The turbulent transport of fully developed combined convection between vertical smooth parallel plates, where the inertia force acts parallel to the buoyant force, is investigated numerically by combining different types of two-equation turbulence models that are applicable to the velocity and the temperature fields. One purpose of the present paper is to analyze the turbulent transport phenomena affected by buoyancy, which they have not been discussed empirically owing to the difficulty of measurement. In particular, the behavior of turbulent Prandtl number has not been addressed numerically and empirically for the buoyant-dominated flows such as natural convection and combined convection. A second purpose is to confirm the applicability of the two-equation turbulence models to turbulent combined convection. Turbulent transport in combined convection is modeled by introducing various buoyant-induced terms to the statistical turbulent quantities such as Reynolds stress and turbulent heat flux. It was found that the models utilized can simulate the heat transfer and fluid flow of turbulent combined convection.
Cationic surfactant solutions that form rod-like micelles are known to cause remarkable dragreducing effect. However, heat transfer reduction also occurs simultaneously in the drag-reducing systems. Application of this drag-reduction technology to the heat transfer medium in a district heating and cooling system may thus decrease the heat transfer capacity of the heat exchanger in the refrigerator. In this work, we evaluated the heat transfer characteristics of a drag-reducing aqueous solution containing oleylbis (hydroxyethyl) methylammonium chloride as the cationic surfactant and sodium salicylate as the counter ion. The heat transfer tubes examined were smooth copper tubes and the internally grooved tube with spiral ridges inside, both of which are employed in refrigerators. In the grooved tube with redge of narrow pitch, it was found that heat transfer reduction did not occur in the velocity range. It was also found that the heat transfer reduction correlated well with the wall shear rate.
Leaching velocity of Au, Ag, Pt and Pd was investigtated using four leaching agents : aqua regia, I2/KI, bleaching powder and thiourea. In the aqua regia leaching, Pd and Au are rapidly leached, while Ag and Pt are little leached. In the 12/KI leaching, Au and Pd are rapidly leached, whereas Ag and Pt are not leached enough. In the bleaching powder leaching, Au and Pd are rapidly leached compared with a small leached velocity of Ag and Pt. On the other hand, Au and Ag are rapidly leached by the thiourea leaching method, but then Pd and Pt are not leached at all. These leaching phenomena can be explained by the ability to form stable complexes with precious metal ions and the oxidation power of the leaching agents.
Four independent stream functions which satisfied the boundary conditions were presumed for an agitated vessel. Differential equations for the stream functions, which were derived from the Navier-Stokes equation, were solved numerically. An analysis of the cross-correlation of the velocity components showed that the low frequency fluctuations in the flow corresponded to large-scale flow patterns over the entire vessel. The correspondence was also observed experimentally. The period of the low frequency motion was about 34 times that of the external input stream function, which agreed with the value of 20-30 times the blade passage frequency that was found experimentally. The increase in the number of the stream functions from 3 to 4 contributed to describing the characteristics of the local phenomena in the flow rather than to changing the dynamics, as was shown by the results of the frequency analysis and the mutual correlation function. It was confirmed that this deterministic analysis with the small number of variables was very effective to predict the dynamic behavior for the low frequency fluctuations in an agitated vessel.
The thermal degradation rate constant of plastics containing polypropylene, polyethylene and polystyrene was analysed by using the distributed activation energy model. The values of activation energy E and frequency factor ko were widely distributed and differed between samples tested. The ko value was well correlated with E. It is extremely important to take the E distribution into consideration in estimating the weight of un-volatilized matter accumulated in the waste plastics degradation reactor.
Preparation and processing of semiconductor nanoparticles by using reverse micellar systems were investigated. Size-controlled nanoparticles of metal sulfides such as CdS, ZnS and their composites, and metal oxides such as Ti02 were successfully prepared, and the formation mechanisms are discussed. The immobilization of these nanoparticles on polymer or silica supports through several new techniques including surface modification and in situ polymerization was investigated. The properties of the resulting semiconductor nanoparticles-polymer and -silica composites as photo-functional materials such as photocatalysts were elucidated.
Fine particle materials were prepared by using an emulsion liquid membrane (ELM, water-in-oil-in-water (W/O/W) emulsion) system. Metal ions were extracted from the external water phase into the organic membrane phase containing extractant (cation carrier), and then stripped into the internal water phase to make submicron-or micron-sized oxalate, carbonate and phosphate particles, of which the size, morphology and crystal structure were well-controlled. As case studies, the preparation of well-defined spherical oxalate particles of rare earth metals, spherical calcium carbonate particles of hollow structure, spherical calcium phosphate particles, composite Sr-Pb oxalate particles, acicular Co ferrite and Ni ferrite fine particles, and rare earth oxide spherical phosphor particles was demonstrated, and the properties and functions of the internal water phase as a microreactor are discussed.
Corrosion behaviors of polymeric materials were classified into diffusion-controlled systems and reaction-controlled systems. In the former, in which the diffusion coefficient is small, the polymer decomposed from its surface. In the latter, in which the reaction rate of decomposition is small, the polymer degraded after penetration of the ambient solution. In the corrosion of polyamide (PA) by sulfuric acid, mechanism found to involve the simultaneous diffusion of sulfuric acid into PA and the hydrolysis of PA. A kinetic equation representing the decrease in molecular weight of PA by hydrolysis was then proposed, and the change in sulfuric acid concentration distribution over time was calculated using the experimentally determined diffusion coefficient of sulfuric acid into PA. Finally, the rate of PA corrosion was estimated numerically by combining the change in sulfuric acid concentration and the kinetic equation of molecular weight decrease. The analytical results agreed well with the experimental ones. A generalized corrosion model could be established by adjusting the diffusion coefficient and the rate constant of the kinetic equation in the analytical expression.
Magnetic iron fine-particles were produced by dehydration and reduction of acicular a-goethite particles. To discuss the relationship between the particle structure and coercivity of the produced iron fine particles, morphological properties such as size and acicularity during reaction processes were quantitatively measured. The experimental results showed that average particle sizes and aspect ratios of the iron fine particles are reduced by up to 25 and 40% of those of the goethite particles, respectively. The presence of water vapor during the hematite reduction process inhibited the decrease in the aspect ratio, thereby improving the coercivity of the product iron particles. Furthermore, the relationship between the aspect ratio and coercivity of the iron particles can largely be explained by the Jacobs-Bean model.
The accuracy of measuring thermal energy of carbon dioxide removal was confirmed to be improved by using an advanced bench-scale CO2 recovery equipment (gas throughput 6 m3/h). The energy for regeneration of spent liquor was evaluated to be 4.8 x 103kJ/kg CO2 in the case of monoethanolamine as an absorbent. This value is found to compare to that encountered in a pilot plant (gas throughput 600 m3/h), whose value has been found to be 3.9 x 103kJ/kg CO2. Such a bench-scale test can reduce the liquid quantity to 1/50 of that used in a pilot plant.
Membrane separation technology, one of the most important industrial separation technologies, has been applied to various industrial fields. One of the serious problems in the membrane separation is fouling due to contamination of the membrane, and cross-flow system commonly used does not generate sufficient shear rate in the fluid near the membrane surface to prevent the fouling. Therefore, rotating membrane and vibrating membrane system have been proposed and tested. Of these, vibrating membrane system effectively provides the biggest shear rate in the fluid near the membrane surface, but its performance has not been explicitly shown in previous studies. The purpose of this study is to investigate the effects of the membrane vibration on separation characteristics. The permeate flux for a latex solution through the membrane was measured under several vibrating conditions and the effects of the amplitude and frequency of vibration on the permeate flux were investigated. The results show that the permeate flux increases with the shear rate in the fluid near the membrane surface and the effect of frequency on the permeate flux is more significant than that of the amplitude.
Following the authors' previous numerical and experimental analyses of a reverse osmosis desalination system utilizing the static pressure head in the case of a seawater channel laminated on one side with a reverse osmosis membrane, numerical analysis is performed for a system in which the seawater channel is laminated with the membrane on both sides. A dimensionless expression is formulated from the numerical results to predict the transmitted fresh water flow rate from the submerged depth, the physical properties of seawater, the permeability of the membrane, and the width and the axial length of the seawater channel. It is also estimated that the present desalination system may reduce the specific power consumption in the order of 50% in comparison with those of reverse osmosis desalination systems on land.
Control of granule compressive properties is important for making higher reliability ceramics. In this paper, the effect of ambient conditions (temperature and relative humidity) during preservation and compressive strength is examined for irdividual granules. The compressive strength of the individual granule was fand to depend on the ambient greatly conditions. The reason is explained qualitatively in terms of the relation between the glass transition point of the PVA used as a binder in the granules and the relative humidity.
A theoretical model is proposed to describe the hysteresis of phase inversion and the effects of stirrer speed and physical properties on phase inversion. The model represents phase inversion as the structural instability of the equation of population balance in agitated liquid-liquid dispersion systems. Phase inversion experiments were performed on liquid-liquid dispersion systems composed of water and hydrocarbon mixtures whose densities were adjusted to that of water with carbon tetrachloride. Good agreement was demonstrated between the volume fraction of the dispersed phase estimated by the model and that obtained experimentally.
This study examines the effects of imperfect mixing on the ease of control in continuous crystallization processes. A compartment model was employed to describe imperfect mixing in a crystallizer vessel, and size-dependent classification functions were introduced to describe the internal classification of crystals. The size-dependent classification functions were built by performing intensive CFD (computational fluid dynamics) calculations. The nucleation rate equation used in the perfect mixing model was extended to allow the domination of nucleation by crystal-impeller collision to be considered. The index of ease of control was used to evaluate how easily a crystallizer can be controlled. This index indicates the strength of control action relative to that of the physical feedback effects which cause oscillation. In this work, the idea of ease of control was extended so that the ease of control could be evaluated based on the compartment model. It was shown that the imperfect mixing and the internal classification strongly influence the operating conditions under which a crystallizer can be controlled easily. The internal classification also strongly affects the spatial distribution of supersaturation in the crystallizer vessel.
A method based on the comparison of current and previous distributions of class frequency is proposed to detect state changes. The proposed method was successfully applied to an industrial waste-water plant using the classes obtained as the outputs from the ART2 neural networks.
In photooxidation tests of nicotinamide adenine dinucleotide (NADH) in titanium dioxide slurry containing Ag+, Cu2+, Ni2+, Fe3+, [Fe(CN)6]3- or Fe(III)-EDTA as an electron acceptor, the oxidation rate of NADH was the highest when Fe(III)-EDTA was included in the slurry. In the range of initial concentrations of Fe(III)-EDTA of 0-100 x 10-3 mol/m3, it was found that the oxidation rate of NADH increased with an increase in Fe(III)-EDTA concentration during the early phase of photoreaction, and thereafter the reaction system reached a pseudo-steady state with elapsed time, giving an approximately constant oxidation rate of NADH.
The application of temperature swing adsorption (TSA) method for De-NOx and De-SOx from flue gas was examined. The honeycomb adsorbent used in the TSA was continuously rotated to effect reiteration of the adsorption and desorption steps. In this study, silicalite was used in the De-SOx TSA plant and Co ion-exchanged ZSM-5 was used in the De-NOx TSA plant to separate SO2 and NO from artificial flue gas. By optimization of operating conditions in the single De-SOx TSA plant, the reduction efficiency of SOx was about 93%. In the combined De-SOx TSA plant and De-NOx TSA plant, the reduction efficiencies of NOx and SOx were about 80% and 83%.
A dechlorination process to utilize poly(vinyl chloride) (PVC) in ironmaking has been developed in a 1,000 t/y semi-commercial facility with a newly designed indirect heating rotary kiln. In this process, coarse coke was supplied to prevent agglomeration of PVC particles and adhesion to the inner wall of the kiln during PVC dechlorination. A dechlorination efficiency of over 95% was attained at a processing temperature of 325°C and a retention time of 30 min. In addition to HCl, C1-C4 hydrocarbons, benzene and tar were generated by PVC pyrolysis. The content of these by-products was less then 3% under the conditions of 95% dechlorination efficiency, although it increased slightly with an increase in processing temperature and retention time of PVC. The supply of coarse coke with PVC was also fund to be effective in promoting heat transfer to the PVC layer in the kiln. The results obtained in the 1,000 t/y semi-commercial plants, it was verified that this dechlorination process could be smoothly operated due to the coke particles. It can be concluded that this process contributes to the favorable recycling of waste PVC.
High temperature air combustion technology uses a high- cycle regenerative heat exchanger for preheating the furnace air to above 1,000°C, much higher than in conventional furnaces, and then fuel is injected into the air. This technology has found many practical applications in a variety of industrial furnaces. All investigations and discussions hitherto have focused on the steady-state condition, but in view of variations in the cycle time, and the fact that ejection of fuel and air, diffusion, mixing, ignition and combustion occur continuously and repeatedly, non-steady state and unstable phenomena can be expected. If the system is in an unsteady state, then it must be considered in a different way. Here, this problem is discussed based on combustion analysis results. High temperature air combustion flame has a wide spatial distribution of gas, and then that analysis should be implemented by utilizing the concept of a uniformly stirred reactor. Here we analyzed the test data using plug-flow type and well-stirred type reactors for a combustion exothermic model.
As a clean-up method for benz(a)anthracene (BAA)-contaminated soils (initial conc.: 500 mgkg-1), Fenton oxidation followed microbial treatment was carried out. First, we investigated the effect of the amounts of adedd of ethanol, Fe2+, and H2O2 on BAA removal, the results demonstrating that 0.75 or 1.0 ml of ethanol, 0.2 ml of 0.5 M Fe2+, and 0.25 or 0.3 ml of 30% H2O2 per 1 g of Kawazuna or Taisekido were ophnal. Second, under these addition amounts, 51% or 43% of benz(a)anthracene-7,12-dione (BAADI) was generated during oxidation of 97% BAA for Kawazuna or Taisekido, respectively. Third, when the biodegradability of BAA-contaminated Taisekido before and after Fenton oxidation was compated, it was found that 98% of BAADI was degraded after 63 d in comparison with only 12% of BAA over the same period. The results demonstrated that Fenton oxidation enhances the biodegradability of BAA through BAADI.