A NEW INTENSITY MODULATION BASED FIBER OPTIC PROBE FOR BUBBLE SHAPE DETECTION, VELOCITY, AND DIAMETER MEASUREMENTS

In this article a new noncontact fiber optic probe, previously develop ed for bubble velocity measurements, is described. The sensing element is based on the optical interaction between the bubble and two focuse d laser beams. Not only the reflected but also the refracted beams are detected by the probe to perform bubble parameter measurements. The m easurement principle is based on a transit-time technique, used, for e xample, in laser dual focus velocimetry or cross-correlation based mea suring systems. The measurement system makes use of optical fiber comp onents. The probe is designed for measurements on two-phase bubble flo ws without contact between the bubble and the probe tip and with minim al disturbance to the flow in the measurement region. The probe tip di ameter is only 4 mm. No optical access to the flow is necessary becaus e the probe can be installed inside the flow. Performances of the prob e are theoretically and experimentally analyzed. Bubble-laser beam int eraction has been analyzed by developing a special purpose simulation software. The probe was then tested in a hydraulic test rig circulated by a vertical air-water bubble flow at velocities up to 2 m/s and bub ble diameter from 1 to 4 mm. The developed probe was calibrated by a l aser Doppler velocimeter and classical photographic techniques. First results have shown uncertainty values of about 2% (one standard deviat ion) for velocity measurements. (C) 1996 American Institute of Physics .