Katsuji Noda

Minimum fluidization velocity of binary mixture of particles with large size ratio

Abstract The minimum fluidization velocities for systems of binary particles of greatly different sizes and densities have been studied experimentally. Particles of different shapes such as wood chips, rubber sheets, glass beads, iron beads, soya beans and small beans were used as coarse particles and nearly spherical fine particles of sands and glass beads were used as a fluidized medium. The correlation for the estimation of the true minimum fluidization velocity at which both coarse and fine particles are completely fluidized was obtained by the modification of the equation of Wen and Yu. This equation provides a good estimate of the minimum fluidization velocity for binary systems.

Prediction of minimum fluidization velocity for vibrated fluidized bed

Abstract The prediction of minimum fluidization velocity for vibrated fluidized bed was performed. The Geldart group A and C particles were used as the fluidizing particles. The method based on Ergun equation was used to predict the minimum fluidization velocity. The calculated results were compared with the experimental data. The calculated results of minimum fluidization velocity are in good agreement with experimental data for Geldart group A particles. For group C particles, the difference between the calculated results and experimental data is large because of the formation of agglomerates. In this case, the determination of agglomerate diameter is considered to be necessary to predict the minimum fluidization velocity.

Effect of particle diameter on fluidization under vibration

Abstract The effect of particle diameter on fluidization under vibration was studied. Glass beads with diameters ranging from 6 to 100 μm and pertaining to the Geldart groups C and A, were used as fluidizing medium. In order to examine the effect of vibration on the fluidization characteristics of the particles, minimum fluidization velocity ( u mf ), void fraction ( e mf ) at u mf and flow patterns in the bed were measured. For group C powders, u mf decreased with increasing the vibration strength, while for group A powders, u mf remained almost constant. With vibration, the flow patterns in the bed were changed, especially in the case of group C powders. For larger powders of 30 μm, channels and cracks were not observed in the bed. However, for smaller powders than 20 μm, stable channels and cracks were observed under no vibration and they disappeared by vibration. The lower limit of the gas velocity at which the channeling in the bed was not observed was lowered as the vibration strength increases. For smaller powders, the flow pattern in the bed becomes complex as various sizes of agglomerates occur and thus makes vibration difficult to propagate in the bed.

Crystal growth of ZnO by chemical transport using HgCl2 as a transport agent

Crystal growth of ZnO has been carried out by chemical transport in a closed tube using HgCl2 as a transport agent, and prismatic or needle-form crystals have been obtained. The transport rate has been discussed by comparing with theoretical calculations. The crystal grown were colorless and emitted no luminescence under UV excitation. The effect of excess Zn on these properties has also been discussed by comparing with the case of using NH4Cl as a transport agent.

Effect of Fluidizing Particle on Drying Characteristics of Porous Materials in Superheated Steam Fluidized Bed under Reduced Pressure

The hygroscopic porous particle was used as the fluidizing particle for the superheated steam fluidized bed drying under reduced pressure. A relatively large material was immersed in the fluidized bed as the drying sample. The drying characteristics of the sample were examined experimentally and the results were compared with those in the case of inert particle fluidized bed. The water transfer from the sample to the fluidizing particle bed in the case of hygroscopic porous particle facilitated the drying regardless of pressure and temperature in the drying chamber. The increment degree of the sample temperature at the earlier period of drying was smaller in the case of hygroscopic porous particle than in the case of inert particle, and the phenomenon was more remarkable in the case of superheated steam than in the case of hot air.

Indole acetic acid and abscisic acid levels in new shoots and fibrous roots of citrus scion-rootstock combinations.

Citrus rootstocks are important for the growth of scion varieties, but it is not clear how they regulate scion vigor. We studied three citrus rootstock cultivars; ‘Flying Dragon’ (Poncirus trifoliata var. monstrosa) a dwarfing rootstock, ‘Swingle’ citrumelo (P. trifoliata Citrus paradisi) a vigorous rootstock, and trifoliate orange (P. trifoliata) as the control. Tender buds from new shoots of ‘Eureka’ lemon were cleft grafted on etiolated rootstock seedlings. Eighteen months after grafting, the dry matter of each part of the young grafts was measured. Top weight was the greatest on ‘Swingle’ citrumelo and smallest on ‘Flying Dragon’, but there was no distinct difference in root growth among the rootstocks. Endogenous indole acetic acid (IAA) and abscisic acid (ABA) were measured in the new shoots and fibrous roots. The IAA level in the new shoots was highest in ‘Swingle’ citrumelo and lowest in ‘Flying Dragon’. The ABA level in the new shoots was highest in ‘Flying Dragon’ and lowest in ‘Swingle’ citrumelo. Both the IAA and ABA levels in the fibrous roots were highest in the strains of Poncirus trifoliata and lowest in ‘Swingle’ citrumelo. The vigorous rootstock ‘Swingle’ citrumelo had the highest T‐R and IAA‐ABA ratios in the new shoots. # 2000 Elsevier Science B.V. All rights reserved.

Drying Characteristics of Porous Materials in a Fluidized Bed under Reduced Pressure

Abstract The drying of porous materials immersed in the fluidized bed under reduced pressure was performed, and the results were compared with those of hot air drying. The pressure in drying chamber was changed (5.0–101.3 kPa) and the effect of it was examined. The temperature of the sample center becomes lower as the pressure in drying chamber decreases, and the temperature in fluidized-bed drying is higher than that in hot air drying at the same pressure. The effect of pressure in drying chamber on the sample temperature is significant for different temperatures of drying gas.

Comparison of three vibrational modes (twist, vertical and horizontal) for fluidization of fine particles

Abstract The effects of three vibrational modes (twist, vertical and horizontal) on flow patterns are discussed. The particles used are four powders (glass beads, 6-100 μm), which are Geldart group A or group C. The fluidity of particles is evaluated with vibration strength (A), minimum fluidization velocity ( u mf ), void fraction and flow patterns in the bed. The effect of vibrational mode on the flow patterns appears in whole bed motion, which is horizontal rotation or vertical rotation caused by twist or horizontal vibrational mode, respectively. For 60 and 100 μm particles, bubble behavior is dominant higher than u mf . Thus, the effects of vibrational mode on the flow patterns in the bed and u mf are not significant. For 30 μm particles, the horizontal rotation or vertical rotation are caused by twist or horizontal vibrational mode, respectively. For 6 μm particles, vertical rotation was not observed. When horizontal vibration is added to the bed, the lower limit of gas velocity for channel breakage for 6 μm is the lowest among the three vibrational modes. It is considered that the horizontal vibration affects channel breakage as the shear force.

Characteristics of vibro-fluidization for fine powder under reduced pressure

Abstract A cohesive powder (Geldart group C) was fluidized under reduced pressure ( P = 0:5 - 10 kPa) with vibration. The fluidized powder was composed of glass beads 6 μm in diameter. The bed pressure drop was measured by decreasing gas velocity and the flow patterns in the bed were observed. A slanting particle flow, which was not observed at atmospheric pressure in a previous study, appeared at a lower pressure than about P = 20 kPa and with a larger vibration strength than the critical vibration strength, A cr. Under the above conditions, the pressure drop curve changed abnormally due to the occurrence of this slanting particle flow. On the other hand, when the vibration strength was smaller than A cr, a typical pressure drop curve was obtained. In light of these results, the interrelation between the slanting particle flow and the change in the pressure drop curve was examined.

Bubbling and Bed Expansion Behavior Under Vibration in a Gas-Solid Fluidized Bed

The effect of vibration on the flow patterns and fluidization characteristics including the minimum fluidization velocity (u mf ), the void fraction (e mf ) at u mf and the bed expansion ratio were examined. The powders used were spherical glass beads and their diameters were 6, 20, 30, 60 and 100 μm. For group A powders, the manner in which the vibration affects the bubble formation was examined from the bed expansion ratio and the index of n/4.65. The area of the homogeneous fluidization region was also observed. The homogeneous fluidization region was broadened at a certain vibration strength, where the value of n/4.65 was a minimum. The bubble formation was observed even for 20 μm powder (group C), at large vibration strengths and at high gas velocities. Under such conditions, the bed expansion ratio increased suddenly due to bubble formation. The bubbles broke the irregular bed structure, including various properties of agglomerates. Although the channel breakage was dominant flow pattern for group C powders, the bubbles also played an important role in the improvement of the fluidization.