Vortex Flow Meters
Vortex Flow meter, also known as vortex shedding flow meters or oscillatory flow meter is a device that measures the vibration of the downstream vortexes that is caused by a barrier in the moving stream. However, it is not limited to just measuring liquids, but also gasses and steam. Vortex Shedding or Vortex flow is an oscillating flow that takes place when a fluid, just like air or water go past the bluff body. In this flow, vortices are then created behind the body and detach it to the sides of the body periodically. It can be installed vertically, horizontally, or at any angle as long as they are kept flooded.
The measuring of the velocity is based on a theory or principle, the Karman vortex street. This principle proves that when an obstruction is placed in a path of a flow it can produce a series of vortex or vortices alternating from each side of the obstruction, these frequencies of alternating vortices is proportional to the flow rate being obstructed. The Vortex flow meter uses a shredded bar or bluff bar in the path of the flow, this means that there is a very low-pressure drop across the flow meter. Also, it allows high sensitivity of the readings at low flow rates, with means a large turn down ratio. The design of the flow meter is made up three parts. The 316 stainless steel, the bluff body, and the transmitter.
· The bluff body can vary in shape. It can be square, rectangular, t-shaped, trapezoidal. The dimension of the body depends on the characteristics that you want the flow meter to have. However, testing reveals that linearity, low Reynold number limitation and sensitivity to velocity profile distortion vary slightly with buff body shape. In size, though, the bluff body must have a width that is large enough fraction of the pipe diameter that the entire flow participates in the shedding. Protruding edges must be located in the bluff body on the upstream face to fix the lines of flow separation not minding the flow rate. The bluff body length in the direction of the flow must be a certain multiple of the bluff body’s width.
· The majority of vortex meter use piezoelectric or capacitance- type sensors to detect the pressure oscillation around the body. These detectors respond to pressure oscillation with a low voltage output signal, which has the same frequency. Some sensors are modular, inexpensive, easily replaced and can easily be replaced and can operate over a wide range of temperature ranges from cryogenic liquids to superheated steam. Such sensors can be located both inside and outside. Wetted sensors are stressed directly by the vortex pressure fluctuations, to withstand corrosion and erosion effects, it is protected with hard protective cases. In external sensors, the piezoelectric strain gauges, sense, that the vortex shedding indirectly through the force exerted on the shredder bar. It is preferred on highly erosive or corrosive applications to reduce maintenance costs. The internal sensors provide better rangeability, and they are less sensitive to pipe vibrations.
There are two types of Vortex. It can be irrotational vortices or rotational vortices. Irrational vortex or free vortices are the absence of external forces, a vortex in general usually evolves fairly quickly toward the irrotational flow pattern where the flow velocity is inversely proportional to the distance. Rotational vortex is a vortex which gas non-zero away from the ore, it can be maintained indefinitely in the state only through the application of some extra force, that is not generated by the fluid motion itself. These types of the vortex are used to calculate the speed of the vortex.
Vortex flow meters are usually made with obstruction objects mounted in a flow. The vortex frequency is proportional to the flow and is detected by a pressure sensor, transmitter or ultrasonic sensor. It also has these following features, for it to function properly:
· Accuracy: readings are ± 1 % accurate.
· Power Supply: 110 -120V with a built in power supply
· Range-ability: typical 10:1
· Response time: Fast and could just take up to two seconds
Also, it includes a high-quality analog display, there is also a rest transmitter build in the device. The intelligent signal processing ensures maximum measurement reliability and stability when using the device this is where the anti- shock built within the device gets handy.
Vortex Meters are used in few industries. It can be used in:
· Machinery sector
· Oil and gas industries
· Power plants
· Chemical and petrochemical industries
· Paints, sealants and coating making
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