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 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?

Flow rate is the quantity of fluid that passes via a unit of time. In water assets, circulate is often measured in cubic feet per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a variety of different items. The measurement of water useful resource circulate is essential for functions similar to system management, billing, design and lots of other purposes. There are several methods to measure circulate in a water resource system. This article outlines a variety of the extra widespread strategies of move measurement and supplies some helpful details about circulate units measurement.

Continuity of circulate equation

For water flowing in a pipe beneath steady-state situations (i.e., not various with time), continuity implies that water flowing into one end of the pipe should move out of the other end. This also implies that the flow in the pipe is the same at any point alongside the length of the pipe. The continuity equation can be expressed as

Flow = Velocity * Area

The idea of continuity in regular state situations ends in the product of velocity * space being equal to a relentless at any level in the pipe. This is a helpful 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 ft per second and the cross-sectional area of the move is measured at 10 square feet. Flow price = 10 feet per second * 10 square ft = one hundred cubic toes per second.

Common circulate unit metering methods in open channels

Eyeball method

It is typically useful to estimate the circulate velocity and cross-sectional area by eye and then multiply the flow velocity by the area to obtain the move velocity (continuity equation). A ruler or tape measure can be used to enhance the accuracy of cross-sectional space measurements, and a stopwatch can be used to enhance velocity measurements by timing floating debris shifting a set distance. The eyeball method can be used to estimate circulate when solely an “order of magnitude” of move is required or when the move 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 conditions exist, the Manning’s equation can be utilized to calculate flow by measuring depth only. The Manning’s equation is an empirical equation that describes the relationship between move price in an open channel underneath uniform circulate circumstances and depth, slope and channel friction coefficient (Manning’s n). Uniform flow means that depth does not vary with the length of the conduit or channel. Flow measurements utilizing Manning’s equation for depth are not applicable to gradually altering circulate conditions, similar to backwater conditions upstream of a dam or weir.

The depth flow methodology of move measurement is more correct than the “eyeball” methodology. The main problem with depth-only flow measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform move conditions. This methodology 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 assistance of complex river hydraulic fashions to account for complicated channel geometry and channel friction situations.

Main equipment

The main gadget is used to measure move in open channels, using constructions similar to flumes, weirs or dams, to measure move by measuring depth. The measured depth can then be converted to a move fee utilizing an equation or rated curve equation.

Primary gadgets work by forcing the move through a path of crucial depth, for example at the top of a weir or on the throat of a flume. In technical phrases, the crucial depth is outlined as the depth of the minimum specific vitality state that leads to a particular discharge. In practice, this minimal state of energy signifies that only one flow corresponds to the important depth. Therefore, measuring solely the depth produces a measurement of the corresponding flux and is due to this fact called a “primary” gadget.

Primary gadgets are a really handy method of move measurement as a end result of the depth could be measured from above the flow with out the necessity to insert a sensor in the water. This makes main move meters more reliable and easier to take care of. A disadvantage of primary gadgets is that they’ll trigger head loss and backwater within the system. Primary units are often thought-about to be essentially the most accurate methodology of measuring open channel move.

Surface Velocity Meters

An area velocity meter is an open channel move meter that measures move by making two separate measurements of depth and velocity. The depth is converted to a cross-sectional space utilizing the geometry of the pipe or channel. The move rate is then calculated by multiplying the circulate area by the velocity using the continuity equation, therefore the title “AV meter”. Velocity is often measured using 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 floor velocity optically to estimate velocity.

AV meters are often used to measure open channel move in sewers because the probes are comparatively small and they are often installed in current sewer pipes without inflicting significant head loss in the pipe. This additionally permits them to be used for momentary or short-term flow metering applications for sewer research. one disadvantage of AV meters is that the sensor should be installed within the fluid. In sewers, this requires frequent maintenance to clean the sensor. AV meters are sometimes thought-about less correct than main circulate meters as a outcome of main gadgets only have to measure depth and depth measurements are extra accurate than velocity measurements.

Transport time meters

Transport time meters had been developed within the oil business to precisely measure flow in large pipelines. They have been used with some success for open channel circulate 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 circulate meters, they ship ultrasound waves between two sensors separated from one another by a certain distance along the length of the pipe and uses the transmission time of the sound waves to calculate the rate of the water move. Because the pace of sound within the water is known, the pace of the water could be calculated 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 move meters because of the many sensors and complex installation concerned. They may be extra accurate due to the capacity to split the flow into horizontal cross sections and measure the velocity of each part.

Flow unit measurement strategies in full tube functions

Venturi meters

Venturi flow meters use the Venturi effect to measure move in a full or pressurized pipe through the use of the converging part of the pipe to limit the flow. According to the continuity equation, the cross-sectional space of the converging part is small and subsequently the speed is higher in the throat. Due to vitality conservation and Bernoulli’s precept, larger velocities within the throat lead to a drop in throat stress. The move rate can then be determined by measuring the pressure drop in the convergent section and calculating the flow price utilizing Bernoulli’s equation. Venturi meters are more common in water metering functions as a end result of the stress measurement ports can turn out to be clogged in wastewater applications.

Magnetic flowmeter

The electromagnetic circulate meter works by making use of 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 law 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 flow fee.

An advantage of the magnetometer is that the metering section is identical 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 functions, but nowadays open channel magnetometers can be used.

Turbine flowmeter

A turbine flow meter is a mechanical move meter that makes use of a rotating turbine in flow to measure the circulate of water in a pipe. The speed of the turbine is proportional to the speed and the flow rate can then be calculated utilizing the continuity equation. Turbine circulate meters are solely used for water purposes as a outcome of potential problems with wastewater solids collection and clogging turbines.

Conclusion

There are many ways to measure flow. Each method has different benefits, disadvantages and accuracy in several purposes.

It is essential to know the characteristics of varied move measurement techniques to assist choose the right sort of move metering on your application or to correctly interpret the flow measurements of existing move meters. Tools like Apure (IoT-based water data analysis) help to examine measurements collected by move meters and perform diagnostics to understand move meter performance and quickly process and analyze the info. Contact us for technical or product service support.

More articles on flow meters:

Mass circulate rate vs volumetric flow price

Relation between circulate and strain

Ultrasonic circulate meter working precept

Difference between circulate meter and flow 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 methodology

Flow depth (Manning)

Main gear

Surface Velocity Meters

Transport time meters

Flow unit measurement strategies in full tube purposes

Venturi meters

Magnetic flowmeter

Turbine flowmeter

Conclusion

What is move units?

Flow fee is the amount of fluid that passes by way of a unit of time. In water sources, move is often measured in cubic toes per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or quite a lot of other units. The measurement of water useful resource move is necessary for applications similar to system control, billing, design and a lot of other purposes. There are a number of methods to measure flow in a water useful resource system. This article outlines a variety of the extra frequent strategies of move measurement and offers some helpful information about flow items measurement.

Continuity of move equation

For water flowing in a pipe underneath steady-state circumstances (i.e., not varying with time), continuity implies that water flowing into one finish of the pipe must flow out of the opposite finish. This also signifies that the circulate in the pipe is similar at any point alongside the size of the pipe. The continuity equation can be expressed as

Flow = Velocity * Area

The concept of continuity in regular state conditions leads to the product of velocity * area being equal to a constant at any level in the pipe. This is a useful precept for making flow measurements, as shown below.

This is an instance of using the continuity equation to calculate circulate. Velocity is measured at 10 feet per second and the cross-sectional space of the circulate is measured at 10 square feet. Flow rate = 10 ft per second * 10 square ft = a hundred cubic toes per second.

Common circulate unit metering strategies in open channels

Eyeball method

It is sometimes useful to estimate the move velocity and cross-sectional area by eye after which multiply the move velocity by the area to acquire the flow velocity (continuity equation). A ruler or tape measure can be used to enhance the accuracy of cross-sectional space measurements, and a stopwatch can be utilized to enhance velocity measurements by timing floating debris transferring a set distance. The eyeball methodology can be used to estimate move when solely an “order of magnitude” of circulate is required or when the move fee 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 move 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 relationship between circulate rate in an open channel underneath uniform move situations and depth, slope and channel friction coefficient (Manning’s n). Uniform move means that depth doesn’t range with the size of the conduit or channel. Flow measurements using Manning’s equation for depth aren’t relevant to progressively changing flow conditions, similar to backwater situations upstream of a dam or weir.

The depth move methodology of circulate measurement is more correct than the “eyeball” methodology. The main problem with depth-only flow measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform flow conditions. This method is commonly used with ultrasonic move meters to estimate the move 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 complicated river hydraulic fashions to account for complicated channel geometry and channel friction circumstances.

เกจวัดแรงดัน is used to measure move in open channels, using buildings similar to flumes, weirs or dams, to measure flow 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 circulate by way of a path of critical depth, for example on the high of a weir or at the throat of a flume. In technical terms, the important depth is defined because the depth of the minimal particular energy state that ends in a specific discharge. In digital pressure gauge , this minimal state of power means that just one move corresponds to the crucial depth. Therefore, measuring solely the depth produces a measurement of the corresponding flux and is subsequently called a “primary” system.

Primary gadgets are a really convenient technique of flow measurement as a outcome of the depth could be measured from above the circulate without the necessity to insert a sensor within the water. This makes major move meters extra reliable and easier to hold up. A disadvantage of major devices is that they can cause head loss and backwater in the system. Primary devices are often thought-about to be probably the most correct technique of measuring open channel circulate.

Surface Velocity Meters

An space velocity meter is an open channel move meter that measures flow 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 flow space by the rate utilizing the continuity equation, therefore the name “AV meter”. Velocity is usually measured using a Doppler sensor, which displays ultrasound waves back from particles within the fluid and makes use of the Doppler shift in the reflected 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 can be installed in current sewer pipes without inflicting vital head loss in the pipe. This also permits them to be used for temporary or short-term move metering purposes for sewer research. one disadvantage of AV meters is that the sensor must be installed in the fluid. In sewers, this requires frequent upkeep to scrub the sensor. AV meters are sometimes thought of less correct than primary flow meters as a end result of major units only have to measure depth and depth measurements are more accurate than velocity measurements.

Transport time meters

Transport time meters had been developed within the oil industry to precisely measure flow in massive 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 a substitute 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 sure distance alongside the size of the pipe and makes use of the transmission time of the sound waves to calculate the speed of the water flow. Because the pace of sound within the water is known, the velocity of the water may be calculated based on the offset in ultrasonic wave transmission time that occurs because of the velocity of the water.

Transmission time meters could be costly relative to Doppler circulate meters as a outcome of many sensors and complicated installation involved. They could be more accurate as a result of capability to split the move into horizontal cross sections and measure the velocity of every part.

Flow unit measurement methods in full tube applications

Venturi meters

Venturi flow meters use the Venturi effect to measure flow in a full or pressurized pipe through the use of the converging section of the pipe to limit the circulate. According to the continuity equation, the cross-sectional area of the converging section is small and subsequently the velocity is larger in the throat. Due to power conservation and Bernoulli’s principle, larger velocities in the throat lead to a drop in throat stress. The circulate fee can then be determined by measuring the pressure drop within the convergent part and calculating the circulate rate using Bernoulli’s equation. Venturi meters are more common in water metering purposes because the pressure measurement ports can become clogged in wastewater functions.

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 difference that could 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 circulate rate.

An advantage of the magnetometer is that the metering section is the same diameter as the adjoining pipe, so the magnetometer causes no extra head loss. For the most part, magnetometers are used for full (pressure) pipe purposes, but these days open channel magnetometers may also be used.

Turbine flowmeter

A turbine circulate meter is a mechanical move meter that makes use of a rotating turbine in flow to measure the flow of water in a pipe. The velocity of the turbine is proportional to the speed and the flow price can then be calculated utilizing the continuity equation. Turbine flow meters are solely used for water purposes as a result of potential problems with wastewater solids assortment and clogging generators.

Conclusion

There are many ways to measure flow. Each technique has totally different advantages, disadvantages and accuracy in numerous applications.

It is essential to know the characteristics of various circulate measurement methods to help select the proper sort of flow metering in your utility or to correctly interpret the circulate measurements of current move meters. Tools like Apure (IoT-based water data analysis) assist to examine measurements collected by circulate meters and carry out diagnostics to understand move meter performance and rapidly process and analyze the information. Contact us for technical or product service assist.

More articles on move meters:

Mass move fee vs volumetric move rate

Relation between move and strain

Ultrasonic move meter working principle

Difference between move meter and flow transmitter