Measuring particle dynamics in a fluidized bed using digital in-line holography

Abstract

The quantification of three-dimensional (3D) particle behavior in a fluidized bed is crucial for improving the fundamental understanding and engineering design of such multiphase systems commonly used in industry. This work reports recent development and application of digital in-line holography (DIH) on the in-situ measurement of (a) solid circulation rate, (b) particle size distribution, (c) 3D location, and (d) velocity distribution in the particle field. A Hough-transform-based hologram processing algorithm was developed and tested over a range of flow conditions. Using a hopper system for precise control of particle feed rate, real-time solid flow rates and particle size distributions were measured using DIH. These measurements were then compared to high-precision mass flow measurements made using an electronic balance and size-distribution measurements using a QIPIC® particle size and shape analyzer. DIH is then employed to measure particulate flows in a small-scale circulating fluidized bed system by imaging the standpipe region with 12.7 mm ID. Solid circulation rates evolution was measured and its mean value was in good agreement with the pressure-based estimations. Moreover, DIH is demonstrated to be capable of resolving fine particles with 10 – 40 µm in size, resulting from attrition in the bed of solids. Different from large particles that is dominated by gravitational settling, the motion of small particles is mainly affected by the flow, which has great potential to be used to investigate flow conditions around the large particles.