Vortex flowmeters are based on taking into account the periodicity of pressure changes that are formed in the flow after a certain obstacle in the pipeline, or during the oscillation and vortex formation of the jet.
Dignity
The first devices of this type appeared in the 60s of the last century. Their main inconvenience was the small range of measurement parameters and a significant error. Electronic modern vortex flowmeter has become more perfect, efficient and has acquired many advantages, which include the following:
- relative simplicity of the measurement system;
- data is always stable, independent of temperature and available pressure;
- high precision measurements;
- measuring linear signals;
- robust and simple design;
- wide measuring range;
- static elements;
- Self-diagnosis function available on some models.
Flaws
VortexThe Rosemount flowmeter is designed for use in pipes with diameters from 20 mm to 300 mm, as smaller pipelines are characterized by intermittent vortex formation, and larger pipelines are difficult to operate. At the same time, it is not possible to use it at a low flow rate, due to the complexity of measuring the signal and a significant decrease in pressure. Also, vibration and sound types of pulsation affect the operation of the device. The vibrating pipeline and compressors act as interference. Their elimination is possible with the help of a jet straightener mounted at the inlet, or by installing an additional transducer with opposite connection and electronic filters, in case of difference between the measuring signals and pulsation frequencies.
Classification
There are three options for devices, divided by type of converter:
- A vortex flow meter in which an immovable body plays the role of a primary transducer. Gradually, flying vortices form in it on both sides after bypassing the immovable body, due to which the pulsation is formed.
- Mechanisms with a rotating flow of the primary converter, which create a pressure pulsation due to the adoption of a funnel shape in the expanded part of the pipeline.
- Vortex flowmeters with a jet as a transducer. In this case, the pressure pulsation is provided by jet oscillations.
The first two options are more suitable for the definition of a vortex flowmeter. But in view of the changeable nature of the movement of the flow of the thirdtype, 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 bypassing the body, the flow changes the trajectory of the direction of the jets, at the same time their speed increases and the pressure decreases. The reverse change occurs after the midsection of the object. On its back, low pressure is formed, and on the front - high. After the passage of the body, the boundary layer moves away, and under the influence of low compression, a vortex is created, as well as when the trajectory changes. This is typical for both lobes of a streamlined body. Alternate formation of vortices is carried out on both sides, since they interfere with the formation of each other. This marks the creation of the Karman track.
Special wrap body has self-cleaning working surfaces thanks to vortices, even in heavily polluted environments, they are always clean.
Dimensions and rapidity of the flow are directly proportional to the periodicity of the occurrence of vortices, which corresponds to the speed at a constant size, and as a consequence of the volume flow. If stable vortex formation occurs at low flow rates, then the flow meter will measure 20 l/min.
Streamlined structure body
The vortex flowmeter is usually based on a prismatic elementtrapezoidal, triangular or rectangular. 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.
The vortex flow meter in some cases can use two streamlined devices to increase the output signals, in which case they are located at a set distance. On the side parts of the rectangular second prisms there are piezoelectric elements hidden by elastic thin membranes, due to which there is no possibility of exposure to acoustic interference.
Types of transformations
There are several ways to transform output signals from vortex changes. The most widespread are the speed of flows from streamlined elements and systematic changes in pressure. The sensing element consists of one or two conductor type hot-wire anemometers. An ultrasonic, integrating, capacitive and inductive flow transducer is used. For proper operation, the vortex flowmeter must have a free, flat section of pipe in front of it.
Difficulties in operation in pipes with an increased diameter are caused by the following reasons:
- decrease in regularity of vortex formation;
- poor vortex shedding performance;
- decrease in the total number of fluctuations.
Funnelvortex flowmeters: principle of operation
In these devices, the converters have a mechanism that ensures the twisting of the flow transmitted through a part of the pipeline to its expanded side or through small cylindrical nozzles. A shape in the form of a funnel is formed in a 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 displacement of the core, while it is equal to the volume flow rate or linear velocity. Conductor hot-wire anemometers or an electromechanical element convert the speed or pulsation frequency for the measuring channels. The process consists of two phases: first, the transfer of the volume flow to the frequency of the ongoing vortex precession is formed, then the frequency is converted 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 that, in the rim pipe, the nature of the movement changes, the jet oscillates.
The jet, squeezed in the lower element of the diffuser in the hydraulic return converters, only partially exits through the outlet pipe. In circlingthe upper channel diverts the proportion of the jet and when passing through the first nozzle, it is transferred to the lower position in the flow from the second nozzle. Then a part is separated and passes into the bypassing upper channel, the process of oscillations occurs after the transfer down, while there is a simultaneous change in pressure in both sides of the flow.
This type of converter is more rational. Due to it, a strict course of oscillation is formed and there is a direct effect of the oscillation frequency on the flow rate.
Yokogawa's vortex meters are most widely used in pipelines with a small diameter, up to a maximum of 90 mm. In some cases, devices of this type are used as replacements for partial transducers.
Today, the quality of manufacturing flowmeters is constantly evolving and new features are emerging, despite the fact that such devices have a fairly long period of use. Developers are looking for more efficient design solutions, creating technological options that are more effective.
