Yuji Tatemoto

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.

Aerobic copper/TEMPO-catalyzed oxidation of primary alcohols to aldehydes using a microbubble strategy to increase gas concentration in liquid phase reactions

An efficient method for the synthesis of aldehydes was achieved by using air-microbubble techniques in aerobic copper/TEMPO-catalyzed oxidation of primary alcohols. Use of air-microbubbles to improve gas absorption into liquid phase is proven to be highly beneficial for gas/liquid phase reactions.

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.

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.

EFFECTS OF OPERATIONAL CONDITIONS ON DRYING CHARACTERISTICS IN CLOSED SUPERHEATED STEAM DRYING

The effects of operational conditions on the drying performance in closed superheated steam drying were examined theoretically and experimentally. The vapor generated from the sample was circulated in the drying chamber. In the theoretical analysis, the replacement of air with vapor in drying chamber and the convective vapor transfer in sample were considered. At the start of drying, the drying chamber was filled with air. As the drying proceeded, the air was replaced with the vapor generated from sample. The calculated results explained the characteristics of experimental data. The pore diameter of sample had little effect on the drying characteristics. During the internal evaporation period, the evaporation occurred in the narrow zone, which moved from the surface to the bottom of sample. The convective vapor transfer in sample had a significant influence on the drying performance. The excess increments in temperature and velocity of drying gas hardly contributed to shortening the drying time.

EFFECT OF FLUIDIZING PARTICLE ON DRYING CHARACTERISTICS OF POROUS MATERIAL IN FLUIDIZED BED

The drying characteristics of porous material in fluidized bed were examined theoretically and experimentally. The brick ball was used as the sample and immersed in the fluidized bed. The glass beads were used as the fluidizing particles and the particle diameters were changed. When the pore diameter of sample was relatively large, the fluidizing particles were adhered on the sample surface. In the theoretical analysis, the heat and mass transfers in adhered particle layer were considered. The fluidizing particles were adhered on the sample surface during the earlier period of drying. The sample temperature largely decreased when the mass of adhered particle decreased. The calculated results are in good agreement with experimental data. The diameter of fluidizing particle had a small effect on the drying time. The excess increments in drying gas temperature hardly contributed to shortening the drying time.

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.

Effect of Humidity on Drying of Porous Materials in Fluidized Bed under Reduced Pressure

For fluidized bed drying under a reduced pressure, the effect of the humidity of the drying gas on the drying characteristics of porous materials immersed in the bed was examined experimentally and theoretically. The temperature at the sample center increased with the humidity at relatively high pressures in the drying chamber (101.3 and 50 kPa), and the degree of the increment in the temperature with the humidity increased with the chamber pressure. The effect of the humidity on the temperature at the sample center and the drying time was insignificant at a relatively low chamber pressure (20 kPa).

Drying of Suspensions in a Fluidized Bed of Inert Particles Under Reduced Pressure

A drying method in which a heat-sensitive material is immersed in a fluidized bed under reduced pressure was used to continuously obtain dispersed, dry, fine powders of that material from a dilute suspension or solution at a low temperature with a high drying rate. The mass velocities of the drying gas, sample flow rate, and chamber pressure were varied, and the effects of these variations on the corresponding drying characteristics were examined. The fluidization state of a fluidized bed of inert particles strongly affects the drying rate in the bed and has a greater effect than the chamber pressure on the corresponding drying characteristics. In other words, it is important to maintain a vigorous fluidization state to achieve a high drying rate. Although the maximum drying rate is independent of the chamber pressure, it can be achieved at a low mass velocity of the drying gas under reduced pressure. That is, at a low chamber pressure a high drying rate can be achieved, even at a relatively low mass velocity of the drying gas. The bed temperature at the time of drying is strongly influenced by the drying rate and decreases linearly with an increase in the maximum drying rate when the sample flow rate is equal to the drying rate.