Table of Contents
What is move units?
Continuity of move equation
Common flow unit metering methods in open channels
Eyeball methodology
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 move units?
Flow fee is the quantity of fluid that passes by way of a unit of time. In water assets, circulate is often measured in cubic toes per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or quite so much of different models. The measurement of water useful resource flow is necessary for applications such as system control, billing, design and heaps of different purposes. There are a number of methods to measure flow in a water useful resource system. This article outlines a variety of the more widespread strategies of move measurement and offers some useful details about move models measurement.
Continuity of move equation
For water flowing in a pipe under steady-state circumstances (i.e., not various with time), continuity means that water flowing into one finish of the pipe must flow out of the opposite end. This additionally signifies that the flow in the pipe is the same at any point along the length of the pipe. The continuity equation may be expressed as
Flow = Velocity * Area
The idea of continuity in regular state conditions results in the product of velocity * area being equal to a continuing at any level in the pipe. This is a useful precept for making move measurements, as shown below.
This is an example of using the continuity equation to calculate circulate. 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 square toes = a hundred cubic ft per second.
Common flow unit metering strategies in open channels
Eyeball method
It is sometimes helpful to estimate the circulate velocity and cross-sectional space by eye after which multiply the move velocity by the world to obtain the move velocity (continuity equation). A ruler or tape measure can be used 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 methodology can be utilized to estimate circulate when only an “order of magnitude” of circulate is required or when the circulate price is simply too low to be measured with a move meter.
Flow depth (Manning)
When the channel cross-sectional area and channel slope are known and uniform flow situations exist, the Manning’s equation can be used to calculate move by measuring depth solely. The Manning’s equation is an empirical equation that describes the relationship between flow fee in an open channel underneath uniform circulate situations and depth, slope and channel friction coefficient (Manning’s n). Uniform circulate means that depth doesn’t vary with the size of the conduit or channel. Flow measurements utilizing Manning’s equation for depth aren’t applicable to gradually changing flow conditions, such as backwater conditions upstream of a dam or weir.
The depth circulate methodology of circulate measurement is more accurate than the “eyeball” technique. The major problem with depth-only circulate measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform move conditions. This method is usually used with ultrasonic circulate meters to estimate the move 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 complicated river hydraulic fashions to account for complicated channel geometry and channel friction circumstances.
Main equipment
The primary device is used to measure move in open channels, utilizing constructions similar to flumes, weirs or dams, to measure flow by measuring depth. The measured depth can then be transformed to a move rate using an equation or rated curve equation.
Primary gadgets work by forcing the flow through a path of critical depth, for example on the prime of a weir or on the throat of a flume. In technical phrases, the important depth is outlined because the depth of the minimum specific energy state that ends in a selected discharge. In practice, this minimum state of vitality means that just one move corresponds to the important depth. Therefore, measuring only the depth produces a measurement of the corresponding flux and is subsequently known as a “primary” gadget.
Primary units are a very convenient methodology of move measurement as a end result of the depth may be measured from above the flow with out the necessity to insert a sensor in the water. This makes main move meters extra reliable and simpler to keep up. A drawback of main devices is that they can trigger head loss and backwater in the system. Primary devices are sometimes thought-about to be the most correct method of measuring open channel flow.
Surface Velocity Meters
An area velocity meter is an open channel move 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 flow rate is then calculated by multiplying the move space by the velocity utilizing the continuity equation, hence the name “AV meter”. Velocity is usually measured using a Doppler sensor, which reflects ultrasound waves again from particles in the fluid and uses the Doppler shift in the reflected sound signal to estimate velocity. Some AV meters measure floor velocity optically to estimate velocity.
AV meters are sometimes used to measure open channel flow in sewers as a outcome of the probes are comparatively small and they are often installed in existing sewer pipes with out causing important head loss in the pipe. This also permits them for use for short-term or short-term circulate metering purposes for sewer studies. one drawback of AV meters is that the sensor must be installed within the fluid. In sewers, this requires frequent upkeep to wash the sensor. AV meters are often considered much less accurate than major flow meters as a end result of primary devices solely must measure depth and depth measurements are more correct than velocity measurements.
Transport time meters
Transport time meters were developed in the oil business to precisely measure flow in giant 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 within the water like Doppler move meters, they ship ultrasound waves between two sensors separated from each other by a certain distance alongside the length of the pipe and uses the transmission time of the sound waves to calculate the speed of the water circulate. Because the velocity of sound in the water is thought, the velocity of the water could be calculated primarily based on the offset in ultrasonic wave transmission time that happens because of the velocity of the water.
Transmission time meters could be expensive relative to Doppler flow meters as a result of many sensors and sophisticated set up concerned. They may be extra correct because of the capacity to separate the flow into horizontal cross sections and measure the rate of each part.
Flow unit measurement strategies in full tube purposes
Venturi meters
Venturi circulate meters use the Venturi impact to measure move in a full or pressurized pipe by using the converging section of the pipe to restrict the flow. According to the continuity equation, the cross-sectional area of the converging part is small and subsequently the rate is greater within the throat. Due to energy conservation and Bernoulli’s precept, larger velocities within the throat end in a drop in throat pressure. The circulate rate can then be decided by measuring the strain drop within the convergent section and calculating the circulate fee using Bernoulli’s equation. Venturi meters are extra frequent in water metering functions as a result of the stress measurement ports can turn into clogged in wastewater purposes.
Magnetic flowmeter
The electromagnetic circulate meter works by making use of a magnetic field to the fluid passing through the pipe. This causes a small electron potential distinction that could 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 circulate rate.
An benefit of the magnetometer is that the metering section is the same diameter as the adjacent pipe, so the magnetometer causes no extra head loss. For essentially the most part, magnetometers are used for full (pressure) pipe applications, but nowadays open channel magnetometers may additionally be used.
Turbine flowmeter
A turbine move meter is a mechanical flow meter that makes use of 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 rate 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 turbines.
Conclusion
There are some ways to measure circulate. Each methodology has completely different advantages, disadvantages and accuracy in numerous applications.
It is necessary to know the characteristics of varied circulate measurement strategies to assist select the best sort of flow metering on your software or to properly interpret the circulate measurements of existing circulate meters. Tools like Apure (IoT-based water data analysis) assist to look at measurements collected by circulate meters and perform diagnostics to understand move meter performance and shortly process and analyze the info. Contact us for technical or product service support.
More articles on circulate meters:
Mass flow rate vs volumetric circulate price
Relation between flow and strain
Ultrasonic flow meter working principle
Difference between circulate meter and move transmitter
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Table of Contents
What is flow units?
Continuity of move equation
Common flow unit metering strategies in open channels
Eyeball technique
Flow depth (Manning)
Main equipment
Surface Velocity Meters
Transport time meters
Flow unit measurement methods in full tube applications
Venturi meters
Magnetic flowmeter
Turbine flowmeter
Conclusion
What is circulate units?
Flow rate is the amount of fluid that passes via a unit of time. In pressure gauge octa , flow is often measured in cubic toes per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a selection of other units. The measurement of water useful resource circulate is necessary for purposes corresponding to system control, billing, design and plenty of other functions. There are several methods to measure move in a water resource system. This article outlines some of the more common strategies of move measurement and offers some useful information about flow items measurement.
Continuity of flow equation
For water flowing in a pipe underneath steady-state circumstances (i.e., not various with time), continuity signifies that water flowing into one end of the pipe should move out of the other end. This additionally means that the circulate in the pipe is similar at any point along the size of the pipe. The continuity equation can be expressed as
Flow = Velocity * Area
The idea of continuity in steady state conditions results in the product of velocity * space being equal to a constant at any level within the pipe. This is a useful precept for making move measurements, as shown beneath.
This is an example of utilizing the continuity equation to calculate move. Velocity is measured at 10 feet per second and the cross-sectional area of the move is measured at 10 square toes. Flow fee = 10 toes per second * 10 sq. ft = one hundred cubic toes per second.
Common move unit metering methods in open channels
Eyeball methodology
It is sometimes helpful to estimate the flow 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 used to enhance the accuracy of cross-sectional space measurements, and a stopwatch can be used to improve velocity measurements by timing floating particles transferring a set distance. The eyeball method can be utilized to estimate move when solely an “order of magnitude” of flow is required or when the circulate fee is simply 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 used to calculate circulate by measuring depth solely. The Manning’s equation is an empirical equation that describes the connection between move fee in an open channel beneath uniform flow situations and depth, slope and channel friction coefficient (Manning’s n). Uniform circulate signifies that depth doesn’t range with the length of the conduit or channel. Flow measurements using Manning’s equation for depth usually are not applicable to steadily altering circulate situations, such as backwater circumstances upstream of a dam or weir.
The depth flow methodology of flow measurement is extra correct than the “eyeball” methodology. The major challenge with depth-only move measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform circulate situations. This methodology is often used with ultrasonic flow meters to estimate the move of a river by measuring only the water level 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 situations.
Main gear
The major system is used to measure circulate in open channels, utilizing structures similar to flumes, weirs or dams, to measure circulate by measuring depth. The measured depth can then be transformed to a move price using an equation or rated curve equation.
Primary gadgets work by forcing the move by way of a path of crucial depth, for example at the high of a weir or at the throat of a flume. In technical terms, the critical depth is outlined as the depth of the minimal particular power state that ends in a specific discharge. In practice, this minimum state of energy signifies that only one move corresponds to the crucial depth. Therefore, measuring solely the depth produces a measurement of the corresponding flux and is subsequently known as a “primary” system.
Primary gadgets are a very convenient method of move measurement as a outcome of the depth can be measured from above the move without the necessity to insert a sensor within the water. This makes major move meters extra reliable and easier to take care of. A drawback of primary units is that they’ll trigger head loss and backwater within the system. Primary units are often considered to be essentially the most correct technique of measuring open channel flow.
Surface Velocity Meters
An space velocity meter is an open channel move meter that measures move 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 move fee is then calculated by multiplying the flow area by the velocity using the continuity equation, hence the name “AV meter”. Velocity is often measured utilizing a Doppler sensor, which displays ultrasound waves again from particles within the fluid and makes use of the Doppler shift within the mirrored sound signal to estimate velocity. Some AV meters measure surface velocity optically to estimate velocity.
AV meters are sometimes used to measure open channel move in sewers as a outcome of the probes are relatively small and they are often put in in existing sewer pipes with out inflicting important head loss within the pipe. This additionally permits them to be used for short-term or short-term flow metering functions for sewer research. one disadvantage of AV meters is that the sensor have to be installed within the fluid. In sewers, this requires frequent maintenance to clean the sensor. AV meters are sometimes thought-about much less correct than major circulate meters as a outcome of main gadgets solely need to measure depth and depth measurements are extra accurate than velocity measurements.
Transport time meters
Transport time meters have been developed within the oil industry to accurately measure flow in large pipelines. digital pressure gauge have been used with some success for open channel flow in water metering functions. 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 move meters, they send ultrasound waves between two sensors separated from each other by a certain 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 speed of sound within the water is understood, the pace of the water may be calculated primarily based on the offset in ultrasonic wave transmission time that happens because of the speed of the water.
Transmission time meters may be costly relative to Doppler circulate meters as a result of many sensors and complex set up involved. They could be more accurate due to the ability to split the move into horizontal cross sections and measure the velocity of each section.
Flow unit measurement strategies in full tube purposes
Venturi meters
Venturi circulate meters use the Venturi impact to measure move in a full or pressurized pipe through the use of the converging part of the pipe to limit the move. According to the continuity equation, the cross-sectional area of the converging section is small and therefore the speed is larger in the throat. Due to energy conservation and Bernoulli’s precept, greater velocities in the throat result in a drop in throat stress. The circulate fee can then be decided by measuring the strain drop within the convergent part and calculating the move rate 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 flow meter works by applying a magnetic field to the fluid passing by way of the pipe. This causes a small electron potential distinction that can be measured by the electrode sensor (due to Faraday’s regulation 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 flow rate.
An benefit of the magnetometer is that the metering section is similar diameter as the adjoining pipe, so the magnetometer causes no extra head loss. For the most part, magnetometers are used for full (pressure) pipe applications, but these days open channel magnetometers may also be used.
Turbine flowmeter
A turbine move meter is a mechanical flow meter that uses a rotating turbine in move to measure the circulate of water in a pipe. The speed of the turbine is proportional to the speed and the flow fee can then be calculated utilizing the continuity equation. Turbine move meters are solely used for water purposes due to potential problems with wastewater solids assortment and clogging generators.
Conclusion
There are many ways to measure flow. Each method has different benefits, disadvantages and accuracy in several functions.
It is necessary to know the characteristics of various circulate measurement strategies to assist choose the proper sort of move metering in your application or to correctly interpret the move measurements of present move meters. Tools like Apure (IoT-based water data analysis) help to examine measurements collected by move 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 support.
More articles on circulate meters:
Mass flow fee vs volumetric circulate rate
Relation between circulate and stress
Ultrasonic move meter working principle
Difference between circulate meter and circulate transmitter