THE ACCURACY OF A MONOFIBER OPTICAL PROBE

The optical probe is an instrument commonly used for investigation of dense multiphase flows, e.g. sprays or bubbly flows. The method is based on measuring of the amount of light reflected from a tip of an optical fiber, which is placed in the flow. This amount depends on the refractive index of the surrounding media and the instrument can hence detect the presence of a bubble or drop at its sensitive tip. The intrusive nature of the instrument decreases the measurement accuracy. In this contribution, the accuracy of optical probe in a bubbly flow is deduced from high-speed imaging of bubble-probe interaction. A dimensionless criterion useful for the estimation of the error of indicated void fraction is developed. It is also observed that the probe deformability may significantly decrease the probe accuracy.