High quality, large-scale silica glass crucibles are strongly required for large-diameter silicon crystal production using the Czochralski process. Silica glass crucibles are usually produced from silica powder, which is fused at high temperature in an arc. In this study, we made a numerical analysis model taking account of the high temperature plasma jet induced by the arc between carbon electrodes, and measured the temperature variation of the fusing silica powder in a crucible-production process to verify the propriety of the analytical model. The calculated results were found to show good agreement with the actual temperature measurements. The arc furnace was found to have two different heating conditions that depend on the crucible positions. One is put under the control of high-temperature jet generated by the arc. The other is put under the control of radiation heat transfer near the electrodes. Our developed calculation model is expected to be of use in clasifying the optimum conditions for the fusing mechanism in the arc furnace.
To examine the effect of thermal diffusion on thermal CVD, compositional separation by thermal-diffusion effect in a locally heated rectangular flow channel was investigated experimentally and theoretically. Experiments were conducted for two binary gas mixtures (He-SF6 and Ne-SF6). The local concentration of SF6 was measured by a QMS by using a fused quartz capillary tube (75 μm I.D. and 900 mm in length) inserted into the flow channel to sample the mixtures. A series of three-dimensional numerical simulations of thermal diffusion in complex flow structures by means of the control volume method was conducted for the flow system. The numerical results showed reasonable agreement with the experimental results for these gas mixtures, for which an accurate value of thermal diffusion factor is known.
A preconditioning iterative method was applied to the numerical computation of natural convection in a confined region by the SIMPLE (Semi-Implicit Method for Pressure-Linked Equations) algorithm. The preconditioning was carried out by multiplying the matrix which consists of the entries of the coefficient matrix of a linear system of equations. It was concluded that the preconditioning is especially effective for the linear system of equations whose degree of diagonal dominance of the coefficient matrix is weak, such as of pressure correction. The computational time with the proposed precondition ingiterative method in the present study was almost 2.3 times faster than that by the standard SIMPLE algorithm.
The fourth-order central finite difference scheme was applied to the convection terms in three-dimensional Navier-Stokes equations to simulate directly the flow fields in a medium Reynolds number (Re=4,500) non-baffled stirred tank. The multi-block method was used for the computation. The rotational cylindrical coordinates with a constant angular velocity were used for the flow region including impellers and a disc. The usual cylindrical coordinates were applied to the other flow regions. The calculation was performed tosimulate the phenomena occuring in the case of water in a period of 64 seconds, which is sufficient time for obtaining various flow mechanisms and time averaged flow characteristics in a stirred tank. Visualization of the calculated results shows the mechanism of large scale vortices, their interactions and merger. The calculated results are in good agrement with the measured data. This means that the simulation well describes the fluid motion in a real stirred tank with impellers of complex geometry.
Air and particle motions in a bubbling fluidized bed of 310 pm glass beads, which were classified as B particles in the Geldart map, were numerically simulated. The two-dimensional Navier-Stokes equations for the air motion and the Lagrangian equations for the particle motion were simultaneously solved by taking into account the multi-body collisions among particles calculated using DEM and the mutual interaction between the air and the particles based on the drag and the lift forces. Comparison of the calculated and the experimental results showed that the calculated results represent well the real particle and air motions in the bubbling fluidized bed and clarify the mechanism of the various bubble dynamics, for example, bubble formation, coalescence and disruption in the bubbling fluidized bed. It was also found that the very high air fluctuating kinetic energy in the fluidized bed was mainly yielded by the pressure gradient velocity correlations and dissipated by the air particle interactions. Then the expression of the pressure term for the continuum model of the particle phase in the fluidized bed is the most important matter.
The purpose of present work was to observe isolated mixing regions (IMRs) under laminar flow conditions in a Taylor-vortex-flow reactor with the aspect ratio Γ = 2. In the range less than Re = 200, the IMRs took clearly the form of two toroidal vortices, one each in the upper and lower circulating flows. A simple core torus was observed in the case of a rotating inner cylinder with smooth surface, while a set of thin tori spirally wrapping around the core of the IMR was observed in the case of an inner cylinder with surface protrusions. Different numbers of tori were obtained for different numbers of protrusions, even at nearly the same Reynolds number. Hence, it can be considered that these structures of IMR depend on periodical perturbations caused by the rotating inner cylinder with protrusions. Numerical investigation using a Lagragian procedure determined the number of perturbations, ne, during one revolution of a marker particle around the IMR. It was found that ne corresponded to the number of thin tori. This indicates that the Poincare-Birkhoff theorem is applicable to the geometrical structures of the IMRs.
Experimental and theoretical studies have been conducted about the effect of apex cone at the inlet of cyclone dust box on particle classification. It was also examined about fine control of cut size with new type cyclone. By use of the apex cone at the inlet of the dust box, it is possible to decrease the fluid velocity component in the dust box and to reduce the re-entrainment of particles from the dust box. The cut size of the cyclone with the apex cone is smaller than that without the apex cone. The experimental results obtained agreed with numerical simulation. A new type of cyclone with an apex cone which is covered with a apecially shaped ring allowed cutsize movement from 2 to 40 am. Regarding the movement of cut size by the blow-up method, the cut sizeis related to the degree of incoming fluid volume inside the dust box. From the visual observation, the cut size increases with the decrease of flowing fluid inside the dust box.
Two-dimensional numerical computations were performed to investigate non-absorbable gas diffusing behavior in the evaporator-absorber in an absorption chiller. In this paper, special attention was paid to the effect of initial condition of non-absorbable gas distribution. When non-absorbable gas is distributed uniformly in the evaporator-absorber, overall heat transfer coefficient does not markedly decrease until the mean concentration of non-absorbable gas becomes 5 vol%. On the other hand, when non-absorbable gas is injected at a point near the upper corner of the evaporator in the same way as in the experiments, overall heat transfer coefficient markedly decreases and agrees with the experimental results. This indicates that the initial condition of non-absorbable gas distribution seriously affects the heat transfer characteristics of the absorber.Under uniform initial conditions, non-absorbable gas is kept in the recirculation region formed between the evaporator and the absorber when the mean concentration of non-absorbable gas is small. Upon injection, however, non-absorbable gas penetrates deeply into the upper region of the absorber. This causes the recirculation region disappearance. Then, the heat transfer markedly decreases in the absorber.
An experimental study was conducted on the spectral characteristics of a round water jet with an annular air flow. The round liquid jet was ranged in the turbulent flow region, whereas the annular air flow is ranged from laminar to semi-turbulent flow. A high-speed video camera and image processing techniques were used to measure the time variations of liquid jet profiles in the radial direction. Power spectra and auto correlations of surface disturbances were calculated using FFT. Surface disturbance shaving a specific frequency showed the maximum growth rate. This specific frequency increased as the air flow velocity increased. From the results of autocorrelations of surface disturbances, the symmetric mode of surface disturbances showed periodicity, whereas the asymmetric mode showed a random nature. The periods of symmetrical waves became shorter with an increase of air flow velocity. The characteristics of droplet formation due to the disintegration of a liquid jet were also examined. The frequencies of droplet formation were measured from the mass median diameter of droplets and mass flow rates of the liquid jet. They showed reasonable agreements with the frequencies of the surface disturbance having the maximum growth rate.
Numerical and experimental studies have been conducted on steam-reforming of methane in a packed bed type membrane reactor with silica-zirconia porous membrane. Methane conversion of the membrane reactor exceeded the thermodynamic equilibrium value, and puerility of production of H2 was generally above 95 vol%. The model provided good agreement between experimental and theoretical results. In the application of the porous membrane to the membrane reactor, water vapor permeation had a significant influence on the performance of the membrane reactor.
To investigate the effect of temperature and coexisting gas on the HCl removal from hot flue gas by limestone, the HCl absorption by limestone and the HCl emission from CaCl2 were experimentally studied, focusing on the time course of their reactions. A continuous HCl analyzer was used to measure the HCl concentration in the gas at the exit of the fixed bed reactor including limestone or CaCl2 particles. The melting point of CaCl2, of 1,045 K seriously affects both the absorption and the emission of HCl. The optimum temperature for the HCl absorption by limestone lies in the range between 923 K and 1,023 K. The emission of HCl from CaCl2 markedly increases above the temperature of 1,045 K. Of coexisting gases, SO2 interferes with the reaction between HCl and limestone. A higher ratio of moisture in the gas gives rise to a higher HCl emission from CaCl2.
Decomposition reactions of polyvinyl alcohol in high temperature and high pressure water were analyzed in the temperature range of 200 to 400°C and pressure range of 1.5 to 33.8 MPa. Qualitative analysis of reaction products showed that not only organic acids but also aromatic compounds such as benzaldehyde, benzophenone and acetophenone were present in liquid-phase products. These compounds were produced from polyvinyl alcohol by cyclization reactions accompanying thermal degradation and elimination of side chains.
Biodegradable capsules which consisted of recycled paper fibers as matrix material and limonene as core material were prepared by the simple nozzle method. Methyl cellulose was used as a binder of matrix fiber. Capsules were prepared by gelling methyl cellulose with tannic acid. It was investigated how such preparing conditions of capsules as the concentrations of methyl cellulose and fibers affected a few characteristics of capsules. It was found that the structure, mechanical strength and water absorbed and drying properties were strongly dependent on the preparing conditions.
Carbon dioxide removal was carried out for LNG-fired power station flue gas, using a pilot-scale absorber of about 25 m in height at an exhaust gas flow rate of 555 m3/h. The relationship between amine loss discharged from a C02 recovery system and the operating conditions and configuration of the washing water line equipped with an absorber unit were examined. The test result showed that outlet alkali (amine) concentration in the gas phase decreases with decreasing absorber outlet temperature. The alkali concentration was confirmed to decrease with a decrease in the alkali concentration in washing water. An improvement of washing water line by dividing it into two steps was found to be remarkably effective to decrease outlet alkali concentration. In the case of KS-1 solution, which is composed of sterically hindered amine and alkanolamine, excellent results were obtained by such a strategy to reduce amine loss : outlet alkali concentration ranged from 2.3 ppm to 10.4 ppm, and average amine loss amounted to 0.11 g-amine/kgCO2. This degree of amine loss is as low as 1/20 th of that of the conventional process. Both a low impact on the environment and a reasonable cost reduction can be attained by adopting a two-step washing water line.
Concentrations of particles which are collected with a suction nozzle from a space with dispersal particles tend generally to have a scatter. It is important to clarify the statistical properties of this scatter. The statistical properties of particle numbers collected by nozzle were simulated by generating particles in an imaginary two-dimensional space by the Monte Calro method. It was founded that the particle numbers collected from a subject space with dispersed particles obeyed the Poisson process in the case of both random distributions and distributions that were not variable with time. When the distributions of particles in the subject space varied with time, the values of the variances of collected particle numbers tended to be greater than their mean of values. In the simulation based on an assumed mass logarithmic normal distribution of particles in the subject space, the collected mass median diameters were estimated to be smaller with decreasing collected total mass of particles of less than 10μg.
Drops of sodium alginate solution were injected into calcium chloride solution of 10 wt% through a rotating nozzle to prepare calcium alginate micro-gel beads. We found that calcium alginate micro-gel beads of approximately uniform size could be prepared by this method. The average diameters of these calcium alginate gel beads 0.27-2.08 mm, which agreed approximately with values calculated by the estimation equation of drop diameters in the liquid-liquid system reported previously. The condition for proparing calcium alginate gel beads of uniform size was that (inside diameter of nozzle)2 x (rotation acceleration) / (viscosity of sodium alginate solution) ≒ฺ < 4.5 x 10-5 m4/ (kg s) .
Chaotic phenomena are observed in the combustion control systems of refuse incinerators. Since chaotic behavior is not desirable in refuse combustion control, it is necessary to develop a new control system which does not generate the chaotic behavior. In this paper, a new model is constructed with the aim of developing a refuse combustion control system in future studies. The model is based on operation data of a plant and its structure is easy to understand. A numerical simulation was carried out using the model obtained and the results were compared with the plant data from the viewpoint of the chaotic analysis. It was found that both of the steam flow rates are chaotic oscillations in which the embedding dimensions, the fractal dimensions and the maximum Lyapunov exponents are equal to each other.
We have proposed a new incineration system for clean and effective treatment system for waste liquids. Its main part consists of a triple coaxial tube burner, which is combined with a circulating fluidized bed and the SNCR method using a urea solution. In this paper, we focused on simultaneous reduction characteristics of NOx and SO2. Experimental results for the injection of urea solution show that the NOx reduction effect is inhibited by the temperature fall that results from of introduction particles into the riser. However, appropriate feed position and rate of introduction can improve this problem. We investigated the relationship between Ca/S molar ratio and SO2 reduction characteristics by experiments using limestone. SO2removal efficiency reached 93% at Ca/S=5.0 in this work. A model of intra-particle diffusion control of SO2 can explain this correlation. NOx emission behavior in experiments using limestone indicated the possibility of simultaneous reduction of NOx and SO2 in this system.
As a means to remediate benzo (a) pyrene [B (a) P] in ethanol used in washing B (a) P-contaminated soil, we investigated hybrid treatment (i. e., Fenton oxidation-microbial degradation) of concentrated B (a) P in ethanol (i. e., 62.3—108.5 mg L-1), where more than 99.8% of B (a) P was removed under a pseudo-first order reaction by Fenton oxidation. GC-MS and HPLC-UV analysis identified B(a) P-1, 6-, -3, 6-, and -6,12-dione as Fenton oxidation products, all of which are known to have lower toxicity than B (a) P. After Fenton oxidation, microbial treatment demonstrated that B (a) P-1,6-, -3,6-, and -6,12-dione are more easily degraded than B (a) P. These results indicate that the proposed hybrid treatment can be effectively applied to remediate B (a) P in ethanol washing solution.
Fundamental de-chlorination characteristics of Refuse-Derived Fuels (RDF), which were developed for use as a source of thermal energy, were studied by using both practical RDF and simulated RDF. For the simulated RDF polyvinyl chloride (PVC) or NaCl was added as a chlorine source. In the experiments, single pellets of RDF were burned in an electrically heated batch furnace. The de-chlorination efficiency was calculated by analysis of Cl in the residue after combustion. The efficiency obtained was compared with that obtained by chemical equilibrium calculation. HCl was found to be mainly emitted during the volatile matter combustion. The de-chlorination characteristics for PVC addition differ from that for NaCl addition. For the RDF with PVC and Ca(OH)2 addition, the de-chlorination reaction depends on the furnace temperature, and the optimum temperature is about 923 K. At low temperature the de-chlorination rate is slower than the evolution rate of HCl gas, whereas high temperature, CaCl2, which is produced by the de-chlorination reaction, is decomposed during the char combustion. For the NaCl addition, C1 is not absorbed into a Ca compound. According to chemical equilibrium calculation, NaCl is evaporated as a form of NaCl and Na2Cl2 vapors, and HCl is not produced.
To clarify the reaction mechanism of selective non-catalytic NO reduction using urea solution, we investigated the reaction kinetics. The mechanism of urea decomposition, which is the first step in the reaction, was considered by comparison of calculated and experimental results. In addition, the main reaction route was determined by sensitivity analysis. The model in which 1 mol each of ammonia and isocyanic acid are formed from urea explained the experimental results better than the model in which 2 mol of ammonia are formed. Sensitivity analysis indicated that the OH radical converts ammonia into NH2, Which reacts with NO to form NNH and finally N2. We also clarified the mechanism of decomposition of ammonia and isocyanic acid after the reduction of NO concentration.