Useful details about flow models

Table of Contents

What is circulate units?

Continuity of circulate equation

Common move unit metering methods in open channels

Eyeball technique

Flow depth (Manning)

Main equipment

Surface Velocity Meters

Transport time meters

Flow unit measurement methods in full tube purposes

Venturi meters

Magnetic flowmeter

Turbine flowmeter

Conclusion

What is flow units?

pressure gauge is the quantity of fluid that passes through a unit of time. In water assets, circulate is commonly measured in cubic ft per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a variety of different items. The measurement of water resource circulate is important for purposes such as system management, billing, design and lots of other applications. There are several methods to measure move in a water resource system. This article outlines a few of the extra widespread strategies of flow measurement and offers some helpful information about circulate models measurement.
Continuity of flow equation

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

Flow = Velocity * Area

The idea of continuity in regular state situations results in the product of velocity * space being equal to a constant at any point in the pipe. This is a useful principle for making circulate measurements, as proven under.
This is an example of using the continuity equation to calculate circulate. Velocity is measured at 10 toes per second and the cross-sectional area of the flow is measured at 10 sq. feet. Flow rate = 10 toes per second * 10 square toes = one hundred cubic feet per second.
Common circulate unit metering methods in open channels

Eyeball technique

It is usually helpful to estimate the move velocity and cross-sectional space by eye after which multiply the move velocity by the realm to obtain the flow 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 enhance velocity measurements by timing floating particles transferring a set distance. The eyeball methodology can be utilized to estimate flow when solely an “order of magnitude” of flow is required or when the circulate rate is simply too low to be measured with a flow meter.
Flow depth (Manning)

When the channel cross-sectional area and channel slope are recognized and uniform move 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 flow rate in an open channel beneath uniform move circumstances and depth, slope and channel friction coefficient (Manning’s n). Uniform move signifies that depth does not range with the size of the conduit or channel. Flow measurements utilizing Manning’s equation for depth aren’t relevant to progressively altering flow situations, corresponding to backwater situations upstream of a dam or weir.
The depth circulate technique of move measurement is more correct 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 conditions. This technique is often used with ultrasonic move meters to estimate the circulate of a river by measuring only the water stage of the river. Often in these causes, the river level/flow relationship is developed with the help of complicated river hydraulic models to account for complex channel geometry and channel friction situations.
Main equipment

The major gadget is used to measure move in open channels, using constructions similar to flumes, weirs or dams, to measure circulate by measuring depth. The measured depth can then be transformed to a circulate fee utilizing an equation or rated curve equation.
Primary units work by forcing the flow by way of a path of critical depth, for instance on the high of a weir or at the throat of a flume. In technical phrases, the important depth is defined because the depth of the minimum specific vitality state that ends in a particular discharge. In follow, this minimal state of vitality signifies that just one circulate corresponds to the crucial depth. Therefore, measuring solely the depth produces a measurement of the corresponding flux and is therefore called a “primary” gadget.
Primary units are a really convenient method of flow measurement because the depth could be measured from above the move without the want to insert a sensor within the water. This makes major flow meters extra reliable and simpler to take care of. A drawback of primary gadgets is that they’ll trigger head loss and backwater within the system. Primary gadgets are sometimes considered to be the most correct methodology of measuring open channel move.
Surface Velocity Meters

An area velocity meter is an open channel flow meter that measures flow 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 move rate is then calculated by multiplying the move space by the speed using the continuity equation, hence the identify “AV meter”. Velocity is often measured utilizing a Doppler sensor, which reflects ultrasound waves back from particles in the fluid and makes use of the Doppler shift in the reflected sound signal 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 because the probes are comparatively small and they can be installed in existing sewer pipes without causing vital head loss in the pipe. This also allows them for use for short-term or short-term move metering applications for sewer research. one drawback of AV meters is that the sensor should be put in within the fluid. In sewers, this requires frequent upkeep to wash the sensor. AV meters are sometimes considered less accurate than main move meters because major gadgets solely must measure depth and depth measurements are extra accurate than velocity measurements.
Transport time meters

Transport time meters were developed within the oil industry to precisely measure flow in massive pipelines. They have been used with some success for open channel flow in water metering applications. Transport time meters also use ultrasound like Doppler meters, but instead of bouncing the sound waves off particles in the water like Doppler flow 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 rate of the water move. Because the speed of sound in the water is thought, the velocity of the water can be calculated based mostly on the offset in ultrasonic wave transmission time that occurs as a end result of pace of the water.
Transmission time meters could be costly relative to Doppler move meters due to the many sensors and complicated set up involved. They can be extra correct because of the ability to separate the flow into horizontal cross sections and measure the rate of every part.
Flow unit measurement methods in full tube purposes

Venturi meters

Venturi flow meters use the Venturi impact to measure circulate in a full or pressurized pipe by utilizing the converging part of the pipe to restrict the move. According to the continuity equation, the cross-sectional space of the converging part is small and therefore the speed is greater in the throat. Due to vitality conservation and Bernoulli’s principle, greater velocities within the throat result in a drop in throat strain. The flow rate can then be determined by measuring the stress drop in the convergent part and calculating the circulate price utilizing Bernoulli’s equation. Venturi meters are extra widespread in water metering functions because the strain measurement ports can turn out to be clogged in wastewater applications.
Magnetic flowmeter

The electromagnetic move meter works by applying a magnetic area to the fluid passing via 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 velocity of the water, and the continuity equation can then be used to calculate the move price.
An benefit of the magnetometer is that the metering section is identical diameter because the adjacent pipe, so the magnetometer causes no additional head loss. For the most half, magnetometers are used for full (pressure) pipe applications, however these days open channel magnetometers can additionally be used.
Turbine flowmeter

A turbine circulate meter is a mechanical move meter that uses a rotating turbine in move to measure the move of water in a pipe. The pace of the turbine is proportional to the rate and the circulate price can then be calculated utilizing the continuity equation. Turbine circulate meters are only used for water purposes due to potential problems with wastewater solids assortment and clogging generators.
Conclusion

There are some ways to measure circulate. Each methodology has completely different benefits, disadvantages and accuracy in numerous applications.
It is essential to understand the characteristics of various circulate measurement techniques to assist select the proper sort of move metering in your utility or to properly interpret the flow measurements of present circulate meters. Tools like Apure (IoT-based water data analysis) assist to examine measurements collected by flow meters and carry out diagnostics to grasp flow meter performance and rapidly course of and analyze the info. Contact us for technical or product service help.
More articles on circulate meters:
Mass flow rate vs volumetric circulate price

Relation between flow and strain

Ultrasonic move meter working precept

Difference between flow meter and move transmitter
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Table of Contents

What is circulate units?

Continuity of circulate equation

Common circulate unit metering methods in open channels

Eyeball methodology

Flow depth (Manning)

Main equipment

Surface Velocity Meters

Transport time meters

Flow unit measurement methods in full tube functions

Venturi meters

Magnetic flowmeter

Turbine flowmeter

Conclusion

What is flow units?

Flow fee is the volume of fluid that passes by way of a unit of time. In water sources, move is often measured in cubic ft per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a big selection of different items. The measurement of water resource move is important for purposes such as system control, billing, design and lots of other applications. There are several methods to measure move in a water useful resource system. This article outlines a variety of the more frequent methods of circulate measurement and provides some helpful information about flow units measurement.
Continuity of move equation

For water flowing in a pipe underneath steady-state situations (i.e., not varying with time), continuity signifies that water flowing into one finish of the pipe should move out of the opposite finish. This additionally implies that the circulate in the pipe is identical at any level along the length of the pipe. The continuity equation could be expressed as

Flow = Velocity * Area

The concept of continuity in regular state circumstances ends in the product of velocity * area being equal to a relentless at any level within the pipe. This is a helpful principle for making flow measurements, as shown beneath.
This is an example of utilizing the continuity equation to calculate flow. Velocity is measured at 10 toes per second and the cross-sectional area of the move is measured at 10 sq. toes. Flow price = 10 toes per second * 10 sq. toes = one hundred cubic feet per second.
Common circulate unit metering methods in open channels

Eyeball method

It is typically helpful to estimate the move velocity and cross-sectional space by eye and then multiply the flow velocity by the area to acquire the circulate 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 used to enhance velocity measurements by timing floating particles shifting a set distance. The eyeball technique can be utilized to estimate move when solely an “order of magnitude” of flow is required or when the circulate rate is merely too low to be measured with a move meter.
Flow depth (Manning)

When the channel cross-sectional space and channel slope are known 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 move rate in an open channel beneath uniform move circumstances and depth, slope and channel friction coefficient (Manning’s n). Uniform circulate means that depth does not vary with the size of the conduit or channel. Flow measurements utilizing Manning’s equation for depth aren’t relevant to steadily changing move situations, corresponding to backwater situations upstream of a dam or weir.
The depth flow methodology of move measurement is extra accurate than the “eyeball” technique. The major problem with depth-only move measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform circulate circumstances. This methodology is commonly used with ultrasonic circulate meters to estimate the move of a river by measuring only the water stage of the river. Often in these causes, the river level/flow relationship is developed with the help of advanced river hydraulic fashions to account for complicated channel geometry and channel friction circumstances.
Main equipment

The major system 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 flow fee using an equation or rated curve equation.
Primary devices work by forcing the circulate through a path of important depth, for instance on the top of a weir or at the throat of a flume. In technical phrases, the critical depth is defined as the depth of the minimum specific energy state that ends in a particular discharge. In practice, this minimal state of vitality means that just one flow corresponds to the important depth. Therefore, measuring only the depth produces a measurement of the corresponding flux and is subsequently called a “primary” gadget.
Primary devices are a really handy method of circulate measurement as a outcome of the depth may be measured from above the move without the need to insert a sensor in the water. This makes primary move meters extra reliable and easier to maintain. A disadvantage of major devices is that they can trigger head loss and backwater in the system. Primary units are often thought-about to be essentially the most accurate method of measuring open channel circulate.
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 area using the geometry of the pipe or channel. The move rate is then calculated by multiplying the flow area by the rate utilizing the continuity equation, therefore the identify “AV meter”. Velocity is typically measured utilizing a Doppler sensor, which reflects ultrasound waves back from particles in 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 often used to measure open channel flow in sewers because the probes are comparatively small and they are often put in in present sewer pipes without inflicting important head loss in the pipe. This additionally allows them to be used for momentary or short-term move metering purposes for sewer studies. one disadvantage of AV meters is that the sensor should be put in in the fluid. In sewers, this requires frequent upkeep to wash the sensor. AV meters are often thought of less correct than main move meters because major units only have to measure depth and depth measurements are extra correct than velocity measurements.
Transport time meters

Transport time meters have been developed within the oil trade to precisely measure move in massive pipelines. They have been used with some success for open channel circulate in water metering applications. Transport time meters also use ultrasound like Doppler meters, but as a substitute 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 size of the pipe and uses the transmission time of the sound waves to calculate the rate of the water circulate. 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 because of the velocity of the water.
Transmission time meters can be costly relative to Doppler circulate meters as a outcome of many sensors and complex set up involved. They may be extra correct as a end result of capability to split the flow into horizontal cross sections and measure the speed of every part.
Flow unit measurement strategies 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 circulate. According to the continuity equation, the cross-sectional space of the converging part is small and due to this fact the velocity is higher in the throat. Due to vitality conservation and Bernoulli’s precept, greater velocities in the throat lead to a drop in throat pressure. The move fee can then be determined by measuring the stress drop within the convergent section and calculating the flow rate utilizing Bernoulli’s equation. Venturi meters are more frequent in water metering functions because the stress measurement ports can become clogged in wastewater purposes.
Magnetic flowmeter

The electromagnetic flow meter works by making use of a magnetic subject to the fluid passing by way of the pipe. This causes a small electron potential difference 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 move price.
An benefit of the magnetometer is that the metering section is similar diameter as the adjoining pipe, so the magnetometer causes no additional head loss. For essentially the most half, magnetometers are used for full (pressure) pipe purposes, however these days open channel magnetometers can also be used.
Turbine flowmeter

A turbine move meter is a mechanical flow meter that makes use of a rotating turbine in flow to measure the flow of water in a pipe. The speed of the turbine is proportional to the speed and the circulate price can then be calculated utilizing the continuity equation. Turbine circulate meters are only used for water functions due to potential issues with wastewater solids collection and clogging turbines.
Conclusion

There are many ways to measure circulate. Each method has different benefits, disadvantages and accuracy in different applications.
It is important to know the traits of various move measurement strategies to help select the best sort of move metering on your application or to properly interpret the flow measurements of current move meters. Tools like Apure (IoT-based water data analysis) help to examine measurements collected by flow meters and perform diagnostics to understand move meter efficiency and quickly process and analyze the information. Contact us for technical or product service assist.
More articles on move meters:
Mass flow rate vs volumetric move price

Relation between move and stress

Ultrasonic move meter working principle

Difference between flow meter and flow transmitter

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