In low Reynolds number flow conditions, an isolated mixing region (IMR) consisting of two troidal regions is formed in a stirred vessel, and furthermore one or several string IMRs are occasionally observed surrounding the troidal IMR. The string IMR has a closed spiral curve and rotates around the troidal IMR. The winding number and the mean rotating velocity of the string IMR are generally different from those of the fluid particle orbits. In this study, we explain the mechanism of the string IMR formation where the rotating motion of fluid particles is synchronized with the perturbation of the propagative wave motion caused by the passage of paddle blades. We proposed equations that relate the string number, winding numbers and mean rotational velocities of the string IMR to the rotational speed of fluid particles and the number and rotational speed of paddle blades. These relations were validated by comparison of the calculated results obtained by the simplified flow model with experimental results.
A numerical method for simulating gas-liquid-solid three-phase flows in a slurry bubble column reactor was developed based on a mixing model and an artificial neural network (ANN). Macroscopic variables required for the mathematical closure of the mixing model, such as the gas holdup, dispersion coefficient, and reaction rate, were evaluated by use of ANN, rather than empirical correlations. In contrast to the empirical correlations, ANN possesses the following advantages: (1) it is applicable to a wide range of flow conditions owing to its generalization ability, and (2) the accuracy is easily improved through a learning process using an up-to-date database. For the validation of ANN, gas holdups in an air-water bubble column were measured. Then simulations of gas-liquid-solid three-phase flows in a Fischer-Tropsch (FT) reactor were carried out using the combination of the mixing model and ANN to demonstrate its potential. The results obtained are as follows: (1) ANN accurately evaluates the gas holdups in the air-water bubble column, (2) the combination of the mixing model and ANN gives good predictions for CO conversions in FT synthesis, and (3) the accuracy of ANN is easily improved through the re-learning process. These results imply that the proposed method can be a framework for simulating multiphase flows in large industrial systems.
The difference in power consumption between dished-bottom and flat-bottom mixing vessels were investigated. In turbulent mixing vessels with standard baffle conditions and a radial flow type impeller, a difference of up to 20% in power consumption was found between the dished and flat bottoms. In vessels with pitched blade paddle and propeller type impellers and non-baffled vessels showed the same power consumption regardless the bottom geometry.
Numerous studies on power consumption in mixing vessels have been reported, and several power correlations have been developed for non-baffled mixing vessels, for example, Nagata's correlations. However, baffled mixing vessels with different impeller geometries have different power numbers. In this paper, the effects of vessel bottom shape, number of blades, and impeller position on power number were measured for several impellers with geometries that had been assumed to have the same power in Nagata's concept. It was found that power numbers in baffled vessels varied greatly with impeller geometry, while Nagata's concept is valid for non-baffled vessels, regardless of impeller position.
A new analytical model for predicting the mass transport characteristics in hemodiafiltration was presented, which was consistent with in vitro measurements reported by earlier researchers. In this model, Zydneys' equation (1993), modified Rautenbachs' equation (1989) and Fukudas' equation (1992) were used for convective solute transport, and for boundary-layer solute transport on the blood side and the dialysate side, respectively, and the Poiseuille equation was added as a gravity effect term because of vertical setting of the hemodiafilter. The model was applied to study the influence of hollow fiber membrane geometry on the performance of hemodiafilter, and it was found that the clearance of low molecular weight solute depends on fiber geometry more strongly than that of medium molecular weight solute. That is, for a given membrane surface area, the smaller the diameter of the hollow fiber is, the longer is its length and the faster is the blood flow velocity, resulting in larger clearance of low molecular weight solute. On the other hand, the clearance of medium molecular weight solute depend hardly on fiber geometry, but greatly on ultrafiltration flow rate.
The removal of photoresist with novolac resin on a semiconductor wafer by high concentration aqueous ozone was found to proceed by a two-stage chemical process. It was also found that the two-stage removal process of the photoresist resin is accelerated by the optimized ultraviolet rays. That is, in the first stage, hydroxide radicals produced from the ozone by the ultraviolet rays oxidize the photoresist resin into the polyphenol. In the second stage, the polyphenol is easily removed from the semiconductor wafer by the ozone, since the polyphenol is more reactive to the ozone, which acts to remove electrons from the polyphenol. On the other hand, since too strong ultraviolet ray change most of the ozone into oxygen, removal efficiency is controlled by the balance between the ozone concentration and the intensity of ultraviolet rays.
In this paper, sucrose sensor utilizing two enzymes, invertase (INV) and glucose oxidase (GOD), was developed without utilizing pig kidney mutarotase, which catalyses mutarotation reaction (the conversion of α-D-glucose to β-D-glucose). The GOD electrode and the GOD+INV electrode were made by immobilizing enzymes on platinum electrode with glutaraldehyde. The effects of phosphate ion concentration and temperature on sucrose measurements were studied. In respect of responsivity and durability of enzymes, the optimum temperature and phosphate ion concentration was found to be 308 K and 0.5 mol·L−1, respectively. The concentrations of sucrose and glucose were measured by using two electrodes, GOD electrode and GOD+INV electrode. This study showed that sucrose concentration can be determined from the deviation of the current of GOD+INV electrode from that of GOD electrode.
Zigzag microchannels are commonly used in microreactor and μTAS, because they are the simplest structures that can function both as a path for liquid transportation and a fluid mixing device. In ordinary zigzag channels, the bending direction alternates, and as a result, the convective fluid mixing effect at one bend is partially cancelled at the next bend. Therefore, the zigzag channel with m alternating bends does not exhibit m times as much mixing performance as a channel with a single bend even. In this study, the mixing performance of four special types of zigzag channels was compared. These channels had m successive 90° bends in the same direction, then m successive 90° bends in the opposite direction, and this pattern was repeated numerous times. Experiments with channels having m=1, 2, 3, or 4 were performed to determine mixing efficiency and the flow condition as Re number.
A commercial acrylic emulsion paint with added ethanol was prepared as a model paint with two volatile components. A convective batch-drying experiment of the model paint coated on an iron plate base was performed, and the temperature and weight changes of the coat were measured simultaneously. Basic equations of the temperature-change method derived for the volatile single-component system proposed previously by the authors were extended to give equations for two volatile components. Drying rates of water and ethanol of the coated model paint were successfully obtained by substitution of the temperature and weight changes of the coat into the extended equations. The method proposed in this study for measuring the drying rates of two volatile components is convenient in obviating the need for composition analysis of the drying vapor or drying coat. However, its use is restricted to cases in which the weight change of the drying sample can be measured successively with low air speed and air temperature, and cannot be applied directly to a system of three volatile components.
The effect of sulfur dioxide partial pressure and reaction temperature on the composition of the poly-hydriodic acid solution produced in the Bunsen reaction, is a unit reaction in the IS process for thermochemical hydrogen production, was studied experimentally under iodine saturation. The ratio of (HI/(HI+H2O)) of the poly-hydriodic acid solution assuming an ideal desulfurization was increased with sulfur dioxide partial pressure and reaction temperature. An experimental equation for the ratio of (HI/(HI+H2O)) was obtained as a function of sulfur dioxide partial pressure and reaction temperature.