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Volume 35, Issue 1
Displaying 1-15 of 15 articles from this issue
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Transport Phenomena, Fluid Mechanics and Mixing
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Numerical Computation of Apex Angle Effects on Taylor Vortices in Rotating Conical Cylinders SystemsMohamed Nabil Noui-Mehidi, Naoto Ohmura, Kunio KataokaArticle type: Research Papers
Subject area: Transport Phenomena, Fluid Mechanics and Mixing
2002 Volume 35 Issue 1 Pages 22-31
Published: 2002
Released on J-STAGE: June 14, 2002
JOURNAL RESTRICTED ACCESSThe occurrence of Taylor vortices between two conical cylinders of the inner one rotating and the outer one at rest is numerically simulated by the integration of time-dependent Navier-Stokes equations of the primitive variables. The motion is initiated by a progressive acceleration following a linear path of the inner conical cylinder rotation from the state of rest until its final rotation speed. In the integrated equations, the use of a coordinate transformation permitted to point out the apex angle α in the circular coordinates system and then to study the effects of α on the transient development of the Taylor-vortex structures, the steady states and the flow field characteristics. The numerical calculations have been achieved by the use of the SMAC method applied to a finite difference scheme for the case of a finite length. As a result, the symmetry of the Taylor vortices formed with regard to the mid plane for α = 0 does not exist anymore when the apex angle α becomes greater. The study of the flow field details showed that the contribution of the centrifugal forces becomes more important for increasing α due to the increase of the azimuthal component.View full abstractDownload PDF (2008K) -
A. S. Khare, K. NiranjanArticle type: Short Communications
Subject area: Transport Phenomena, Fluid Mechanics and Mixing
2002 Volume 35 Issue 1 Pages 107-110
Published: 2002
Released on J-STAGE: June 14, 2002
JOURNAL RESTRICTED ACCESSThis study reports on the unaerated power number (Np) and the ratio of aerated to unaerated power consumption (PG/P) for three disc type impellers in water and highly viscous Newtonian and non-Newtonian liquids. Modified disc type impellers (i.e. CBDT—concave bladed disc turbine and Scaba 6SRGT) were found to give lower Np and higher PG/P values than the flat bladed disc turbine or Rushton turbine (DT), in all liquids. Higher PG/P values are generally assumed to imply superior mass transfer potential of a given impeller. However, an examination of gas hold-up (which is closely linked to mass transfer) generated by DT, CBDT and Scaba 6SRGT, suggests that this is not necessarily true and further investigations may be necessary.View full abstractDownload PDF (464K)
Materials and Devices
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Yoshiyuki Shirakawa, Manabu Satake, Atsuko Shimosaka, Jusuke Hidaka, M ...Article type: Research Papers
Subject area: Materials and Devices
2002 Volume 35 Issue 1 Pages 63-67
Published: 2002
Released on J-STAGE: June 14, 2002
JOURNAL RESTRICTED ACCESSThermal and electrical properties in hybrid materials consisting of p-type amorphous selenium and n-type In2Se3 nanocrystals have been investigated. The In-Se system shows a monotectic reaction at the selenium rich region in the solidification process. A rapid quenching method was therefore used in order to fabricate amorphous samples embedding nanocrystals of which the average size was 45 nm under the present condition.
In the hybrid samples, melting point depression is observed by DTA measurements, and increases with increasing the numbers of the nanocrystals for an effect of the interface between the nanocrystals and the amorphous Se matrix. Green bodies of the amorphous Se are found to show negative differential conductivity (NDC). It seems that NDC is caused from dangling bonds, whose numbers are determined in the amorphization process. The dependence of the electrical conductivity of the hybrid green bodies on the In2Se3 concentration changes rapidly due to percolation transition. Electrical modification of amorphous Se can be performed by the addition of n-type nanocrystals, In2Se3. It is important for material design to modify the electrical properties without any restriction, because the electrical modification of an amorphous matrix by adding impurities has a solubility limit. The electrical properties in the present hybridisation are described in terms of the interfacial effect and the percolation phenomenon.View full abstractDownload PDF (443K)
Separations
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Hiroyuki Yoshida, Steffen Oehlenschlaeger, Yuji Minami, Masaaki Terash ...Article type: Research Papers
Subject area: Separations
2002 Volume 35 Issue 1 Pages 32-39
Published: 2002
Released on J-STAGE: June 14, 2002
JOURNAL RESTRICTED ACCESSA new method is proposed to improve the adsorption properties of basic, macroreticular (MR) anion exchange resins by forming a material composite with chitosan. In this study, one strong basic and one weak basic MR resins were used as matrixes for the new composites. Chitosan was accumulated in the macropores of the resins, and breakthrough curves for adsorption of CO2 on the new adsorbents were measured. The resulting equilibrium and kinetic data were compared with those of the original resins. The composite of strong basic MR resin and chitosan showed a more than three times higher adsorption capacity for CO2 than the pure resin. On the other hand, the mass transport in the adsorbent slowed down due to a narrowing of the pores by deposited chitosan.View full abstractDownload PDF (996K) -
Hideaki Yunoki, Kazuhito Nagata, Ken-Ichi Kokubo, Akira Ito, Atsuo Wat ...Article type: Research Papers
Subject area: Separations
2002 Volume 35 Issue 1 Pages 76-82
Published: 2002
Released on J-STAGE: June 14, 2002
JOURNAL RESTRICTED ACCESSNanofiltration experiments were carried out in order to investigate the effects of the mixture ratio and the change in concentration polarization on the operating conditions, in particular, the cross-flow velocity for the mixed solutions of sodium chloride (NaCl) and monosodium glutamate (MSG). The rejections of Cl– strongly depended on the mixture ratio but slightly on the concentration. The rejections of MSG were only slightly influenced by the mixture ratio and concentration. The apparent rejection of Cl– decreased with decreasing cross-flow velocity for the mixed solution in which the rejection of Cl– was positive (the concentration of Cl– was higher than that of MSG), and increased with decreasing cross-flow velocity for the mixed solution in which the rejection of Cl– was negative (the concentration of Cl– was lower than that of MSG). The effect of the cross-flow velocity on the apparent rejection of Cl– was reversed as the MSG concentration increased. These results suggest that the rejection of Cl– in the mixed solution could be governed by the accumulated solute of higher concentration. The change in the operating conditions appropriately corresponding to the mixture ratio with time would be required in order to effectively operate the concentration and/or diafiltration process.View full abstractDownload PDF (687K) -
Ryuich Egashira, Junjiro KawasakiArticle type: Research Papers
Subject area: Separations
2002 Volume 35 Issue 1 Pages 94-99
Published: 2002
Released on J-STAGE: June 14, 2002
JOURNAL RESTRICTED ACCESSIt is essential to know the mechanism and mass transfer rate of hydrocarbon permeation in the column type apparatus, which will be used as a permeator in a practical stage, for the permeator design, the selections of operating conditions, and, furthermore, the process design. The objective of this paper was to obtain the information on this mass transfer rate in the packed column selected among various column type permeators by authors in the previous study.
The permeation of hydrocarbon in the packed column was simulated by the multi-layer liquid membrane model. In the first, the results of this simulation were compared with those of the previous experiments. The dimensionless overall permeation coefficients estimated by the model agreed roughly with the experimental results. This revealed that this simple model could be used to study the mass transfer rate in the column. Secondly, further calculations by the model were carried out under wider ranges of operation factors. These calculations could clarify the effects of these factors on the rate.
The information acquired in these calculations can be useful for the permeator design, selections of operating conditions, and the design of other operations accompanying the permeator in the liquid membrane process, e.g., the emulsifier.View full abstractDownload PDF (2566K) -
Hideki Mori, Chikara Ito, Kenji Taguchi, Tsutomu AragakiArticle type: Short Communications
Subject area: Separations
2002 Volume 35 Issue 1 Pages 100-106
Published: 2002
Released on J-STAGE: June 14, 2002
JOURNAL RESTRICTED ACCESSThis paper presents a simulation algorithm for a distillation column with simplified heat and mass transfer models. The proposed simplified model neglects the liquid phase film resistance, thus reduces the number of variables and basic equations to about 2/3 and makes the algorithm more straightforward compared with the rigorous model. Simulation results are compared under different operating conditions. They show that (1) the simplified model can give simulation results close to those obtained by the rigorous model, and (2) it is numerically stable and yields the results with less calculation time.View full abstractDownload PDF (504K)
Particle Technology and Fluidization
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Ryusei Ito, Boris Golman, Kunio ShinoharaArticle type: Research Papers
Subject area: Particle Technology and Fluidization
2002 Volume 35 Issue 1 Pages 40-45
Published: 2002
Released on J-STAGE: June 14, 2002
JOURNAL RESTRICTED ACCESSThe dry based coating of core particles with soluble powder dispersed inside an impermeable layer of biodegradable wax was performed to control the release rate of core material. The mathematical model was developed to describe the release profiles by diffusion of core material through the percolation paths formed with soluble powder inside the coating layer. Then, the effective diffusivity was estimated by a random walk model. The experimental release profiles for the urea core particles coated with urea powder dispersed inside a lauric acid layer were quantitatively compared with simulated ones for different volume fractions of soluble powder and thickness of the coating layer. As a result, the low release rate of core material was proven to be obtained with low volume fraction of soluble powder dispersed in the thick coating layer.View full abstractDownload PDF (3154K) -
Myonghwa Lee, Yoshio Otani, Norikazu Namiki, Hitoshi EmiArticle type: Research Papers
Subject area: Particle Technology and Fluidization
2002 Volume 35 Issue 1 Pages 57-62
Published: 2002
Released on J-STAGE: June 14, 2002
JOURNAL RESTRICTED ACCESSElectret filters are frequently used in air cleaners because they have a lower pressure drop than the mechanical filters at the same collection efficiency. Manufacturers of electret filters have tried to increase the electrical charge density of electret fibers in order to improve the collection performance. Through these efforts, high-performance electret filter (HPEF) is developed and a question is raised on whether the previous prediction equations for collection efficiency are applicable to these HPEF because the prediction equations were never tested for such high charge density electret filters. In the present work, we measured the collection efficiencies of recently-developed HPEF and studied the applicability of previous prediction equations for collection efficiencies. As a result, HPEF had the electrical charge density twenty times as high as that of the previously-studied electret filter and the single fiber efficiency was close to the maximum limit determined by the packing density of fibers. Furthermore, it is found that the electrical charge of HPEF is fairly stable against organic solvent, leaving one-third of initial charge after soaking it with ethanol.
In predicting the collection efficiency of HPEF, the conventional equation can be applied to the collection by induced force, however that by Coulombic force is not applicable because the single fiber efficiency due to induced force and Brownian diffusion is high and close to the upper limit without the collection by Coulombic force.View full abstractDownload PDF (563K)
Process Systems Engineering
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Cheng-Liang Chen, Tzxy-Chyi Wang, Shuo-Huan HsuArticle type: Research Papers
Subject area: Process Systems Engineering
2002 Volume 35 Issue 1 Pages 83-93
Published: 2002
Released on J-STAGE: June 14, 2002
JOURNAL RESTRICTED ACCESSA Linear Matrix Inequality (LMI) approach for designing the H∞ Proportional-Integral (PI) controller for a nonlinear dynamic system is studied. A local linear model containing time-varying norm-bounded uncertain parameters is identified at first. The robust PI control design problem based on the norm-bounded uncertain linear model is then transformed into a standard H∞ control problem, where the latter is further formulated as LMIs. By adopting the LMI expression, a symmetric positive definite matrix P with guaranteed overall system’s quadratic stability can be easily determined. The matrix P can finally be used to infer the robust PI controller parameters. One chemical process, a non-isothermal continuous-stirred-tank reactor (CSTR) with a first-order exothermic reaction, is illustrated to demonstrate the effectiveness of the proposed LMI-based H∞ PI controller design method for nonlinear dynamic processes.View full abstractDownload PDF (571K)
Safety, Environment and Energy
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Eri Yamamoto, Fujio Watanabe, Noriyuki Kobayashi, Masanobu HasataniArticle type: Research Papers
Subject area: Safety, Environment and Energy
2002 Volume 35 Issue 1 Pages 1-8
Published: 2002
Released on J-STAGE: June 14, 2002
JOURNAL RESTRICTED ACCESSStudies of the adsorption mechanism were carried out experimentally and numerically were based on the temperature data inside the adsorbent particle and adsorptivity profiles at the adsorption/desorption process by a volumetric method using two different types of relatively large silica-gel particles. Although the adsorption equilibria of the two silica-gels showed different types of curve, the intraparticle temperature profiles show almost the same, i.e. the temperature at the surface is initially slightly higher than that at the center, and then all points reached their respective maximum temperatures at the same time, with the temperature at the center point being the highest and at the surface the lowest. These tendencies were fitted with the simulation results of the molecular diffusion model rather than those of the surface diffusion model. This shows that the adsorption phenomena can take place not only at the surface but inside the adsorbent particle, implying that molecular vapor diffusion has a great influence on adsorptivity, therefore, it can be said that the molecular diffusion model was adopted to describe silica-gel/water adsorption.View full abstractDownload PDF (1575K) -
Mohd. Ali Hassan, Osamu Nawata, Yoshihito Shirai, Nor Aini Abdul Rahma ...Article type: Research Papers
Subject area: Safety, Environment and Energy
2002 Volume 35 Issue 1 Pages 9-14
Published: 2002
Released on J-STAGE: June 14, 2002
JOURNAL RESTRICTED ACCESSIn our previous reports, we have described the production of organic acids from palm oil mill effluent (POME) which were used as fermentation substrates to produce polyhydroxyalkanoates (PHA). Here we propose a zero emission from palm oil industry incorporating the production of PHA from POME. Our results showed that by evaporation, the organic acids could be concentrated to about 100 g·l–1 for use as substrates for the fed-batch PHA fermentation. Upon condensation of the steam, the water had a COD of 80 ppm, low enough for it to be either recycled or discharged. It was confirmed that the energy for the evaporation can be provided by combusting solid wastes such as shells and empty oil palm bunches. The concentrated organic acids were successfully converted to PHA by Ralstonia eutropha strain ATCC 17699 under a non-sterile fermentation system when the initial cell density was kept high at 4 g·l–1. After 150 hours, 20 g·l–1 cells were obtained with more than 50% PHA content. A repeated fed-batch system was also performed to obtain a high cell inoculum and to mimic the operation of a large PHA production fermentor at C/N ratios of 15 and 30 respectively, with only acetic and propionic acids as carbon sources. It was suggested that the energy for this proposed process could be sufficiently supplied by combustion of the solid wastes from the palm oil mill.View full abstractDownload PDF (1233K) -
Rui WangArticle type: Research Papers
Subject area: Safety, Environment and Energy
2002 Volume 35 Issue 1 Pages 15-21
Published: 2002
Released on J-STAGE: June 14, 2002
JOURNAL RESTRICTED ACCESSHydrogen sulfide, as a highly undesirable contaminant, is most widely emitted from factories and waste treatment facilities. An innovative approach to low sulfur containing gas desulfurization and sulfur recovery involving the use of heteropoly compounds is presented in this paper. The favorable redox potential of heteropoly compounds makes it thermodynamically feasible for them to oxidate H2S to elemental sulfur and to be regenerated by air. The presence of Na2CO3 in the absorbent system can improve the absorption rate of H2S, and NaCl can accelerate the absorbent regeneration. The regeneration time decreases with the increase in the absorbent concentration, temperature and the regeneration air flow rate, and it increases with the increase in the feed gas H2S concentration. With the aid of TGA (thermogravimetric analysis) and ES (electron spectrum), the principal component of the sedimentation product from the process of desulfurization was confirmed to be elemental sulfur.View full abstractDownload PDF (443K) -
Yoshinori Itaya, Takuya Oyashiki, Masanobu HasataniArticle type: Research Papers
Subject area: Safety, Environment and Energy
2002 Volume 35 Issue 1 Pages 46-56
Published: 2002
Released on J-STAGE: June 14, 2002
JOURNAL RESTRICTED ACCESSThe objective of this paper is to study the hydrogen production mechanism by fuel-rich combustion of a methane-air mixture in a ceramic burner. Experiments were carried out in a combustor with a silica-alumina porous ceramic plate of 20 mm thickness and 0.32 porosity set at the bottom of a combustion chamber. The premixed gas of methane and air passed through the porous ceramic plate and was ignited above the plate. The flammability limit was up to 2.5 in equivalence ratio for methane-air combustion in the ceramic burner. Then hydrogen yield in the combustion gas was about 10% in mole fraction. Setting a wire net at the downstream of the flame extended the flammability limit in the fuel-rich region. It was caused by combustion temperature elevation. These results imply the applicability of the ceramic burner to non-catalytic reforming of methane.
The behavior of the partial oxidization and pyrolysis in this ceramic burner was analyzed numerically by a chemical kinetic model. The model takes account of 31 chemical species and 147 elementary reactions. The species include C1 to C3 hydrocarbons and radicals. A set of the ordinary differential equations for the reaction rates was integrated by the Gear’s method. The model expressed the experimental results well in the equivalence ratio less than 2.0 in which no soot emission takes place. This model was also applied to analyze the yield mechanism of hydrogen molecule products in the fuel-rich combustion of the methane-air mixture. Hydrocarbons and radicals of CH3, CH2O and C2H6 were significant intermediates for the elementary reactions related to the hydrogen yield. The transient behaviors of hydrogen yield are influenced sensitively by the three major reactions. These results imply that the conversion of methane to hydrogen can be predicted by the limited sequential reactions.View full abstractDownload PDF (1169K) -
Hiroshi Hayashi, Motomi Ono, Satoshi Tsuneda, Akira HirataArticle type: Research Papers
Subject area: Safety, Environment and Energy
2002 Volume 35 Issue 1 Pages 68-75
Published: 2002
Released on J-STAGE: June 14, 2002
JOURNAL RESTRICTED ACCESSA novel technique of immobilizing nitrifying bacteria using fibrous material, the three-dimensional immobilization with a fibrous network (3-D IFN), is proposed and its use in a high-rate nitrifying bioreactor is investigated. The fibrous carrier employed is ferro-nickel fibrous slag (FS), which is industrial solid waste from a ferro-nickel electrosmelting process. Since cell immobilization with FS is readily carried out within 90 seconds, this method is by far more rapid than any other cell immobilization techniques. A fixed-bed nitrifying reactor packed with cell-immobilizing FS is examined by both batch-mode and continuous feeding tests. By controlling the circulation flow rate, the transport of dissolved oxygen to the immobilized cells is improved, which is a distinct characteristic of this reactor. The continuous feeding test revealed that the ammonia removal rate of the reactor reached 6.5 kg-N/(m3-reactor)/d, which was extremely high compared with that of the conventional fixed-bed reactor for wastewater treatment. It is demonstrated that the 3-D IFN is a simple yet effective cell immobilization technique that can be successfully used in a high-rate nitrifying reactor.View full abstractDownload PDF (3660K)
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