Table of Contents
What is flow units?
Continuity of move equation
Common move unit metering strategies in open channels
Eyeball methodology
Flow depth (Manning)
Main gear
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 price is the quantity of fluid that passes via a unit of time. In water resources, flow is often measured in cubic feet per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a wide range of different models. The measurement of water resource move is essential for functions such as system management, billing, design and many other purposes. There are a quantity of methods to measure flow in a water useful resource system. This article outlines a few of the extra frequent strategies of move measurement and supplies some helpful details about circulate models measurement.
Continuity of flow equation
For water flowing in a pipe underneath steady-state situations (i.e., not varying with time), continuity means that water flowing into one finish of the pipe must circulate out of the other finish. This also implies that the flow within the pipe is identical at any point along the length of the pipe. The continuity equation may be expressed as
Flow = Velocity * Area
The idea of continuity in steady state situations results in the product of velocity * area being equal to a constant at any point within the pipe. This is a useful precept for making flow measurements, as shown below.
This is an instance of utilizing the continuity equation to calculate flow. Velocity is measured at 10 toes per second and the cross-sectional space of the flow is measured at 10 square toes. Flow price = 10 ft per second * 10 sq. ft = one hundred cubic toes per second.
Common flow unit metering strategies in open channels
Eyeball methodology
It is typically helpful to estimate the circulate velocity and cross-sectional area by eye after which multiply the circulate 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 space measurements, and a stopwatch can be used to improve velocity measurements by timing floating particles moving a set distance. The eyeball technique can be utilized to estimate circulate when only an “order of magnitude” of move is required or when the flow rate 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 circumstances 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 relationship between move fee in an open channel underneath uniform circulate situations 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 are not relevant to gradually changing flow situations, similar to backwater conditions upstream of a dam or weir.
The depth move methodology of circulate measurement is extra correct than the “eyeball” methodology. The main 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 commonly used with ultrasonic circulate meters to estimate the flow 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 complex river hydraulic models to account for complex channel geometry and channel friction conditions.
Main gear
The primary device is used to measure flow in open channels, utilizing buildings similar to flumes, weirs or dams, to measure move by measuring depth. pressure gauge 0 10 bar ราคา measured depth can then be converted to a move rate using an equation or rated curve equation.
Primary units work by forcing the circulate through a path of critical depth, for instance on the high of a weir or on the throat of a flume. In technical terms, the important depth is defined because the depth of the minimum particular power state that results in a selected discharge. In follow, this minimal state of energy signifies that just one move corresponds to the critical depth. Therefore, measuring only the depth produces a measurement of the corresponding flux and is subsequently called a “primary” device.
Primary units are a very convenient technique of circulate measurement as a outcome of the depth can be measured from above the move with out the want to insert a sensor in the water. This makes main move meters extra dependable and easier to take care of. A drawback of major gadgets is that they will cause head loss and backwater in the system. Primary gadgets are often thought-about to be essentially the most correct method of measuring open channel circulate.
Surface Velocity Meters
An space 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 area using the geometry of the pipe or channel. The move rate is then calculated by multiplying the flow space by the speed using the continuity equation, hence the identify “AV meter”. Velocity is usually measured using a Doppler sensor, which reflects ultrasound waves back from particles within 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 flow in sewers because the probes are relatively small and they are often put in in existing sewer pipes without inflicting vital head loss within the pipe. This also permits them for use for temporary or short-term circulate metering purposes for sewer studies. one disadvantage of AV meters is that the sensor must be installed within the fluid. In sewers, this requires frequent upkeep to clean the sensor. AV meters are often thought-about much less correct than main move meters as a outcome of major devices solely have to measure depth and depth measurements are more correct than velocity measurements.
Transport time meters
Transport time meters have been developed within the oil trade to precisely measure move 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 flow meters, they send ultrasound waves between two sensors separated from one another by a certain distance along the size of the pipe and uses the transmission time of the sound waves to calculate the velocity of the water circulate. Because the pace of sound within the water is thought, the speed of the water can be calculated based on the offset in ultrasonic wave transmission time that occurs because of the velocity of the water.
Transmission time meters can be expensive relative to Doppler circulate meters as a end result of many sensors and complex installation concerned. They may be extra correct due to the ability to split the circulate into horizontal cross sections and measure the rate of each part.
Flow unit measurement strategies in full tube functions
Venturi meters
Venturi move meters use the Venturi impact to measure flow in a full or pressurized pipe through the use of the converging part of the pipe to restrict the flow. According to the continuity equation, the cross-sectional space of the converging section is small and therefore the rate is larger in the throat. Due to vitality conservation and Bernoulli’s principle, higher velocities in the throat result in a drop in throat strain. The circulate price can then be determined by measuring the pressure drop in the convergent part and calculating the flow price utilizing Bernoulli’s equation. Venturi meters are extra frequent in water metering applications because the stress measurement ports can become clogged in wastewater applications.
Magnetic flowmeter
The electromagnetic circulate meter works by making use of a magnetic area 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 legislation 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 rate.
An advantage of the magnetometer is that the metering section is the same diameter because the adjacent pipe, so the magnetometer causes no extra head loss. For essentially the most part, magnetometers are used for full (pressure) pipe applications, however nowadays open channel magnetometers can be used.
Turbine flowmeter
A turbine move meter is a mechanical circulate meter that uses a rotating turbine in circulate to measure the move of water in a pipe. The pace of the turbine is proportional to the velocity and the flow fee can then be calculated using the continuity equation. Turbine move meters are solely used for water purposes as a result of potential issues with wastewater solids assortment and clogging turbines.
Conclusion
There are many ways to measure move. Each technique has completely different advantages, disadvantages and accuracy in several applications.
It is important to know the traits of assorted circulate measurement techniques to assist select the best kind of circulate metering for your application or to properly interpret the circulate measurements of existing circulate meters. Tools like Apure (IoT-based water information analysis) help to examine measurements collected by circulate meters and carry out diagnostics to know flow meter efficiency and shortly course of and analyze the info. Contact us for technical or product service help.
More articles on move meters:
Mass move price vs volumetric move rate
Relation between move and pressure
Ultrasonic move meter working principle
Difference between circulate meter and circulate transmitter
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Table of Contents
What is move units?
Continuity of flow 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 purposes
Venturi meters
Magnetic flowmeter
Turbine flowmeter
Conclusion
What is move units?
Flow price is the amount of fluid that passes by way of a unit of time. In water sources, move is usually measured in cubic ft per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a selection of different units. The measurement of water resource move is necessary for purposes corresponding to system management, billing, design and plenty of other purposes. There are several ways to measure flow in a water useful resource system. This article outlines a few of the more common methods of flow measurement and provides some useful details about move items measurement.
Continuity of circulate equation
For water flowing in a pipe under steady-state conditions (i.e., not varying with time), continuity means that water flowing into one finish of the pipe should flow out of the opposite finish. This also means that the circulate within the pipe is identical at any level along the size of the pipe. The continuity equation could be expressed as
Flow = Velocity * Area
The idea of continuity in regular state situations ends in the product of velocity * area being equal to a constant at any point within the pipe. This is a helpful principle for making circulate measurements, as shown below.
This is an example of using the continuity equation to calculate circulate. Velocity is measured at 10 ft per second and the cross-sectional space of the circulate is measured at 10 sq. ft. Flow price = 10 toes per second * 10 sq. feet = 100 cubic ft per second.
Common move unit metering methods in open channels
Eyeball method
It is usually useful to estimate the circulate velocity and cross-sectional space by eye after which multiply the flow velocity by the area to obtain the circulate velocity (continuity equation). A ruler or tape measure can be utilized to improve the accuracy of cross-sectional space measurements, and a stopwatch can be used to enhance velocity measurements by timing floating particles transferring a set distance. The eyeball methodology can be used to estimate move when only an “order of magnitude” of circulate is required or when the move price is simply 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 move circumstances exist, the Manning’s equation can be used to calculate move by measuring depth only. The Manning’s equation is an empirical equation that describes the connection between circulate rate in an open channel beneath uniform flow situations and depth, slope and channel friction coefficient (Manning’s n). Uniform flow signifies that depth does not vary with the length of the conduit or channel. Flow measurements using Manning’s equation for depth usually are not relevant to progressively changing move situations, corresponding to backwater situations upstream of a dam or weir.
The depth circulate technique of flow measurement is extra accurate than the “eyeball” method. The primary challenge with depth-only circulate measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform circulate circumstances. This technique is often used with ultrasonic flow meters to estimate the circulate 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 assistance of complex river hydraulic fashions to account for advanced channel geometry and channel friction conditions.
Main tools
The main gadget is used to measure circulate in open channels, utilizing constructions similar to flumes, weirs or dams, to measure circulate by measuring depth. The measured depth can then be converted to a flow fee using an equation or rated curve equation.
Primary units work by forcing the flow through 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 outlined as the depth of the minimal specific energy state that results in a selected discharge. In follow, this minimum state of energy means that just one circulate corresponds to the crucial depth. Therefore, measuring solely the depth produces a measurement of the corresponding flux and is subsequently referred to as a “primary” gadget.
Primary gadgets are a really convenient technique of flow measurement because the depth can be measured from above the flow without the necessity to insert a sensor within the water. This makes primary move meters more reliable and easier to take care of. A drawback of main gadgets is that they can trigger head loss and backwater in the system. Primary gadgets are sometimes thought-about to be essentially the most correct technique of measuring open channel circulate.
Surface Velocity Meters
An space velocity meter is an open channel flow meter that measures flow 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 fee is then calculated by multiplying the move area by the velocity using the continuity equation, hence the name “AV meter”. Velocity is usually measured utilizing a Doppler sensor, which reflects ultrasound waves back from particles within 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 often used to measure open channel circulate in sewers because the probes are relatively small and they can be put in in present sewer pipes with out inflicting important head loss in the pipe. This also allows them for use for momentary or short-term circulate metering functions for sewer research. one disadvantage of AV meters is that the sensor have to be installed in the fluid. In sewers, this requires frequent maintenance to scrub the sensor. AV meters are often considered much less correct than major move meters because primary devices only must measure depth and depth measurements are extra accurate than velocity measurements.
Transport time meters
Transport time meters had been developed within the oil industry to accurately measure circulate in large 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 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 sure distance along the size 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 understood, the speed of the water can be calculated based mostly on the offset in ultrasonic wave transmission time that occurs as a end result of velocity of the water.
Transmission time meters can be expensive relative to Doppler move meters as a end result of many sensors and complicated installation involved. They may be extra correct as a end result of capacity to separate the circulate into horizontal cross sections and measure the velocity of each part.
Flow unit measurement methods in full tube functions
Venturi meters
Venturi circulate meters use the Venturi effect to measure move 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 therefore the rate is higher within the throat. Due to power conservation and Bernoulli’s precept, higher velocities in the throat result in a drop in throat stress. The move rate can then be decided by measuring the strain drop in the convergent part and calculating the flow rate utilizing Bernoulli’s equation. Venturi meters are extra common in water metering purposes as a outcome of the pressure measurement ports can become clogged in wastewater purposes.
Magnetic flowmeter
The electromagnetic move meter works by applying a magnetic subject to the fluid passing via the pipe. This causes a small electron potential distinction that could 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 circulate price.
An advantage of the magnetometer is that the metering part is the same diameter as the adjoining pipe, so the magnetometer causes no extra head loss. For the most half, magnetometers are used for full (pressure) pipe applications, however nowadays open channel magnetometers can also be used.
Turbine flowmeter
A turbine flow meter is a mechanical flow meter that makes use of 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. Turbine move meters are solely used for water purposes as a result of potential problems with wastewater solids assortment and clogging generators.
Conclusion
There are some ways to measure flow. Each technique has totally different advantages, disadvantages and accuracy in several purposes.
It is important to grasp the characteristics of various move measurement techniques to help select the proper sort of move metering on your application or to properly interpret the flow measurements of existing flow meters. Tools like Apure (IoT-based water data analysis) assist to look at measurements collected by move meters and perform diagnostics to know circulate meter efficiency and rapidly process and analyze the information. Contact us for technical or product service help.
More articles on flow meters:
Mass circulate fee vs volumetric flow rate
Relation between flow and strain
Ultrasonic circulate meter working precept
Difference between flow meter and flow transmitter