Miniature optical fiber sensor used to measure the local void fraction.

In this report, we propose an optical fiber sensor which can be utilized to measure the void fraction. The sensor consists of two multimode optical fibers. They are glued together at the active part of the sensor. The tip of the probe is ground and polished in order to reflect back, depending upon the refractive indices of the surrounding liquid material and of the probe material, according to Snell's law. The method has been validated by comparison with an electrical probe and photographic methods. The experimental results show that the size of a bubble larger than 0.8 mm can be determined with an accuracy of 15% by using the optical fiber probe, 40μm in diameter. A profile of void fraction for Freon-11 nucleate boiling around the horizontal cylinder is measured.