Table of Contents
What is circulate units?
Continuity of move equation
Common circulate unit metering methods in open channels
Eyeball method
Flow depth (Manning)
Main tools
Surface Velocity Meters
Transport time meters
Flow unit measurement methods in full tube applications
Venturi meters
Magnetic flowmeter
Turbine flowmeter
Conclusion
What is flow units?
Flow rate is the amount of fluid that passes through a unit of time. In water sources, flow is usually measured in cubic ft per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a wide range of different units. The measurement of water useful resource circulate is essential for purposes such as system control, billing, design and plenty of other functions. There are several ways to measure flow in a water resource system. This article outlines some of the more frequent methods of flow measurement and offers some useful information about circulate models measurement.
Continuity of move equation
For water flowing in a pipe beneath steady-state situations (i.e., not varying with time), continuity means that water flowing into one finish of the pipe should move out of the opposite finish. This also implies that the flow 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 situations results in the product of velocity * area being equal to a relentless at any point within the pipe. This is a helpful principle for making flow measurements, as proven 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 move is measured at 10 square ft. Flow rate = 10 feet per second * 10 sq. feet = 100 cubic toes per second.
Common circulate unit metering methods in open channels
Eyeball method
It is usually helpful to estimate the flow velocity and cross-sectional area by eye and then multiply the flow velocity by the realm to acquire the flow 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 debris shifting a set distance. The eyeball method can be utilized to estimate move when solely an “order of magnitude” of circulate 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 area and channel slope are known and uniform circulate circumstances exist, the Manning’s equation can be utilized to calculate circulate 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 move situations and depth, slope and channel friction coefficient (Manning’s n). Uniform flow means that depth does not range with the size of the conduit or channel. Flow measurements using Manning’s equation for depth aren’t applicable to steadily changing flow conditions, such as backwater situations upstream of a dam or weir.
The depth move methodology of circulate measurement is more correct than the “eyeball” technique. The major problem with depth-only flow measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform circulate circumstances. This method is usually used with ultrasonic circulate meters to estimate the move 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 complex river hydraulic models to account for complex channel geometry and channel friction circumstances.
Main tools
The primary device is used to measure flow in open channels, utilizing constructions similar to flumes, weirs or dams, to measure move by measuring depth. The measured depth can then be converted to a circulate rate using an equation or rated curve equation.
Primary gadgets work by forcing the move by way of a path of critical depth, for instance on the prime of a weir or on the throat of a flume. In technical phrases, the critical depth is defined because the depth of the minimum specific power state that results in a selected discharge. In practice, this minimal state of power means that only one circulate corresponds to the critical 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 methodology of circulate measurement as a result of the depth may be measured from above the circulate with out the want to insert a sensor within the water. This makes main circulate meters extra dependable and easier to maintain. A drawback of main gadgets is that they can trigger head loss and backwater in the system. Primary gadgets are often thought of to be the most correct technique 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 transformed to a cross-sectional space utilizing the geometry of the pipe or channel. The flow price is then calculated by multiplying the move area by the rate using the continuity equation, hence the title “AV meter”. Velocity is typically measured using a Doppler sensor, which reflects ultrasound waves again from particles in the fluid and makes use of the Doppler shift in 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 move in sewers because the probes are comparatively small and they can be put in in existing sewer pipes without inflicting significant head loss within the pipe. This also allows them for use for momentary or short-term circulate metering purposes for sewer studies. one disadvantage of AV meters is that the sensor must be put in within the fluid. In sewers, this requires frequent upkeep to wash the sensor. AV meters are often thought-about much less correct than main flow meters as a end result of primary gadgets only need to measure depth and depth measurements are more accurate than velocity measurements.
Transport time meters
Transport time meters were developed in the oil business to accurately measure move in giant pipelines. They have been used with some success for open channel move in water metering purposes. Transport time meters also use ultrasound like Doppler meters, however instead of bouncing the sound waves off particles in the water like Doppler move 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 circulate. Because the pace of sound in the water is known, the speed of the water may be calculated based mostly on the offset in ultrasonic wave transmission time that occurs due to the speed of the water.
Transmission time meters can be expensive relative to Doppler flow meters as a outcome of many sensors and complicated installation concerned. They can be extra accurate as a outcome of ability to split the circulate into horizontal cross sections and measure the speed of every part.
Flow unit measurement strategies in full tube applications
Venturi meters
Venturi flow meters use the Venturi effect to measure circulate 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 therefore the rate is larger in the throat. Due to vitality conservation and Bernoulli’s principle, higher velocities within the throat end in a drop in throat pressure. The flow price can then be determined by measuring the strain drop within the convergent part and calculating the circulate price utilizing Bernoulli’s equation. Venturi meters are extra frequent in water metering purposes because the stress measurement ports can become clogged in wastewater purposes.
Magnetic flowmeter
The electromagnetic flow meter works by making use of a magnetic field 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 rate 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 part is identical diameter because the adjacent pipe, so the magnetometer causes no further head loss. For probably the most half, magnetometers are used for full (pressure) pipe functions, but these days open channel magnetometers can be used.
Turbine flowmeter
A turbine move 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 velocity and the flow fee can then be calculated using the continuity equation. เกจวัดแรงดันnuovafima are solely used for water functions as a result of potential issues with wastewater solids assortment and clogging generators.
Conclusion
There are many ways to measure move. Each method has totally different advantages, disadvantages and accuracy in numerous applications.
It is essential to know the characteristics of varied move measurement techniques to assist select the right kind of flow metering in your utility or to properly interpret the flow measurements of existing circulate meters. Tools like Apure (IoT-based water knowledge analysis) help to examine measurements collected by flow meters and carry out diagnostics to understand move meter efficiency and quickly process and analyze the information. Contact us for technical or product service help.
More articles on flow meters:
Mass flow rate vs volumetric move rate
Relation between flow and strain
Ultrasonic flow meter working principle
Difference between flow meter and circulate transmitter
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Table of Contents
What is circulate units?
Continuity of circulate equation
Common move unit metering strategies in open channels
Eyeball technique
Flow depth (Manning)
Main equipment
Surface Velocity Meters
Transport time meters
Flow unit measurement strategies in full tube applications
Venturi meters
Magnetic flowmeter
Turbine flowmeter
Conclusion
What is move units?
Flow fee is the quantity of fluid that passes through a unit of time. In water sources, move is commonly measured in cubic feet per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a wide selection of different units. The measurement of water resource circulate is important for purposes similar to system control, billing, design and lots of other functions. There are several methods to measure move in a water resource system. This article outlines some of the more common methods of circulate measurement and offers some helpful details about circulate items measurement.
Continuity of move equation
For water flowing in a pipe under steady-state conditions (i.e., not varying with time), continuity implies that water flowing into one end of the pipe should flow out of the other finish. This additionally implies that the circulate within the pipe is identical at any level 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 useful precept for making move measurements, as shown below.
This is an instance 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 sq. feet. Flow price = 10 feet per second * 10 square feet = 100 cubic ft per second.
Common circulate unit metering methods in open channels
Eyeball technique
It is typically helpful to estimate the circulate velocity and cross-sectional area 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 used to improve the accuracy of cross-sectional area measurements, and a stopwatch can be utilized to improve velocity measurements by timing floating debris moving a set distance. The eyeball technique can be utilized to estimate flow when solely an “order of magnitude” of flow is required or when the flow price is too low to be measured with a flow meter.
Flow depth (Manning)
When the channel cross-sectional space and channel slope are recognized and uniform flow conditions exist, the Manning’s equation can be used to calculate flow by measuring depth solely. The Manning’s equation is an empirical equation that describes the connection between flow price in an open channel under uniform circulate situations and depth, slope and channel friction coefficient (Manning’s n). Uniform circulate implies that depth doesn’t range with the size of the conduit or channel. Flow measurements using Manning’s equation for depth aren’t applicable to steadily changing circulate circumstances, similar to backwater conditions upstream of a dam or weir.
The depth circulate method of flow measurement is more accurate than the “eyeball” method. The major challenge with depth-only flow measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform circulate circumstances. This technique is commonly used with ultrasonic flow meters to estimate the flow of a river by measuring only the water degree 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 tools
The primary system is used to measure move in open channels, utilizing constructions corresponding to flumes, weirs or dams, to measure move by measuring depth. The measured depth can then be converted to a circulate rate using an equation or rated curve equation.
Primary units work by forcing the circulate via a path of crucial depth, for instance on the prime of a weir or at the throat of a flume. In technical terms, the critical depth is defined because the depth of the minimal specific power state that leads to a specific discharge. In follow, this minimal state of energy implies that just 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” system.
Primary units are a very handy methodology of flow measurement because the depth can be measured from above the flow without the necessity to insert a sensor in the water. This makes primary flow meters more reliable and easier to maintain up. A disadvantage of primary gadgets is that they’ll cause head loss and backwater within the system. Primary devices are sometimes thought of to be the most accurate method of measuring open channel flow.
Surface Velocity Meters
An space velocity meter is an open channel move 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 flow space by the rate utilizing the continuity equation, therefore the identify “AV meter”. Velocity is often measured using a Doppler sensor, which displays ultrasound waves again 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 circulate in sewers because the probes are comparatively small and they are often installed in current sewer pipes without causing important head loss in the pipe. This also permits them for use for momentary or short-term move metering purposes for sewer research. one disadvantage of AV meters is that the sensor have to be put in in the fluid. In sewers, this requires frequent maintenance to scrub the sensor. AV meters are often thought of less accurate than main circulate meters as a end result of primary devices solely must measure depth and depth measurements are more accurate than velocity measurements.
Transport time meters
Transport time meters have been developed in the oil business to precisely measure move 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 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 flow. Because the pace of sound in the water is known, the speed of the water may be calculated primarily based on the offset in ultrasonic wave transmission time that occurs due to the speed of the water.
Transmission time meters could be costly relative to Doppler circulate meters because of the many sensors and sophisticated installation involved. They may be extra correct as a outcome of capacity to split the move into horizontal cross sections and measure the rate of each section.
Flow unit measurement strategies in full tube purposes
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 move. According to the continuity equation, the cross-sectional space of the converging section is small and subsequently the velocity is higher within the throat. Due to power conservation and Bernoulli’s precept, higher velocities in the throat end in a drop in throat strain. The move fee can then be decided by measuring the strain drop within the convergent part and calculating the circulate price using Bernoulli’s equation. Venturi meters are more widespread in water metering purposes because the pressure measurement ports can turn out to be clogged in wastewater functions.
Magnetic flowmeter
The electromagnetic flow 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 difference is proportional to the speed 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 the same diameter because the adjoining pipe, so the magnetometer causes no extra head loss. For essentially the most part, magnetometers are used for full (pressure) pipe functions, but these days open channel magnetometers can additionally be used.
Turbine flowmeter
A turbine circulate meter is a mechanical circulate meter that uses a rotating turbine in move to measure the flow of water in a pipe. The pace of the turbine is proportional to the velocity and the move fee can then be calculated using the continuity equation. Turbine flow meters are solely used for water purposes due to potential issues with wastewater solids collection and clogging turbines.
Conclusion
There are many ways to measure circulate. Each technique has totally different benefits, disadvantages and accuracy in numerous applications.
It is essential to grasp the traits of varied move measurement strategies to help choose the right sort of move metering on your application or to properly interpret the move measurements of present flow meters. Tools like Apure (IoT-based water knowledge analysis) help to examine measurements collected by move meters and carry out diagnostics to understand move meter efficiency and shortly process and analyze the data. Contact us for technical or product service assist.
More articles on move meters:
Mass circulate price vs volumetric circulate price
Relation between flow and strain
Ultrasonic circulate meter working precept
Difference between flow meter and circulate transmitter