Vortex Shedding Optical Flowmeter based on Photonic Crystal Fiber.

In the present work we propose a PCF (photonic crystal fiber) based Modal interferometer detector for sensing low flow velocity by detecting the frequency of vortices shed from a bluff body. The proposed novel design encapsulates the interferometric arm inside a metal casing to protect the sensor from harsh process fluids. The characterization of the developed probe is conducted under no flow conditions using a piezo actuator to evaluate the sensor response over wide frequency range (0-500 Hz). The developed sensors shows a reasonably flat response in the tested frequency range. Experiments are conducted by employing the developed sensor behind a bluff body of a vortex flowmeter to measure the frequency of the shed vortices and hence, the fluid flow rate. The low flow rate sensitivity of the vortex flowmeter is improved many folds by using the present sensor and the minimum Reynolds number detected is Re = 5000. A linear trend is observed between the frequency of the vortices and the flow velocity which is desirable for fluid flow measurement. The PCF based interferometric sensor with metal encapsulation makes the vortex flowmeter, sensitive at low flow rates, robust and economical to be used in industrial application.