Boundary-Driven type Non-Equilibrium Molecular Dynamics (BD-NEMD) simulations have been carried out to investigate effusion processes of pure propane from the inside membrane to the gas phase by using two types of silicalite membrane models: an SC surface model that has an outer surface terminated at the cross section passing through the center of straight channels, and an IS surface model that has an outer surface terminated at the cross section passing through the center of intersections. In all simulations, the silicalite membrane and the propane molecule are represented by flexible (movable) models. It is found that the average effusion flux and the local density around the outer surface for the IS surface model are larger than those for the SC surface model. The potential and kinetic energy profiles have shown that effusing molecules take extra kinetic energy from membrane atoms to go over the potential barrier at the membrane exit. It is suggested that the existence of weak adsorption sites on the outer surface is essentially important for inorganic membranes to have high permeation fluxes.
The transport phenomena in a bioartificial liver (BAL) were investigated experimentally from a viewpoint of fluid mechanics. BAL used in this study was a type of utilizing a hollow-fiber dialyzer. The suspension of hepatocytes was packed in the lumens and the blood was fed into the shell side. In the BAL, the permeation rate of the substances in the blood including oxygen is one of the most important factors for the evaluation of the performance. It has been considered that the permeation is driven by concentration difference between the lumen and the shell side. According to the increase of the permeability of the membrane, the permeation driven by the transmembrane pressure (TMP) is expected to become dominant. In this study, the axial pressure distributions in the shell side were measured. Water suspension of starch powder used as a model of the suspension of hepatocytes was injected into lumens. On the other hand, an aqueous solution of glycerol was fed into the shell side instead of blood. Based on the results, it was confirmed that the permeation driven by TMP occurred. In addition, the importance of the permeation was discussed.
An unsteady mixing speed was applied to laminar mixing in a vessel containing a conventional impeller. Three non-circle cams were combined to generate the unsteady speed in an impeller revolution. The mixing performances of the unsteady speed impeller were compared with those of a conventional impeller operated under a steady speed. The mixing time and the flow pattern were measured by flow visualization using the discoloration method in which sodium thiosulfate reacts with an iodine solution. Because the unsteady motion moved the center of the vortices, the doughnut rings above and below the impeller disappeared when unsteady mixing was employed.
The influence of contamination and agitation on single drop mass transfer was investigated, using a pilot rotating disc contactor. The chemical system of toluene–acetone–water, having a high interfacial tension, was used with the advantage of high accuracy and repeatability in using GC for analysis. It is ideally required to account for the extent of contaimnation in a quantitative manner and in both phases with a single parameter. For this purpose and for design applications, an improvement was made on a combined mass transfer model, to be consistent with experimental data without mathematical assumption. The influence of drop size was also considered. Based on the series of experimental data, a correlation was proposed for the coefficient of this model.
In this study, zeolite particles were charge-reversed by chemically modifying them with aluminum and it was verified by EDXS that aluminum replaced sodium from the zeolite structure. The charge-reversed zeolite particles were subsequently used in fluoride removal from aqueous solution. The influence of the experimental variables such as particle size, initial fluoride concentration and temperature on the fluoride diffusion kinetics, was investigated using a batch adsorber. A model that lumps internal mass transfer phenomenon, i.e. pore and surface diffusion, was used to describe the uptake kinetics. From the model, a diffusional time constant and a corresponding effective diffusion coefficient were determined. Results demonstrate that the internal mass transfer rate is enhanced with an increase in temperature and decreases in particle size and initial concentration. It is also found that the diffusional time constant correlates well with the reciprocal of the square of zeolite particle radius corroborating that internal mass transfer plays a limiting role in fluoride sorption. An examination of the thermodynamic parameters reveals that the interaction between fluoride and charge-reversed zeolite particles is endothermic and spontaneous in nature.
As described in the previous papers, K2CO3 supported on activated carbon sorbed CO2 from moist feed gas at 353 K to form KHCO3 and the entrapped CO2 was then efficiently released by steam flushing at 423 K, followed by condensation of the excess steam through a heat exchanger to afford CO2 in high purity. In the present study, various alkali carbonates supported on activated carbon were employed to recover CO2 from moist gases at different temperatures. Carbon dioxide can be sorbed at higher temperatures in the order of the impregnated salt, Na2CO3 < K2CO3 < Rb2CO3 ~ Cs2CO3, indicating the applicability of CO2 sorbents from moist flue gases at temperatures of 313–393 K by selecting the type of alkali carbonate for impregnation. By employing a bench-scale apparatus packed with the sorbent, materials (CO2, water) balance and heat balance during CO2 sorption/release steps were measured in order to elucidate the CO2 recovery performance. The CO2 uptake increased in the order of the impregnated salt, Cs2CO3 ~ K2CO3 < Na2CO3, while heat for the CO2 release per unit mass of recovered CO2 decreased in the order of Na2CO3 > K2CO3 > Cs2CO3, providing a more energy-conservative CO2 recovery process for moist flue gases at 313–393 K than conventional amine absorption methods.
Ceria nanoparticles (average secondary particle size: 80 nm) in an aqueous suspension were successfully extracted to the toluene phase by using surfactants as the extracting agent. AOT (Aerosol® OT: diisooctyl sodium sulfosuccinate) and AOT mixed with SPAN65 (SPAN®65: sorbitan tristearate) were found to be effective in extracting ceria nanoparticles. Addition of SPAN65 markedly enhanced the extracting capability. The ceria nanoparticles recovered using the mixed surfactant were successfully redispersed in polymethylmetacrylate (PMMA) with optical transparency retained. Addition of SPAN65 is considered to increase the spontaneous curvature radius of the surfactant layer to surround the ceria nanoparticles successfully.
Emulsion polymerization of vinyl acetate was performed in a system of two continuous stirred tank reactors in series to observe dynamic chemical processes. Monomer and an aqueous solution of initiator and emulsifier were separately and continuously fed into the first reactor. The concentration of emulsifier was considerably lower than the critical micelle concentration. The reacting latex solution discharged from the first reactor was fed into the second reactor. The mean residence time and the speed of the rotational impeller were varied as control parameters. After a transitional period, a steady state of almost constant monomer conversion was attained. Even while this steady state was maintained, the particle-size distribution varied periodically. The mean diameter of latex particles also oscillated over time. A broader distribution was obtained in the second reactor, where, from a certain sampling time, a bimodal particle-size distribution was observed. These results indicate that the aggregation process predominates over the reaction process in the second reactor. It was also found that oscillatory behavior can be controlled by adjusting the rotational speed of the impeller and the mean residence time, with the former influencing the amplitude of oscillation and the latter the period thereof.
We have measured the change in concentrations of the ferrous and divalent metal ions over time in a three-phase system consisting of air, a pH-controlled solution of ferrous and various divalent ions (Co, Zn, Ni and Cd), and precipitated ferrite. To quantitatively interpret the kinetics of the ferrite formation process, we proposed a reaction model which takes into account the absorption rate and the chemical reaction rates in the aqueous phase. The concentration changes early in the reaction can be expressed by a model with two fitting parameters. The value of the fitting parameter k1, which expresses the oxidation rate of the ferrous ion, greatly depends on the specific divalent metal ion used and its initial concentration. The decrease in the relative concentration of the ferrous ion (Y = CA/CA0) correlates with the decrease in the concentration of the divalent metal ions, (X = CM/CM0). To quantitatively express the relationship between X and Y, using the model we derive a theoretical equation with a fitting parameter, (k2/kM), which is the ratio of rate constants for magnetite and ferrite formations. The value of this parameter decreases for a lower initial concentration ratio of ferrous ion to divalent ion in the following order: cobalt, zinc, nickel and cadmium. The order corresponds to the fixation of the divalent metal ions into the ferrite at equilibrium.
Decomposition of calcium carbonate in the temperature range 1180–1353 K was investigated by employing a thermogravimetric analysis system, an X-ray diffractometer, a scanning electron microscope and a surface area analyzer. Experimental results indicated that calcium carbonate decomposed almost completely in 210 s under 1303 K. Shape and size of a CaCO3 grain did not change during decomposition. Specific surface area and specific pore volume increased while pore diameter was unchanged after decomposition. The apparent activation energy was found to be 84.89 kJ/mol.
Light-leakage type photocatalytic fibers coated with a titanium oxide layer were fabricated to decontaminate aqueous waste solution. The titanium oxide layer was prepared by a sol-gel process using titanium tetra-butoxide and salt catalyst, and characterized by SEM and EDX analyses. The titanium oxide layer was sufficiently dense and stable against long term UV-irradiation in aqueous solutions. The fibers were bundled into a tube of about 3 mm in diameter, constituting a tubular reactor that promotes photocatalytic degradation of basic dyes by a single pass process.
In this paper, design of multi-loop PI/PID controllers for an MIMO process which contains pure integrators and dead times is presented. A modified RGA is proposed to overcome the difficulty encountered in computing the RGA of the integrating process for loop pairing. After loop pairing, the design of N-loop controllers is decomposed into the design of N effective loops. From the controllers of these effective loops, multi-loop PI/PID controllers are determined. Each controller of the effective loops is derived from an equivalent system having cascaded loops. A method for synthesis of such controllers consists of two major steps. As a first step, a robust open-loop stable process is obtained by closing inner loops around those integrating processes. The controllers in the inner loop are aimed at good stability robustness without too much concern on the performances. For this reason, synthesis of these controllers is much easier. Then, in the second step, multi-loop controllers are designed to cascade those inner loops with emphases on both performance and robustness. The controllers obtained in the two steps are then used to derive the final multi-loop SISO controllers. Numerical examples are used to illustrate the design and the performances of the proposed design method.
Microbubble can extreamly enhance the gas–liquid mass transfer because of the increase in interfacial surface. For these characteristics, microbubble technologies have been widely applied to many technologies in recent years. In this work, we tried to apply a microbubble aeration technology to cultivation for aerobic yeast. Rhodoturula mucilaginosa YR-2 was used as yeast and cultivated. As a result, it revealed that it was possible to cultivate at a very low flow rate of microbubble aeration, which was between 1/100 and 1/10 of the gas flow rate required at conventional aeration by a sparger.
For the adequate treatment of patients, it is important to have an accurate and reliable algorithm developed for construction of a diagnosis system that can deal with gene expression data of DNA microarray, or proteomic data obtained by means of mass spectrometry (MS). It is also necessary that this algorithm is fast because these data consist of thousands of attributes (genes or proteins). We have developed a boosted fuzzy classifier with a SWEEP operator (BFCS) method on the basis of the fuzzy theory and boosting algorithm. This method has been applied for the construction of class predictors for cancer diagnosis using clinical data for breast cancer or proteomic pattern data of MS for ovarian cancer. The model performance has been evaluated by comparison with a conventional method such as a support vector machine (SVM) and a fuzzy neural network combined with the SWEEP operator (FNN-SWEEP) method previously proposed by us. The BFCS algorithm is 1,000 to 10,000 times faster than the other two methods. The constructed BFCS class predictors could discriminate classes of breast cancer and ovarian cancer with the same or higher accuracy than the other two methods. Furthermore, BFCS enabled the calculation of the reliability index for each patient, while the feature is not incorporated into a conventional algorithm. Based on this index, the discriminated group with 100% prediction accuracy was separated from the others.
Total surface area, total pore volume, average pore diameter and morphology of the solid sample containing spent ZnO catalyst, carbon and calcium carbonate during zinc recovery reaction were monitored by a surface area meter and a scanning electron microscope, respectively. The experimental results indicated that total surface area, total pore volume and average pore diameter of the solid sample were first in increment with the reaction time, then reached a maximum, and after that decreased. These physical properties were also found to decrease upon increasing the temperature. But, the effect of temperature was not significant at high temperatures. The scanning electron microscopic studies showed that the spent catalyst became porous and round for long reaction times or high reaction temperatures due to the evolution of zinc vapor and sintering.