The tracer diffusion of a charged particle in an oppositely charged cubic lattice as a simplest model of charged hydrogel was studied by a Brownian dynamics simulation. The effect of the electrostatic attractive interaction between the tracer particle and the cubic lattice on the self-diffusion coefficient was mainly discussed, when the mesh size of the cubic lattice was sufficiently larger than the diameter of the particle. The charge density of the cubic lattice structure and the electrolyte concentration in the solvent were varied. The electrostatic force acting on the tracer particle was calculated using the potential screened by an electric double layer. The self-diffusion coefficient of the tracer particle significantly decreases as the charge density of the cubic lattice increases, while the increase in the electrolyte concentration in the solvent induces the disappearance of the effect of electrostatic attractive interaction on the self-diffusion coefficient, resulting into the asymptotical behavior to those observed in the non-charged cubic lattice. 2-Order reduction in the self-diffusion coefficient was obtained in this simulation and this shows the applicability of the control of diffusivity of ionic solutes in the swollen hydrogel by means of introducing ionic species covalently into the hydrogels. In the spatial distribution of the probability density of the charged tracer particle, the stochastic path along which the tracer particle tends to move was observed in the charged cubic lattice, which is caused by electrostatic potentials. The reduction of the self-diffusion coefficient in the charged cubic lattice is due to the transient entrapment at the point of local minimum of potential energy inside the stochastic paths.
Mixing performances of a new mixing equipment which has a vibrating motor with some fin oscillators on a pair of shafts were investigated. This mixing equipment, which is mainly used for industrial plating processes, was usually operated at the vibrating frequency from 30 Hz to 60 Hz with the amplitude from 1 mm to 10 mm. The mixing time and the circulation time were measured and the flow pattern and the mixing process were visualized. The mixing time and the circulation time took the optimum values (the minimum values) for the equipment design at the frequency range from 40 Hz to 50 Hz irrespective to the configuration of the fins. The complete mixing was achieved in three to four circulations of the liquid in the vessel. From the visualization of the flow pattern and the mixing process it was shown that a primary circulation flow passing through the fins was very important for the mixing operation.
Georgiou et al. proposed the singular finite element method (SFEM) for solving Newtonian flow problems related to singularity, such that velocity and pressure behave like rn and rn–1, respectively, near the singularity, where n is a constant (0 < n < 1) and r is the radial distance from singularity in the sense of polar coordinates; and they successfully predicted several singular problems of Newtonian fluids using the SFEM. In this study we have attempted to incorporate their SFEM in the decoupled FEM associated with several numerical techniques for solving the die-swell flow of viscoelastic (Giesekus) fluids, where the singular shape functions similar to those of Georgiou et al. (1990) are used for velocity and pressure, but as for elastic stress we have approximately adopted the same shape functions as those for velocity, and we refer to this method as the SFEM(vpE); and it is found that this newly developed scheme can predict the die-swell flow of viscoelastic fluids up to We = 130; and while the SFEM (vp), which employs the singular shape functions only for velocity and pressure but a subelement scheme for elastic stress instead, fails to converge over We = 14. It is also found that the SFEM (vpE) gives more smooth and accurate results than those obtained from the ordinary FEM with less memory size.
Effect of inhomogeneous mixing on chemical reactions in a Taylor vortex flow reactor was experimentally investigated by using a second-order reaction system. The flow-visualization experiment by a laser induced fluorescence method was also carried out to observe the cross-sectional view of mixing behavior in the inside of Taylor vortex cells. In the reaction experiment, the reaction among hydrogen peroxide, iodide ions and hydrogen ions, i.e. 2H+ + 2I– + H2O2 → I2 + 2H2O, was used. The temporal evolution of the concentration of iodine was observed from the temporal variation of color of iodine. The flow-visualization experiment clearly revealed the existence of two different mixing zones within a Taylor vortex cell at low Reynolds numbers. Namely, the fluid flowing near the cell boundary was axially well-mixed, while the fluid element confined to the vortex core region was poorly exchanged with the outer well-mixed flow region. This vortex core region, called an isolated mixing region (IMR), decreased as increasing the Reynolds number. It has been found in the reaction experiment that the reaction rate is larger in laminar and singly-periodic wavy Taylor vortex flow regimes than in quasi-periodic and chaotic Taylor vortex flow regimes.
In order to evaluate adsorption of CO species onto precious metal electrodes during electrochemical oxidation of methanol under hot aqueous conditions, adsorption of carbon monoxide (CO) on a Pt electrode was studied in hot aqueous solution of 0.005 M H2SO4–0.2 M Na2SO4 by a fast potential sweep method at temperatures ranging from 423 to 533 K under the corresponding vapor pressure. An electrochemical half cell fabricated in a pressure vessel was employed to realize electrochemical measurement under this high temperature and pressure. Adsorption characteristics of CO were determined at CO partial pressure up to 0.39 MPa. Increasing temperature resulted in a decrease in the adsorption amount of CO on Pt electrodes. Under 0.1 MPa of the CO partial pressure, CO almost covers the electrode at 423 K, while a negligible amount is adsorbed at 533 K. At 473 K, CO surface coverage on a Pt electrode in aqueous solution increased with the CO partial pressure.
The performance and the characteristics of an oxygen acceptor prepared from barium peroxide and magnesium oxide were investigated for application to oxygen production. Reaction was run in an isothermal and isobaric condition, and the effects of temperature, oxygen pressure and the size of a sample pellet on the BaO-BaO2 equilibrium and reaction rate were investigated over a range of temperature 973–1173 K and oxygen pressure 0–0.3 MPa. It was found that both oxidation of barium oxide and reduction of barium peroxide are the first order reaction, and the BaO-BaO2 equilibrium and reaction rate vary markedly by the change of temperature and/or oxygen pressure but little affected by the size of a sample. Low temperature and high oxygen pressure are favorable to oxidation, and high temperature and low oxygen pressure are favorable to reduction. A reaction rate constant is independent of the starting BaO-BaO2 composition under fixed values of temperature and oxygen pressure. For a fixed equilibrium composition in oxidation or reduction, rate constants (ko + kr) at different temperatures are nearly the same. In the whole range of equilibrium composition, a rate constant ko increases with an increase in the mole fraction of barium peroxide at new equilibrium, while a rate constant kr increases with an increase in the mole fraction of barium oxide at new equilibrium.
The percolation model is used to predict the liquid distribution in a trickle bed with different packed structures. The experimental work is also performed to verify the calculated results. The effects of addition of bulking agents and the packed structure on the liquid flow rate distribution are examined. The addition of bulking agents reduces the channeling liquid flow in the trickle bed, especially when small hydrophilic particles are packed. The calculated results on the liquid distribution well reproduce the experimental data. The percolation model is proved to be a useful tool for the estimation of the liquid flow distribution in the trickle bed packed with bulking agents as in the case of the biofilter.
The objective of this study is to develop and evaluate a new Monte-Carlo simulation method to predict the hydrodynamics of rotating disc contactors (RDC) with continuous flows of liquid phases and with drop breakage. This method has the advantage of using individual drops controlled by breakage phenomenological parameters of probability of breakage, number of generated drops and their size distribution. Drop coalescence is ignored due to the very low hold-up and the high interfacial tension of the chemical system. The Monte Carlo stochastic method is applied by using the elements of generated vectors of random numbers having given distribution and with sequences of repeatable or non-repeatble. The limiting values are obtained from correlations that are based on single drop experiments. A stage-wise explicit calculation method with the use of a population balance is employed to follow the steady flow of dispersed phase. The generated results are compared with the experimental results obtained from a pilot RDC and a good agreement is observed. The changes of local hold-up and mean drop size along the column are also described reasonably.
Batch cooling crystallization of potassium alum in aqueous solution was conducted over a wide range of seed loading with various average seed sizes under the natural cooling condition. A solution of a low saturation temperature was used. In this dilute solution the supersaturation during crystallization did not become high so that agglomeration of the original seeds was avoided even for small seeds. The critical seed loading ratio Cs*, the critical value of the ratio of seed mass to the theoretical crystal yield, above which loading seed crystals were grown with no secondary nucleation, was determined. It was correlated as a second order equation of mean mass size Ls [μm], as Cs* = 2.17 × 10–6Ls2. The value of Cs* was confirmed, by comparing with previous data published by the present authors, not to change significantly with crystallizer volume, stirrer speed, the saturation temperature of the solution (i.e., the solution concentration) and the cooling mode. This correlation is shown to be conveniently used to determine the seed amount satisfying an optimal seeding condition of Cs ≥ Cs* for a given seed size. The mean mass size of product crystals and the volume of a crystallizer required for a desired production is easily determined for this optimal seed loading condition by the aid of a simple mass balance.
The minimum fluidization velocity was measured for various binary particle mixtures of coarse particles of group A or B and fine particles including group C particles of Geldart classification in the range where the weight fraction of the fine particles was less than 15 wt%. The minimum fluidization velocity decreased with the increase in the fraction of the fine particles in all cases; especially in the systems with group C particles, a remarkable decrease in the minimum fluidization velocity was observed with the increase in the fine particle fraction. Such a decrease in the minimum fluidization velocity observed in the systems with group C particles was expressed by the formation of aggregated particles consisted of the coarse and the fine particles. Mixing/segregation appearance of the system was also observed, revealing that group C particles can be fluidized and mixed homogeneously with coarse particles in a certain rage of the fine particle fraction. The range of the fine particle fraction for homogeneous mixing was dependent on the systems.
Experiments were carried out extensively to study the effectiveness of promoters in reducing bed expansion in gas-solid fluidized beds with distributors of varying open areas. Four types of rod promoters, seven types of disk promoters along with one blade promoter were used in beds supported respectively on five distributors with open areas of 12.9, 8.96, 5.74, 3.23 and 1.43% of the column section. Four correlations for bed expansion ratio were developed respectively for the unpromoted and the promoted beds with rod, disk and blade type promoters. The values of bed expansion ratio obtained from the developed correlations agreed fairly well with the experimental values.
A novel nonlinear Partial Least Square (PLS) method is proposed to enhance modeling capability for nonlinear chemical processes. The proposed method incorporates a modified back-propagation algorithm for artificial neural network within Nonlinear Iterative Partial Least Square (NIPALS) algorithm for PLS methods, without deteriorating the robustness of PLS methods. The modified back-propagation algorithm iteratively updates the weights within the networks. The proposed method circumvents the pseudo-inverse calculation of the error-based neural network PLS proposed by Baffi et al. (1999b), and thus makes the weight updating procedure more stable and the solutions more accurate. The modeling capability of the proposed method was investigated through three case studies: 1) a pH neutralization process, 2) cosmetic data, and 3) an industrial crude column process. Simulation results showed that the proposed method represented more stable convergence and enhanced prediction power than those of the linear PLS, the neural network PLS, and the error-based neural network PLS.
High cell density culture of a recombinant yeast, Candida utilis KU101, were investigated in a jar fermentor under the fed-batch mode to achieve efficient production of single chain monellin. Cell yields for glucose, ammonia, inorganic phosphate and the trace elements, B3+, Cu2+, Fe3+, I–, Mn2+, Mo6+ and Zn2+ were determined. Fed-batch culture was carried out by a nutrient feeding strategy determined from the cell yields. However, growth of the recombinant C. utilis stopped when the cell density reached about 60 g/l and the monellin productivity was only 3.4 g/l. The inhibition was not caused by accumulation of metabolites, nor by the depletion of glucose, ammonia, inorganic phosphate or trace elements during the cultivation. By analyzing the supernatant of the culture broth in detail, it was shown that cell growth was slightly inhibited by concentrations of sodium or potassium ions above 100 mM. Dynamic experiments on the respiratory activity of the yeast revealed that high sodium and potassium ion concentrations adversely affected the oxygen uptake rate of the cells. Furthermore, the inhibitory effect of sodium ions on oxygen uptake was more severe. Sodium ions accumulated up to a concentration of 175 mM in the fed-batch culture mainly due to phosphate feeding. Based on these facts, a modified fed-batch culture was carried out by substituting the sodium salt with the potassium salt for phosphate which resulted in a greater cell density (112 g/l) and a higher yield of monellin (6.0 g/l).
A surfactant-lipase complex is immobilized in a polyethylene glycol (PEG) microsphere to realize the repeated use of the enzyme complex in organic solvents. The preparation is based on the emulsion-drying method. The enzyme complex dissolving in an internal oil phase is entrapped into the polymer matrix during lyophilization. The immobilized lipase complex exhibits a high catalytic activity comparable to that of the free lipase complex to an esterification reaction in nonaqueous media, while the powder lipase shows no enzymatic activity. The PEG microspheres containing the lipase complex can be readily recovered by facile filtration. The high activity was completely preserved after re-using ten times.