Table of Contents
What is flow units?
Continuity of move equation
Common move unit metering methods in open channels
Eyeball methodology
Flow depth (Manning)
Main equipment
Surface Velocity Meters
Transport time meters
Flow unit measurement strategies in full tube purposes
Venturi meters
Magnetic flowmeter
Turbine flowmeter
Conclusion
What is move units?
Flow rate is the volume of fluid that passes through a unit of time. In water assets, flow is commonly measured in cubic feet per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a variety of different items. The measurement of water useful resource circulate is important for purposes such as system management, billing, design and lots of different applications. There are several methods to measure flow in a water useful resource system. This article outlines a few of the extra common strategies of circulate measurement and provides some helpful information about circulate models measurement.
Continuity of move equation
For water flowing in a pipe under steady-state conditions (i.e., not varying with time), continuity means that water flowing into one end of the pipe must move out of the other end. This also implies that the flow in the pipe is identical at any point alongside the size of the pipe. The continuity equation could be expressed as
Flow = Velocity * Area
The idea of continuity in steady state conditions leads to the product of velocity * space being equal to a continuing at any point within the pipe. This is a helpful precept for making flow measurements, as proven under.
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. ft. Flow rate = 10 toes per second * 10 sq. toes = a hundred cubic feet per second.
Common flow unit metering methods in open channels
Eyeball methodology
It is sometimes useful to estimate the move velocity and cross-sectional area by eye and then multiply the flow velocity by the area to acquire the flow velocity (continuity equation). A ruler or tape measure can be utilized to enhance the accuracy of cross-sectional area measurements, and a stopwatch can be utilized to improve velocity measurements by timing floating particles shifting a set distance. The eyeball technique can be utilized to estimate circulate when only an “order of magnitude” of circulate is required or when the move rate is 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 move situations 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 relationship between circulate fee in an open channel beneath uniform flow circumstances and depth, slope and channel friction coefficient (Manning’s n). Uniform move means that depth does not vary with the size of the conduit or channel. Flow measurements using Manning’s equation for depth aren’t relevant to steadily altering move circumstances, similar to backwater situations upstream of a dam or weir.
The depth circulate methodology of circulate measurement is more accurate than the “eyeball” methodology. The main problem with depth-only move measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform move circumstances. This technique is commonly used with ultrasonic circulate meters to estimate the move 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 complicated river hydraulic fashions to account for advanced channel geometry and channel friction situations.
Main gear
The primary gadget is used to measure flow in open channels, utilizing buildings similar to flumes, weirs or dams, to measure move by measuring depth. The measured depth can then be transformed to a move fee using an equation or rated curve equation.
Primary gadgets work by forcing the circulate by way of a path of important depth, for instance on the top of a weir or on the throat of a flume. In technical phrases, the crucial depth is defined because the depth of the minimal specific vitality state that results in a particular discharge. In follow, this minimum state of power implies 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 methodology of circulate measurement as a end result of the depth can be measured from above the circulate with out the necessity to insert a sensor within the water. This makes major flow meters more 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 units are often considered to be the most accurate methodology of measuring open channel flow.
Surface Velocity Meters
An area velocity meter is an open channel flow meter that measures circulate by making two separate measurements of depth and velocity. The depth is converted to a cross-sectional area utilizing the geometry of the pipe or channel. The flow rate is then calculated by multiplying the circulate space by the speed utilizing the continuity equation, therefore the title “AV meter”. Velocity is often measured utilizing a Doppler sensor, which reflects ultrasound waves again from particles within 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 flow in sewers because the probes are comparatively small and they can be installed in existing sewer pipes with out inflicting important head loss in the pipe. This additionally permits 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 maintenance to scrub the sensor. AV meters are sometimes thought-about less accurate than main move meters as a outcome of major units solely must measure depth and depth measurements are more accurate than velocity measurements.
Transport time meters
Transport time meters were developed in the oil industry to accurately measure circulate in massive pipelines. They have been used with some success for open channel move in water metering applications. Transport time meters also use ultrasound like Doppler meters, but instead of bouncing the sound waves off particles within the water like Doppler flow meters, they ship ultrasound waves between two sensors separated from each other by a certain distance along the size of the pipe and makes use of the transmission time of the sound waves to calculate the speed of the water circulate. Because the pace of sound in the water is understood, the pace of the water may be calculated based mostly on the offset in ultrasonic wave transmission time that happens due to the speed of the water.
Transmission time meters could be expensive relative to Doppler circulate meters because of the many sensors and sophisticated set up involved. They could be extra accurate due to the ability to split the move into horizontal cross sections and measure the velocity of every part.
Flow unit measurement strategies in full tube functions
Venturi meters
Venturi flow meters use the Venturi effect to measure flow in a full or pressurized pipe by using the converging section of the pipe to limit the flow. According to the continuity equation, the cross-sectional space of the converging section is small and due to this fact the velocity is higher within the throat. Due to vitality conservation and Bernoulli’s principle, higher velocities in the throat end in a drop in throat pressure. The move rate can then be determined by measuring the strain drop in the convergent section and calculating the circulate fee utilizing Bernoulli’s equation. Venturi meters are extra widespread in water metering functions as a result of the strain measurement ports can turn into clogged in wastewater applications.
Magnetic flowmeter
The electromagnetic flow meter works by making use of 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 regulation and electromagnetic induction). The magnitude of the electron potential distinction is proportional to the rate of the water, and the continuity equation can then be used to calculate the flow price.
An advantage 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 half, magnetometers are used for full (pressure) pipe purposes, but nowadays open channel magnetometers can additionally be used.
Turbine flowmeter
A turbine flow meter is a mechanical circulate meter that uses a rotating turbine in move to measure the flow of water in a pipe. The speed of the turbine is proportional to the rate and the flow fee can then be calculated using the continuity equation. pressure gauge are solely used for water purposes due to potential problems with wastewater solids assortment and clogging turbines.
Conclusion
There are many ways to measure circulate. Each methodology has totally different advantages, disadvantages and accuracy in several functions.
It is essential to grasp the characteristics of varied move measurement strategies to assist choose the best sort of move metering in your software or to properly interpret the flow measurements of present circulate meters. Tools like Apure (IoT-based water information analysis) assist to examine measurements collected by flow meters and carry out diagnostics to know circulate meter performance and shortly course of and analyze the information. Contact us for technical or product service help.
More articles on move meters:
Mass move rate vs volumetric circulate fee
Relation between move and strain
Ultrasonic move meter working principle
Difference between flow meter and flow transmitter
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Table of Contents
What is move units?
Continuity of circulate equation
Common circulate unit metering methods in open channels
Eyeball method
Flow depth (Manning)
Main gear
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 fee is the quantity of fluid that passes by way of a unit of time. In water sources, move is commonly measured in cubic toes per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or quite so much of other units. The measurement of water useful resource circulate is essential for functions corresponding to system control, billing, design and a lot of other purposes. There are a quantity of methods to measure flow in a water useful resource system. This article outlines a variety of the more frequent strategies of flow measurement and offers some useful details about flow units measurement.
Continuity of flow equation
For water flowing in a pipe beneath steady-state circumstances (i.e., not various with time), continuity implies that water flowing into one finish of the pipe must move out of the opposite end. This additionally implies that the flow within the pipe is similar at any level along the length of the pipe. The continuity equation may be expressed as
Flow = Velocity * Area
The concept of continuity in steady state circumstances leads to the product of velocity * space being equal to a constant at any level in the pipe. This is a helpful principle for making flow measurements, as proven below.
This is an instance of using the continuity equation to calculate move. Velocity is measured at 10 feet per second and the cross-sectional space of the flow is measured at 10 sq. feet. Flow rate = 10 feet per second * 10 sq. ft = 100 cubic toes per second.
Common circulate unit metering strategies in open channels
Eyeball technique
It is usually helpful to estimate the circulate velocity and cross-sectional space by eye and then multiply the move velocity by the world to acquire the move velocity (continuity equation). A ruler or tape measure can be used to enhance the accuracy of cross-sectional area measurements, and a stopwatch can be used 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 circulate is required or when the flow 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 known and uniform flow conditions exist, the Manning’s equation can be utilized to calculate circulate by measuring depth only. The Manning’s equation is an empirical equation that describes the relationship between circulate fee in an open channel under uniform move conditions and depth, slope and channel friction coefficient (Manning’s n). Uniform move means that depth does not differ with the length of the conduit or channel. Flow measurements utilizing Manning’s equation for depth are not applicable to gradually altering move situations, such as backwater conditions upstream of a dam or weir.
The depth circulate methodology of circulate measurement is extra 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 circumstances. This technique is usually used with ultrasonic flow meters to estimate the circulate 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 assistance of advanced river hydraulic fashions to account for complex channel geometry and channel friction conditions.
Main tools
The major system is used to measure move in open channels, utilizing structures such as flumes, weirs or dams, to measure circulate by measuring depth. The measured depth can then be transformed to a circulate fee using an equation or rated curve equation.
Primary units work by forcing the move via a path of important depth, for instance at 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 minimal particular vitality state that results in a specific discharge. In practice, this minimal state of energy implies that only one circulate corresponds to the crucial depth. Therefore, measuring only the depth produces a measurement of the corresponding flux and is therefore referred to as a “primary” device.
Primary gadgets are a very handy methodology of circulate measurement as a end 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 flow meters extra reliable and simpler to take care of. A drawback of major units is that they’ll trigger head loss and backwater in the system. Primary gadgets are sometimes thought of to be essentially the most correct technique of measuring open channel circulate.
Surface Velocity Meters
An space velocity meter is an open channel circulate 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 circulate fee is then calculated by multiplying the flow space by the rate using the continuity equation, hence the title “AV meter”. Velocity is typically measured utilizing a Doppler sensor, which displays ultrasound waves back from particles in the fluid and makes use of the Doppler shift in the reflected sound signal to estimate velocity. เพรสเชอร์เกจ measure floor velocity optically to estimate velocity.
AV meters are often used to measure open channel circulate in sewers as a outcome of the probes are comparatively small and they can be installed in present sewer pipes with out inflicting important head loss in the pipe. This additionally permits them to be used for momentary or short-term flow metering purposes for sewer studies. one disadvantage of AV meters is that the sensor must be installed in the fluid. In sewers, this requires frequent maintenance to wash the sensor. AV meters are often thought of much less accurate than primary move meters as a outcome of primary gadgets solely must measure depth and depth measurements are more accurate than velocity measurements.
Transport time meters
Transport time meters had been developed in the oil trade to accurately measure circulate in large pipelines. They have been used with some success for open channel flow in water metering purposes. 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 circulate meters, they send ultrasound waves between two sensors separated from one another 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 move. Because the pace of sound in the water is known, 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 speed of the water.
Transmission time meters can be costly relative to Doppler flow meters because of the many sensors and complicated installation concerned. They can be more accurate due to the capacity to split the circulate into horizontal cross sections and measure the rate of every part.
Flow unit measurement strategies in full tube applications
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 restrict the circulate. According to the continuity equation, the cross-sectional area of the converging part is small and therefore the rate is greater in the throat. Due to energy conservation and Bernoulli’s precept, larger velocities within the throat end in a drop in throat stress. The circulate rate can then be decided by measuring the stress drop within the convergent section and calculating the flow fee using Bernoulli’s equation. Venturi meters are extra frequent in water metering functions as a end result of the strain measurement ports can become clogged in wastewater applications.
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 can be measured by the electrode sensor (due to Faraday’s law and electromagnetic induction). The magnitude of the electron potential distinction is proportional to the velocity of the water, and the continuity equation can then be used to calculate the flow 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 the most half, magnetometers are used for full (pressure) pipe functions, however nowadays open channel magnetometers can additionally 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 move of water in a pipe. The pace of the turbine is proportional to the rate and the flow rate can then be calculated utilizing the continuity equation. Turbine circulate meters are solely used for water applications due to potential issues with wastewater solids assortment and clogging turbines.
Conclusion
There are some ways to measure move. Each method has completely different benefits, disadvantages and accuracy in different purposes.
It is important to grasp the characteristics of varied circulate measurement strategies to assist choose the best sort of flow metering on your application or to correctly interpret the flow measurements of current circulate meters. Tools like Apure (IoT-based water knowledge analysis) assist to examine measurements collected by flow meters and perform diagnostics to understand flow meter efficiency and shortly process and analyze the info. Contact us for technical or product service support.
More articles on flow meters:
Mass move fee vs volumetric circulate price
Relation between flow and strain
Ultrasonic circulate meter working principle
Difference between move meter and flow transmitter