Many industries and tasks can benefit from the use of steam applications. Steam is a powerful carrier of heat energy since it is cheap, efficient, and safe. Its versatility makes it an indispensable part of any system that needs to disperse heat. However, additional caution is required whenever steam is involved in a procedure. Water droplets from condensation can create excessive wear and tear on equipment, and increased temperatures and pressures pose serious safety concerns. The superheated and saturated steam flow can be measured with equal accuracy using a vortex steam flow meter. The ingenuity of their on-site construction improves the security and productivity of these procedures. The most accurate method for measuring steam mass flow is to use a combination of pressure and temperature sensors and cutting-edge Vortex technology.
What is a Vortex Flow Meter?
Volumetric flow meters, or vortex meters, measure the volume of a liquid as it flows by a vortex created by a bluff object. The vortex shedding principle, by which vortices (or eddies) are shed sporadically downstream of an object, is the basis for operating a vortex steam flow meter. Vortex shedding happens at a rate proportionate to the speed of the liquid passing through the meter.
Vortex flow meters excel when measuring flows where the introduction of moving parts is problematic. They come in various materials, including plastic, brass, and industrial grade. Since there are no moving parts, there is less wear than with other types of flow meters, and the sensitivity to changes in the process conditions is also lower.
Working Principle of Vortex Flow Meter
A vortex flow meter’s cylinder or bluff body is installed in a spool of pipe, where it generates a series of revolving vortices. The fluid’s speed is directly related to the frequency of the alternating vortex. Since the signal is read electronically and converted to a flow rate, there are no moving parts in a vortex steam flow meter that could break down and require maintenance. Similarly to DP flow meters, vortex meters are effective with most clean fluids.
Oscillatory flow meters and vortex shedding flow meters are two more names for vortex flow meters. These flow meters are employed to assess the disturbances in the stream’s downstream vortices due to an impediment. Vortex shedding happens at each barrier at a crucial liquid flow speed. When alternating low-pressure zones are created downstream, a vortex will shed at that precise moment. The barrier can advance into the low-pressure zone because of the irregular pressure zones. Sensors measuring the vortices provide a straightforward method for determining the flow rate. Hence,
A vortex flow meter consists primarily of the following parts:
– The flow meter bore is supported by a strut mounted on the bluff body.
– A sensor that detects the vortex and sends out a voltage spike when one is present.
– A signal amplifying and conditioning transmitter with a flow-rate-related output.
Applications and Limitations
Batching and other intermittent flow applications could be better fits for vortex meters. The reason for this is that if the dribble flow rate is adjusted too low at the batching station, the meter will reach its minimum Reynolds number limit. The magnitude of the resulting inaccuracy increases as the batch size decreases.
A weak-pressure pulse is generated by low-pressure (low density) gases, especially at low fluid velocities. As a result, the meter’s rangeability could be better in such settings, making it impossible to measure low flows accurately. However, the vortex flowmeter is still viable if the lowered rangeability is tolerable and the meter is appropriately sized for normal flow.
The meter’s K factor changes when process fluid coats the bluff body in sludge and slurry operations. Flowmeters that generate vortices should be avoided in these circumstances. However, the application is more likely to be successful if the dirty fluid contains only trace amounts of non-coating solids. A two-year test on a limestone slurry proved this. Even though the bluff body and flow tube were badly scarred and pitted, the K factor had only changed by 0.3% from the factory setting at the end of the test.
Specifications for a Vortex Flow Meter
Measurement Fluid: Fluids in the liquid, gas, steam, or superheated steam phases are preferred.
Temperature of the Process: -29 to 250 °C
Pressure in the Process: the flange pressure rating of -0.1 MPa
Wafer: 15-100 mm
Flange: 15-400 mm
Liquid: Reynolds number-dependent reading error of 0.75%
Steam, Gas: 1.0% of reading (variable concerning flow rate)
Transmission: Dual-mode output support for both analog and transistor contact signals.
Mode of Interaction: Fieldbuses HART 7, HART 5, BRAIN, and FOUNDATION
Measurements and Variability
The volumetric flow rate is closely related to the velocity of the fluid in the pipe and the frequency of vortex shedding. However, the flow must be turbulent for vortex shedding, so other fluid properties have no bearing on the shedding frequency. How often vortices form and how fast the fluid is moving is:
St = f(d/V)
Where St is the Strouhal number, d is the width of the bluff body, V is the fluid’s mean velocity, and f is the vortex scattering frequency. The Strouhal number stays the same over Reynolds numbers, and its value is found by observing how things work.
Since the volumetric flow rate Q is proportional to the product of the mean fluid velocity U and the open cross-sectional area A:
Q = AV = (A f d B) / St
where B is the blockage factor, which is calculated by dividing the area of the pipe’s full bore by the area of the pipe’s open space left by the bluff body. The rewritten form of this equation is as follows:
Q = fK
The meter coefficient is k = (A f d) / (B f d). Similar to how turbines and other flow meters measure frequency, the K factor can be expressed as the number of pulses per unit volume. Counting the pulses over a certain amount of time will thus yield the flow rate. Depending on the flow rate, the nature of the process fluid, and the meter’s size, the vortex’s frequency can be anywhere from one to hundreds of pulses per second. The frequency of gas service is around 10 times that of liquid service.
Ranges of Excellence for a Vortex Flow Meter
To calculate the force exerted by the vortex pressure pulse, we need to multiply the fluid density by the square of the fluid velocity. The meter’s sensitivity is set by the turbulence in the flow and the force needed to activate the sensor. This force must stand out clearly from background noise. For instance, a standard 2-inch vortex meter may measure water flows anywhere from 12 to 230 gallons per minute. The range of the meter will shift if the fluid has a different density or viscosity than water.
Selecting a meter that can accommodate the smallest and largest possible process flows is crucial for reducing measurement noise. The minimum flow rate to be measured should ideally double the meter’s minimum flow detection rate. The meter’s maximum capacity should be at least five times higher than the highest flow rate expected to pass through it.