Yoshiyuki Bando

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.

Ultrasonic Decomposition of a Mixture of Phenol and p-Chlorophenol in Aqueous Solution

The ultrasonic decomposition of a mixture of two hydrophilic organic compounds, phenol and p-chlorophenol, in aqueous solution was investigated. The effect of the initial concentration of phenol and p-chlorophenol on the overall decomposition rate was examined experimentally. The overall decomposition rate constant of p-chlorophenol became lower as the initial concentration of phenol increased. The overall decomposition rate constant of phenol decreased with increasing initial concentration of p-chlorophenol, and remained unchanged when the initial concentration of p-chlorophenol was above a certain value. It was considered that phenol was decomposed by thermal degradation in addition to OH radical degradation. The decomposition of a mixture of phenol and p-chlorophenol in aqueous solution was simply modeled and kinetic analysis was performed. It was found that the initial decomposition rate of p-chlorophenol was higher than that of phenol due to OH radical degradation. The OH radicals were effectively used to decompose p-chlorophenol and phenol.

Development of rectangular airlift bubble column installed with support material for enhancement of nitrogen removal.

To enhance nitrogen removal during wastewater treatment using activated sludge, a rectangular airlift bubble column installed with support material is proposed. The flow characteristics and nitrogen removal performance were examined and compared with those of a column without support material. In the two columns, the riser was aerobic and the lower part of downcomer was anaerobic. The effects of operational conditions on the liquid circulation flow rate and liquid-phase volumetric mass transfer coefficient were examined. Using these flow characteristics, the distribution of dissolved oxygen (DO) concentration in the column was calculated. From the DO distribution, the anaerobic volume fraction in the column was estimated. The optimal anaerobic volume fraction for nitrogen removal was found to be approximately 50%. The column installed with support material showed higher nitrogen removal than the column without it.

Analysis of liquid distribution in non-uniformly packed trickle bed with single phase flow

Abstract The distribution of liquid flow rate is measured in a rectangular bed non-uniformly packed with different particles. The effects of particle properties (size and wettability), liquid properties (viscosity and surface tension) and packed structure on the liquid flow rate distribution are examined. The liquid trickle flow is strongly affected by the capillary force. An experimental equation expressing the liquid flow distribution at the interface between different particles is derived by means of the capillary number. A percolation model combined with the above experimental equation is developed to simulate the liquid flow distribution in the trickle bed. For the trickle flow of liquid droplet, the gravitational and capillary forces are considered to work on the liquid droplet, and the driving force for stochastic liquid flow is assumed to be the potential of the local liquid holdup. Besides a dropping flow in the vertical direction, a permeation flow in the horizontal direction is supposed. The results calculated by the percolation model are in good agreement with the experimental data for various packed systems.

Development of Bubble Column for Foam Separation

The foam separation of metal in model wastewater is performed by using two different bubble columns in a continuous operation mode. The equipment and operation conditions are changed, and the foam flow rate and metal concentration in foam flow are measured. The foam flow ratio (the ratio of foam flow rate to the inlet one) increases with increasing gas velocity, with decreasing liquid velocity, with decreasing foam layer height and with decreasing metal concentration in model wastewater. Metal enrichment (the ratio of metal concentration in foam flow to that in inlet flow) shows the reverse tendencies. When a draft tube is inserted in the bubbling layer, the foam flow rate decreases. The enrichment is strongly governed by the foam flow ratio. Since the foam flow ratio is adjusted by means of the equipment and operation conditions, the metal concentration in foam flow is controlled to be a desired value.

The heat transfer performance of a gas-solid contactor with regularly arranged baffle plates

Abstract The heat transfer coefficients between gas and solid particles in a countercurrent gas-solid contactor with regularly arranged baffle plates have been obtained by temperature profiles and from the heat balance equations in consideration of heat loss through the wall. A critical point of gas flow rate, Gld, has been observed for the present countercurrent gas-solid contactor. At Gld (loading point) the holdup of solid particles begins to increase with increasing gas flow rate, G. The heat transfer coefficient between gas and particles, h, shows a broad maximum at Gld, but the volumetric heat transfer coefficient, hap, where ap is the specific surface area of particles, increases with increasing G in the present range of G.

Drying Characteristics In Superheated Steam Drying at Reduced Pressure

Abstract The superheated steam drying at reduced pressure is performed, and the effects of operational conditions such as drying pressure and temperature on the drying characteristics are examined. In order to obtain the basic guideline for the design of the superheated steam dryer at reduced pressure, the heat flux to sample was calculated and the optimal conditions were estimated. After the sample temperature reached at the boiling point, the temperature was maintained at the boiling point and the drying rate became almost constant. Once the sample was dried out, the temperature suddenly increased up to the drying gas temperature. From the calculation of combined heat flux, the followings were found. The contribution of radiative heat transfer to the combined heat flux became larger as the drying pressure was lower. The combined heat flux had a maximum value against the drying pressure. The optimum drying pressure, which gave the maximum heat flux, became lower as the drying gas temperature decreased. It was found that reduction in the drying pressure is effective for the enhancement in drying performance.

Performance improvement of municipal solid waste drying in RDF production process

The drying characteristics of municipal solid waste were experimentally examined. A mixture of pulp (water soluble pulp), plastic (polyvinyl chloride powder), protein (soybean protein powder) and water was used as the model refuse. The operational conditions were varied and the changes in weight and temperature with time were measured. The hard layer is formed on the drying side of the sample due to protein denaturation. With increasing CaO content, this hard layer becomes thinner and more cracks are generated. As a result, when the temperature of drying gas is relatively high, the drying rate is higher in the case with CaO than in the case without CaO. It is found that the uniform addition of CaO to the refuse and CO/sub 2/ in the drying gas enhance the drying rate in the RDF production.

Collection characteristics of "volume heat trap" type multipass solar collector - Effect of flow mode and thermal resistance of partitioning plate.

体積受熱型ソーラコレクタの集熱効率を改良するために, 作動流体層を透過率の高い仕切板にてマルチレイヤ化あるいはマルチパス化することを考え, この場合の集熱特性に及ぼす流通方式および仕切板の伝熱抵抗の影響について検討した.流通方式および仕切板の異なるコレクタを試作し, 層内温度分布および集熱効率を測定した.また, 層内自然対流を考慮に入れた理論解析を行い, 実験結果と比較検討した.その結果, 作動流体層を仕切板によって分割する場合, 流通方式および仕切板の伝熱抵抗によって層内温度分布や集熱効率は大きく影響されることが認められた.また, 仕切板の伝熱抵抗が大きい場合の集熱効率はマルチパス化の方がマルチレイヤ化よりも高くなることがわかった.