Vortex Flow Meters
Yokogawa released the world's first vortex flowmeter in 1968. Thanks to its long-term stability and high accuracy, our customers have achieved significant improvements in productivity over the past forty years. In response to ever changing market needs, Yokogawa has gone on to release high temperature, cryogenic, dual-sensor, reduced bore, and FOUNDATION Fieldbus communication versions of this product.
Yokogawa's forty+ years of Vortex Flowmeter innovation.
-
For high temperature or cryogenic flow measurement.
Vortex Flow Meters - Principle of Operation
Vortex Flow Meters use the Von Karman Effect to measure the rate of flow of a fluid or gas.
What is the Von Karman Effect?
Early in the 20th century, a Hungarian-American mathematician and physicist, Theodore von Karman, discovered that a fluid or gas flowing perpendicularly pass a bluff body would generate alternating vortices on both sides of the body. The path of these vortices is called the Von Karman Street.
Von Karman found that if the frequency of these vortices was measured, that the frequency is proportional to the flow velocity that is generating the vortices. This frequency is called the Karmen Vortex Frequency. The relationship of the fequency and the flow velocity can be mathematically expressed with the following formula:
From the equation, we can see that the frequency is proportional to the velocity. If we can measure the frequency (f), know the Strouhal number (St), know the shedder bar width (d); we can solve for v (velocity).
How do we measure the frequency of the vortices?
As vortices form and pass the shedder bar (the bluff body), they create a low pressure as compared to the rest of the fluid. This low pressure produces a differential pressure (dp) across the shedder bar. The high pressure side of the dp exerts stress on the shedder bar in the direction of the low pressure. As the location of the low pressure side alternates due to the vortices switching from side-to-side, the change in direction of the exerted force causes the shedder bar to oscillate. This oscillation is equal to the Karmen Vortex Frequency.
There are several methods in the marketplace to measure the oscillation. Diaphragms or capacitance sensors are two of the more common; but, the best method is the use of Piezo-electric crystal sensors. These sensors, when compressed, produce an electric signal that can be sent to the Flow meter's electronics. Now that the Karmen Vortex Frequency is measured (and we know the St and d), the flow meter electronics can do simple calculations to determine volumetric flow through the pipe.
What are the advantages of using Vortex Flow Meters?
- High Accuracy
The accuracy of the vortex flow meter is ±1% (pulse output) of the indicated value for both liquids and gases and is higher compared to orifice flow meters. For liquids, an accuracy of ±0.75% is available depending on the fluid type and their conditions.
- Wide Rangeability
Rangeability is defined as the ratio of maximum value to minimum value of the measureable range. It is braod rangeability the allows vortex flow meters to operate in processes where the measuring point may fluctuate greatly.
- Output is Proportional to Flow Rate
Since the output is directly proportional to the flow rate (flow velocity), no square root calculation is needed, while orifice flow meters require square root calculations.
- No Zero-point Fluctuation
Since frequency is poutput from the sensor, zero-point shift does not occur.
- Minimal Pressure Loss
Since only the vortex shedder is placed in the pipe of the vortex flow meter, the fluid pressure loss due to the small restriction in the flow piping is small compared with flow meter a having an orifice plate.
- Fieldbus technology introduced to realize predictive and preventive maintenance.
- ISAE to improve the reliability of diagnosis and parameter setting, utilizing data collected by PRM.
- Yokogawa's integrated solution contributed to reliable and efficient operation.
- All the instrument information is fully integrated with the instrument management system.
Measuring energy consumption is an important factor in the quest to improve energy efficiency. Efficient and accurate metering is paramount to determining excess use, along with an accurate picture of where the steam is being used. The more accurate and reliable measurements that are made, the more informed decisions can be taken that affect costs and product quality. Traditionally the most common method of steam metering is the orifice plate and differential pressure transmitter technique. General areas of concern with this type of measurement are the orifice plate's susceptibility to wear introducing immediate inaccuracies, the relatively high permanent pressure losses introduced into the system by the orifice place and the small measuring range, typically 3:1.
Yokogawa's digitalYEWFLO Reduced Bore Type Vortex Flow meter features a cast stainless steel body and a concentric reducer and expander that enable stable flow rate measurements in low-flow conditions. This expands the range of measurements that can be performed, from the higher flow rates down to the lower end of the flow span, which is normally difficult for Vortex Flow meters, and ensures stable and accurate flow rate output.
Progress in digital signal processing and network technologies has enabled advanced functions which cannot be achieved by traditional field devices with 4-20 mA signal, to be implemented on field devices. Standardization of international fieldbus specifications, notably the FOUNDATION™ Fieldbus, has enabled users to build optimum field networks comprised of freely chosen field devices from various device vendors.
Vortex flow meters utilize a fluid phenomenon in which frequencies of Karman vortex streets released from a shedder bar inserted in a flow are proportional to flow velocities.
Vortex flow meters have been appreciated by users as volume flow meters, which can, in principle, be applied to any flow measurement of liquid, gas, or steam. Volume flow measurement is enough for substances with small variations in density such as liquid.
The operating principle of the vortex flow meters YEWFLO series, which first became commercially available in 1979, is based on the phenomenon in which the frequency of a Kàrmàn vortex train that occurs from a vortex shedder placed in a fluid flow, is proportional to the speed of that flow.