A knowledge of the actual flow velocities in the feed well of gravity settlers of the Bayer process is essential for their optimal design and operation. The velocities to be measured range from 0 to 50 cm/s. The required meter should be portable, rugged, caustic resistant to temperatures approaching that of boiling water and useable in an industrial confined environment. An intrusive flowmeter meeting these requirements was designed and tested. The working principle of the meter is based on the electrolysis of water producing hydrogen and oxygen gases. The electrolysis current is related to the mass transfer of reactants and products to and from the electrodes. This mass transfer is affected by the fluid flow in the neighborhood of the electrodes. Calibration curves thus permit the measurement of fluid flow in the 5 to 50 cm/s range from a simple electrical current reading. The precision is of the order of 10 percent but could be improved by incorporating a feedback system to maintain the electrode potential constant. The low velocity limitation is caused by fluid convection induced by the generation of gas bubbles.
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