Vortex flowmeters are based on taking into account the frequency of pressure changes that form in the stream after a certain obstacle in the pipeline, or during the oscillation and vortex formation of the jet.
Advantages
The first devices of this type appeared in the 60s of the last century. Their main disadvantage was a small range of measurement parameters and a significant error. The modern electronic vortex flowmeter has become more advanced, efficient and has gained many advantages, which include the following:
- the relative simplicity of the measurement system;
- data is always stable, independent of temperature and available pressure;
- high accuracy measurements;
- measuring linear signals;
- reliable and simple design;
- wide range of measurements;
- static elements;
- the presence of a self-diagnosis function in some models.
disadvantages
Rosemount Vortex Flowmeter It is designed for operation in pipes with a diametric size of 20 to 300 mm, since pipelines with a smaller size are characterized by inconsistent vortex formation, and operation with a larger size is quite difficult. At the same time, it is not possible to use at a low flow rate, due to the complexity of signal measurement and a significant reduction in pressure. Also, vibration and sound types of pulsation affect the operation of the device. The vibrating piping and compressors act as interference. Their elimination is possible with the help of a rectifier mounted at the input, or the installation of an additional converter with a counter connection and electronic filters, in case of difference in measuring signals and pulsating frequencies.
Classification
There are three options for devices that are divided by type of converter:
- Vortex flowmeter in which an immovable body plays the role of a primary transducer. Gradually from both sides, flying vortices are formed in it after going around the immovable body, due to which ripple is formed.
- Mechanisms with a rotating flow of the primary transducer, which create pressure pulsation due to the adoption of a funnel shape in the extended part of the pipeline.
- Vortex flowmeters having a jet as a transducer. In this case, the pressure pulsation is provided by the oscillations of the jet.
The first two versions of devices are more suitable for the definition of a vortex flowmeter. But in view of the variable nature of the movement of the flow of the third type, it also belongs to this category. The greatest similarity of the characteristics of the process is noted in the first and third options.
Vortex steam flowmeter with streamlined transducer
When the body is circumvented, the flow changes the direction of the jets, while their speed increases and pressure decreases. The reverse change occurs after the mid-section of the object. Low pressure is formed on its back, and high on the front. After the passage of the body, the boundary layer departs, and under the influence of low compression a vortex is created, as well as when the trajectory of movement changes. This is characteristic of both lobes of the streamlined body. The vortices are alternately formed on both sides, since they interfere with the formation of each other. At the same time, the creation of the Pocket path is noted.
The special flow body has work planes with self-cleaning due to the vortices, even if the environment is highly polluted, they are always clean.
The dimensions and swiftness of the flow are directly proportional to the periodicity of the occurrence of vortices, which corresponds to speed with an unchanged size, and as a consequence of volume flow. If the stable formation of vortices occurs at a low flow rate, then the measurement range of the flow meter will be 20 l / min.
Streamlined body construction
A vortex flowmeter is typically based on a prismatic element of a trapezoidal, triangular or rectangular shape. The design of the first option goes towards the water flow. Given some loss of pressure, such elements form oscillations with sufficient regularity and strength. In addition, special convenience is noted when converting output signals.
In some cases, a vortex flowmeter can use two streamlined devices to increase the output signals, in which case they are located at a set distance. On the lateral parts of the rectangular second prisms there are piezoelectric elements hidden by thin elastic membranes, due to which there is no possibility of exposure to acoustic noise.
Transformation Types
There are several ways to convert the output from swirl changes. The most widespread are the speed of flows from streamlined elements and systematic changes in pressure. The sensitive element consists of one or two conductive type hot-wire anemometers. An ultrasonic, integrating, capacitive and inductive flow transducer is used. For proper operation, the vortex flowmeter must have a free, even part of the pipe in front of itself.
The difficulties of operation in pipes with increased diameter are caused by the following reasons:
- decrease in the frequency of vortex formation;
- low productivity of vortex formation;
- decrease in the total number of vibrations.
Funnel vortex flow meters: principle of operation
In these devices, the converters have a mechanism for twisting the flow transmitted through a portion of the pipeline to its expanded side or through cylindrical small nozzles. A funnel-shaped form is formed in the pipe, and an axis with a vortex core moving around it rotates around its axis. The flow in the upper part has a pressure that pulsates simultaneously with the angular movement of the core, while it is equal to the flow rate or linear velocity. Conducting hot-wire anemometers or an electromechanical element convert the ripple velocity or frequency for the measurement channels. The process consists of two phases: first, the transfer of volumetric flow to the frequency of the precession of the vortex is formed, then the frequency turns into a signal.
Oscillating Jet Flow Meter
Passing through the nozzle, the gas or liquid flow is in a diffuser with a cross section in the form of a rectangle. In some cases, the flow is alternately pressed at a certain moment to different walls of the diffuser. The electrifying property of the jet of the relaxation device reduces the pressure in the upper region of the bypass pipe, while in the lower part it remains the same and a movement is created that transfers the jet to the lower part of the diffuser. After, in the rim tube, the nature of the movement changes, oscillation of the jet occurs.
The jet squeezed in the lower element of the diffuser in the hydraulic return coupling transducers only partially exits through the outlet pipe. A fraction of the jet is diverted to the upper channel, and when passing through the first nozzle, it is transferred to the lower position in the stream from the second nozzle. Then the part is separated and goes into the upper channel, the oscillation process begins after a downward movement, and at the same time the pressure changes on both sides of the flow.
A converter of this type is more rational. Due to it, a strict oscillation course is formed and there is a direct effect of the oscillation frequency on the flow rate.
The most common vortex flowmeter Yokogawa purchased in pipelines with a small diameter, up to a maximum of 90 mm. In some cases, devices of this type are used as a replacement for partial converters.
Today, the manufacturing quality of flowmeters is constantly evolving and new functions appear, despite the fact that such devices have a fairly long period of use. Developers are engaged in the search for more effective design solutions, create technological options that are more effective.