Katsuya Funatsu

Experimental investigation of a free falling powder jet and the air entrainment

Abstract The characteristics of a free falling powder jet of glass beads are investigated in terms of axial velocity profile at several distances ranging between 1 to 1500 mm from different orifices using a laser-Doppler velocimeter. The free falling velocity of a particle in the powder jet is larger than that of the single particle in an unbounded fluid vs and increases with increasing mass flow rate. A uniform profile exists near the orifice. At a long distance from the orifice, the velocity profiles of powder jet are like those of a single-phase free turbulent jet, provided that the outer edge of the powder jet does not extend past the radius where the velocity is slightly greater than vs. The diffusion of the powder jet is very small as compared with that of a single-phase jet.

Motion of a single capsule in a hydraulic pipeline

The method of characteristics is used to numerically analyse the motion of a single solid capsule in a hydraulic horizontal straight pipe. The capsule is assumed to be a point mass and the coaxial-annular-flow model around the capsule is used to derive the boundary conditions for water flow at the capsule discontinuity. The results are compared with experimental measurements which were taken in a pipeline 28 m in length and with an inside diameter of 40 mm. The capsule had wheels to keep its position coaxial with the pipe axis and always had a higher velocity than the water flow. The measurements are explained quite well by the analysis.

Spouting of fine powder from vertically vibrated bed

Abstract Experimental and numerical studies of spouting of powder from vertically vibrated bed are performed. The powder flows out vigorously through a side orifice of the vertically vibrated vessel in which the powder is contained, provided that the vibration acceleration is greater than the gravitational one. The mechanism of the efflux and the relationship between the efflux rate and the vibration condition are examined. The interstitial air pressure in the bed is measured and is compared to the numerical analysis considering the relative motion of the powder bed to the vibrated vessel and percolation air flow. The outflow behavior of powder is observed by using a high-speed video camera. The experimental and the numerical results show that the powder spouts out intermittently with periodic air outflow, which is generated in response to the change of the gap between the bed and the vessel base. Furthermore, it is found that the efflux rate of powder is in proportion to the generated air pressure and in inverse proportion to the vibration frequency.

Motion of a single particle in a horizontal pipe

The motion of a single particle in a smooth horizontal pipe is investigated experimentally and numerically with respect to particle trajectory height, velocity and angular velocity. The particle trajectory height is experimentally determined by using a particle collecting net. Both results show that a spherical particle finally moves near the smooth pipe bottom and the angular velocity of the particle takes a maximum against gas velocity for a given distance from the particle feeding point.

Effect of Particle Properties on Slug Flow Conveying in a Horizontal Pneumatic Pipeline

The influence of particle properties on slug flow conveying was experimentally examined by using polyethylene particles of different densities from 825 kg/m3 to 945 kg/m3 in a horizontal pipeline 5.5 m in length, inside diameter of 32 mm, for air speeds below 8 m/s. It was found that hardness affects the slug flow conveying in such a way that for soft particles lower limiting velocity as well as boundary air velocities for suspension flow and slug flow increases. Additionally, it was found that the frictional characteristics of a particle influence its flow pattern. Also, there are two types of slug flow, that is, a solitary slug flow and a consecutive slug flow. In a solitary slug flow, there is at most only one plug in the pipeline. In a consecutive slug flow, the particles are conveyed continuously as slugs. There is always at least one slug in the pipeline.

Interstitial fluid pressure and voidage in flushing phenomenon of fine powders

Fine powders were flooded out of a small side orifice near the bottom of a cylindrical vessel by a piston load exerted on the top surface. It is found that there is a unique relationship for each powder between the interstitial fluid pressure and voidage at the onset and end of flushing, independent of the piston load and the initial voidage, and that powder with a small relaxation time easily gives rise to flushing.

Granular jump in low velocity pneumatic conveying of solid particles in a horizontal pipeline

An experiment is presented here that shows a discontinuous change of flow pattern like hydraulic jumps in gravity flow of granular materials. In the upstream of jump the flow pattern is heterogeneous suspension flow where the particles mainly travel near the pipe bottom and suddenly changes to suspension flow accompanied with the particle settled layer of definite height where the particle velocity is decreased. The position of jump can be adjusted by changing the gas velocity. The experiment is carried out in a horizontal straight pipe of 30 mm in diameter and 5 m in length. Polystyrene beads are used, the diameter and the material density being 1.65 mm and 1034 kg/m 3 , respectively. This chapter experimentally examines the flow when the rear side of the settled layer is ceased, while the particle conveying is steadily maintained. In the upstream the flow pattern is heterogeneous suspension flow where the particles mainly travel near the pipe bottom, and it suddenly changes to suspension flow over the particle settled layer of definite height. Here, this change of flow pattern is called as a granular jump. This kind of discontinuous change of flow pattern likes hydraulic jumps in gravity flow of granular materials, where the particle flow is driven by gravity.

Neutral stability of the laminar boundary along a concave wall.

ゲルトラうずの中立安定性を実験的,理論的に調べた.実験では,水槽内を一定曲率の凹面を一定速度で走行させ有限翼列によって与えられる外乱の増幅,減衰を水素気泡法によって観察し,低波数での安定判別を行った.理論では平行流,非平行流の仮定のもとでそれぞれの中立安定曲線を求めた.その結果中立安定域に対して平行流のゲルトラモデルは妥当な仮定ではなく,傾向としてはスミスモデルが実験と良い一致を示すことがわかった.