Browsing by Author "Yang, Jyh-Shing"

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    Hydrodynamics and heat transfer in shallow fluidized beds
    Yang, Jyh-Shing (Virginia Polytechnic Institute and State University, 1986)
    The use of shallow fluidized beds for heat exchange has been suggested because they give high bed-to-surface heat transfer rate and require very low bed pressure. However, in comparison with research on deep fluidized beds, only relatively few studies have been devoted to heat transfer in shallow beds, and results from the available literature are often inconsistent. This study represents an integrated research on the hydrodynamics and bed-to-surface heat transfer in shallow beds. The results from this study provide the quantitative basis for the design and efficient operation of shallow fluidized-bed heat-recovery systems. Based upon their physical appearance, shallow fluidized beds have been categorized into nine different types. A "phase diagram" (plot of superficial gas velocity versus static bed height) can be used to delineate the ranges of fluidization variables within which each type of shallow beds will be seen. Pressure-drop data in gas flowing upward through a shallow bed reflect pressure recovery in jets formed immediately above a gas distributor at the bottom of the bed. Pressure-recovery data provide an effective means of distinguishing a shallow bed from a deep one, and suggest that the power consumption across a fluidized bed can be reduced dramatically by dividing a single deep bed into many multi-staged shallow beds. A computerized light probe has been developed for measurements of particle volume-fraction distribution and its statical fluctuation (standard deviation). These data have been shown to quantitatively define: (1) different types of shallow beds; (2) relative magnitude of solid mixing; (3) bed surface and bed height; and (4) jet penetration depth. Based upon observations of the hydrodynamic behavior of shallow fluidized beds, three regions can be identified for heat-transfer applications: a jet-affected region at the bottom, a free-board region at the top, and, sandwiched between theses, a homogeneous region. Only heat-transfer data in the homogeneous region are sufficiently well-behaved to be subjected to quantitative correlation in terms of fluidization variables. For relatively coarse particles (Geldart's Group B particles) the vigor of solid mixing can be the most important factor in affecting the heat-transfer performance. Bed voidage and static electricity effects are found to be important for smaller and/or lighter particles (i.e., Geldart's Group A particles).
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    Pulseback of panel bed contactor for carbon and water
    Yang, Jyh-Shing (Virginia Polytechnic Institute and State University, 1982)
    A method for removing chemical contaminants, such as phenol, from a stream of waste water has been proposed. The method uses a device for contacting water with activated carbon, called a "panel bed". In this device, water flows across a bed of activated carbon retained within a set of parallel louvers. Construction permits contaminants in the entering stream of water to be adsorbed on carbon particles, starting from the entrances of the spaces between the louvers. A pulseback technique is used to remove the region containing "contaminated" activated carbon. Pulseback is applied periodically after appropriate intervals of operation. This research aims to determine operating characteristics of a panel bed and focuses on the study of pulseback. From a previous design of a panel bed filter for removing fly ash from stack gases, and from a basic study of characteristics of activated carbon adsorption isotherms, a panel bed was constructed which was believed to be suitable for contacting activated carbon with waste water. Pulseback consists of a reverse transient flow of water across the panel bed of activated carbon. Detailed descriptions of pulseback equipment, data on the spill of carbon that accompanies pulseback, and correlation of the carbon spill data are included. The carbon spill during pulseback appears to correlate with "active time", where this term refers to the time during which a reverse pressure difference, created by the reverse transient flow of water, exceeds a critical minimum value necessary for any spill at all to occur. For the specific design of equipment used in this study, the spill is relatively small if the active time is less than 60 milliseconds. Beyond 60 milliseconds, for the specific equipment used, the spill is linear with active time, and occurs at a rate that appears related to Zenz's modification of the Francis weir formula to describe efflux of solids from a static bed through an opening.