Flowmeter Types And Their Principles PdfBy Calandre L. In and pdf 27.03.2021 at 00:48 9 min read
File Name: flowmeter types and their principles .zip
Measuring the flow of liquids is a critical need in many industrial plants. In some operations, the ability to conduct accurate flow measurements is so important that it can make the difference between making a profit or taking a loss. In other cases, inaccurate flow measurements or failure to take measurements can cause serious or even disastrous results.
From single-use to magnetic to variable-area to Coriolis, the options in flowmeters are plentiful. Yet there are distinct differences in functionality, accuracy, and certainly price. Ultrasonic sensors that accurately and non-invasively measure through commonly used tubing is an excellent multi-use option that is positioned on the higher end of the price scale.
CORIOLIS MASS FLOW MEASURING PRINCIPLE
From single-use to magnetic to variable-area to Coriolis, the options in flowmeters are plentiful. Yet there are distinct differences in functionality, accuracy, and certainly price.
Ultrasonic sensors that accurately and non-invasively measure through commonly used tubing is an excellent multi-use option that is positioned on the higher end of the price scale. If low unit price is desirable without sacrificing accuracy, then single-use turbine type sensors are a good option particularly if working fluid is low viscosity. If higher viscosity working fluids are involved, the single-use flow through disposable ultrasonic sensors are the best fit. Single-Use flowmeters Figure 1 are used in high hygiene applications such as biopharma, food, or semiconductor fabrication when a CIP option is not optimal.
Sensor types include invasive sensors that come in contact with the working fluid and are discarded after each use and non-invasive models that do not come in contact with the working fluid and are therefore reusable. Given the high value placed on typical working fluids, sensor reliability, accuracy, and compatibility with the workflow are key requirements for single-use flowmeters. If extremely tight accuracies are desired, Coriolis Snapshot: Extremely high accuracy and no pressure drop.
The meters track mass flow and offer a very high turn-down ratio. Yet initial expense is high, clogging can occur, and meters are larger in overall size. Coriolis flowmeters offer true mass flow measurement through two designs: a single tube or two parallel tubes. They operate via an oscillation which is induced in the tube s at a reference frequency.
Among the most accurate of technologies available, Coriolis flowmeters are suitable for a wide and growing range of gas and liquid applications. These devices provide multiparameter data on mass, density, and temperature. They are used in pharmaceutical manufacturing, wastewater treatment facilities, nuclear facilities, natural gas measurement and custody transfer.
Differential Pressure Snapshot: Very high accuracy, multiple calibrations, outputs and size. At the same time, this model can be used with water or gases only and cannot handle particulates.
It also requires power. Differential pressure flowmeters Figure 2 measure changes in pressure to determine flow velocity. They feature a flow-restrictive orifice or laminar flow element that evaluates the pressure drop through the restriction. The pressure drop between upstream and downstream points is proportional to the rate of flow.
This technology works well when no moving parts are desired, or when an ultrafast response time is required. Differential Pressure flowmeters are typically found in more industrial applications, such as measuring the output of fuels for example, benzines or jet fuel , in specialty chemical manufacturing, simple water measurement testing, or on aquafarms.
They are also used in labs to measure and control the flow of gases when mixing them or separating them through chromatography. Gear Snapshot: High accuracy; measurement is independent of fluid viscosity. No straight pipe runs required. Accuracy degrades slightly when measuring the flow of low-viscosity fluids.
Gear meters employ oval counter-synchronized rotors gears which are interlocked to rotate with the passing of liquid. The amount of fluid passing through the oval gears is well controlled, giving the meters a high level of accuracy.
Designs are typically rugged and simple, allowing for installation in the most aggressive environments. In fact, gear meters are one of a few types which are suited to high-viscosity fluids.
Used in hydraulics and other applications involving very viscous liquids, gear flowmeters work well in the pulp and paper industry, fuel or oil transfer, and manufacturing. Because the gears are stainless steel, they are ideal for the petrochemical industry or any application incorporating light to heavy oils. Magnetic Snapshot: No obstruction of flow path, no pressure drop, no moving parts. These meters can handle heavy slurries. Yet, the fluid measured must be conductive or water-based, and the meter must be grounded.
Magnetic meters or magmeters are available in two design styles: insertion and full-bore. Coils in the meter produce a magnetic field. When a conductive fluid is passed through the field, a voltage is produced through an electrode in the meter wall or insertion probe; this generated voltage is proportional to the flow.
Magmeters operate by measuring the electrical content of water or other fluids. The magnetic technology contains no moving parts, and the full-bore designs offer no intrusions into the flow stream. They should not be used with low conductivity fluids such as de-ionized water. Paddle Wheel Snapshot: Fast response time. Easy maintenance. Some may be difficult to install. Uses moving parts and requires a full pipe. Paddle wheel meters Figure 3 include those with rotating paddle wheels, propellers, and oscillating disks multi-jet types.
The rotating component is designed to provide a pulse when passing either a magnetic or optical sensor. The frequency of the pulses is proportional to the velocity of the fluid at one point in the pipe or channel. These designs offer relatively high accuracy for their low cost.
Some insertion versions are very easy to install while other styles are more difficult. These meters are also used in utilities and the oil and gas industries and can work with viscous fluids if a turbulent flow is present. Thermal Dispersion Snapshot: No moving parts. Measures the mass of the gas, not the volume, so it is very accurate.
However, the gas must be dry and free of particulates. Response time is fairly slow. Thermal dispersion meters operate with a side-stream flow of gas which is directed through a capillary. The capillary includes two external heater-sensor coils, one downstream from the other. Gas flow carries heat from the upstream coil to the downstream coil. The resultant temperature-dependent resistance differential at each coil is then measured. The gradient at the coils is linearly proportional to the instantaneous flow rate.
With minimal invasiveness and no moving parts, these meters are used for chemical line monitoring, purging instrument air lines, and filtration loading. They may also control the flow in gas mixing and OEM applications. Turbine Snapshot: High accuracy, millisecond response time, along with high pressure and temperature capabilities. Conversely, their moving parts can wear or become clogged. Not for low flow. Turbine meters contain a bladed rotor positioned along the centerline of the flow stream.
The frequency of the pulses is proportional to the velocity of the fluid. Some designs offer high levels of accuracy and can handle slightly higher viscosity fluids than basic propeller-type designs.
Also, some turbine designs meet sanitary guidelines. Irrigation and water purification are two common applications for turbine flowmeters. They are also used in the oil and gas, utilities, and wastewater industries. These meters are not the best choice for low-flow applications.
Ultrasonic Snapshot: Very high accuracy. No pressure drops, no obstruction of flow path and no moving parts. Low maintenance costs. They are priced higher than some other technologies. Not a good choice for low-flow applications.
Ultrasonic meters Figure 4 offer more advanced technology and greater versatility than some other types. These designs measure the frequency shift of an ultrasonic signal that is sent through the fluid. Two types of ultrasonic meters are Doppler and transit-time. Doppler technologies utilize particles or aeration in the fluid as a reflective mechanism to gauge the velocity of the fluid. Transit-time technologies rely on a frequency difference in forward and reverse signals sent though a clean liquid to gauge the velocity of the fluid; the fluid must not have solids or aeration, as they will distort the sonic pulses.
These are ideal technologies to create flow profiles through an existing process, when modifying piping is not possible.
Because of their versatility, ultrasonic flowmeters are used in a long list of industries, including facilities management, pulp and paper manufacturing, chemical manufacturing, and mining. Ultrasonic meters can be used to measure the corrosiveness of slurry fluid flow. Variable Area Snapshot: Easy setup and use with low setup cost. Very low maintenance. Can be used for both liquids and gases. Yet, these meters provide low accuracy and may not withstand caustic media.
No data output or recording capabilities. Variable Area flowmeters Figure 5 are the veterans in the industry and are the most commonly used.
They are also referred to as rotameters. Their design consists of a float—usually a sphere—enclosed in a tube. The float responds to change in velocity of the fluid gas, air, or liquid by moving up or down the flow tube. The variable area principle of operation is: fluid flow velocity raises a float in a tapered tube, increasing the area for passage of the fluid.
The greater the flow, the higher the float rises. The height of the float is directly proportional to the flow rate.
Differential Pressure Flowmeter Technology
A flow meter or flow sensor is an instrument used to measure linear, nonlinear, mass or volumetric flow rate of a liquid or a gas. When choosing flowmeters, one should consider such intangible factors as familiarity of plant personnel, their experience with calibration and maintenance, spare parts availability, and mean time between failure history, etc. It is also recommended that the cost of the installation be computed only after taking these steps. One of the most common flow measurement mistakes is the reversal of this sequence: instead of selecting a sensor which will perform properly, an attempt is made to justify the use of a device because it is less expensive. Those "inexpensive" purchases can be the most costly installations. This page will help you better understand flow meters, but you can also speak to our application engineers at anytime if you have any special flow measurement challenges. First Steps to Choose the Right Flow Meter The first step in flow sensor selection is to determine if the flowrate information should be continuous or totalized, and whether this information is needed locally or remotely.
The operating principle of a Coriolis flow meter is basic but very effective. A Coriolis flow meter contains a tube which is energized by a fixed vibration. When a fluid gas or liquid passes through this tube the mass flow momentum will cause a change in the tube vibration, the tube will twist resulting in a phase shift. This phase shift can be measured and a linear output derived proportional to flow.
A flow meter is used in different types of applications to measure the volumetric flowrate or mass flowrate. The specific application defines the type and capacity of the flow meter. Fluids, gases and liquids, are measured in terms of volumetric flowrate and mass flowrate. There are numerous types of flow meters depending upon the application, the specific fluid and the construction, including materials, of the flow meter.
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