Table of Contents
What is circulate units?
Continuity of move equation
Common flow 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 circulate units?
Flow fee is the volume of fluid that passes via 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 a big selection of other models. The measurement of water useful resource circulate is essential for applications corresponding to system control, billing, design and many other functions. There are a quantity of ways to measure circulate in a water useful resource system. This article outlines a variety of the extra common methods of flow measurement and offers some helpful details about flow models measurement.
Continuity of circulate 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 flow out of the opposite end. This additionally implies 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 steady state situations results in the product of velocity * space being equal to a relentless at any point in the pipe. This is a helpful principle for making move measurements, as proven beneath.
This is an example of using the continuity equation to calculate circulate. Velocity is measured at 10 toes per second and the cross-sectional area of the move is measured at 10 sq. toes. Flow fee = 10 ft per second * 10 sq. feet = a hundred cubic ft per second.
Common circulate unit metering strategies in open channels
Eyeball technique
It is sometimes helpful to estimate the flow velocity and cross-sectional area by eye and then multiply the flow velocity by the realm to obtain the circulate 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 improve velocity measurements by timing floating particles shifting a set distance. The eyeball technique can be used to estimate move when solely an “order of magnitude” of flow is required or when the circulate fee is too low to be measured with a circulate meter.
Flow depth (Manning)
When the channel cross-sectional space and channel slope are identified and uniform flow circumstances 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 move price in an open channel under uniform circulate conditions and depth, slope and channel friction coefficient (Manning’s n). Uniform move means that depth does not range with the size of the conduit or channel. Flow measurements utilizing Manning’s equation for depth are not relevant to gradually altering move conditions, similar to backwater conditions upstream of a dam or weir.
The depth circulate methodology of move measurement is more correct than the “eyeball” methodology. The major challenge with depth-only flow 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 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 primary system is used to measure flow in open channels, utilizing structures corresponding to flumes, weirs or dams, to measure move by measuring depth. The measured depth can then be converted to a move rate utilizing an equation or rated curve equation.
Primary devices work by forcing the move through a path of important depth, for instance on the high of a weir or on the throat of a flume. In technical phrases, the crucial depth is defined because the depth of the minimum particular power state that ends in a selected discharge. In apply, this minimal state of vitality implies that only one flow corresponds to the important depth. Therefore, measuring solely the depth produces a measurement of the corresponding flux and is therefore called a “primary” gadget.
Primary gadgets are a very convenient methodology of flow measurement because the depth could be measured from above the flow with out the want to insert a sensor in the water. This makes primary circulate meters extra dependable and simpler to keep up. A disadvantage of main devices is that they can cause head loss and backwater within the system. Primary units are often thought-about to be the most accurate 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 space utilizing 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 name “AV meter”. Velocity is usually measured utilizing a Doppler sensor, which displays ultrasound waves again from particles within the fluid and uses the Doppler shift within 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 circulate in sewers because the probes are comparatively small and they are often installed in present sewer pipes with out inflicting significant head loss within the pipe. This additionally allows them to be used 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 maintenance to clean the sensor. AV meters are sometimes thought of less correct than major circulate meters as a result of main units solely need to measure depth and depth measurements are extra correct than velocity measurements.
Transport time meters
Transport time meters were developed in the oil industry to precisely measure move in large pipelines. They have been used with some success for open channel flow in water metering functions. Transport time meters also use ultrasound like Doppler meters, but instead of bouncing the sound waves off particles within the water like Doppler move meters, they send 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 velocity of the water flow. Because the speed of sound in the water is known, the velocity of the water may be calculated based on the offset in ultrasonic wave transmission time that happens due to the velocity of the water.
Transmission time meters may be expensive relative to Doppler move meters because of the many sensors and complicated set up involved. They can be extra correct as a end result of ability to split the move into horizontal cross sections and measure the speed of every part.
Flow unit measurement methods in full tube applications
Venturi meters
Venturi flow meters use the Venturi impact to measure flow in a full or pressurized pipe by utilizing the converging section of the pipe to limit the move. According to the continuity equation, the cross-sectional area of the converging part is small and due to this fact the speed is greater within the throat. Due to vitality conservation and Bernoulli’s precept, larger velocities within the throat lead to a drop in throat stress. The move fee can then be determined by measuring the stress drop in the convergent section and calculating the circulate rate using Bernoulli’s equation. Venturi meters are extra common in water metering applications as a end result of the pressure 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 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 difference is proportional to the speed 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 identical diameter because the adjoining pipe, so the magnetometer causes no additional head loss. For the most part, magnetometers are used for full (pressure) pipe applications, but nowadays open channel magnetometers can be used.
Turbine flowmeter
A turbine move meter is a mechanical move meter that makes use of a rotating turbine in circulate to measure the move of water in a pipe. The speed of the turbine is proportional to the rate and the flow fee can then be calculated utilizing the continuity equation. Turbine circulate meters are only used for water functions as a end result of potential problems with wastewater solids collection and clogging generators.
Conclusion
There are many ways to measure move. Each method has different advantages, disadvantages and accuracy in different functions.
It is important to grasp the traits of assorted move measurement techniques to help choose the best sort of move metering in your software or to correctly interpret the flow measurements of current move meters. Tools like Apure (IoT-based water information analysis) assist to look at measurements collected by move meters and carry out diagnostics to grasp move meter efficiency and shortly course of and analyze the data. Contact us for technical or product service assist.
More articles on flow meters:
Mass flow price vs volumetric flow fee
Relation between circulate and stress
Ultrasonic circulate meter working precept
Difference between circulate meter and circulate transmitter
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Table of Contents
What is move units?
Continuity of circulate equation
Common move unit metering methods in open channels
Eyeball technique
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?
เกจวัดแรงดันน้ำ10บาร์ is the volume of fluid that passes by way of a unit of time. In water resources, circulate is commonly measured in cubic feet per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or quite a lot of other models. The measurement of water useful resource move is necessary for functions such as system control, billing, design and many other applications. There are a number of methods to measure flow in a water useful resource system. This article outlines some of the extra common methods of flow measurement and provides some useful details about circulate models measurement.
Continuity of circulate equation
For water flowing in a pipe beneath steady-state circumstances (i.e., not varying with time), continuity means that water flowing into one end of the pipe should circulate out of the opposite end. This additionally means that the circulate within the pipe is similar at any point along the size of the pipe. The continuity equation may be expressed as
Flow = Velocity * Area
The idea of continuity in steady state circumstances results in the product of velocity * area being equal to a continuing at any level within 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 flow. Velocity is measured at 10 feet per second and the cross-sectional space of the move is measured at 10 sq. toes. Flow fee = 10 toes per second * 10 sq. toes = one hundred cubic feet per second.
Common flow unit metering strategies in open channels
Eyeball methodology
It is usually helpful to estimate the move velocity and cross-sectional area by eye and then multiply the flow velocity by the world to acquire the move 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 improve velocity measurements by timing floating particles shifting a set distance. The eyeball technique can be utilized to estimate move when only an “order of magnitude” of circulate is required or when the circulate rate is merely too low to be measured with a move meter.
Flow depth (Manning)
When the channel cross-sectional area and channel slope are known and uniform move situations exist, the Manning’s equation can be used 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 underneath uniform circulate situations and depth, slope and channel friction coefficient (Manning’s n). Uniform flow implies that depth does not vary with the size of the conduit or channel. Flow measurements using Manning’s equation for depth are not applicable to steadily changing move situations, corresponding to backwater conditions upstream of a dam or weir.
The depth flow methodology of circulate measurement is more correct than the “eyeball” methodology. The major challenge with depth-only flow 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 move meters to estimate the move 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 assistance of advanced river hydraulic fashions to account for complex channel geometry and channel friction conditions.
Main tools
The primary gadget is used to measure circulate in open channels, using structures similar to flumes, weirs or dams, to measure circulate by measuring depth. The measured depth can then be transformed to a flow fee utilizing an equation or rated curve equation.
Primary units work by forcing the flow through a path of critical depth, for example on the high of a weir or on the throat of a flume. In technical terms, the important depth is defined as the depth of the minimal specific vitality state that ends in a specific discharge. In practice, this minimum state of vitality means that just one move corresponds to the critical depth. Therefore, measuring solely the depth produces a measurement of the corresponding flux and is therefore known as a “primary” system.
Primary gadgets are a really handy technique of circulate measurement because the depth could be measured from above the move without the necessity to insert a sensor within the water. This makes major flow meters more reliable and easier to maintain. A drawback of primary units is that they can trigger head loss and backwater in the system. Primary units are often considered to be probably the most accurate method of measuring open channel circulate.
Surface Velocity Meters
An space 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 space using the geometry of the pipe or channel. The circulate fee is then calculated by multiplying the move space by the velocity using the continuity equation, therefore the name “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 within the reflected 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 result of the probes are comparatively small and they can be put in in existing sewer pipes without causing important head loss in the pipe. This also allows them to be used for temporary or short-term flow metering applications for sewer studies. one drawback of AV meters is that the sensor should be installed in the fluid. In sewers, this requires frequent maintenance to scrub the sensor. AV meters are often thought of less correct than major circulate meters as a result of primary devices solely need to measure depth and depth measurements are extra correct than velocity measurements.
Transport time meters
Transport time meters were developed in the oil business to precisely measure flow in massive pipelines. They have been used with some success for open channel circulate in water metering purposes. Transport time meters additionally use ultrasound like Doppler meters, but instead of bouncing the sound waves off particles in the water like Doppler flow meters, they send ultrasound waves between two sensors separated from each other by a certain distance along the size of the pipe and uses the transmission time of the sound waves to calculate the speed of the water flow. Because the pace of sound in the water is thought, the speed of the water can be calculated primarily based on the offset in ultrasonic wave transmission time that happens as a end result of speed of the water.
Transmission time meters can be costly relative to Doppler circulate meters as a end result of many sensors and complex set up concerned. They could be more accurate due to the capacity to split the move into horizontal cross sections and measure the speed of each section.
Flow unit measurement strategies in full tube purposes
Venturi meters
Venturi circulate meters use the Venturi effect to measure move in a full or pressurized pipe by utilizing the converging section of the pipe to limit the move. According to the continuity equation, the cross-sectional space of the converging part is small and subsequently the speed is greater in the throat. Due to vitality conservation and Bernoulli’s principle, higher velocities in the throat end in a drop in throat strain. The move fee can then be decided by measuring the stress drop in the convergent part and calculating the flow price utilizing Bernoulli’s equation. Venturi meters are extra widespread in water metering applications as a result of the pressure measurement ports can turn into clogged in wastewater functions.
Magnetic flowmeter
The electromagnetic circulate meter works by making use of a magnetic subject to the fluid passing through 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 distinction is proportional to the speed 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 because the adjacent pipe, so the magnetometer causes no extra head loss. For essentially the most half, magnetometers are used for full (pressure) pipe applications, but nowadays open channel magnetometers can also be used.
Turbine flowmeter
A turbine move meter is a mechanical move meter that makes use of a rotating turbine in circulate to measure the circulate of water in a pipe. The speed of the turbine is proportional to the rate and the flow rate can then be calculated using the continuity equation. Turbine flow meters are solely used for water applications because of potential issues with wastewater solids collection and clogging turbines.
Conclusion
There are many ways to measure move. Each method has completely different benefits, disadvantages and accuracy in different functions.
It is necessary to understand the characteristics of varied circulate measurement techniques to assist select the best kind of circulate metering in your software or to correctly interpret the circulate measurements of present move meters. Tools like Apure (IoT-based water information analysis) help to look at measurements collected by flow meters and carry out diagnostics to know circulate meter performance and shortly process and analyze the information. Contact us for technical or product service assist.
More articles on flow meters:
Mass move rate vs volumetric circulate rate
Relation between circulate and strain
Ultrasonic circulate meter working principle
Difference between flow meter and flow transmitter