Table of Contents
What is flow units?
Continuity of move equation
Common flow 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 move units?
Flow price is the volume of fluid that passes via a unit of time. In water resources, move is often measured in cubic ft per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a selection of different models. The measurement of water resource circulate is necessary for functions such as system control, billing, design and lots of other purposes. There are a number of ways to measure circulate in a water resource system. This article outlines a few of the extra common methods of circulate measurement and supplies some useful details about move items measurement.
Continuity of circulate 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 must flow out of the opposite end. This also signifies that the circulate within the pipe is the same at any level along the size of the pipe. The continuity equation could be expressed as
Flow = Velocity * Area
The concept of continuity in steady state conditions leads to the product of velocity * area being equal to a relentless at any level in the pipe. This is a helpful precept for making move measurements, as shown under.
This is an example of utilizing the continuity equation to calculate move. 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 toes per second * 10 square ft = one hundred cubic feet per second.
Common move unit metering methods in open channels
Eyeball methodology
It is sometimes helpful to estimate the circulate velocity and cross-sectional area by eye and then multiply the flow velocity by the world to obtain 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 shifting a set distance. The eyeball technique can be utilized to estimate move when solely an “order of magnitude” of circulate is required or when the circulate price is just too low to be measured with a move meter.
Flow depth (Manning)
When the channel cross-sectional space and channel slope are recognized and uniform move circumstances exist, the Manning’s equation can be used to calculate circulate by measuring depth only. The Manning’s equation is an empirical equation that describes the connection between circulate price in an open channel under uniform move conditions 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 using Manning’s equation for depth usually are not applicable to gradually altering flow situations, corresponding to backwater situations upstream of a dam or weir.
The depth move methodology of flow measurement is extra accurate than the “eyeball” technique. The primary problem with depth-only move measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform move situations. This technique is commonly 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 complex river hydraulic models to account for complicated channel geometry and channel friction circumstances.
Main equipment
The main system is used to measure move 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 flow rate utilizing an equation or rated curve equation.
Primary gadgets work by forcing the flow via a path of critical depth, for example at the high of a weir or at the throat of a flume. In technical phrases, the crucial depth is defined as the depth of the minimum particular power state that leads to a selected discharge. In apply, this minimal state of power implies that only one flow corresponds to the critical depth. Therefore, measuring solely the depth produces a measurement of the corresponding flux and is due to this fact known as a “primary” gadget.
Primary devices are a really convenient method of circulate measurement as a end result of the depth may be measured from above the move without the want to insert a sensor within the water. This makes primary flow meters extra reliable and easier to maintain. A drawback of primary gadgets is that they will cause head loss and backwater in the system. Primary devices are sometimes considered to be essentially the most correct methodology of measuring open channel circulate.
Surface Velocity Meters
An area velocity meter is an open channel circulate meter that measures circulate 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 fee is then calculated by multiplying the circulate area by the rate utilizing the continuity equation, therefore the name “AV meter”. Velocity is typically measured utilizing a Doppler sensor, which displays ultrasound waves back from particles within the fluid and uses the Doppler shift within the reflected 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 as a outcome of the probes are relatively small and they are often put in in existing sewer pipes without inflicting significant head loss in the pipe. This also permits them to be used for temporary or short-term circulate metering functions for sewer studies. one drawback of AV meters is that the sensor have to be put in in the fluid. In sewers, this requires frequent maintenance to wash the sensor. AV meters are often considered much less accurate than primary move meters as a result of major gadgets only must measure depth and depth measurements are more correct than velocity measurements.
Transport time meters
Transport time meters have been developed in the oil business to accurately measure flow in large 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, however instead of bouncing the sound waves off particles within the water like Doppler circulate meters, they send ultrasound waves between two sensors separated from each other by a sure distance alongside the length of the pipe and makes use of the transmission time of the sound waves to calculate the speed of the water circulate. Because the velocity of sound within the water is understood, the pace of the water can be calculated primarily based on the offset in ultrasonic wave transmission time that occurs as a outcome of pace of the water.
Transmission time meters can be expensive relative to Doppler circulate meters as a outcome of many sensors and sophisticated installation concerned. They can be more correct as a result of ability to split the circulate into horizontal cross sections and measure the rate of each part.
Flow unit measurement methods in full tube applications
Venturi meters
Venturi move 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 space of the converging part is small and therefore the rate is larger within the throat. Due to energy conservation and Bernoulli’s precept, larger velocities within the throat lead to a drop in throat pressure. The circulate fee can then be decided by measuring the strain drop within the convergent section and calculating the flow rate utilizing Bernoulli’s equation. Venturi meters are extra widespread in water metering purposes as a result of the pressure measurement ports can turn out to be clogged in wastewater applications.
Magnetic flowmeter
The electromagnetic move meter works by applying a magnetic field 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 rate.
An benefit of the magnetometer is that the metering part is identical diameter because the adjoining pipe, so the magnetometer causes no additional head loss. For probably the most half, magnetometers are used for full (pressure) pipe functions, but these days open channel magnetometers may additionally be used.
Turbine flowmeter
A turbine move 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 move fee can then be calculated using the continuity equation. Turbine flow meters are solely used for water functions due to potential problems with wastewater solids assortment and clogging generators.
Conclusion
There are many ways to measure flow. Each technique has totally different advantages, disadvantages and accuracy in several functions.
It is important to grasp the characteristics of assorted circulate measurement techniques to assist choose the right sort of circulate metering on your software or to correctly interpret the circulate measurements of present circulate meters. Tools like Apure (IoT-based water knowledge analysis) assist to look at measurements collected by flow meters and carry out diagnostics to understand circulate meter efficiency and quickly course of and analyze the info. Contact us for technical or product service help.
More articles on circulate meters:
Mass circulate fee vs volumetric move price
Relation between flow and pressure
Ultrasonic circulate meter working principle
Difference between circulate meter and circulate transmitter
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Table of Contents
What is flow units?
Continuity of flow equation
Common move unit metering methods in open channels
Eyeball technique
Flow depth (Manning)
Main gear
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 fee is the volume of fluid that passes by way of a unit of time. In water assets, circulate is usually measured in cubic toes per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a selection of other models. The measurement of water useful resource flow is essential for functions such as system control, billing, design and many different functions. There are several ways to measure flow in a water useful resource system. This article outlines a few of the extra widespread methods of circulate measurement and supplies some helpful information about flow units 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 end of the pipe should flow out of the other finish. This also implies that the move within the pipe is similar at any level along the size of the pipe. The continuity equation can be expressed as
Flow = Velocity * Area
The concept of continuity in steady state conditions ends in the product of velocity * area being equal to a constant at any level within the pipe. This is a helpful precept for making flow measurements, as proven below.
This is an instance of using the continuity equation to calculate move. Velocity is measured at 10 ft per second and the cross-sectional area of the circulate is measured at 10 square toes. Flow fee = 10 ft per second * 10 square ft = a hundred cubic ft per second.
Common circulate unit metering methods in open channels
Eyeball methodology
It is sometimes useful to estimate the flow velocity and cross-sectional space by eye after which multiply the circulate velocity by the realm 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 moving a set distance. The eyeball method can be used to estimate move when solely an “order of magnitude” of move is required or when the circulate fee is merely 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 conditions 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 connection between flow price in an open channel underneath uniform flow situations and depth, slope and channel friction coefficient (Manning’s n). Uniform circulate means that depth doesn’t differ with the size of the conduit or channel. Flow measurements using Manning’s equation for depth aren’t applicable to gradually altering move situations, similar to backwater circumstances upstream of a dam or weir.
The depth move method of move measurement is extra correct than the “eyeball” methodology. The major challenge with depth-only circulate measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform move situations. This methodology is commonly used with ultrasonic flow 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 complex river hydraulic models to account for complicated channel geometry and channel friction circumstances.
Main gear
The major system is used to measure circulate in open channels, using buildings such as 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 units work by forcing the circulate via a path of critical depth, for example at the prime of a weir or on the throat of a flume. In technical phrases, the crucial depth is defined as the depth of the minimal particular energy state that results in a specific discharge. In apply, this minimum state of vitality means that just one flow corresponds to the crucial depth. Therefore, measuring only 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 very handy methodology of flow measurement because the depth could be measured from above the flow without the want to insert a sensor in the water. This makes primary move meters extra dependable and easier to maintain. A disadvantage of primary devices is that they will trigger head loss and backwater within the system. Primary units are sometimes thought of to be essentially the most correct method of measuring open channel flow.
Surface Velocity Meters
An area velocity meter is an open channel circulate meter that measures flow by making two separate measurements of depth and velocity. เกจวัดแรงดัน is converted to a cross-sectional area using the geometry of the pipe or channel. The flow fee is then calculated by multiplying the flow space by the rate using the continuity equation, therefore the title “AV meter”. Velocity is typically measured utilizing a Doppler sensor, which displays ultrasound waves again from particles within the fluid and uses 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 circulate in sewers as a end result of the probes are comparatively small and they are often put in in current sewer pipes with out inflicting important head loss in the pipe. This also allows them for use for short-term 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 upkeep to wash the sensor. AV meters are often thought-about less correct than primary circulate meters because primary devices solely need to measure depth and depth measurements are extra correct than velocity measurements.
Transport time meters
Transport time meters have been developed in the oil trade to precisely measure flow in massive pipelines. They have been used with some success for open channel move in water metering functions. Transport time meters also use ultrasound like Doppler meters, however instead of bouncing the sound waves off particles in the water like Doppler flow 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 flow. Because the velocity of sound in the water is understood, the velocity of the water may be calculated based on the offset in ultrasonic wave transmission time that occurs due to the velocity of the water.
Transmission time meters may be costly relative to Doppler circulate meters due to the many sensors and sophisticated installation involved. They could be more accurate as a result of capability to split the flow into horizontal cross sections and measure the rate of every section.
Flow unit measurement strategies in full tube purposes
Venturi meters
Venturi move meters use the Venturi effect to measure flow in a full or pressurized pipe by using 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 subsequently the rate is larger within the throat. Due to energy conservation and Bernoulli’s precept, higher velocities in the throat lead to a drop in throat pressure. The circulate fee can then be decided by measuring the pressure drop in the convergent section and calculating the circulate price utilizing Bernoulli’s equation. Venturi meters are more widespread in water metering purposes because the stress 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 via the pipe. This causes a small electron potential difference that might 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 circulate rate.
An advantage of the magnetometer is that the metering part is the same diameter as the adjoining pipe, so the magnetometer causes no further 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 move meter that makes use of a rotating turbine in circulate to measure the flow of water in a pipe. The pace of the turbine is proportional to the speed and the circulate fee can then be calculated using the continuity equation. Turbine move meters are only used for water functions because of potential problems with wastewater solids assortment and clogging turbines.
Conclusion
There are some ways to measure flow. Each methodology has different advantages, disadvantages and accuracy in numerous applications.
It is necessary to understand the traits of various move measurement techniques to help select the best type of flow metering for your application or to correctly interpret the circulate measurements of current flow meters. Tools like Apure (IoT-based water knowledge analysis) assist to look at measurements collected by move meters and carry out diagnostics to grasp flow meter performance and rapidly process and analyze the information. Contact us for technical or product service help.
More articles on move meters:
Mass move fee vs volumetric flow fee
Relation between move and pressure
Ultrasonic move meter working precept
Difference between move meter and move transmitter