The impact of high order refraction on optical microbubble sizing in multiphase flows

Abstract

The measurements of bubble size and velocity in multiphase flows are important in many researches and industrial applications. It has been found that the high order refraction has great impact on PDA sizing method when the relative refractive index of media is less than one. Although the spatial frequencies of first order refraction and surface reflection become identical at the optimized scattering angle by using previously proposed method, the second order, as well as high order, refractions can not be neglected, because of different spatial frequency and motion direction. The problem has been investigated and a model of phase-size correlation, which also takes the high order refractions into consideration, is introduced to improve the accuracy of bubble sizing. In this study a method based on the recently developed dual mechanisms' scattering model was further developed. Two scattering phases measured by photodetectors are used to calculate the particle size. By utilizing the conversion factor of second order refraction, as well as some high order refractions, the particle diameter can be solved numerically. Hence, the model relaxes the assumption of single scattering mechanism in conventional phase-Doppler anemometry. To demonstrate the capability of the newly developed method, the model was simulated numerically by using Generalized Lorenz Mie Theory (GLMT). The optical parameters such as the measurement volume size, the focus lengths of the sending and receiving lenses, the size and shape of the receiving aperture, the particle size and its trajectory, and the phase conversion factors are used to analyze the performance of the newly developed method. The results of simulation are compared with those based on the conventional method. An optimization method for accurately sizing air-bubble in water has been suggested.

Fringe probing of liquid film thickness of a plug bubble in a micropipe

“…In this paper, a novel optical diagnostic technique [10,11] has been further extended to probe the liquid film thickness in micro capillary two-phase flows. The spatial frequencies from the multiscattering measured by CCD camera are used to determine the film thickness.…”