Table of Contents

What is move units?

Continuity of flow 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 functions

Venturi meters

Magnetic flowmeter

Turbine flowmeter

Conclusion

What is circulate units?

Flow price is the quantity of fluid that passes by way of 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 a selection of different units. The measurement of water useful resource flow is essential for functions similar to system control, billing, design and many different applications. There are a number of ways to measure move in a water resource system. This article outlines a number of the more frequent methods of move measurement and provides some helpful information about move items measurement.

Continuity of circulate equation

For water flowing in a pipe beneath steady-state conditions (i.e., not various with time), continuity implies that water flowing into one end of the pipe must circulate out of the other end. This additionally signifies that the circulate in the pipe is identical at any level alongside the length of the pipe. The continuity equation can be expressed as

Flow = Velocity * Area

The idea of continuity in steady state situations results in the product of velocity * space being equal to a relentless at any point in the pipe. This is a useful principle for making circulate measurements, as proven below.

This is an instance of using the continuity equation to calculate move. Velocity is measured at 10 toes per second and the cross-sectional space of the circulate is measured at 10 square ft. Flow price = 10 toes per second * 10 sq. ft = 100 cubic ft per second.

Common move unit metering methods in open channels

Eyeball method

It is typically useful to estimate the flow velocity and cross-sectional space by eye and then multiply the move velocity by the area to acquire the circulate velocity (continuity equation). A ruler or tape measure can be used to improve the accuracy of cross-sectional area measurements, and a stopwatch can be utilized to improve velocity measurements by timing floating particles transferring a set distance. The eyeball methodology can be utilized to estimate circulate when only an “order of magnitude” of circulate is required or when the circulate fee is merely 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 flow conditions exist, the Manning’s equation can be utilized to calculate flow by measuring depth solely. The Manning’s equation is an empirical equation that describes the connection between circulate fee in an open channel under uniform move conditions and depth, slope and channel friction coefficient (Manning’s n). Uniform move implies that depth does not range with the size of the conduit or channel. Flow measurements using Manning’s equation for depth usually are not relevant to steadily changing move conditions, corresponding to backwater situations upstream of a dam or weir.

The depth flow method of move measurement is more correct than the “eyeball” method. The main problem with depth-only circulate measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform flow conditions. This technique is often used with ultrasonic circulate meters to estimate the circulate 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 help of advanced river hydraulic models to account for complicated channel geometry and channel friction circumstances.

Main tools

The major device is used to measure circulate in open channels, using structures corresponding to flumes, weirs or dams, to measure circulate by measuring depth. The measured depth can then be transformed to a circulate rate utilizing an equation or rated curve equation.

Primary units work by forcing the circulate via a path of important depth, for instance on the high of a weir or on the throat of a flume. In technical phrases, the important depth is defined as the depth of the minimum specific power state that results in a specific discharge. In apply, this minimum state of power means that only one circulate corresponds to the important depth. Therefore, measuring solely the depth produces a measurement of the corresponding flux and is due to this fact called a “primary” device.

Primary devices are a very convenient method of circulate measurement as a outcome of the depth could be measured from above the circulate without the necessity to insert a sensor in the water. This makes major circulate meters extra dependable and easier to take care of. A disadvantage of primary devices is that they’ll trigger head loss and backwater within the system. Primary gadgets are often thought of to be essentially the most correct method of measuring open channel flow.

Surface Velocity Meters

An space velocity meter is an open channel flow meter that measures move by making two separate measurements of depth and velocity. The depth is converted to a cross-sectional area using the geometry of the pipe or channel. The circulate price is then calculated by multiplying the move space by the rate using the continuity equation, hence the name “AV meter”. Velocity is often measured utilizing a Doppler sensor, which reflects ultrasound waves back from particles within the fluid and makes use of the Doppler shift within 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 flow in sewers because the probes are relatively small and they are often installed in existing sewer pipes with out inflicting vital head loss in the pipe. This additionally permits them for use for temporary or short-term flow metering functions for sewer research. one disadvantage of AV meters is that the sensor have to be installed in the fluid. In sewers, this requires frequent maintenance to wash the sensor. AV meters are sometimes thought-about less correct than major circulate meters as a result of main units only need to measure depth and depth measurements are more correct than velocity measurements.

Transport time meters

Transport time meters had been developed in the oil industry to accurately measure circulate in large pipelines. They have been used with some success for open channel circulate in water metering applications. Transport time meters additionally use ultrasound like Doppler meters, but as an alternative of bouncing the sound waves off particles within the water like Doppler flow meters, they send ultrasound waves between two sensors separated from each other by a sure distance along the length of the pipe and makes use of the transmission time of the sound waves to calculate the rate of the water flow. Because the velocity of sound within the water is known, the speed of the water can be calculated based on the offset in ultrasonic wave transmission time that occurs due to the speed of the water.

Transmission time meters may be costly relative to Doppler circulate meters because of the many sensors and complicated set up concerned. They can be extra accurate because of the capacity 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 circulate meters use the Venturi impact to measure flow in a full or pressurized pipe by utilizing the converging part of the pipe to restrict the circulate. According to the continuity equation, the cross-sectional area of the converging part is small and due to this fact the rate is greater in the throat. Due to power conservation and Bernoulli’s precept, larger velocities within the throat end in a drop in throat pressure. The circulate rate can then be determined by measuring the pressure drop in the convergent part and calculating the move price using Bernoulli’s equation. Venturi meters are extra widespread in water metering purposes as a outcome of the strain measurement ports can turn out to be clogged in wastewater applications.

Magnetic flowmeter

The electromagnetic circulate meter works by making use of a magnetic area to the fluid passing by way of the pipe. This causes a small electron potential difference that can be measured by the electrode sensor (due to Faraday’s legislation and electromagnetic induction). The magnitude of the electron potential difference is proportional to the speed of the water, and the continuity equation can then be used to calculate the flow rate.

An advantage of the magnetometer is that the metering part is identical diameter because the adjacent pipe, so the magnetometer causes no extra head loss. For the most part, magnetometers are used for full (pressure) pipe functions, but nowadays open channel magnetometers can additionally be used.

Turbine flowmeter

A turbine circulate meter is a mechanical circulate meter that makes use of a rotating turbine in circulate to measure the circulate of water in a pipe. The velocity of the turbine is proportional to the rate and the flow rate can then be calculated utilizing the continuity equation. Turbine move meters are solely used for water functions because of potential issues with wastewater solids assortment and clogging generators.

Conclusion

There are many ways to measure flow. Each methodology has totally different advantages, disadvantages and accuracy in different functions.

It is important to grasp the characteristics of various move measurement methods to assist select the right type of move metering in your utility or to correctly interpret the circulate measurements of existing move meters. Tools like Apure (IoT-based water knowledge analysis) help to look at measurements collected by flow meters and perform diagnostics to understand move meter performance and rapidly course of and analyze the info. Contact us for technical or product service help.

More articles on flow meters:

Mass flow price vs volumetric flow price

Relation between move and pressure

Ultrasonic circulate meter working principle

Difference between move meter and move transmitter

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Table of Contents

What is move units?

Continuity of move equation

Common move unit metering strategies in open channels

Eyeball methodology

Flow depth (Manning)

Main gear

Surface Velocity Meters

Transport time meters

Flow unit measurement methods in full tube purposes

Venturi meters

Magnetic flowmeter

Turbine flowmeter

Conclusion

What is circulate units?

Flow price is the quantity of fluid that passes by way of a unit of time. In water sources, flow is commonly measured in cubic feet per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a selection of different units. The measurement of water useful resource move is essential for functions similar to system control, billing, design and many other functions. There are several ways to measure flow in a water useful resource system. This article outlines a few of the extra frequent methods of circulate measurement and provides some helpful information about move items measurement.

Continuity of move equation

For water flowing in a pipe under steady-state situations (i.e., not various with time), continuity implies that water flowing into one end of the pipe should move out of the opposite end. This also means that the move within the pipe is the same at any level along the length of the pipe. The continuity equation could be expressed as

Flow = Velocity * Area

The concept of continuity in steady state situations leads to the product of velocity * area being equal to a continuing at any point in the pipe. This is a useful precept for making move measurements, as shown under.

This is an instance of utilizing the continuity equation to calculate move. Velocity is measured at 10 toes per second and the cross-sectional area of the circulate is measured at 10 sq. feet. Flow rate = 10 toes per second * 10 sq. toes = 100 cubic feet per second.

Common flow unit metering strategies in open channels

Eyeball technique

It is sometimes helpful to estimate the flow velocity and cross-sectional space 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 utilized to improve the accuracy of cross-sectional space measurements, and a stopwatch can be utilized to enhance velocity measurements by timing floating particles transferring a set distance. The eyeball methodology can be used to estimate circulate when only an “order of magnitude” of circulate is required or when the circulate rate is just too low to be measured with a flow meter.

pressure gauge 10 bar (Manning)

When the channel cross-sectional area and channel slope are recognized and uniform circulate circumstances exist, the Manning’s equation can be used to calculate flow by measuring depth only. The Manning’s equation is an empirical equation that describes the connection between flow fee in an open channel under uniform move circumstances and depth, slope and channel friction coefficient (Manning’s n). Uniform flow implies that depth does not differ with the length of the conduit or channel. Flow measurements using Manning’s equation for depth usually are not relevant to steadily changing flow circumstances, such as backwater conditions upstream of a dam or weir.

The depth move methodology of move measurement is extra accurate than the “eyeball” method. 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 often used with ultrasonic move meters to estimate the flow of a river by measuring solely the water stage of the river. Often in these causes, the river level/flow relationship is developed with the help of advanced river hydraulic models to account for complex channel geometry and channel friction situations.

Main gear

The primary system is used to measure circulate in open channels, utilizing structures such as flumes, weirs or dams, to measure flow by measuring depth. The measured depth can then be transformed to a flow rate using an equation or rated curve equation.

Primary gadgets work by forcing the circulate through a path of important depth, for instance on the high of a weir or on the throat of a flume. In technical phrases, the critical depth is outlined because the depth of the minimum particular power state that leads to a specific discharge. In practice, this minimum state of vitality signifies that only one circulate corresponds to the critical depth. Therefore, measuring only the depth produces a measurement of the corresponding flux and is therefore known as a “primary” device.

Primary devices are a really handy methodology of move measurement as a result of the depth can be measured from above the circulate with out the necessity to insert a sensor within the water. This makes main circulate meters more dependable and simpler to maintain up. A disadvantage of major units is that they’ll trigger head loss and backwater within the system. Primary gadgets are sometimes considered to be essentially the most correct methodology of measuring open channel move.

Surface Velocity Meters

An area velocity meter is an open channel move meter that measures circulate by making two separate measurements of depth and velocity. The depth is transformed to a cross-sectional area utilizing the geometry of the pipe or channel. The flow price is then calculated by multiplying the move space by the velocity using the continuity equation, therefore the name “AV meter”. Velocity is typically measured utilizing a Doppler sensor, which reflects ultrasound waves again from particles in the fluid and makes use of the Doppler shift in the mirrored sound signal to estimate velocity. Some AV meters measure floor velocity optically to estimate velocity.

AV meters are often used to measure open channel move in sewers because the probes are relatively small and they can be installed in present sewer pipes without inflicting significant head loss within the pipe. This additionally permits them for use for short-term or short-term flow metering functions for sewer studies. one drawback of AV meters is that the sensor should be put in within the fluid. In sewers, this requires frequent maintenance to scrub the sensor. AV meters are often considered much less accurate than major flow meters as a outcome of main devices solely must measure depth and depth measurements are extra correct than velocity measurements.

Transport time meters

Transport time meters were developed within the oil trade to accurately measure circulate in large pipelines. They have been used with some success for open channel move in water metering applications. Transport time meters additionally use ultrasound like Doppler meters, however as an alternative of bouncing the sound waves off particles in the water like Doppler move meters, they ship ultrasound waves between two sensors separated from one another by a sure distance alongside the length of the pipe and makes use of the transmission time of the sound waves to calculate the velocity of the water circulate. Because the pace of sound in the water is thought, the speed of the water may be calculated based mostly on the offset in ultrasonic wave transmission time that happens as a outcome of speed of the water.

Transmission time meters could be expensive relative to Doppler circulate meters due to the many sensors and complicated installation concerned. They may be extra accurate because of the ability to split the flow into horizontal cross sections and measure the velocity of each section.

Flow unit measurement strategies in full tube functions

Venturi meters

Venturi move meters use the Venturi impact to measure flow in a full or pressurized pipe by utilizing the converging part of the pipe to restrict the flow. According to the continuity equation, the cross-sectional space of the converging part is small and subsequently the speed is greater in the throat. Due to power conservation and Bernoulli’s principle, higher velocities within the throat end in a drop in throat strain. The move price can then be decided by measuring the pressure drop in the convergent section and calculating the circulate fee using Bernoulli’s equation. Venturi meters are extra frequent in water metering functions as a end result of the pressure measurement ports can turn into clogged in wastewater purposes.

Magnetic flowmeter

The electromagnetic circulate meter works by applying a magnetic subject to the fluid passing through the pipe. This causes a small electron potential distinction that may 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 velocity of the water, and the continuity equation can then be used to calculate the circulate price.

An benefit of the magnetometer is that the metering section is identical diameter as the adjoining pipe, so the magnetometer causes no extra head loss. For essentially the most part, magnetometers are used for full (pressure) pipe functions, however nowadays open channel magnetometers may also be used.

Turbine flowmeter

A turbine circulate meter is a mechanical move meter that uses a rotating turbine in circulate to measure the circulate of water in a pipe. The speed of the turbine is proportional to the speed and the flow price can then be calculated utilizing the continuity equation. Turbine flow meters are solely used for water applications due to potential issues with wastewater solids assortment and clogging generators.

Conclusion

There are many ways to measure move. Each technique has completely different advantages, disadvantages and accuracy in different applications.

It is necessary to grasp the traits of assorted move measurement methods to assist choose the proper sort of flow metering for your utility or to properly interpret the move measurements of existing flow meters. Tools like Apure (IoT-based water information analysis) help to look at measurements collected by circulate meters and perform diagnostics to understand flow meter efficiency and shortly process and analyze the information. Contact us for technical or product service support.

More articles on circulate meters:

Mass circulate rate vs volumetric flow fee

Relation between circulate and pressure

Ultrasonic flow meter working principle

Difference between flow meter and flow transmitter