Particle Scattering Photography Approach for Poorly Illuminated Multiphase Reactors. I: Theoretical Model and Simulation

Abstract

The great challenge is encountered in photographic measurement, with regard to distinctly distinguishing the particle profiles from the background (continuous phase) in poorly illuminated multiphase reactors. In this work, a novel approach utilizing particle scattering is proposed to enhance the brightness contrast. The theoretical basis of this approach is described in detail. A single particle scattering model based on noncoherent scattering hypothesis is built up to evaluate the scattering property. The quantitative relationships between scattering flux and scattering coefficient/absorption coefficient are established. Furthermore, the partial light fluxes projected onto the focal plane by single particles of different sizes are also calculated. Combined with the particle scattering and dispersion, an optimal particle size of ∼0.5–1.5 μm is designated. On this basis, four representative oxide powders are tested as scattering particles, i.e., TiO2, Al2O3, CuO, and SiO2; in addition, the TiO2 particles are found to perform the best, based on the theoretical simulation.

Particle Scattering Photography Approach for Poorly Illuminated Multiphase Reactors. II: Experimental Validation and Optimization

“…When the particle size increases by a factor of 10, N mc decreases to 1/1000 of the original. Considering the TiO 2 density, the particle concentration C mc is set to ∼22.5 g/L, according to the scattering constraints described in ref 13. From the pre-experiments, it is noticed that trace scattering particles (≪22.5 g/L) have an obvious ability to improve the image quality greatly.…”

“…8 Many nonintrusive techniques have been developed, including electrical resistance tomography (ERT), electrical capacitance tomography (ECT), 9,10 and computerized tomography (CT). 11,12 As depicted in Part I, 13 optical photography is used more and more for the particle measurement in recent years. Especially, invasive optical photography using a vision probe can well overcome the limits of noninvasive optical photography, such as dense suspensions, 14,15 opaque wall, 16,17 and viewport installation.…”

“…21 However, as low-brightness dispersed phase being measured, both dispersed and continuous phases are images of low grayness, corresponding to an A-B interval in the photographic characteristic curve in Figure 1 in Part I. 13 It is very difficult to distinguish the objects (the dispersed phase) from the background (the continuous phase) in these images.…”

“…However, these approaches will cause much more serious invasive errors. 13 In the work of Laakkonen et al, back illumination by a powerful light source outside of the tank was implemented in a small transparent tank. 25 High-quality images of the bubbles were obtained, and, in addition, this operation did not disturb the flow field.…”

“…25 High-quality images of the bubbles were obtained, and, in addition, this operation did not disturb the flow field. However, one must say that imaging would be problematic in the following cases: (1) medium or dense particle number density; (2) In Part I, 13 a novel particle scattering photography approach has been proposed. Specifically, when trace tiny particles are added into the measured suspension, the incident light will be scattered into all directions by the particle surfaces, so that the condition of illumination to the measurement volume is improved.…”