to provide flowmeter set up providers, it’s estimated that about 75% of customers install their own tools. But installation errors can occur. One of the commonest conditions is not permitting sufficient upstream and downstream straight pipe for the flowmeter.
Each design has some tolerance for erratic velocity circumstances within the piping, but all installations require correct piping configurations to operate effectively. Proper piping provides the proper circulate pattern for the system. Without it, accuracy and performance may be adversely affected. Flow meters are sometimes installed backwards (especially orifice plates). Pressure sensing strains may also be reversed.
For electrical parts, intrinsic safety is a vital consideration in hazardous areas. Most flowmeter suppliers provide intrinsically protected designs for this kind of use.
Stray magnetic fields are current in most industrial plants. Power traces, relays, solenoids, transformers, motors and generators all contribute their share of interference. Users should be sure that the flowmeter they choose just isn’t topic to such disturbances. The downside occurs primarily with the electronics within the secondary elements that must be protected. Strict adherence to the manufacturer’s really helpful set up practices can often prevent such problems.
Calibration
All move meters require an initial calibration. In most instances, the instrument is calibrated by the producer for the desired conditions of use. However, if certified personnel are available at the manufacturing unit, the consumer can carry out his own calibration.
digital pressure gauge for recalibration depends tremendously on how properly the meter is matched to the applying. Certain fluids that move by way of the meter tend to be abrasive, aggressive or corrosive. Over time, some parts of the device will degrade sufficient to affect efficiency. Some designs are extra vulnerable to wreck than others. For instance, wear on individual turbine blades may cause performance modifications. If the application is crucial, the accuracy of the flow meter must be checked frequently. In different circumstances, recalibration may not be required for a quantity of years as a outcome of the appliance is not crucial and would not otherwise change the meter’s performance. Some flowmeters require special tools for calibration. Most producers will provide such companies at their crops or user services, and they’ll bring the tools with them for on-site calibration.
Maintenance
Many elements can affect upkeep necessities and the anticipated lifetime of a circulate meter. The main issue, of course, is matching the correct instrument to the particular utility. Poorly selected tools will always cause problems early on. Flowmeters with out transferring elements normally require less consideration than units with transferring components. But all flowmeters will ultimately require some kind of maintenance.
The primary factor in a differential stress flowmeter requires a lot of piping, valves and fittings when related to the secondary element, so maintenance could be a recurring activity in such installations. Pulse traces can become clogged or corroded and have to be cleaned or replaced. And, improperly positioned secondary parts can lead to measurement errors. Repositioning components could be expensive.
Flow meters with transferring parts require periodic internal inspection, especially if the liquid being measured is dirty or viscous. Installing a filter earlier than such units will assist cut back fouling and wear. Accessible instruments similar to ultrasonic or electromagnetic meters could have issues with the electronics of their secondary parts. Pressure transducers associated with secondary components must be eliminated and inspected periodically.
Applications where coatings may occur are additionally potential problems for accessible instruments similar to magnetic or ultrasonic devices. If the coating is insulated, the operation of the magnetic circulate meter can finally be impaired if the electrodes are insulated from the liquid. This state of affairs could be averted by regular cleansing. With ultrasonic move meters, the refraction angle could change and the acoustic power absorbed by the coating may cause the move meter to not work.
More articles on circulate meters:
Relation between flow and stress
Difference between flow meter and circulate transmitter
Water stage sensor varieties and works
Solution of water pollutionn
รับตัวแทนจำหน่าย และขายส่งฟิตติ้งสแตนเลส , มีสินค้าพร้อมส่ง , ไม่ต้องสต๊อกสินค้า , จัดส่งฟรีกรุงเทพ ปริมณฑล , ต่างจังหวัดจัดส่งขนส่ง ฟรีทั่วประเทศไทย
octa-gauge.com & radiusglobal.co.th Shop power by Odoo ERP
