Table of Contents
What is move units?
Continuity of flow equation
Common circulate unit metering strategies 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 move units?
Flow price is the quantity of fluid that passes by way of a unit of time. In water resources, circulate is usually measured in cubic toes per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a wide range of other items. The measurement of water useful resource flow is essential for purposes similar to system management, billing, design and many other applications. There are several methods to measure flow in a water resource system. This article outlines a few of the more widespread strategies of move measurement and offers some helpful details about circulate units measurement.
Continuity of flow equation
For water flowing in a pipe underneath steady-state situations (i.e., not varying with time), continuity implies that water flowing into one end of the pipe must circulate out of the other end. This additionally signifies that the flow in the pipe is identical at any point alongside the length of the pipe. The continuity equation can be expressed as
Flow = Velocity * Area
The concept of continuity in regular state situations results in the product of velocity * space being equal to a relentless at any point within the pipe. This is a useful precept for making move measurements, as proven beneath.
This is an instance of using the continuity equation to calculate flow. Velocity is measured at 10 feet per second and the cross-sectional area of the flow is measured at 10 sq. toes. Flow fee = 10 ft per second * 10 sq. feet = 100 cubic toes per second.
Common flow unit metering strategies in open channels
Eyeball methodology
It is usually helpful to estimate the circulate velocity and cross-sectional area by eye after which multiply the circulate velocity by the world to acquire the flow 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 utilized to enhance velocity measurements by timing floating particles transferring a set distance. The eyeball methodology can be used to estimate move when solely an “order of magnitude” of move is required or when the flow price is just 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 circulate conditions exist, the Manning’s equation can be utilized to calculate move by measuring depth only. The Manning’s equation is an empirical equation that describes the connection between circulate price in an open channel beneath uniform move circumstances and depth, slope and channel friction coefficient (Manning’s n). Uniform flow implies that depth doesn’t range with the length of the conduit or channel. Flow measurements utilizing Manning’s equation for depth usually are not applicable to steadily altering move circumstances, similar to backwater situations upstream of a dam or weir.
The depth flow methodology 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 move conditions. This technique is usually used with ultrasonic circulate 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 assistance of complicated river hydraulic models to account for complex channel geometry and channel friction situations.
Main gear
The primary system is used to measure flow in open channels, using buildings similar to flumes, weirs or dams, to measure flow by measuring depth. The measured depth can then be transformed to a flow rate using an equation or rated curve equation.
Primary gadgets work by forcing the flow via a path of critical 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 minimum particular vitality state that results in a specific discharge. In apply, this minimum state of power means that only one circulate 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” system.
Primary gadgets are a really convenient method of circulate measurement as a outcome of the depth may be measured from above the move without the want to insert a sensor in the water. This makes major flow meters more dependable and simpler to maintain. A drawback of primary units is that they will cause head loss and backwater in the system. Primary devices are sometimes considered to be probably the most accurate technique 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. The depth is transformed to a cross-sectional space using the geometry of the pipe or channel. The circulate rate is then calculated by multiplying the move area by the speed utilizing the continuity equation, hence the identify “AV meter”. Velocity is usually measured utilizing a Doppler sensor, which displays ultrasound waves again from particles within the fluid and makes use of the Doppler shift within 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 circulate in sewers because the probes are relatively small and they are often put in in current sewer pipes without causing important head loss within the pipe. This additionally permits them to be used for momentary 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 upkeep to wash the sensor. AV meters are sometimes thought-about less correct than major circulate meters as a end result of primary devices solely have to measure depth and depth measurements are more correct than velocity measurements.
Transport time meters
Transport time meters had been developed within the oil business to precisely measure circulate in large pipelines. They have been used with some success for open channel circulate in water metering functions. Transport time meters also use ultrasound like Doppler meters, however as an alternative of bouncing the sound waves off particles within 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 makes use of the transmission time of the sound waves to calculate the velocity 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 end result of speed of the water.
Transmission time meters may be expensive relative to Doppler flow meters due to the many sensors and complex installation concerned. They may be extra accurate due to the capability to separate the flow into horizontal cross sections and measure the speed of every section.
Flow unit measurement strategies in full tube functions
Venturi meters
Venturi move meters use the Venturi effect to measure move in a full or pressurized pipe through the use of the converging section of the pipe to restrict the flow. According to the continuity equation, the cross-sectional space of the converging part is small and therefore the velocity is higher within the throat. Due to power conservation and Bernoulli’s precept, greater velocities within the throat lead to a drop in throat pressure. The move rate can then be decided by measuring the pressure drop in the convergent section and calculating the flow rate utilizing Bernoulli’s equation. Venturi meters are extra widespread in water metering functions as a end result of the pressure measurement ports can turn out to be clogged in wastewater purposes.
Magnetic flowmeter
The electromagnetic flow meter works by making use of a magnetic field to the fluid passing via the pipe. This causes a small electron potential distinction 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 advantage of the magnetometer is that the metering part is the same diameter because the adjacent pipe, so the magnetometer causes no extra head loss. For probably the most part, magnetometers are used for full (pressure) pipe purposes, however nowadays open channel magnetometers can 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 flow of water in a pipe. The pace of the turbine is proportional to the speed and the move fee can then be calculated using the continuity equation. Turbine move meters are only used for water applications because of potential problems with wastewater solids assortment and clogging turbines.
Conclusion
There are many ways to measure flow. Each technique has totally different advantages, disadvantages and accuracy in several applications.
It is essential to understand the traits of varied circulate measurement techniques to assist select the proper sort of move metering for your utility or to properly interpret the move measurements of present move meters. Tools like Apure (IoT-based water data analysis) help to look at measurements collected by flow meters and carry out diagnostics to understand flow meter efficiency and shortly course of and analyze the information. Contact us for technical or product service support.
More articles on circulate meters:
Mass flow rate vs volumetric move price
Relation between circulate and pressure
Ultrasonic circulate meter working principle
Difference between flow meter and move transmitter
All the numerous particulars to keep in mind that come with #keyword# could be enough to bring on a major headache. Once you have your resolve, and a firm photo of your goal in mind, just work through the steps one by one. Help with just about any subject matter can be found on the web. That said, the site that I advocate, that will offer you the most help at this point, is #links#.
Table of Contents
What is flow units?
Continuity of move 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 strategies in full tube purposes
Venturi meters
Magnetic flowmeter
Turbine flowmeter
Conclusion
What is flow units?
Flow rate is the amount of fluid that passes via a unit of time. In water assets, flow is commonly measured in cubic ft per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a wide range of different items. The measurement of water resource circulate is important for purposes such as system control, billing, design and heaps of other functions. There are several ways to measure flow in a water resource system. This article outlines some of the extra frequent strategies of flow measurement and offers some useful information about move units measurement.
Continuity of circulate equation
For water flowing in a pipe under steady-state circumstances (i.e., not varying with time), continuity implies that water flowing into one end of the pipe should flow out of the opposite end. This additionally means that the flow within the pipe is similar at any point along the length of the pipe. The continuity equation can be expressed as
Flow = Velocity * Area
The idea of continuity in regular state circumstances leads to the product of velocity * space being equal to a continuing at any level in the pipe. This is a helpful principle for making circulate measurements, as shown below.
This is an example of utilizing the continuity equation to calculate flow. Velocity is measured at 10 ft per second and the cross-sectional space of the flow is measured at 10 square feet. Flow fee = 10 toes per second * 10 square ft = 100 cubic toes per second.
Common move unit metering methods in open channels
Eyeball methodology
It is sometimes helpful to estimate the move velocity and cross-sectional area by eye after which multiply the flow velocity by the world to obtain the flow velocity (continuity equation). A ruler or tape measure can be utilized to improve 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 method can be utilized to estimate flow when only an “order of magnitude” of flow is required or when the flow 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 circulate by measuring depth only. The Manning’s equation is an empirical equation that describes the connection between flow fee in an open channel underneath uniform flow situations and depth, slope and channel friction coefficient (Manning’s n). Uniform flow means that depth doesn’t vary with the length of the conduit or channel. Flow measurements using Manning’s equation for depth usually are not applicable to steadily changing circulate circumstances, such as backwater situations upstream of a dam or weir.
The depth move methodology of circulate measurement is more accurate 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 flow conditions. This methodology is usually used with ultrasonic flow meters to estimate the flow 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 complicated channel geometry and channel friction circumstances.
Main gear
The main system is used to measure flow in open channels, utilizing buildings corresponding to flumes, weirs or dams, to measure flow by measuring depth. The measured depth can then be transformed to a move price using an equation or rated curve equation.
Primary devices work by forcing the circulate through a path of crucial depth, for instance at 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 minimal specific energy state that leads to a selected discharge. In apply, this minimal state of power means that only one circulate corresponds to the critical depth. Therefore, measuring only ไดอะแฟรม produces a measurement of the corresponding flux and is therefore known as a “primary” system.
Primary gadgets are a very handy method of move measurement as a result of the depth may be measured from above the flow with out the necessity to insert a sensor within the water. This makes major move meters extra reliable and simpler to maintain. A disadvantage of primary units is that they’ll cause head loss and backwater in the system. Primary devices are sometimes thought-about to be probably the most correct methodology of measuring open channel circulate.
Surface Velocity Meters
An area velocity meter is an open channel circulate meter that measures move 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 circulate rate is then calculated by multiplying the flow area by the speed using the continuity equation, hence the identify “AV meter”. Velocity is typically measured using a Doppler sensor, which reflects ultrasound waves back from particles within the fluid and uses the Doppler shift within the mirrored sound signal to estimate velocity. Some AV meters measure floor velocity optically to estimate velocity.
AV meters are sometimes used to measure open channel circulate in sewers as a outcome of the probes are comparatively small and they can be installed in existing sewer pipes with out inflicting important head loss within the pipe. This also allows them for use for momentary or short-term move metering applications for sewer research. 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 thought of much less correct than primary move meters because major units solely must measure depth and depth measurements are extra accurate 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 move in water metering applications. Transport time meters also use ultrasound like Doppler meters, but as an alternative of bouncing the sound waves off particles within the water like Doppler move meters, they ship ultrasound waves between two sensors separated from one another 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 move. Because the velocity of sound in the water is known, the velocity of the water may be calculated based mostly on the offset in ultrasonic wave transmission time that happens because of the velocity of the water.
Transmission time meters can be expensive relative to Doppler circulate meters because of the many sensors and complex installation concerned. They could be extra correct because of the ability to separate the flow into horizontal cross sections and measure the velocity of every part.
Flow unit measurement strategies in full tube applications
Venturi meters
Venturi flow meters use the Venturi impact to measure flow in a full or pressurized pipe through the use of the converging section of the pipe to restrict 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 in the throat. Due to power conservation and Bernoulli’s principle, greater velocities within the throat result in a drop in throat pressure. The move price can then be determined by measuring the pressure drop in the convergent part and calculating the circulate rate using Bernoulli’s equation. Venturi meters are more common in water metering functions as a outcome of the strain measurement ports can turn into clogged in wastewater purposes.
Magnetic flowmeter
The electromagnetic flow meter works by making use of a magnetic field to the fluid passing via the pipe. This causes a small electron potential distinction that might be measured by the electrode sensor (due to Faraday’s legislation 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 circulate price.
An benefit of the magnetometer is that the metering part is similar 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 circulate meter is a mechanical move meter that uses a rotating turbine in flow to measure the move of water in a pipe. The velocity of the turbine is proportional to the velocity and the flow rate can then be calculated utilizing the continuity equation. Turbine flow meters are solely used for water purposes as a end result of potential problems with wastewater solids collection and clogging turbines.
Conclusion
There are many ways to measure circulate. Each methodology has completely different advantages, disadvantages and accuracy in numerous applications.
It is essential to understand the traits of varied flow measurement techniques to help choose the proper type of flow metering for your application or to properly interpret the circulate measurements of present flow meters. Tools like Apure (IoT-based water data analysis) assist to look at measurements collected by move meters and carry out diagnostics to know flow meter performance and rapidly course of and analyze the information. Contact us for technical or product service assist.
More articles on move meters:
Mass move rate vs volumetric move price
Relation between circulate and pressure
Ultrasonic flow meter working precept
Difference between circulate meter and move transmitter