Table of Contents
What is circulate units?
Continuity of circulate equation
Common circulate unit metering strategies in open channels
Eyeball technique
Flow depth (Manning)
Main tools
Surface Velocity Meters
Transport time meters
Flow unit measurement strategies in full tube purposes
Venturi meters
Magnetic flowmeter
Turbine flowmeter
Conclusion
What is flow units?
Flow fee is the quantity of fluid that passes via a unit of time. In water assets, flow is commonly measured in cubic toes per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a big selection of different units. The measurement of water useful resource move is important for applications similar to system management, billing, design and lots of other purposes. There are several ways to measure move in a water useful resource system. This article outlines a variety of the extra common methods of circulate measurement and provides some helpful details about move items measurement.
Continuity of circulate equation
For water flowing in a pipe underneath steady-state conditions (i.e., not various with time), continuity signifies that water flowing into one finish of the pipe should flow out of the opposite finish. This additionally signifies that the circulate within the pipe is identical at any point alongside the size of the pipe. The continuity equation could be expressed as
Flow = Velocity * Area
The concept of continuity in regular state circumstances results in the product of velocity * space being equal to a continuing at any level within the pipe. This is a helpful principle for making flow measurements, as proven beneath.
This is an instance of using the continuity equation to calculate move. Velocity is measured at 10 toes per second and the cross-sectional area of the flow is measured at 10 sq. ft. Flow rate = 10 toes per second * 10 square toes = one hundred cubic feet per second.
Common circulate unit metering methods in open channels
Eyeball methodology
It is usually useful to estimate the flow velocity and cross-sectional space by eye and then multiply the flow velocity by the area to obtain the move velocity (continuity equation). A ruler or tape measure can be utilized to enhance the accuracy of cross-sectional space measurements, and a stopwatch can be used to improve velocity measurements by timing floating debris transferring a set distance. The eyeball methodology can be used to estimate move when solely an “order of magnitude” of flow is required or when the flow rate is too low to be measured with a circulate meter.
Flow depth (Manning)
When the channel cross-sectional space and channel slope are identified and uniform move conditions exist, the Manning’s equation can be utilized to calculate flow by measuring depth only. The Manning’s equation is an empirical equation that describes the connection between flow price in an open channel underneath uniform move conditions and depth, slope and channel friction coefficient (Manning’s n). Uniform move means that depth doesn’t range with the length of the conduit or channel. Flow measurements using Manning’s equation for depth are not applicable to steadily changing circulate conditions, corresponding to backwater conditions upstream of a dam or weir.
The depth flow methodology of circulate measurement is more accurate than the “eyeball” technique. The major challenge with depth-only flow measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform circulate situations. This methodology is usually used with ultrasonic circulate meters to estimate the move of a river by measuring solely the water level of the river. Often in these causes, the river level/flow relationship is developed with the assistance of complicated river hydraulic models to account for complicated channel geometry and channel friction conditions.
Main equipment
The primary device is used to measure flow in open channels, utilizing structures such as flumes, weirs or dams, to measure move by measuring depth. The measured depth can then be converted to a flow price using an equation or rated curve equation.
Primary gadgets work by forcing the circulate by way of a path of important depth, for example at the prime of a weir or at the throat of a flume. In technical terms, the important depth is outlined because the depth of the minimal particular power state that leads to a specific discharge. In practice, this minimal state of vitality means that just one move corresponds to the critical depth. Therefore, measuring solely the depth produces a measurement of the corresponding flux and is due to this fact referred to as a “primary” device.
Primary gadgets are a really handy methodology of circulate measurement as a end result of the depth can be measured from above the move without the need to insert a sensor within the water. This makes main move meters more reliable and easier to maintain. A disadvantage of major devices is that they’ll cause head loss and backwater in the system. Primary units are sometimes thought of to be probably the most correct method of measuring open channel move.
Surface Velocity Meters
An space velocity meter is an open channel flow meter that measures flow by making two separate measurements of depth and velocity. The depth is transformed to a cross-sectional space utilizing the geometry of the pipe or channel. The circulate rate is then calculated by multiplying the circulate space by the velocity using the continuity equation, therefore the name “AV meter”. Velocity is usually measured utilizing a Doppler sensor, which reflects ultrasound waves again from particles within the fluid and uses the Doppler shift in the mirrored sound sign to estimate velocity. Some AV meters measure surface velocity optically to estimate velocity.
AV meters are sometimes used to measure open channel circulate in sewers as a result of the probes are relatively small and they are often put in in present sewer pipes with out causing vital head loss in the pipe. This additionally allows them for use for momentary or short-term move metering applications for sewer research. one drawback of AV meters is that the sensor must be put in within the fluid. In sewers, this requires frequent upkeep to scrub the sensor. AV meters are sometimes considered much less correct than primary flow meters because primary devices only must measure depth and depth measurements are extra accurate than velocity measurements.
Transport time meters
Transport time meters were developed within the oil trade to precisely measure circulate in giant pipelines. They have been used with some success for open channel circulate in water metering purposes. Transport time meters also use ultrasound like Doppler meters, but as an alternative of bouncing the sound waves off particles in the water like Doppler circulate meters, they ship ultrasound waves between two sensors separated from one another by a sure distance alongside the length of the pipe and uses the transmission time of the sound waves to calculate the rate of the water move. Because the velocity of sound in the water is thought, the pace of the water may be calculated primarily based on the offset in ultrasonic wave transmission time that occurs as a result of pace of the water.
Transmission time meters may be costly relative to Doppler flow meters as a result of many sensors and sophisticated installation concerned. They could be more accurate because of the capability to split the flow into horizontal cross sections and measure the speed of each part.
Flow unit measurement methods in full tube purposes
Venturi meters
Venturi flow meters use the Venturi impact to measure move in a full or pressurized pipe by using the converging part of the pipe to limit the circulate. According to the continuity equation, the cross-sectional area of the converging section is small and subsequently the rate is greater within the throat. Due to power conservation and Bernoulli’s principle, larger velocities within the throat end in a drop in throat stress. The flow rate can then be decided by measuring the stress drop within the convergent part and calculating the move rate utilizing Bernoulli’s equation. Venturi meters are more common in water metering functions as a result of the pressure measurement ports can turn into clogged in wastewater applications.
Magnetic flowmeter
The electromagnetic circulate meter works by applying a magnetic field to the fluid passing via the pipe. This causes a small electron potential distinction that might be measured by the electrode sensor (due to Faraday’s law and electromagnetic induction). The magnitude of the electron potential difference is proportional to the rate of the water, and the continuity equation can then be used to calculate the circulate fee.
An benefit of the magnetometer is that the metering section is identical diameter because the adjoining pipe, so the magnetometer causes no additional head loss. For probably the most part, magnetometers are used for full (pressure) pipe purposes, however these days open channel magnetometers can additionally be used.
Turbine flowmeter
A turbine circulate meter is a mechanical circulate meter that uses a rotating turbine in move to measure the flow of water in a pipe. The pace of the turbine is proportional to the velocity and the circulate price can then be calculated utilizing the continuity equation. Turbine flow meters are only used for water functions due to potential problems with wastewater solids collection and clogging generators.
Conclusion
There are many ways to measure move. Each methodology has different advantages, disadvantages and accuracy in numerous purposes.
It is essential to understand the traits of varied circulate measurement techniques to help choose the proper kind of move metering for your utility or to properly interpret the flow measurements of existing circulate meters. Tools like Apure (IoT-based water data analysis) assist to examine measurements collected by flow meters and carry out diagnostics to understand circulate meter performance and shortly course of and analyze the info. Contact us for technical or product service assist.
More articles on move meters:
Mass flow fee vs volumetric flow rate
Relation between circulate and stress
Ultrasonic flow meter working principle
Difference between flow meter and move transmitter
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Table of Contents
What is flow units?
Continuity of move equation
Common flow unit metering methods in open channels
Eyeball technique
Flow depth (Manning)
Main tools
Surface Velocity Meters
Transport time meters
Flow unit measurement methods in full tube purposes
Venturi meters
Magnetic flowmeter
Turbine flowmeter
Conclusion
What is move units?
Flow price is the amount of fluid that passes through a unit of time. In water assets, flow is usually measured in cubic feet per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or quite a lot of other models. The measurement of water useful resource move is necessary for purposes corresponding to system control, billing, design and many different functions. There are a number of ways to measure circulate in a water useful resource system. This article outlines some of the extra common strategies of flow measurement and supplies some helpful details about circulate models measurement.
Continuity of flow equation
For water flowing in a pipe under steady-state situations (i.e., not various with time), continuity means that water flowing into one finish of the pipe should move out of the other finish. This additionally means that the move within the pipe is identical at any point along the size of the pipe. The continuity equation may be expressed as
Flow = Velocity * Area
The concept of continuity in regular state circumstances leads to the product of velocity * space being equal to a continuing at any point in the pipe. This is a helpful precept for making flow measurements, as shown beneath.
This is an instance of using the continuity equation to calculate flow. Velocity is measured at 10 ft per second and the cross-sectional area of the flow is measured at 10 square toes. Flow price = 10 ft per second * 10 square toes = a hundred cubic ft per second.
Common move unit metering methods in open channels
Eyeball method
It is sometimes helpful to estimate the flow velocity and cross-sectional area by eye and then multiply the move velocity by the area to acquire the flow velocity (continuity equation). A ruler or tape measure can be used to enhance the accuracy of cross-sectional space measurements, and a stopwatch can be utilized to enhance velocity measurements by timing floating particles moving a set distance. The eyeball methodology can be used to estimate move when solely an “order of magnitude” of move is required or when the move price is simply too low to be measured with a flow meter.
Flow depth (Manning)
When the channel cross-sectional area and channel slope are identified and uniform flow situations exist, the Manning’s equation can be used to calculate flow by measuring depth solely. The Manning’s equation is an empirical equation that describes the relationship between move fee in an open channel underneath uniform move situations and depth, slope and channel friction coefficient (Manning’s n). Uniform flow signifies that depth doesn’t vary with the length of the conduit or channel. Flow measurements utilizing Manning’s equation for depth aren’t relevant to steadily altering flow circumstances, similar to backwater situations upstream of a dam or weir.
The depth circulate methodology of move measurement is more accurate than the “eyeball” technique. The primary problem with depth-only circulate measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform move situations. This method is usually used with ultrasonic circulate meters to estimate the circulate of a river by measuring solely the water degree of the river. Often in these causes, the river level/flow relationship is developed with the assistance of advanced river hydraulic models to account for complex channel geometry and channel friction circumstances.
Main equipment
The major system is used to measure flow in open channels, utilizing buildings similar to flumes, weirs or dams, to measure circulate by measuring depth. The measured depth can then be transformed to a circulate price utilizing an equation or rated curve equation.
Primary gadgets work by forcing the circulate by way of a path of critical depth, for example on the top of a weir or at the throat of a flume. In technical terms, the crucial depth is outlined because the depth of the minimal specific vitality state that leads to a specific discharge. In follow, this minimum state of energy signifies that just one flow corresponds to the important depth. Therefore, measuring solely the depth produces a measurement of the corresponding flux and is therefore called a “primary” system.
Primary gadgets are a very handy methodology of move measurement as a end result of the depth can be measured from above the flow with out the need to insert a sensor in the water. This makes major circulate meters more reliable and easier to take care of. digital pressure gauge of major gadgets is that they will trigger head loss and backwater in the system. Primary units are often thought-about to be probably the most correct method of measuring open channel flow.
Surface Velocity Meters
An space velocity meter is an open channel circulate meter that measures flow by making two separate measurements of depth and velocity. The depth is transformed to a cross-sectional space utilizing the geometry of the pipe or channel. The move fee is then calculated by multiplying the circulate area by the speed using the continuity equation, hence the identify “AV meter”. Velocity is typically measured using a Doppler sensor, which displays ultrasound waves again from particles within the fluid and uses the Doppler shift in the reflected sound sign to estimate velocity. Some AV meters measure surface velocity optically to estimate velocity.
AV meters are often used to measure open channel circulate in sewers as a result of the probes are relatively small and they can be installed in current sewer pipes with out inflicting important head loss in the pipe. This also permits them for use for short-term or short-term move metering applications for sewer research. one disadvantage of AV meters is that the sensor should be installed in the fluid. In sewers, this requires frequent upkeep to wash the sensor. AV meters are often thought of less correct than primary move meters as a end result of primary devices only need to measure depth and depth measurements are extra accurate than velocity measurements.
Transport time meters
Transport time meters were developed within the oil trade to accurately measure flow in massive pipelines. They have been used with some success for open channel circulate in water metering functions. Transport time meters additionally use ultrasound like Doppler meters, however instead of bouncing the sound waves off particles in the water like Doppler move meters, they send ultrasound waves between two sensors separated from each other by a sure distance along the size of the pipe and uses the transmission time of the sound waves to calculate the speed of the water flow. Because the speed of sound within the water is thought, the pace of the water can be calculated based mostly on the offset in ultrasonic wave transmission time that occurs due to the velocity of the water.
Transmission time meters could be costly relative to Doppler move meters because of the many sensors and complicated installation concerned. They could be extra accurate as a outcome of ability to separate the flow into horizontal cross sections and measure the rate of each section.
Flow unit measurement methods in full tube functions
Venturi meters
Venturi circulate meters use the Venturi effect to measure flow in a full or pressurized pipe through the use of the converging section of the pipe to limit the flow. According to the continuity equation, the cross-sectional space of the converging part is small and due to this fact the velocity is higher within the throat. Due to energy conservation and Bernoulli’s principle, higher velocities within the throat end in a drop in throat stress. The circulate fee can then be determined by measuring the strain drop in the convergent section and calculating the flow price using Bernoulli’s equation. Venturi meters are more common in water metering applications as a outcome of the stress measurement ports can turn out to be clogged in wastewater functions.
Magnetic flowmeter
The electromagnetic circulate meter works by applying a magnetic subject to the fluid passing via the pipe. This causes a small electron potential distinction that might be measured by the electrode sensor (due to Faraday’s law and electromagnetic induction). The magnitude of the electron potential difference is proportional to the rate of the water, and the continuity equation can then be used to calculate the move fee.
An advantage of the magnetometer is that the metering part is the same diameter because the adjacent pipe, so the magnetometer causes no additional head loss. For probably the most part, magnetometers are used for full (pressure) pipe purposes, however these days open channel magnetometers can be used.
Turbine flowmeter
A turbine flow meter is a mechanical circulate meter that uses a rotating turbine in move to measure the move of water in a pipe. The velocity of the turbine is proportional to the rate and the circulate rate can then be calculated utilizing the continuity equation. Turbine circulate meters are only used for water applications due to potential problems with wastewater solids collection and clogging generators.
Conclusion
There are many ways to measure move. Each method has different advantages, disadvantages and accuracy in numerous applications.
It is necessary to know the traits of assorted flow measurement strategies to help select the proper sort of circulate metering in your utility or to properly interpret the circulate measurements of existing move meters. Tools like Apure (IoT-based water knowledge analysis) assist to examine measurements collected by move meters and perform diagnostics to grasp flow meter performance and shortly course of and analyze the data. Contact us for technical or product service help.
More articles on flow meters:
Mass circulate price vs volumetric circulate rate
Relation between flow and pressure
Ultrasonic flow meter working precept
Difference between flow meter and move transmitter