Table of Contents
What is circulate units?
Continuity of flow equation
Common flow unit metering strategies in open channels
Eyeball technique
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 circulate units?
Flow price is the amount of fluid that passes via a unit of time. In water resources, flow is usually measured in cubic toes per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or quite so much of different units. The measurement of water resource flow is important for applications similar to system management, billing, design and heaps of different functions. There are a number of ways to measure circulate in a water resource system. This article outlines a variety of the extra widespread methods of move measurement and offers some helpful details about circulate items 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 end of the pipe must flow out of the other finish. This also means that the circulate within the pipe is the same at any level alongside the size of the pipe. The continuity equation could be expressed as
Flow = Velocity * Area
The concept of continuity in steady state circumstances leads to the product of velocity * area being equal to a relentless at any level in the pipe. This is a useful precept for making flow measurements, as proven beneath.
This is an instance of utilizing 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 toes. Flow rate = 10 toes per second * 10 sq. toes = one hundred cubic toes per second.
Common circulate unit metering strategies in open channels
Eyeball technique
It is sometimes helpful to estimate the move velocity and cross-sectional area by eye after which multiply the move velocity by the realm to acquire the move velocity (continuity equation). A ruler or tape measure can be utilized to enhance the accuracy of cross-sectional space measurements, and a stopwatch can be utilized to enhance velocity measurements by timing floating particles moving a set distance. The eyeball methodology can be utilized to estimate flow when only an “order of magnitude” of flow is required or when the circulate 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 recognized and uniform flow circumstances exist, the Manning’s equation can be used to calculate flow by measuring depth only. The Manning’s equation is an empirical equation that describes the relationship between circulate fee in an open channel under uniform flow 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 usually are not relevant to steadily altering circulate situations, corresponding to backwater situations upstream of a dam or weir.
The depth move methodology of move measurement is extra correct than the “eyeball” technique. The major problem with depth-only circulate measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform circulate conditions. This methodology is commonly used with ultrasonic move meters to estimate the flow 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 assistance of complex river hydraulic models to account for complex channel geometry and channel friction circumstances.
Main equipment
The primary gadget is used to measure circulate in open channels, utilizing buildings corresponding to flumes, weirs or dams, to measure circulate by measuring depth. The measured depth can then be converted to a move price using an equation or rated curve equation.
Primary gadgets work by forcing the move via a path of critical depth, for instance on the prime of a weir or on the throat of a flume. In technical phrases, the important depth is defined because the depth of the minimum specific energy state that results in a particular discharge. In practice, this minimum state of power implies that just one circulate corresponds to the crucial depth. Therefore, measuring only the depth produces a measurement of the corresponding flux and is therefore known as a “primary” device.
Primary devices are a really handy technique of circulate measurement as a outcome of the depth may be measured from above the move with out the want to insert a sensor within the water. This makes major move meters extra dependable and simpler to keep up. A disadvantage of primary devices is that they can trigger head loss and backwater in the system. Primary gadgets are sometimes considered to be probably the most correct methodology of measuring open channel move.
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 price is then calculated by multiplying the flow area by the rate utilizing 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 uses the Doppler shift in the mirrored 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 as a result of the probes are comparatively small and they are often put in in current sewer pipes without inflicting vital head loss within the pipe. This also allows them for use for short-term or short-term move metering functions for sewer studies. one drawback of AV meters is that the sensor must be put in within the fluid. In sewers, this requires frequent upkeep to clean the sensor. AV meters are often thought-about much less accurate than main move meters as a outcome of main gadgets only need to measure depth and depth measurements are extra correct than velocity measurements.
Transport time meters
Transport time meters had been developed in the oil trade to precisely measure flow in giant 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, however as a substitute of bouncing the sound waves off particles within the water like Doppler circulate meters, they ship 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 rate of the water circulate. Because the velocity of sound within the water is understood, the velocity of the water may be calculated primarily based on the offset in ultrasonic wave transmission time that happens as a result of speed of the water.
Transmission time meters can be expensive relative to Doppler move meters due to the many sensors and sophisticated installation concerned. They may be extra correct due to the capacity to separate the flow into horizontal cross sections and measure the speed of each section.
Flow unit measurement methods in full tube purposes
Venturi meters
Venturi move meters use the Venturi effect to measure move 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 space of the converging section is small and due to this fact the speed is greater within the throat. Due to power conservation and Bernoulli’s principle, higher velocities in the throat result in a drop in throat stress. The circulate fee can then be decided by measuring the pressure drop within the convergent part and calculating the move price using Bernoulli’s equation. Venturi meters are extra widespread in water metering functions as a result of the strain measurement ports can become clogged in wastewater functions.
Magnetic flowmeter
The electromagnetic flow meter works by applying a magnetic area 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 distinction is proportional to the speed of the water, and the continuity equation can then be used to calculate the flow fee.
An advantage of the magnetometer is that the metering part is the same diameter because the adjacent pipe, so the magnetometer causes no additional head loss. For the most half, magnetometers are used for full (pressure) pipe applications, however 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 circulate to measure the circulate of water in a pipe. The speed of the turbine is proportional to the speed and the move rate can then be calculated utilizing the continuity equation. Turbine circulate meters are only used for water functions as a end result of potential issues with wastewater solids assortment and clogging turbines.
Conclusion
There are some ways to measure circulate. Each method has totally different benefits, disadvantages and accuracy in different applications.
It is important to understand the characteristics of various move measurement techniques to assist select the best type of move metering in your application or to properly interpret the move measurements of current move meters. Tools like Apure (IoT-based water knowledge analysis) help to examine measurements collected by circulate meters and carry out diagnostics to know circulate meter efficiency and shortly process and analyze the information. Contact us for technical or product service assist.
More articles on move meters:
Mass circulate fee vs volumetric flow rate
Relation between flow and stress
Ultrasonic circulate meter working precept
Difference between flow meter and circulate transmitter
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Table of Contents
What is move units?
pressure gauge nuova fima ราคา of flow equation
Common flow unit metering strategies in open channels
Eyeball methodology
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 flow units?
Flow fee is the amount of fluid that passes by way of a unit of time. In water resources, circulate is commonly measured in cubic toes per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or quite lots of other items. The measurement of water resource flow is important for functions corresponding to system control, billing, design and many other purposes. There are several ways to measure move in a water useful resource system. This article outlines a variety of the more common strategies of flow measurement and provides some helpful information about move units measurement.
Continuity of flow equation
For water flowing in a pipe beneath steady-state situations (i.e., not varying with time), continuity implies that water flowing into one end of the pipe must flow out of the opposite finish. This also signifies that the flow within the pipe is identical at any level along the length of the pipe. The continuity equation can be expressed as
Flow = Velocity * Area
The idea of continuity in regular state situations results in the product of velocity * area being equal to a constant at any point in the pipe. This is a useful precept for making flow measurements, as shown below.
This is an example of utilizing the continuity equation to calculate circulate. Velocity is measured at 10 ft per second and the cross-sectional area of the move is measured at 10 sq. feet. Flow rate = 10 ft per second * 10 square feet = a hundred cubic toes per second.
Common flow unit metering methods in open channels
Eyeball methodology
It is typically helpful to estimate the move velocity and cross-sectional space by eye after which multiply the circulate velocity by the world to acquire 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 improve velocity measurements by timing floating particles transferring a set distance. The eyeball technique can be utilized to estimate circulate when solely an “order of magnitude” of flow is required or when the move fee is just 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 move conditions 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 connection between move rate in an open channel beneath uniform move circumstances and depth, slope and channel friction coefficient (Manning’s n). Uniform flow signifies that depth doesn’t differ with the length of the conduit or channel. Flow measurements utilizing Manning’s equation for depth aren’t applicable to gradually altering circulate conditions, corresponding to backwater circumstances upstream of a dam or weir.
The depth flow methodology of circulate measurement is more correct than the “eyeball” technique. 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 method is commonly used with ultrasonic circulate meters to estimate the move 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 help of complicated river hydraulic models to account for complicated channel geometry and channel friction conditions.
Main tools
The primary device is used to measure circulate in open channels, utilizing buildings similar to flumes, weirs or dams, to measure move by measuring depth. The measured depth can then be transformed to a circulate fee using an equation or rated curve equation.
Primary devices work by forcing the flow through a path of important depth, for example on the top of a weir or at the throat of a flume. In technical terms, the crucial depth is defined as the depth of the minimum specific vitality state that results in a particular discharge. In apply, this minimum state of power signifies that only one flow corresponds to the important depth. Therefore, measuring solely the depth produces a measurement of the corresponding flux and is therefore referred to as a “primary” system.
Primary devices are a really handy method of flow measurement as a end result of the depth may be measured from above the move with out the necessity to insert a sensor in the water. This makes main flow meters more reliable and simpler to keep up. A drawback of primary units is that they’ll cause head loss and backwater in the system. Primary gadgets are sometimes considered to be probably the most accurate method of measuring open channel flow.
Surface Velocity Meters
An area 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 area utilizing the geometry of the pipe or channel. The circulate rate is then calculated by multiplying the move area by the velocity utilizing the continuity equation, hence the name “AV meter”. Velocity is typically measured utilizing a Doppler sensor, which displays ultrasound waves again from particles in 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 sometimes used to measure open channel move in sewers as a result of the probes are comparatively small and they are often put in in present sewer pipes without inflicting vital head loss in the pipe. This additionally permits them to be used for momentary or short-term flow metering purposes for sewer research. 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 sometimes considered less correct than main circulate meters because primary units only must measure depth and depth measurements are extra correct than velocity measurements.
Transport time meters
Transport time meters had been developed in the oil trade to precisely measure circulate in giant pipelines. They have been used with some success for open channel flow in water metering applications. Transport time meters additionally use ultrasound like Doppler meters, but as an alternative of bouncing the sound waves off particles in the water like Doppler circulate 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 speed of the water move. Because the velocity of sound within the water is thought, the velocity of the water can be calculated primarily based on the offset in ultrasonic wave transmission time that occurs as a outcome of velocity of the water.
Transmission time meters may be costly relative to Doppler move meters because of the many sensors and complex set up involved. They can be extra correct due to the capacity to split the move into horizontal cross sections and measure the speed of every part.
Flow unit measurement strategies in full tube applications
Venturi meters
Venturi move meters use the Venturi impact to measure move in a full or pressurized pipe by utilizing 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 subsequently the rate is larger in the throat. Due to vitality conservation and Bernoulli’s precept, greater velocities in the throat lead to a drop in throat strain. The circulate price can then be determined by measuring the stress drop within the convergent part and calculating the flow fee utilizing Bernoulli’s equation. Venturi meters are more widespread in water metering applications as a outcome of the strain measurement ports can turn out to be clogged in wastewater purposes.
Magnetic flowmeter
The electromagnetic move meter works by making use of a magnetic area 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 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 move price.
An advantage of the magnetometer is that the metering section is the same diameter as the adjoining pipe, so the magnetometer causes no additional head loss. For essentially the most part, magnetometers are used for full (pressure) pipe applications, however nowadays open channel magnetometers can additionally be used.
Turbine flowmeter
A turbine move meter is a mechanical move meter that makes use of a rotating turbine in move to measure the move of water in a pipe. The pace of the turbine is proportional to the speed and the flow price can then be calculated using the continuity equation. Turbine circulate meters are solely used for water applications as a end result of potential issues with wastewater solids assortment and clogging turbines.
Conclusion
There are many ways to measure flow. Each technique has completely different advantages, disadvantages and accuracy in numerous purposes.
It is important to grasp the characteristics of varied flow measurement techniques to assist select the best sort of move metering for your utility or to correctly interpret the move measurements of present move meters. Tools like Apure (IoT-based water knowledge analysis) help to look at measurements collected by circulate 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 flow fee vs volumetric move fee
Relation between flow and strain
Ultrasonic circulate meter working precept
Difference between flow meter and circulate transmitter