Much research on microbubbles and their drag reduction effect has been reported. However, few studies have focused on nanobubbles, which have sub-micrometer size. Mixtures of surfactants and polymers are known to reduce drag, but their use is limited because of environmental concerns. In this study, nanobubble/water mixtures were passed through several sizes of micro orifices and capillaries, and the resultant pressure drops, as compared with water, were evaluated. For a small orifice (≤50 μm) and capillary (≤70 μm), the experimentally observed pressure drop was less than that for water. This phenomenon is considered in terms of interface behavior and attributed to the electrical interaction between an electric double layer and nanobubbles. The results of this study suggest that the addition of nanobubbles to a liquid results in superior drag reduction.

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The effects of the baffle length on the power consumption of a mixing vessel with several impellers were studied. The power number was generally correlated with the baffle length, the number of baffles and the baffle width. When the number of baffles was unity, experimental values were slightly lower than the calculated ones. The power number of the pitched paddle impeller was correlated with the correlation of Hiraoka et al. (1997).

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Activated carbons (ACs) ware prepared from ubame oak activated with ZnCl₂ and from coconut shell char activated simultaneously with KOH and CO₂. The influences of specific surface area, pore size distribution and surface chemistry on tannic acid and nitrobenzene adsorption were investigated. ZnCl₂ activation increased specific surface area to 1700 m²/g and mesopore volume to 1.1 cm³/g, while KOH–CO₂ activation increased specific surface area to 1900 m²/g and micropore volume to 0.7 cm³/g. Highly mesoporous AC adsorbed 4 times more tannic acid than commercially available AC (Filtrasorb 400). The amount of tannic acid adsorbed was proportional to the mesopore surface area and mesopore volume, while the amount of nitrobenzene adsorbed increased with the increase in the specific surface area rather than mesopore volume.

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Activated carbons with and without surface functional groups were prepared by heat treatment, and their performance in adsorptive removal of 4,6-dimethyldibenzothiophene, a known refractory sulfur compound in n-hexane solvent, at normal temperature and pressure was examined. The results showed that the surface functional groups increased the adsorption capacity of 4,6-dimethyldibenzothiophene, implying the presence of C–O complex sites introduced by oxidation, in addition to Cπ sites, which adsorb aromatic compounds through π–π interactions. The adsorption affinity for 4,6-dimethyldibenzothiophene calculated by the Bi-Langmuir equation was 2.5 times higher for C–O complex sites than Cπ sites. The effects of non-polar and polar solvents on the adsorption of 4,6-dimethyldibenzothiophene were also compared. In non-polar solvent, activated carbons with surface functional groups showed increased adsorption capacity, while in polar solvent they showed the opposite tendency. Moreover, the influence of 1-methylnaphthalene as a competitive inhibitor in n-hexane solvent was examined at a constant concentration of 4,6-dimethyldibenzothiophene. The increase in 1-methylnaphthalene concentration caused a decrease in the adsorption capacity of 4,6-dimethyldibenzothiophene on Cπ sites but did not affect the adsorption on C–O complex sites. Therefore, it was concluded that the C–O complex sites are effective for the adsorption of polar compounds. Furthermore, the introduction of acidic functional groups or other sites that selectively adsorb sulfur compounds could be effective for the adsorptive removal of sulfur compounds such as 4,6-dimethyldibenzothiophene in fuel oil.

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Wakkanai siliceous shale (WSS) is a natural mesoporous material that has high performance of moisture adsorption/desorption in response to relative humidity. The authors have previously applied the technique of impregnation with chloride to enhance the water adsorption performance; and in the present study the moisture sorption mechanism with chloride impregnation was examined by DSC analysis. It was found that the adsorbed water in the pores was divided present in three forms: non-freezing water, freezable bound water and free water. The free water peak was not observed at water content below 320 mg/g. This water content was also consistent with the maximum amount of water adsorbed without surface wetting, which was estimated from color change of WSS surface at various water contents. In addition, from the measurement by a modified nitrogen adsorption method, it was visually shown that the mechanism of moisture sorption gradually proceeded from the smaller mesopores. Moreover, the NaCl impregnation was applied to other porous materials. From the experimental results, the impregnation of silica gel with NaCl is not effective, because of the structural weakness. Therefore the stability of the material to impregnation is an important factor.

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In the PWR nuclear power plant, radioactive gas continuously extracted from the primary coolant is reduced by decay in the long-term storage tank before being discharged into the environment. A new radioactive waste gas treatment system using a charcoal bed is expected to reduce the amount of radioactivity released and simplify the system, while improving system reliability, operation and maintenance. A charcoal bed-type of radioactive gas removal system has been designed and built based on fundamental test data, and the system gradually introduced into new plants has been operated stably. This paper introduces an outline of the system, together with an outline of the fundamental test results and dynamic simulations.

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In this study, direct decomposition of waste oil was attempted by use of plasma-assisted combustion under reduced pressure. Experiments were performed to compare the emission spectrum, composition and production of the gases generated by plasma-assisted combustion and reduced-pressure combustion. It was found that plasma-assisted combustion increased the total emission intensity, and that OH emission intensity was increased more than 30 times. In addition, H₂ and CO increased, whereas CO₂ decreased in the generated gas. This study showed the decomposition characteristics of waste oil during plasma-assisted combustion under reduced pressure, and it indicated the possibility that it can be used as a new waste-treatment technology.

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Fluid catalytic cracking (FCC) has been the most important and flexible conversion process in petroleum refineries. It is economically beneficial in allowing low-value materials of high molecular weight to be cracked into valuable constituents, such as gasoline, diesel and petrochemicals. Therefore, understanding the reaction mechanism of heavy molecules is a key to increase the selectivity of valuable products. To improve FCC performance, generalization of the main factors affecting catalyst structures, feed properties and operation conditions is crucial. Our work mainly focuses on the hydrothermal deactivation behavior of residual fluid catalytic cracking (RFCC) catalysts. There are two steps in this deactivation: an initial rapid drop followed by gradual decline in activity. During the first step, collapse of the outside of zeolite micropores was mainly observed. At that time, significant amount of coke was formed and overcracking occurred, as shown by the MAT result. In the following step, the rate of coke formation and overcracking of the gasoline fraction decreased. Subsequently, the gasoline yield decreased, probably because of gradual and even dealumination of the zeolite crystals, resulting in a lower surface area of zeolite. Finally, the catalyst structure stabilized under the hydrothermal conditions.

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The influence of mass transport inside microreactors containing catalyst layers on the wall was investigated using a mathematical model. In the model, the microreactor was divided into two parts, bulk flow area and catalyst layer, where reactions only occur in the catalyst layer. The concentration profile in the bulk flow area was expressed with a dimensionless equation using Damköhler number and the modified Péclet number. The influence of diffusion in the bulk flow area was judged with the concentration profile. The influence of diffusion in the catalyst layer was determined by well-accepted Thiele modulus and effectiveness factor. Finally, the whole relation between the diffusion in the bulk flow area and catalyst layer was graphically interpreted with the plot of Damköhler number and Thiele modulus against the intrinsic rate constant and catalyst layer thickness. The thickness of the catalyst layer was evaluated with the diagram.

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Phosphorescence-emitting hybrid crystals were synthesized by cooling an aqueous solution of potassium sulfate (host, H) and o-aminobenzene-sulfonate (guest, G, o-ABSA). The Hybrid crystals emitted blue phosphorescence on excitation with 254 nm UV irradiation. This phosphorescence was suggested to arise from interaction between π-electrons of o-ABSA and K⁺ of potassium sulfate. This interaction effectively inhibited thermal agitation and thereby inhibited the non-radiative decay of the triplet excited state of o-ABSA molecules. Moreover, the phosphorescence emitted by the hybrid crystals depended on the G/H ratio, which indicated that fixation of the guest in the host crystal influenced this emission.

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The validity of a correlation model with a lumped parameter system (simple correlation model) was examined for the case of binder segregation during convective drying of slurry slab, which, in contrast with a prediction model by the distributed parameter system (accurate prediction model), was intended to provide rapid feedback of research results. A simple correlation model for binder segregation accompanied by drying shrinkage was proposed for convective drying of slurry slab by expansion of the authors' previous lumped parameter model in series without drying shrinkage. Experimental information about the formation of thin surface-layer rich in binder and the effect of adsorbed binder reported by others was considered in the proposed model. Results calculated with the proposed model from measured drying data showed satisfactory agreement with the authors' previous experimental results. The success of the proposed model in reproducing the experimental results obtained under limited conditions suggests the possibility of developing a generalized simple correlation model for binder segregation during convective drying of slurry slab.

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The thermochemical IS process for hydrogen production involves the use of highly corrosive sulfuric and hydriodic acids at high temperature and pressure, and the development of corrosion-resistant materials for main components is therefore crucial to process development. This paper concerns the development of a sulfuric acid transfer pump, an important component in transferring high-temperature concentrated sulfuric acid in the sulfuric acid decomposition step of the IS process. A reciprocating plunger pump made of SiC ceramics and common metal alloys was designed to meet the required corrosion resistance, thermal resistance and compressive strength for the transfer of high-temperature concentrated sulfuric acid. The pump was test-fabricated, and its performance in an IS test plant with a hydrogen production capacity of 30 m³/h was verified in terms of the pressure resistance and the transfer performance.

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A novel high efficiency solid oxide fuel cell (SOFC) is proposed. The new SOFC comprises a cascade system in a unit, normal flow cells and internal reverse-flow cells. The cell is expected to afford higher energy efficiency through higher fuel utilization. Numerical analysis showed the temperature and current distribution profiles for the new SOFC and conventional type SOFC. By adopting an outside turn-round flow system, a lower heat value (LHV) of 60% was obtained, which is about 10% points higher than that of normal flow cells. Of the two types of internal reverse flow SOFC investigated, the outside turn-round was found to be preferable to the inside turn-round type in terms of temperature and current distribution.

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To obtain fundamental data for developing an efficient recovery process of rare metals from grinding powder and cutting fragment of optical glass, the release of Nb, Ta, La, Gd and coexisting elements (Ti, Zr and Zn) was investigated under the conditions of a heating rate of 30°C/min and terminal temperatures from 200 to 1000°C in a Cl₂ gas stream. The release of Zn, Nb, Ti and La drastically increased above 700°C and attained almost 100% at 1000°C, while that of Zr attained to 10% above 800°C. Carbon addition accelerated the volatilization, and the release of elements other than La and Gd reached 100% by 1000°C. The release of La and Gd was only 2–3% in the temperature from 800 to 1000°C. When the samples were heated at 700°C for 120 min, Ta and Nb were selectively volatilized from solid phase without the release of La and Gd.
Based on the experimental results, a three-step heat treatment process at 500, 700 and 1000°C in a Cl₂ gas stream with carbon addition was proposed to recover the rare metals selectively from the optical glass.

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Hydrothermal treatment was carried out with sewage sludge, and the effect of hydrothermal condition, such as treatment temperature, treatment periods and slurry concentration, on sludge slurry characteristics was evaluated. In the experiment, treatment temperature was changed 393 to 533 K, treatment period was changed 5 to 20 min and slurry concentration was changed around 14.3 to 33.3%. Elementary analysis, particle size distribution measurement and zeta potential measurement of hydrothemally treated slurry were conducted. pH value of the filtrate was also measured. Constant pressure filtration experiment with the slurry was implemented to evaluate dewatering characteristics of the treated slurry. With increasing treatment temperature, solubiliztion ratio of the sludge increased significantly, and 60% of organic material in sewage sludge solubilized into water at the treatment temperature of 533 K. Effect of treatment period on solubilization ratio was minor comparing with the treatment temperature. Due to the solubilization of sludge components, particle diameter decreased with increasing treatment temperature. pH value of the filtrate also decreased with increasing temperature, however, the value increased significantly over 473 K treatments. The property of treated slurry and ph value of the filtrate changed significantly by the hydrolysis and dehydration reaction during the hydrothermal treatment, absolute value of zeta potential also changed obviously. The absolute zeta potential value had a minimum value at 473 K, which was observed similarly in pH value trend. Dewatering ability of slurry treated over 473 K improved drastically and dewatering rate increased with increasing the treatment temperature. Solid content of dewatering slurry became around 52%, which capable of combustion without drying.

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Pulverization experiments with pulverization pots of various sizes were conducted to study the effect of scale-up on the pulverization of woody biomass. The diameter and length of the pots were varied, and the effect of pot-size change on the grindability and productivity of woody biomass was evaluated. From the results, the production rate of woody powder and the energy consumption for woody biomass pulverization in a large-scale vibration mill were estimated. It was found that the pot size significantly influenced the grindability and productivity. With increasing pot diameter, productivity also increased, but grindability as evaluated by the crystallinity index of cellulose decreased significantly. On the other hand, grindability was not notably influenced by the pot length. In a scale-up simulation, the increase in power consumption markedly exceeded the increase of productivity when the pot diameter was increased, and energy consumption per unit of woody powder production also increased significantly. Scale-up of the pot length was able to reduce the energy consumption, but the productivity of woody powder was still very low.

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