In this work, the flow of power-law fluids past a solid sphere with and without radial mass flux has been investigated numerically using a finite difference method based SMAC-implicit algorithm implemented on a spherical staggered grid arrangement. It is clearly shown that the flow and drag phenomena are strongly affected by the pertinent dimensionless parameters like Reynolds number (Re), power-law index (n) and the radial mass flux (φ). The effect of suction (φ < 0) on the flow profile is seen to be strong at high Reynolds numbers in the case of shear-thinning fluids (n < 1), whereas the reverse is seen in Newtonian and shear-thickening fluids (n ≥ 1). On the other hand, irrespective of the value of power-law index, the effect of injection (φ > 0) on the flow profile is significant at all Reynolds numbers. Regardless of the value of the power-law index, the pressure drag coefficient decreases as the value of φ decreases. On the other hand, the friction and total drag coefficients decrease as the value of φ decreases for Newtonian and shear-thinning fluids, whereas an opposite trend is seen in shear-thickening fluids. However, the total drag coefficient is reduced for suction (φ < 0) and augmented for injection (φ > 0) compared to that in the absence of radial mass flux. This is so for all values of power-law index. The present numerical results have been correlated empirically, thereby enabling the prediction of the drag coefficient (hence terminal velocity) in a new application.
Various computer simulations of molten glass flow have been used for the design, operation and trouble shooting of glass tank furnaces. It is necessary to predict the degree of thermal convection of molten glass, whose viscosity is affected by the major composition of glass and thermal conductivity of which varies with the ferrous oxide (FeO) content. The thermal conductivity decreases as the FeO content increases. Thermal convection is characterized by the Rayleigh number, Ra, and the Prandtl number, Pr. Typically, Ra is expected to be large for a small thermal conductivity, but the actual thermal convection is weaker in this case than when the thermal conductivity is large. To elucidate the underlying convection mechanism, a two-dimensional mathematical flow model is developed in this study. Non dimensional formulation of the governing equations shows that Pr–1 affects the degree of thermal convection. The effective value of Ra, Raeff, is introduced to evaluate the influence of temperature-dependent properties on thermal convection. An evaluation method of thermal convection is proposed and extended to glasses with different thermal conductivities.
The synergistic extraction of samarium (Sm(III)) using two different main extractants and three organic phosphine oxides as synergist was examined. A synergistic effect was observed when dibutylmonothiophosphoric acid (DBTPA) was used with tri-n-butylphosphine oxide (TBPO) or dibutylphosphate (DBOBPO). The order of extractability was TBPO > DBOBPO. On the other hand, the extractability of samarium in the DBTPA + tri-n-butylphosphate (TBOPO) system was not significantly greater than the extractability of samarium in the DBTPA system. An antagonistic effect was observed when dibutylphosphoric acid (DBPA) was used as the main extractant and TBPO as the synergist. The extractability of samarium in the DBOBPO/TBOPO system was almost the same as that of samarium in the TBPO system. This difference in the extractabilities observed when using different synergists with the two main extractants probably resulted from the balance between the association abilities of the synergist and the main extractant. This could be explained by the basicity of the oxygen atom in the synergists and the coordination ability of the synergist with the samarium/main extractant complex. This was in turn due to the coordination number of the aforementioned complex.
In order to improve the sonochemical efficiency of a sonoreactor, a metallic reflection plate is set in liquid. With the placement position and the diameter of the reflection plate varied at the same liquid height, a decolorization experiment using iodine and disodium hydrogenphosphate in starch solution has been carried out in order to examine the effects of the reflection plate on ultrasonic reaction. With the placement position of the reflection plate close to the liquid surface, the range of reaction field becomes much larger and the reaction proceeds more quickly. The diameter of the reflection plate has an optimum value for the sonochemical efficiency of the sonoreactor.
In the present study, propylene polymerization using a solid Ziegler–Natta catalyst in a loop reactor is described on the basis of a polymeric multilayer model. The simulated results obtained by using the polymeric multilayer model are found to be in agreement with reference results obtained by using a multigrain particle model. In addition, the effect of the polymerization rate on the intraparticle mass and heat transfer is investigated by considering the polymeric multilayer model and the dependence of the intraparticle monomer concentration and temperature profiles on the polymerization rate is examined.
We focus on extracting the know-how of skilled operators who carry out batch process operations at a chemical company. We start by using a time-series analysis sheet to analyze each problem card recorded in the work place; on the basis of the analysis results and by interviewing a skilled operator, we try to extract know-how and tacit knowledge. We also show various scenarios that could arise when a malfunction occurs by drawing an event tree chart that illustrates multiple protection layers from the viewpoints of safety, quality, cost, etc. This chart shows the appropriate actions to be taken at each stage of an event. As a result, we can compile manuals for handling abnormal situations. This enables the comprehensive recording of operational know-how of the plant and helps operators to be in command of abnormal situations.
The influence of process parameters such as carbon source, initial pH, agitation rate, inoculum size and fermentation temperature on L-(+)-lactic acid production by Rhizopus oryzae were examined in shaken culture. The highest lactic acid concentration of 62 g/L was obtained at 150 g/L glucose concentration, initial medium pH 6, agitation rate 150 rpm, inoculum size 1 × 108 spores/mL and fermentation temperature 32.5°C. The maximum lactic acid concentration of 112 g/L was obtained at an agitation rate of 500 rpm and aeration of 0.75 vvm under optimum conditions found in the shake flask experiments in a 1-L stirred tank bioreactor in batch system. The oxygen transfer characteristic of the lactic acid production process was analyzed. Increases in both the agitation rate and the aeration rate increased the kLa values, with the agitation rate increase being much more effective. The effects of different fed-batch methods were determined. The constant feed rate fed-batch culture was an effective method for the production of lactic acid, the concentration of which reached 134 g/L, 19.6% higher than in the batch fermentation.
The electrochemical properties of composite films consisting of polyaniline (PANI) and carboxydextran-gold hybrid nanomaterials (carDEX-GNP) as a biofuel cell electrode platform were investigated. First, dextran-gold hybrid nanomaterials were synthesized through a series of surface modification of gold nanoparticles. The composite films were formed on a planar gold electrode through electropolymerization after a simple chemical modification of dextran-gold hybrid nanomaterials with carboxyl groups. Cyclic voltammetry indicated that the composite films retained a redox activity in a neutral pH environment. The PANI/carDEX-GNPs composite films showed electrocatalytic activity toward the oxidation of ascorbic acid, indicating that this composite film is an excellent candidate for a biofuel cell electrode.
The solute diffusive permeability of a thin layer of a molecularly imprinted polymer (MIP) changes owing to specific binding of the MIP with a template. This phenomenon, termed the “gate effect,” is applicable to biomimetic sensors. However, the mechanism underlying the gate effect is yet to be clarified. We developed a molecularly imprinted self-supporting membrane (MISSM) and carried out basic studies on the gate effect. Our model MISSM was formed by copolymerization of methacrylic acid (MAA) and 2-vinylpyridine (2-VP) (functional monomers) using triethyleneglycol dimethacrylate, TEDMA, (crosslinker) in the presence of L- (or D-) phenylalanine (template) and was approximately 50 μm thick. The amount of the template adsorbed on the MISSM was sufficiently high for easy quantification, whereas the adsorption of the enantiomer of the template was negligible. Solute permeability in the MISSM increased in the presence of the template, but was insensitive to the enantiomer of the template. The solution content in the MISSM was sensitive to the presence of the template, but was insensitive to the enantiomer of the template. Thus, our model MISSM was found to show chiral-selective gate effect and adsorption, because of which it was considered to be useful in elucidating the mechanism underlying the gate effect.
Nitrification stability and biofilm robustness were examined by comparing a fibrous support membrane-aerated biofilm reactor (FS-MABR), where a woven fibrous support was surrounded on a silicone tube, with an MABR. The overall mass transfer coefficient of oxygen for the FS-MABR, assuming no boundary layer between the fibrous material and bulk liquid, was 5.85 m/d at an air pressure of 27 kPa, which was comparable to that value of the MABR (5.54 m/d). The amount of biomass on the fibrous support with a silicone tube was 2.48 times larger than on the bare silicone. The biomass loss after a high liquid flow rate condition was 49% and 75% in the FS-MABR and MABR, exhibiting robust biofilms grown on the fibrous support. The FS-MABR provided more stable nitrification performance than the MABR irrespective of a high liquid flow rate. Both reactors have deteriorated ammonium (NH4+-N) removal without a high liquid flow rate condition to eliminate excessive biomass, indicating that regular maintenance is essential to eliminate excessive biofilm from a MABR for nitrification, which potentially acts as a NH4+ diffusion barrier.
A polymer electrolyte fuel cell membrane electrode assembly (PEFC MEA) model that focuses on the structural and reaction parameters of catalyst layers has been developed. The reaction and structural parameters were modeled independently by considering the oxygen reduction reaction (ORR) activity in terms of current per unit active surface area of Pt [A cm–2-Pt]. The catalyst layer models were constructed based on an assumption of cylindrical secondary pore structure, which was verified by measuring the primary pore size using mercury porosimetry. We found that penetration of Nafion® electrolyte into the primary pores of Pt/C catalysts was restricted, and thus diffusion and reaction in primary pores became negligible. Moreover, the experimental results demonstrated that for the same catalyst, ORR activity remained almost constant, irrespective of the agglomerate size (i.e., 2.7 × 10–6 A cm–2-Pt at 60°C for Pt/C TEC10E50E in this study). This supported our idea that reaction parameters and structural parameters should be considered independently in PEFC modeling. The cell performance predicted with the developed model was satisfactorily accurate as compared to that obtained from experiments. As a result, the modeling developed in this study can be used to construct simple PEFC models that yield results with good accuracy and can be a useful tool for the development of PEFCs in future.
Polylactic acid (PLA) is synthesized by direct polycondensation without catalyst (NC-DP) method using a lactic acid (HLa) solution which had been refined by concentration, esterification and hydrolysis of fermented broth from fresh cassava roots (FCR). Higher polymerization rates and earlier thermal degradation had been observed, compared with those from a pure lactic acid solution. It is due to residual impurities in refining process, such as butanol (BuOH) and butyl lactate (BuLa), which act as an external catalyst. Additionally, it has been found that thermal degradation of PLA containing these impurities occurs via random scission with vinyl end groups, in regard to specific scission for PLA from a pure HLa solution.