The hydrodynamics of a gas-liquid-solid circulating fluidsized bed was investigated. A new regime, the three phase circulating fluidization regime, was discovered for the first time. The characteristics of this regime were compared with that of the conventional fluidization regime and the transport regime. The particle circulation rate and the gas and solids holdups in circulating fluidization regime were studied.On a ttudit I'hydrodynamique d'un lit fluidid circulant gaz-liquide-solide. Un nouveau r6gime, le d g h e de fluidisation circulant triphasique, a t t t dkouvert pour la premikre fois. Ses caractkristiques sont cornparks h celles du rtgime de fluidisation classique et du rtgime de transport. On a thidit la vitesse de circulation des particules et les retentions de gaz et de solides en rCgime de fluidisation circulant.
Multiple light scattering has been regarded as a barrier in imaging through complex media such as biological tissues. Owing to recent advances in wavefront shaping techniques, optical imaging through intact biological tissues without invasive procedures can now be used for direct experimental studies, presenting promising application opportunities in in vivo imaging and diagnosis. Although most of the recent proof of principle breakthroughs have been achieved in the laboratory setting with specialties in physics and engineering, we anticipate that these technologies can be translated to biological laboratories and clinical settings, which will revolutionize how we diagnose and treat a disease. To provide insight into the physical principle that enables the control of multiple light scattering in biological tissues and how recently developed techniques can improve bioimaging through thick tissues, we summarize recent progress on wavefront shaping techniques for controlling multiple light scattering in biological tissues.
The hybrid method developed in part I of this paper for three dimensional free and forced vibrations of an inclined sag cable with multi-pairs of oil dampers is now applied to cables in a real cable stayed bridge. Damper performance is evaluated in terms of the achievable maximum modal damping ratio and the possible maximum reduction of resonant response of a cable in both in-plane and out-of-plane vibrations. Effects of both cable properties and damper parameters, such as cable sag, cable inclination, damper stiffness, and damper location, are discussed. Optimum parameters for oil dampers, such as damper damping coefficient and damper direction, are sought within a range of practical interest. The sensitivity study is also carried out to see the influence of small deviation of damper direction on damper performance. Finally, an investigation is performed to see how a proper arrangement of two pairs of oil dampers can overcome insufficient damping ratio problem in the first in-plane mode of a long cable due to frequency avoidance. 7 1998 Academic Press Figure 2. Variations of modal damping ratios of short cable with damper size. (a) In-plane; (b) out-of-plane. ---Mode 1; --other modes; short cable, xc /L=0·02, g = 45°, a = 52·8°.Figure 4. Variations of modal damping ratio of long cable with damper size. (a) In-plane; (b) out-of-plane. ---Mode 1; --other modes; long cable, xc /L=0·02; g = 45°, a = 74°.
Optical focusing and imaging through or inside scattering media, such multimode fiber and biological tissues, has significant impact in biomedicine yet considered challenging due to strong scattering nature of light. In the past decade, promising progress has been made in the field, largely benefiting from the invention of iterative optical wavefront shaping, with which deep-tissue high-resolution optical focusing and hence imaging becomes possible. Most of reported iterative algorithms can overcome small perturbations on the noise level but fail to effectively adapt beyond the noise level, e.g. sudden strong perturbations. Re-optimizations are usually needed for significant decorrelation to the medium since these algorithms heavily rely on the optimization performance in the previous iterations. Such ineffectiveness is probably due to the absence of a metric that can gauge the deviation of the instant wavefront from the optimum compensation based on the concurrently measured optical focusing. In this study, a square rule of binary-amplitude modulation, directly relating the measured focusing performance with the error in the optimized wavefront, is theoretically proved and experimentally validated. With this simple rule, it is feasible to quantify how many pixels on the spatial light modulator incorrectly modulate the wavefront for the instant status of the medium or the whole system. As an example of application, we propose a novel algorithm, dynamic mutation algorithm (DMA), which has high adaptability against perturbations by probing how far the optimization has gone toward the theoretically optimal performance. The diminished focus of scattered light can be effectively recovered when perturbations to the medium cause significant drop of the focusing performance, which no existing algorithms can achieve due to their inherent strong dependence on previous optimizations. With further improvement, the square rule and the new algorithm may boost or inspire many applications, such as high-resolution optical imaging and stimulation, in instable or dynamic scattering environments.
Gas-sofids circu fating fluidized beds have been successfully used in cata fytic cracking of heavy oil, coal combustion, and some metallurgical and physical processes (Grace, 1990). Gas-liquid-solids fluidized beds are operated mainly in conventional fluidization regimes without solids circulation or in the transport regime with low solids holdups (less than 5 % ) (Fan, 1989 (Berk et al., 1984). Circulating operation can promote solids mixing and increase product throughput per unit bed cross section, while high shear stress can promote biofilm renewal (Pirozzi et al., 1990 Experimental StudiesThe experimental apparatus is shown in Figure 1. The riser is 140-mm-dia., 3-m-high Plexiglas. Tap water and air were used as liquid and gas phases, respectively. Glass beads of 0.405 mm in mean diameter and density 2,460 kg/m3 were used as the solid phase. In the operation, fluidizing water was introduced from the base of the riser through a liquid distributor, while solids flow rate was regulated by a secondary water flow from a side port near the bottom of the riser. The superficial liquid velocity was calculated based on the total flow rate from both the liquid distributor and the secondary side port. Gas was introduced separately through a gas distributor located well above the bottom liquid distributor. Well-mixed threephase flow was achieved in the test section above the gas distributor. Solids entrained from the top of the riser was separated from the water and returned to a reservoir. The solids circulation rate was determined by measuring the amount of particles collected in a metering tank on the top of the standpipe after the butterfly valve beneath the metering tank was closed, similar to the method used in the gas-solids circulating fluidized bed (Burke11 et al., 1988).Local gas holdup was measured using an electrical conducCorrespondence concerning this article should be addressed to Y. Jin tivity probe. The tip of the probe was a 0.1-mm platinum wire, covered by a 0.2-mm glass tube. The probe was installed with the tip directed downward to minimize the disturbance of local flow patterns. Typical signals from the probe are shown in Figure 2. The output voltage is seen to drop sharply when bubbles pass the probe. The local bubble fraction can thus be determined by:where ti is the exposure time of the probe to bubbles and T is the total record time. The cross-sectional average gas holdup is calculated by:To evaluate the cross-sectional average solids holdup, pressure drops across the test section were also measured. The sectional average solids holdup is evaluated by combining Eqs. 2, 3 and 4:
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