Takashi Shirai

Bio: Takashi Shirai is an academic researcher from Tokyo Institute of Technology. The author has contributed to research in topics: Particle & Fluidized bed. The author has an hindex of 12, co-authored 44 publications receiving 476 citations.

Effect of light-source characteristics on the performance of circular annular photochemical reactor

Abstract: Three light source models, i.e., radial, specular, and diffuse line source models, are compared for light intensity profile, overall rate of reaction, and radial scale-up ratio of annular photochemical reactors, with the assumptions of constant absorption coefficient and constant quantum efficiency. The necessary condition for the radial light model to hold is that, when the ratio of inner radius to height of the reactor m, is 0.1, that of outer radius to inner radius ρ should be less than 3, and that when m is larger ρ should be close to 1. Published reaction data are analyzed according to this condition.

Velocity distributions in the flow of solid particles in an inclined open channel

Abstract: The velocity of solid particles flowing in an inclined open channel of which the bottom plate was covered with very rough sandpaper was measured for three kinds of particle. Except for the region near the bottom plate, the velocity distribution normal to the bottom plate appeared to be linear. The velocity gradient in that region was almost independent of the thickness of the particle layer and increased as the slope of the channel became steep. These observed velocity distributions were analyzed based on the variational principle, by which the velocity distribution could be obtained as the solution which minimized a certain integral consisting of several energy terms. It was found that such analysis could explain the main feature of the particle flow in an inclined channel, and the following relation between stress and rate of deformation was obtained. τyz=kτy-kμy(dvz/dy) It was also found that the critical inclination angle of the channel, which was anticipated by the analysis, corresponded to the angle of repose.

Hydrolysis of cellulose in a cellulase‐bead fluidized bed reactor

Abstract: Cellulase was immobilized in a collagen fibril matrix, and no leakage of cellulase from the collagen fibril matrix was observed. The immobilized cellulase was more stable than the native cellulase. The substrate cellulose was hydrolyzed quantitatively with immobilized cellulase. The final reaction product was identified as glucose. Immobilized cellulase was used in a fluidized bed reactor where the pressure drop of the fluidized bed reactor was low and constant. Cellulose was hydrolyzed to glucose by the cellulase-bead fluidized bed reactor. The minimum flow velocity (Umf) was 0.5 cm/sec and the optimum flow velocity of the cellulose hydrolysis was 1 cm/sec.

The motion of a finite mass of granular material down a rough incline

Abstract: Rock, snow and ice masses are often dislodged on steep slopes of mountainous regions. The masses, which typically are in the form of innumerable discrete blocks or granules, initially accelerate down the slope until the angle of inclination of the bed approaches the horizontal and bed friction eventually brings them to rest. The present paper describes an initial investigation which considers the idealized problem of a finite mass of material released from rest on a rough inclined plane. The granular mass is treated as a frictional Coulomb-like continuum with a Coulomb-like basal friction law. Depth-averaged equations of motion are derived; they bear a superficial resemblance to the nonlinear shallow-water wave equations. Two similarity solutions are found for the motion. They both are of surprisingly simple analytical form and show a rather unanticipated behaviour. One has the form of a pile of granular material in the shape of a parabolic cap and the other has the form of an M-wave with vertical faces at the leading and trailing edges. The linear stability of the similarity solutions is studied. A restricted stability analysis, in which the spread is left unperturbed shows them to be stable, suggesting that mathematically both are possible asymptotic wave forms. Two numerical finite-difference schemes, one of Lagrangian, the other of Eulerian type, are presented. While the Eulerian technique is able to reproduce the M-wave similarity solution, it appears to give spurious results for more general initial conditions and the Lagrangian technique is best suited for the present problem. The numerical predictions are compared with laboratory experiments of Huber (1980) involving the motion of gravel released from rest on a rough inclined plane. Although in these experiments the continuum approximation breaks down at large times when the gravel layer is only a few particle diameters thick, the general features of the development of the gravel mass are well predicted by the numerical solutions.

Rapid granular flows

Abstract: A granular material is a collection of a large number of discrete solid particles. Generally, the interstices between the particles are filled with a fluid such as air or water, and thus, technically, a granular flow is a multiphase process. However, if the particles are closely packed or if they are much denser than the interstitial fluid, the particles alone-and not the fluid or the fluid-particle interactions-will play the greatest role in momentum transport within the material, in which case the interstitial fluid can be ignored in describing the flow behavior. Granular-material fl ows are generally taken to fall into this limiting category and thus may be considered dispersed single-phase rather than multiphase flows. This review addresses the fluidlike behavior of granular solids and, in particular, those flows for which the material is rapidly sheared. I outline what is currently known about rapid granular flows, discuss the various modeling techniques used to describe the motion of the bulk material, and point out many questions that remain to be answered. Depending on the local stress conditions, a granular material may behave as either an elastic solid or a fluid. When a granular material is showing its elastic-solid behavior, it can support the large loads of building foundations or form i nto hills with finite slopes. However, much of the load is supported across frictional bonds between the particles, and, as such, the system's strength is limited to the loads that those bonds can support. When enough of the bonds have been overcome, the system will fail and begin to flow. The initial failure will consist of many-particle blocks moving relative to one another along shear bands that roughly follow stress characteristics through the material. If the motion occurs slowly, particles will stay in contact and interact frictionally with their neighbors over long periods of time. The failure will continue in this

Scaling laws in granular flows down rough inclined planes

Abstract: In this paper, new scaling properties for granular flows down rough inclined planes are presented. In the dense steady uniform flow regime, we have systematically measured the mean velocity of the flow as a function of the inclination of the surface θ and of the thickness h of the layer. The results obtained for different systems of beads corresponding to different surface roughness conditions are shown to collapse into a single curve when properly scaled. The scaling is based on the measurement of the minimum thickness hstop(θ) necessary to observe a steady uniform flow at inclination θ. From this experimental observation an empirical description for granular flows down inclined planes is proposed in terms of a dynamic friction coefficient.

Pyroclastic density currents and the sedimentation of ignimbrites

Abstract: Pyoclastic density currents are awesome volcanic phenomena that can wreak destruction on a regional scale and can impact global climate. They deposit ignimbrites, which include vast impact lansdscape-modifying sheets with volumes exceeding 1000 km3.This book takes stock of our understanding of pyroclastic density currents and presents a new conceptual framework for investigating how ignimbrites are deposited. It integrates the results of field-based studies, laboratory experiments and numerical modelling, including work on clastic sedimentologym and industrial particle transport. Topics covered include the behaviour or particulate currents, mechanisms of clast support and segregation, interpreting ignimbrite lithofacies and architectures, and future research directions. The new approach focuses on processes and conditions within the lower flow-boundary zone of currents. Superb diagrams explain many new concepts, while the 95 photographs make an explanatiry atlas of deposit types. This is essential reading for workers investigating volcanic hazards, and for anyone wishing to interpret modern or ancient ignimbrites, as well as other catastrophically emplaced sediments. “Given the depth of scholarship that they have brought to the subject, the power of their arguments, and the degree of synthesis with other fields, this would seemto qualify as a seminal work… I think that this will be the paper on the topic that others will have to contend with for many years to come.” Marcus Bursik, State University of New York

The Mechanics of Rapid Granular Flows

Abstract: Publisher Summary This chapter discusses the mechanics of rapid granular flows. A “bulk solid” or “granular fluid” may be defined as an assembly of discrete solid components dispersed in a fluid, such that the solid constituents are in contact or near contact with their neighbors. Bulk solids comprise one member of a larger class of two-phase disperse systems made up of solids and fluids; dilute suspensions form another related member, which is more familiar to fluid mechanicists. The section II of this chapter presents a review of the classical papers of Bagnold and a discussion of the various modes and regimes of granular flow. A dimensional analysis provides a physical background to the detailed review of experimental and theoretical work that follows. Section III reviews flows in vertical channels and inclined chutes; it deals primarily with experimental observations of stress, velocity, and bulk-density fields. Laboratory devices and viscometric type experiments designed to determine the stress-strain-rate behavior are discussed in Section IV. Quasi-static testers, suspension viscometers, and high-shear-rate devices are described. Section V reviews theories for high-shear-rate granular flows. It includes continuum models as well as analytical and numerical microstructural models that consider the details of collisions between particles.