Velocity distributions of particles and bubbles were measured by the laser transmission method, which has hitherto been used to measure the specific interfacial area of dispersed phases such as solid particles, liquid droplets, and bubbles. Measurements were carried out using a laser beam oscillator and two optical-fiber probes. Apparent axial velocities were estimated by dividing the distance between the two probes by the time difference between signals from the two probes. As the laser beam oscillator and probes were set outside the column, the velocities of particles and/or bubbles in the column were measured without disturbing the system. To obtain a relationship between the apparent axial velocity measured by the present method and true axial velocity component, the effects of the direction of movement of particles and the distance between the two optical fibers were discussed based on a simple model that takes this direction of movement into account. Comparison of the apparent axial velocities measured by the present method with the velocities measured by use of a video camera showed that the present method gave reasonable results when appropriate correction was made for the effects of the direction of movement of particles. Using the present method, we evaluated the velocity distribution of particles circulating in an external-loop airlift column. The effect of number of particles charged in the airlift column on the velocity distribution was found for low gas velocities. Also, the rising velocity distributions of bubbles in a standard bubble column were measured. Change of the rising velocity distribution with gas velocity was found to correspond with the change of flow pattern from bubbly to churn turbulent flow.
Because flows in a stirred tank are complicated by rotating blades and baffles, the mechanism of fluid mixing is difficult to analyze. The pathlines of fluid particles in this system are characterized by unsteadiness, three-dimensionality and a lack of symmetry. However, the flow field does not necessarily involve the same complexity as the pathlines. In this study, we propose a simplified flow model of the complex flow motion in a stirred tanks, in which the flow velocities are expressed as a linear combination of elementary flows. By tuning the parameters contained in the model equations, changing the combination and relative intensities of the components, we were able to simulate flows corresponding to various shapes, numbers and positions of blades and baffles. This simplified flow model is useful for finding the elementary flow essential to fluid mixing in a stirred tank and elucidating the mechanism of mixing.
Quite a lot of researches on mixing vessels have been studied in chemical engineering area. Because there are a lot of papers and patents, it is difficult to understand mixing operations for engineers to design and operate mixing vessels. In this paper, the authors explain the performances of mixing vessel by the power consumption as the key word. It is shown that we can estimate the flow characteristic, the mixing characteristic, the heat transfer characteristic, and mass transfer characteristics in the turbulent mixing vessel by using the power consumption. Moreover, the power correlations presented by Hiraoka and Kamei were as useful as Nagata's correlations.
Influences of size segregation of fluidized particles and the feeding height of an object on its floating and sinking in a gas-solid fluidized bed were investigated. Unclassified sands were used as fluidized particles in order to reduce cost and skip classification process in fluidized bed medium separation. When superficial air velocity ratio was relatively small, specific gravity at the top and bottom of fluidized bed differed because of particle size segregation. Furthermore, the floating and sinking varied according to the feeding height. As a result, the separation accuracy deteriorated. On the other hand, when superficial air velocity ratio was relatively large, the floating and sinking did not vary with the feeding height. However, the floating and sinking were unstable, and the separation accuracy also deteriorated because fluidization intensity was too strong. Hence, when unclassified sands are employed as fluidized particles, intermediate superficial air velocity ratio should be selected in order to prevent particle size segregation and strong fluidization intensity.
Preparation of composites of spherical reactive polyimide particles (about 3 μm) with an amino group and a spherical porous silica gel (about 50 μm) was investigated by dry impact blending. The composite particles obtained consisted of spherical porous silica gel particles (host particles) covered by a film flat, reactive polyimide particles (guest particles). It was confirmed that the composite particles retained the original form, porosity, and handling of the host particles. In addition, the amino group of the guest particles covering the surface of the composite particles was reactive toward acid chloride.
Waterglass was selected as an inorganic binder for use in solidification by drying, and a packed bed of glass particles wetted lightly with aqueous solution of the binder was solidified by microwave drying. The drying experiment was performed with a constant volume of binder in the dried sample, and the initial liquid fraction (the volume ratio of the binder solution to the void in the packed bed) was changed in the range from 0.10 to 0.35. Changes in the drying rate and the surface temperature were measured. As a result, all of the drying rate curves against the mean moisture content with the different initial liquid fraction partly overlapped in the low range of moisture content and a master curve was obtained, while no master curve was found for the surface temperature curves against the mean moisture content. The result for waterglass binder with an initial liquid fraction of less than 0.15 was compared with the result for gelatin as an organic binder in the authors' previous study. The maximum drying rate of the waterglass binder was more than double that of the gelatin binder.
Sol-gel derived nanoporous TiO2 membranes were prepared by coating a porous support with TiO2 colloidal solution, followed by drying and calcination at 450°C. Self-tuning photocatalytic deposition was applied for the preparation of palladium membrane for hydrogen separation. The result of EPMA for cross section of Pd–TiO2 membrane suggested the thickness of Pd–TiO2 layer was around 1.5 mm. The permeance of hydrogen and nitrogen for Pd–TiO2 membrane at 200°C decreased to about 1/4 of initial values in the first 3.5 h of irradiation and approached steady-state values, indicating the possibility of self-tuning of the palladium layer. It was found that annealing improved hydrogen selectivity. For example, hydrogen to nitrogen permselectivity for Pd–TiO2 membranes annealed at 450°C in air for 8 h increased from 7 to 29 with hydrogen permeance of 6.3×10−6m3·m−2·s−1·kPa−1 at 200°C. This is because palladium particles could plug into the inter-particle pores after annealing the Pd–TiO2 membrane.
Control of an industrial process involves many cascade control systems as well as single control loops, all of which interact with each other. Therefore, from a plant-wide point of view, the industrial process can be regarded as an enormous multivariable control system. To access the performance of industrial process control, it is extremely useful to identify its dynamics. This study proposes a technique for systematic plant-wide closed loop identification.
A coated film sample was prepared by applying commercial glue composed mainly of an aqueous solution of polyvinyl alcohol (PVA) on a polyester sheet. The sample was placed on a thermal insulator, and a batch drying experiment was performed with hot air. In this study a modified temperature change method was proposed. This method obviated the need to measure the overall mass of the moisture removed during drying. The drying rate of the sample was successfully obtained from the modified method by using the surface temperature history during drying measured by a radiation thermometer. The decreasing drying rate measured at the same mean moisture content decreased with increasing film thickness in the high range of the mean moisture content. The rate curves for various film thicknesses overlapped in the low range of the mean moisture content. The result was similar to a previous one for PVA aqueous solution. Additionally, an attempt to correlate the measured drying rate curves by using the drying characteristic model proposed previously by the authors on the basis of the Fick-type diffusion model and considering the acceleration effect on the mass transfer by drying stress showed good agreement between the correlated and the measured results.
SF6 is designated as special reduction gas in the Kyoto Protocol because of its high GWP (23,900 times that of CO2). In Japan, the volume of SF6 emissions is decreasing in spite of increasing SF6 production in recent years. To develop thermal decomposition technology for surplus SF6 and to study the apparent SF6 decomposition rate, we investigated fundamental data such as the rate constant and activation energy of SF6 decomposition using a tube reactor. It was found that SF6 decomposition in both He and Ar base gases was a first-order reaction with respect to SF6 concentration. Activation energy of SF6 decomposition was 354 and 371 kJ·mol−1 in He and Ar base gas, respectively. The rate-determining step of SF6 decomposition was the gas phase reaction.
Elution and removal experiments of heavy metals such as Pb, Cu and Cd from the artificial contaminated soil were carried out by using citric acid and EDTA as chelating agents. Optimum conditions for batch operation were found to be 0.1 mol/dm3 citric acid, pH 3 to 4, and 30 minutes of contact time. When EDTA was used instead of citric acid, a suitable concentration was 0.025 mol/dm3. From consecutive elution experiments by a column method, Volume of eluent required to meet the environmental standard value for soil contamination was investigated. It was found that heavy metals can be removed by passing 14 times as much chelating agent solution as the amount of deposited soil. The obtained dissolution rate is considered to be applicable as a design guide when the method of heap leaching type is applied to the treatment of contaminated soil.