Radial distribution of gas holdup for recirculating turbulent flow in a bubble column is theoretically studied on the basis of time-averaged Navier-Stokes equations for both gas and liquid phases. The basic equations are simplified for the recirculating turbulent flow, and the radial distribution of gas holdup is successfully shown to be parabolic, which is experimentally well-known. On the way of derivation, it is shown that the radial velocity fluctuation of the liquid phase was mainly caused by two adjacent bubbles, and that the radial drug force acting on a bubble is proportional to the Reynolds stress of the gas–liquid multiphase.
A new method for graphical determination of mass transfer (saturation) time in a deep bubble bed (BB) was developed. It is based on the spatial distribution of the local liquid-phase concentrations CL(t) measured by means of an electrical conductivity probe. The raw CL(t) data were obtained in a 0.289-m-ID bubble column equipped with a perforated plate gas distributor (31 holes × ø2 × 10–3 m). Three different clear liquid heights (L0 = 0.56, 1.12 and 1.84 m) were examined. The shallow BB (L0 = 0.56 m) was aerated at superficial gas velocities ug = 0.018, 0.031, and 0.038 m·s–1, respectively. Both medium (L0 = 1.12 m) and deep (L0 = 1.84 m) BBs were aerated only at ug = 0.038 m·s–1 (churn-turbulent flow regime). It was found that the new graphical method is applicable only for a deep BB (L·Dc–1 = 7.3). In that particular case, the difference between the experimental mass transfer time and the graphically determined one is reasonable (the maximum relative error is only 6.9%). Therefore, the new graphical method should be adopted for experimental determination of the mass transfer time in a deep BB. The new method is of practical importance because the industrial bubble columns operate with deep BBs.
Flowability of micrometer-sized particles treated with nanometer-sized particles has been studied by a vibrating capillary method. Two different types of treatments, i.e. dry particle coating based on the mechanofusion and simple mixing through shaking manually, were adopted to prepare composite particles and powder mixtures, respectively. The micrometer-sized core particle was polymethylmethacrylate (PMMA), and the coating nano-particles were TiO2, Al2O3, or SiO2. Surface morphology of the treated particles was analyzed by digital processing of SEM photographs, and flow behavior of powders in the vibrating capillary tube was studied with particular attention to the effects of the kind of nano-particles, its concentration, and the treatment method. Two factors were introduced to evaluate the flowability; one is the critical amplitude of vibration making the powder flow, and the other is the mass flow rate as a function of the vibration amplitude. The experimental results showed that the mechanofusion treatment gave a remarkable improvement in the powder flowability evaluated by the two factors mentioned above. The general tendency of the improvement can be explained by the projected-area ratio defined as the ratio of the total projected-area of nano-particles adhering to core-particle surface and the projected-area of the core-particle itself.
Trioxane extraction with supercritical fluids was directly applied to an actual trioxane synthesis system. The reaction/extraction was conducted for an aqueous solution of formaldehyde with an acid catalyst in the presence of supercritical fluid. It was found that carbon dioxide is the best extractant and a trioxane solution at a concentration of more than 40% was obtained by one pot with supercritical fluid extraction from aqueous formaldehyde and a catalyst. Study on the reactive extraction by supercritical carbon dioxide fed continuously revealed that the larger vapor/liquid phase ratio is preferable, and the optimized reaction temperature is 373 K.
An advanced spent fuel management process using a molten LiCl salt for the purpose of reducing spent oxide fuel to a metallic form generates a waste salt containing alkali, alkaline-earth, and some rare-earth fission products. A periodic removal of the high heat-generating Cs and Sr should be accomplished to reuse the salt since a recycling of the LiCl waste salt to a process stream is required to decrease the total amount of waste to be disposed of. In this study, zeolite 4A was proven to have desirable properties for the removal of the Cs and Sr elements from an LiCl molten salt phase, and the ion-exchange characteristics of zeolite in the molten salt were investigated. The adsorption of the Cs and Sr elements in an LiCl molten salt reaches nearly a constant value after 2–4 h of contact with the zeolite. The salt-occluded zeolite was produced in an LiCl molten salt, and then its ionexchange and salt occlusion properties were studied experimentally. The result indicates that zeolite 4A occluded between 10 and 11.5 salt molecules, and the salt-occluded zeolite was found to be a very effective molecular sieve for sorbing the Cs and Sr in the LiCl waste salt.
A diagnosis system to search multiple origins of failures using a signed digraph has been developed. Under the situation in which measured values of sensors are stuck normal values, the system cannot find multiple origins of failures properly and often makes erroneous or impossible diagnosis. In order to overcome this problem, an improved algorithm which can search the candidates of multiple origins and also the sensors with stuck faults is proposed. The usefulness of this proposed algorithm is demonstrated by its application to tank-pipeline systems.
This research describes the application of a multivariate statistical process control method to a pilot-scale sequencing batch reactor (SBR) using a batchwise nonlinear monitoring technique for a denoising effect. Three-way batch data of normal batches are unfolded batch-wise and then a kernel principal component analysis (KPCA) is applied to capture the nonlinear dynamics within normal batch processes. The developed monitoring method was successfully applied to an 80-l sequencing batch reactor (SBR) for biological wastewater treatment, which is characterized by a variety of nonstationary and nonlinear characteristics. In the multivariate analysis and batch-wise monitoring, the developed nonlinear monitoring method can effectively capture the nonlinear relations within the batch process data and clearly showed the power of nonlinear process monitoring and denoising performance in comparison with linear methods.
We developed smaller sized quantum dots covered with sodium 2-mercaptoethanesulfonate which has a sulfonyl group (QDs-SO3–), and compared its stability in acid, salt and buffer solutions with that of the quantum dots covered with the mercaptoundecanoic acid (QDs-MUA) and covered with the NH2 group (QDs-NH2). We found that the QD-SO3– well disperses in these solutions without quenching and this stability holds on for 24 h. Next, we investigated the effect of Sheep Serum Albumin (SSA) coating. The SSA coating stabilizes the QD-MUA in the solutions. However, for the QD-SO3–, it does not have any significant effect. It implies that the QD-SO3– has advantages over the other quantum dots on the stability in the solutions. These results suggest that the novel surface processing using the sulfonyl group expands the possibilities of applications for various fields.
The metal oxidation for two general cylindrical geometries is analyzed using a perturbation method. Unlike previous models, the reaction rate and the oxygen dissolution into metal are taken into account. One-dimensional Landau transformations is applied to transform a moving domain by volumetric expansion or contraction during oxidation into a fixed domain. The oxide film thickness predicted by the perturbation analysis is compared to that by a numerical analysis as well as to that measured experimentally.
Submicron- and nanometer-sized red luminescent particles (Y2O3:Eu3+) were successfully generated by flame spray pyrolysis (FSP) and the effect of the type of the atomizer, i.e., the ultrasonic nebulizer (UN) and the two-fluid nozzle (TFN) sprayer, on the particle characteristics was investigated. The prepared particles were characterized by field emission-scanning electron microscopy (FE-SEM), an X-ray diffractometry (XRD) analysis and spectrophotometry. UN-FSP produced non aggregated particles with a mean diameter of 754 nm and the relative photoluminescence (PL) intensity (ratio of emission intensity of generated particles to that of commercial particles) varied from 0.36 to 1.01. The Y2O3:Eu3+ particles generated by TFN-FSP were softly agglomerated with a mean diameter of 24 nm and the relative PL intensity ranged from 0.21 to 0.24. Regardless of the type of the atomizer used, the generated particles were dense and spherical in the cubic phase and highly crystalline. These results show that TFN-FSP is a versatile method of producing Y2O3:Eu3+ nanometer-sized particles compared with UN-FSP.
The electrochemical reduction of Ta2O5 in an LiCl–Li2O molten salt system has been studied in an electrolytic cell with an integrated cathode assembly at 650°C. The integrated cathode assembly consists of an electric conductor, Ta2O5 and a porous magnesia membrane. The metallic tantalum is prepared successfully by the mechanism of an electrode reaction followed by a chemical reaction in the range of voltage between –2.47 V and –3.46 V. The chemical and physical properties of the metallic tantalum are influenced by the applied current related to the reaction rate. The XRD analysis indicates that the tantalum samples prepared at the applied current above 1.0 A have both of bcc and tetragonal structures. The particle size of those samples is similar to that of the fresh Ta2O5.
A three-dimensional structure formation simulator of colloidal nanoparticles during drying is developed. Motion of the nanoparticles is modeled by Langevin equation, in which forces exerted on each nanoparticle consist of contact force, capillary force, Brownian force, van der Waals force, electrostatic force and fluid drag force. Drying of the colloid is expressed by a decrease of the thickness of a colloid film. The present simulator is applied to a drying process of the colloid film on a flat substrate, so that a multilayer structure of nanoparticles is formed. The structure formation is visualized with time, and the vertical and the planar structure of nanoparticles are evaluated temporally and quantitatively. The result indicates a mechanism of multilayer structure formation of colloidal nanoparticles during drying.
Environment-friendly anodizing of aluminum was developed. This method used high-pressure carbonic acid aqueous solution as an electrolyte solution. The anodic oxide film was formed under conditions that the anodizing voltage was 50–250 V, the electrolytic temperature 10–70°C, the electrolytic pressure 0.1–30 MPa and the electrolyzing time 10–600 min. The thickness of the oxide film increased with the increase in the anodizing voltage, electrolytic temperature, electrolytic pressure and the electrolyzing time. It was around 0.1–2.0 μm. The growth ratio of the barrier layer, which is defined by dividing the thickness of the barrier layer by the anodizing voltage, was 1.1 nm/V. The ratio of the average cell size to the anodizing voltage was 2.1 nm/V. These values were close to those of oxide films of aluminum produced in a conventional electrolytic bath such as the sulfuric acid bath.
Tetrachloroethylene (PCE) aqueous solution was used as the sample to be decomposed, and the effects of ultrasonic conditions (intensity and frequency) and reactor diameter on the PCE decomposition performance were investigated under a constant volume of liquid. The spatial distribution of PCE concentration in the reactor and the decomposition conversion were measured. The liquid mixing time was measured, and the reaction fields were visualized by using sonochemical luminescence. The spatial distribution of PCE concentration was relatively uniform for 100 and 200 kHz, while the PCE concentration was higher at the lower part of the reactor than at the upper part of the reactor for 500 and 800 kHz. Under the present range of ultrasonic frequency (100–800 kHz), the decomposition conversion increased with decreasing frequency. The reactor diameter was found to have an optimum value for the decomposition performance under the constant liquid volume.
The removal performance of chlorinated organic compound from the porous material under the ultrasonic irradiation was experimentally investigated. As the model PCB and the solvent, o-dichlorobenzene and hexane were used. Wood chips impregnated with o-dichlorobenzene were used as the sample. By the ultrasonic irradiation, the removal ratio rapidly increased and became almost unity after 120 min for the sample with 10 mm in length. The removal rate for the ultrasonic irradiation was much higher than that for shaking. The difference in removal ratio between the ultrasonic irradiation and the shaking became larger as the sample was bigger. The removal ratio increased with increasing sound pressure and became constant beyond a certain sound pressure. Under a fixed sound pressure, the removal ratio at 28 kHz is nearly equal to that at 45 kHz.
An index to express the degree of anxiety/expectation quantitatively is presented. The new index is defined based on the probability of occurrence of the undesirable/desirable matter by introducing the concept of the information entropy and the weight of value of the undesirable/desirable matter. The definition has no factor of feeling and bases only on the change of amount of information entropy about the occurrence/disappearance of the undesirable/desirable matter. Additionally, the way of application and the usefulness of the newly defined index are made clear by applying it to several close-at-hand problems. Particularly, the new index shows its usefulness clearly when it is applied to make decisions with security.