Solid and gas distributions are tomographically quantified as a function of position with high resolution in a series of laboratory fluid beds containing air and polyethylene particles. The resolution used is 0.4 mm by 0.4 mm by 3 mm. The laboratory models are Plexiglas columns of 10 cm in diameter and the settling bed LID ratios vary between one and three. Large particles (up to 1.5 mm in diameter) of high density polyethylene and linear low density polyethylene are used. The superficial gas velocities vary from the minimum fluidization velocity to 50 cmIs. In this paper, the analysis of fluid bed CAT scanner images is extended to show bubble, emulsion and dense phase distribution. The analysis is also used to determine the bubble diameter and to predict the flow direction of solid particles as well as the velocity of descending solids, The voidage frequency distributions of a bed at different gas flow rates are compared to each other and the voidage threshold values corresponding to gas, emulsion and dense phases are determined. These threshold values are used to prepare ternary images that clearly show the parts of the bed cross-section corresponding to bubble. emulsion and dense phases.
he process of fluidization involves the simultaneous flow of solids in contact with a gas, a liquid, or a gas and a liquid. Methods for T direct local measurement of hydrodynamic properties in operating fluidized beds are necessary. Recently, these techniques have become less invasive, more sophisticated and generally more reliable, particularly when applied to laboratory-scale units. Non-invasive techniques, such as radiation attenuation and tomographic imaging, are now used. Gamma-ray imaging is such a technique that has been used for various applications.In the gamma camera technique that is used in this study, the gamma radiation strikes the face of the collimator mounted to the detector head. With a parallel-hole collimator, only those gamma rays, which are travelling perpendicular to the camera face, can pass through the collimator. Others are stopped by the collimator septa (hole dividers). The scintillation crystals change the energy of each gamma ray into a light energy in direct proportion to the energy dissipated within the crystal. These crystal-yielded photons are gathered in a "light pipe" and are directed to an array of photo-multiplier tubes for detection. Each tube converts the light energy into a pulse of electrical energy, which is directly proportional to the number of photons striking the tube. The crystals are sensitive to a specific keV energy range, thus allowing detection of certain emissions while they are not sensing other energy emissions.By allowing only the perpendicular gamma rays to pass the collimator, the scintillation light produced in the crystal shows the same relative positions corresponding to the origin of the emitted gamma rays. The output of each photo-multiplier tube depends on the energy and proximity to the scintillation counter that produced the output. Besides coordinate signals (x-and z-positioning signals), the camera produces signals representing the scintillation energy for each event.Rotating the head of the camera and recording several frames a t different angles can do three-dimensional viewing of a static source. But, in our experiments, dynamic imaging of a small-moving radioactive particle was performed. This type of acquisition produces a two-dimensional image, only. The advantages of the proposed gamma camera technique as it was used in this study are: 1. It does not depend on the attenuation of the gamma ray. This is because the camera detects location and number of counts of the occurrence of the source but the reconstruction algorithm only acquires the location information. 2. Processing times are very small. *Author to whom conespotirierice rnny be aritiressc~ri. E-mail address: ukntitzns(@ ucalgary.ca A scintillation gamma camera was used for measuring the instantaneous velocity profile and average velocity as well as the trajectories of a radioactive particle in small laboratory scale air-polyethylene-fluidized beds. A large number of frames, with frequencies between 1 and 50 Hz, were analyzed to investigate the effects of bed height, gas velocity a...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.