New correlation equations to estimate the geometrical constant G (Takahashi and Sasaki, 1999) for just-drawdown speed of floating solids in solid-liquid agitated vessels were proposed. Different correlation equations were obtained for a radial flow impeller (disk turbine), down-pumping axial flow impellers (pitched paddle and marine propeller) and up-pumping axial flow impellers. The proposed equations are functions of power number Np, characteristic length D, impeller diameter d, distance from the static surface to the top of the impeller ht, and a correction factor for a square tank η. As a result of calculation, it was found that power consumption could be reduced by increasing d/D or decreasing ht/D in the case of radial flow impellers and down-pumping axial flow impellers. Conversely, in the case of up-pumping axial flow impellers, it was found that power consumption could be reduced by reducing d/D and that ht/D exists that minimizes power consumption. By using the proposed correlation equations, just-drawdown speed in a cylindrical tank with industrial baffle conditions and a square tank can be estimated with sufficient accuracy.
To clarify the phenomenon of orthogonal mixed convection heat transfer to water in a horizontal rectangular channel, experimental and numerical investigations were performed for channels of different cross-sectional aspect ratios heated from the bottom wall. First, heat transfer for pure forced convection was measured to obtain the basis of mixed convection heat transfer coefficients by using upper-wall heated channels, which can eliminate the buoyancy flow. A correlation equation was then proposed for pure forced convection heat transfer coefficients obtained from both experimental measurements and numerical solutions. Mixed-convection heat transfer was next measured under various conditions of Reynolds number and Grashof number. As a result, heat transfer was enhanced in all measured regions of Reynolds number. In particular, it was found that aspect ratio and Grashof number had little effect on heat transfer coefficients in the region of extremely low Reynolds number. When the Reynolds number increased, the heat transfer coefficients decreased with the decrease in aspect ratio. This tendency became more prominent as the Grashof number decreased. In the turbulent region, the heat transfer coefficients asymptotically approached those of pure forced convection under the given conditions of aspect ratio or Grashof number. The above results were qualitatively explained by the variations in temperature distributions and flow patterns of the cross-sectional channel obtained from the numerical analysis.
To clarify the effect of SOT medium concentration on the specific growth rate of the blue–green alga S. platensis, the alga was cultured in media containing SOT components at concentrations of 0.050–5.0 times. The specific growth rate of S. platensis decreased in cultures at 4.0 times or higher concentrations of SOT components. It also decreased when the medium was diluted to 0.40 times or lower concentrations of SOT components.
A model-based approach was employed to examine the applicability of a micro-Kalina cycle of up to 20 kW (about 373 K) with a working fluid of ammonia/water for low-grade geothermal heat energy. It was found possible to generate 15–24 kW using hot springs (353–393 K, 10,000 kg/h). It was also found that the micro-Kalina cycle shows a temperature glide like a Lorenz cycle under the simulation conditions, and that it had higher power generation performance than the organic Rankin cycle.
Model-based fault detection and isolation (FDI) is a method based on a mathematical model of a process, and the basic principle of the method, which is classified as a filter type, is the unknown input observer (UIO). This is the monitoring of the estimation error of the actual output. A feature of UIO is its robustness to process modeling errors, which plays an important role in improving the accuracy of FDI. However, conditions for its application are strict, and its application to the system identification model is difficult. In addition, although FDI automation is unavoidable in terms of practical application, past research has focused on improving diagnostic accuracy, and this point has been overlooked. In this study, a novel FDI filter for sensors and actuators based on a system identification model and a method for its automatic and robust application to plant-wide measurement noise are proposed. The effectiveness of the proposal was demonstrated by a simulator of the vinyl acetate monomer manufacturing process, and it was shown that plant-wide FDI can be automatically performed by dividing the large-scale process, identifying the systems, and combining the various models.
Hydrogels based on copolymers of (3-acrylamidopropyl)trimethylammonium chloride (DMAPAA-Q) and N,N′-methylenebisacrylamide were prepared for use in recovery of metal ions. Carbonate ions or oxalate ions, which are suitable for rare earth element (REE) ion recovery, were loaded into the hydrogel by immersing the gel in a solution containing the anions. The anion-loaded hydrogel was then added to a solution of neodymium (Nd) nitrate, dysprosium (Dy) nitrate, cobalt (Co) nitrate, or samarium (Sm) nitrate. The metal ions (Dy, Nd, Co, Sm) diffused into the gel and reacted with the supported anions to form sparingly soluble metal salts in hydrogel, which were easy to recover from the solution. The metal ions could be recovered from mixtures of Dy and Nd nitrates or Co and Sm nitrates in solution, which were assumed to be actual magnet waste solutions, as well as in the case of single ion solutions. Slight differences were found in the amount of each metal ion recovered, which were attributed to differences in solubility product of each ion with the loaded anions carbonate and oxalate. Furthermore, it was found that a gel could be regenerated by immersing it in a solution containing the anions when its recovery amount had reached the maximum value. Gels could be used repeatedly for metal ion recovery without loss of capacity. Therefore, a new metal ion recovery method using hydrogel with a quaternary amine in the sidechain to support anions is presented, which is simpler than the conventional recovery by precipitation or adsorption.
The performance and durability of calcium ferrite in repeated redox reactions was examined for the CO2–CO conversion with a solid oxygen carrier. Experimentally, a thermal-gravimetric analyzer and a fixed-bed flow reactor were used, and the effects of reaction temperature and reaction gas concentration on the oxidation/reduction reactions of calcium ferrite with H2 and CO2 were evaluated. Since CaO is converted to CaCO3 by the reaction of reducing carrier and CO2, calcium ferrite cannot be used as oxygen carrier in the case of high CO2 concentration and low reaction temperature. However, in the case of low CO2 concentration and a reaction temperature at which CaCO3 is not generated, calcium ferrite showed good redox performance regardless of the number of reaction cycles. CO production from CO2 in the fixed-bed flow reactor was also confirmed, and the CO2–CO conversion rate was unchanged after 35 cycles of the redox reaction.