Optical ber probing (OFP) is a very useful and practical technique for investigating and monitoring multiphase systems, and it is particularly suitable for simultaneously measuring a bubble's/droplet's chord length, velocity and number density in an industrial-scale apparatus, as well as a laboratory-scale setup. Here, we outline the principles of OFP and propose several types of optical ber probes that meet the requirements for particular purposes of the multiphase systems in chemical engineering processes. We describe measurement methods that use an optical ber probe suitably tuned for liquid lm and foam, as well as for bubble measurement. The basic measurement principle of OFP is very simple: the probe tip's detection of changes in the refraction indices from a gas phase to a liquid phase or vice versa. For example, to precisely measure a bubble's properties such as the chord length and velocity, it is necessary to determine the precise relationship between the process of the optical ber probe's penetration into the bubble and the optical signal. Since the probing signal provides a variety of information due to the complicated interaction of the laser beams, optical ber and gas-liquid interfaces, it is necessary to use both experimental and computational approaches in order to extract the physical meanings of the probe's signals. Using our own fully-3D ray-tracing simulator and well-arranged high-speed visualization setups, we discuss how to improve the measurement accuracy of OFP. We rst computationally analyze the OFP signals under several penetration conditions, and we explain our recommendations regarding how to improve the accuracy of a single-tip optical ber probe used for measurement in multiphase systems. On the basis of our present ndings and the improvement in measurement accuracy, we then propose several applications of OFP to chemical engineering processes.
Ultrasound techniques are applied in various fields such as washing, fine particle manipulation and solid-liquid separation. In the fine particle manipulation, ultrasonic ranging in MHz band is usually employed. Fine particles with μm order in diameter are treated because of limitations of the wavelength. In contrast, we discovered phenomena that mm-order particles dispersed in water are flocculated spherically by irradiating 20-kHz-band-ultrasound. In order to clarify the mechanism of this flocculation, we investigated the sound pressure profiles in the vessel, and the positions and diameters of the flocculated particle swarm, varying the water depth, ultrasound frequency and particle diameter. From these results, the particle swarm was trapped in the anti-node of the standing wave. The diameter of the particle swarm was dramatically changed by subtle control of the frequency. Based on these results, we will propose a new technique capturing and separating sub mm-or mm-order particles by their diameter.
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