SIMULTANEOUS MEASUREMENT OF LIQUID AND BUBBLE VELOCITIES IN A CYLINDRICAL BATH SUBJECT TO CENTRIC BOTTOM GAS INJECTION

A vertical bubbling jet was generated in a cylindrical bath by injecting air from a single-hole centric nozzle. The axial and radial velocity components of bubble and liquid in the vertical bubbling jet were measured simultaneously using an electro-resistivity probe and a two-dimensional laser Doppler velocimeter. The output signal of the LDV was processed on a personal computer at a sampling frequency of 2 kHz. Hold signals were eliminated. Discrimination of the bubble and liquid velocities was made by referring to the output signal of the electro-resistivity probe. The accuracy of the present velocity measurement of bubbles and liquid was found to be satisfactory from a comparison with results obtained using an image processing technique for high-speed video pictures, a laser void meter or a two-dimensional electro-resistivity probe.