The gas–liquid mass transfer coefficient at extraordinarily large gas flow rates was investigated for a pitched bladed paddle creating upward flow in comparison with those of the Rushton disc turbine and the Scaba SRGT impeller, which are commonly recommended for gas–liquid mixing. The results indicated that the pitched bladed paddle up-pumping gave the enhanced mass transfer coefficient k_La at large gas flow rates compared to Rushton disc turbine and Scaba SRGT. In this study, it was confirmed that the k_La of DT and SRGT depend only on the aerated energy dissipation rate (ε_T)_g at the gas flow rates of 4.8–15.8 vvm. In contrast, the k_La of PPU was shown to be functions of both (ε_T)_g and supercritical gas velocity v_s until 22.2 vvm.

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A numerical model of the drawing of polymer optical fibers (POF) in a steady state has been developed. The continuity and the momentum equations were one-dimensionally treated in the drawing direction, and the energy equation was axisymmetrically solved in the present model. A parameter study on the drawing of optical fibers made of polymethylmethacrylate (PMMA) has been also carried out. The effects of the drawing velocity, the distributions of its ambient temperature and its heat transfer rate were focused on as parameters in this paper. From the results, it is found that five times longer heater than that of the known furnace or the exchange of the ambient gas from air into helium for higher heat transfer rates is required for five times higher-speed drawing.

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The dynamic response of the solid holdup of single- and two-sized particle systems with a step increase and decrease in the liquid fluidization velocity within a vertical column were experimentally investigated using sieved spherical glass beads with average diameters of 166, 225, and 511 μm. Regardless of the particle size and the magnitude of change in liquid fluidization velocity, a similar tendency was observed with regard to the transition of solid holdup profiles between the initial and the final steady state of the particles in a single-sized system. Further, the behaviors of larger particles in a two-sized particle system were found to be almost the same as those in a single-sized particle system, though the smaller particles in a two-sized particle system showed complex behaviors which were greatly differed from those in a single-sized particle system.
Simple mathematical models have been also developed in this regard. In the models, the particle velocities calculated by the void functions of steady state were combined with the continuity equation of the solid phase including the diffused flux. Under the current experimental conditions, the diffusion coefficients were regarded constant in the axial direction within the process, and they only depended on the initial and final superficial liquid velocity and the diameter of the particle.

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The mixing characteristics of a multi-holed static mixer have been studied for Newtonian fluid. A multi-holed static mixer composed of five pairs of 4- and 5-hole elements. The size of straight part of the hole, a, was changed in two steps of 2 mm and 5 mm and its inlet and outlet size, d, was also changed in two steps of 4 or 6 mm in the cases of a = 2 mm. The fluid viscosity and flow rate were also changed as parameters. Flow visualization experiments in a test pipe with 18 mm diameter were performed in order to observe the occupation ratio of dyed fluid, which is injected from the nozzle with 4 mm diameter mounted in the upstream of the static mixer. From the results, it is found that the Reynolds number based on the mean velocity in the 4 hole element and the hole size, Re_a, multiplied by a delivery ratio of the hole, d/a, well correlates the mixing and pressure loss characteristics. This is because there exist two mixing processes in the present static mixing system. One is the mixing process in a small hole by accelerated flow and the other is a delivery effect between holes.

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Two different drying regimes were observed in air-free condenser drying of solvent-polymer solution coatings. The measured solvent drying rate for the constant rate period increases with an increasing solvent partial pressure gradient in the low pressure gradient regime. This drying behavior was quantitatively consistent with the previously proposed one-dimensional theory. At higher pressure gradients above a critical value, however, the solvent evaporation rate reaches a constant value, showing a particular drying-rate limit. The experiments revealed that the configuration of the grooves, on which the condensed solvent forms a continuous liquid layer, plays a key role in the retarded solvent diffusion in the condenser drying system.

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Seeking internal heat integration between the whole rectifying section and the whole stripping section gives rise to two alternatives for the arrangement of a reboiler in an internally heat-integrated distillation column. One is to locate it at the bottom of the process (scheme A) and the other on the pipeline of the feed flow (scheme B). Although the former appears to be less thermodynamically efficient than the latter, it is generally preferable to scheme B from the viewpoint of process dynamics and operation. A detailed simulation study justifies the conclusion.

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The prerequisite condition for maintaining dropwise condensation on a surface is that the condensing surface should have a low surface energy. In the present paper, two different techniques were employed to achieve steam dropwise condensation over a vertical copper tube at atmospheric pressure: one is self-assembled monolayers (SAMs), and the other is electroless composite plating. The use of SAMs of docosanoic acid promotes dropwise condensation. The electroless Ni–P–PTFE coatings also achieve excellent dropwise condensation. Compared with film condensation, the condensation heat transfer coefficient can be enhanced by more than one order of the magnitude on these coated surfaces. The electroless composite coating surface of high PTFE content has a higher condensation heat transfer coefficient than that of low PTFE content. The SAM surface of docosanoic acid has the lowest surface energy which leads to the lowest thermal resistance of liquid condensate, and a negligible thickness of 30 Å with a negligible additional heat transfer resistance, thus it has better heat transfer characteristics than those of the Ni–P–PTFE surfaces.

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A two-fluid Eulerian model has been used to study the effect of various sieve plate gas distributors and gas superficial velocities on the hydrodynamics of three-dimensional flow in bubble columns. Turbulence has been modelled using the k–ε turbulence model. Inclusion of gas distributors showed asymmetric flow patterns which are otherwise smoothened when modelled using a uniform gas source. The asymmetric behaviour increased with an increase in the number of holes giving better mixing. The gas hold-up increased with superficial gas velocity, and was independent of the distributor design at high superficial gas velocities. Comparison of simulation results with the experimental work from the literature has provided a successful validation of the model. This study demonstrates the significance of the real distributor in hydrodynamic studies that has been largely neglected in the past.

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In order to improve the performance of the ultrasonic atomization, the effect of the flow mode of the carrier gas on the atomization characteristics were examined. The rectangular vessel was used to make the two-dimensional flow pattern, and water and nitrogen were used as the liquid sample and the carrier gas. The flow direction of gas to the fountain jet and the heights of gas inlet and outlet were combined and the flow rate of the accompanied liquid was measured.
The flow pattern of the liquid droplet around the fountain jet was affected by the flow direction of the carrier gas. When the height of the gas outlet was located at the middle height of the fountain jet, the flow rate of the accompanied liquid had a maximum and the median diameter of the liquid droplet had a minimum. The countercurrent of the carrier gas is effective for the improvement of the performance of ultrasonic concentration.

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Transient or dynamic responses often occur in continuous aerobic systems like the activated sludge process when environmental variables change. The system’s response to a dynamic load change has yet to be successfully modeled. In this paper we examine previously collected experimental data of the system’s response to a step change. The real time profile of the growth rate μ and the cell/substrate yield, Y, are studied via parametric manipulation. It was observed that both variables, μ and Y, experience an initial step drop and then a hysteresis response to a new steady-state level, following a sudden step change in the feed flow rate. A modified Monod equation is proposed here to qualitatively model the hysteresis dynamic response of a sudden dilution rate change to an open, continuous microbial growth system.

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Straight-through microchannel (MC) emulsification enables formulating monodisperse emulsions using a channel array vertically microfabricated on a plate surface (a straight-through MC). This study investigated the effect of the fluid flow in a channel on the generation of soybean oil-in-water emulsion droplets from an elliptic channel using Computational Fluid Dynamics (CFD). The visualized CFD results demonstrated that droplets with diameters of 32 to 38 μm were stably generated from the channel below the critical flow velocity of the to-be-dispersed phase (U_d). Above the critical U_d, we observed a drastic increase of the resultant droplet diameter. The calculated droplet generation rate achieved a maximum value of about 15 droplets per second at the critical U_d. An analysis of the neck formed inside the channel during droplet generation explained why the droplet generation behavior from the channel drastically changes over the critical U_d. The CFD results obtained in this study were confirmed by our experimental results reported in the literature.

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Surface wave velocity of the methylcellulose (MC) hydrogels in the drying process was measured with three different molecular weights. Surface wave velocity increased with drying time for all samples but there was a period in which the surface wave velocity kept an almost constant value for two samples. A possible explanation for the period was made from the numerical calculation of surface wave velocity using simplified layer model.

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Cooling crystallization of β-sitosterol that is a kind of phytosterol was carried out, where a water-immiscible solvent hexane containing a ppm level of water was used as a solvent. The initial ratio of water and β-sitosterol concentration adopted in this work was 330/10, 1315/10 and 645/20 ppm/(g/L), which corresponded to 0.51, 2.0, and 0.50 in water/β-sitosterol mole ratio, respectively. When the initial ratio of water and β-sitosterol concentration was 1315/10 ppm/(g/L), thin plate-like crystals were precipitated and were identified as the monohydrate crystals of β-sitosterol. On the other hand, when the initial ratio of water and β-sitosterol concentration was 645/20 ppm/(g/L), needle-like crystals of hemihydrate were precipitated. This result meant that the ppm level of water plays an important role for the pseudo-polymorphism. Since the crystal structure of β-sitosterol hemihydrate had never been reported, we determined it by a single crystal XRD analysis.

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With the aim of developing a high performance reactor for proton exchange membrane fuel cell (PEMFC) systems and other applications, steam reforming of ethanol using silica-coated alumite catalysts on aluminum plates (JIS A1050) was performed at atmospheric pressure in a temperature range of 300–600°C. The aluminum material (JIS A1050) was used in a plate type aluminum-clad material which has been used for electrically heatable alumite catalysts having high heat durability. Initial ethanol steam reforming tests performed with either an alumite support (γ-Al₂O₃/Al) or an alumite catalyst (Ni/γ-Al₂O₃/Al) produced ethylene (C₂H₄) as the main byproduct because of the dehydration reaction of ethanol. With the aim of eliminating ethylene formation, a silica coating was applied to anodized aluminum plates (JIS A1050 Al) using a commercially available silica sol with a particle diameter of 22–25 nm. The resulting silica-coated alumite support (silica/Al₂O₃/Al) and silica-coated alumite catalyst (Ni/silica/Al₂O₃/Al) dramatically reduced the formation of ethylene. For example, in the case of the silica-coated alumite catalyst (Ni/silica/Al₂O₃/Al) with a silica-coating time of 20 h, C₂H₄ was reduced by 100% at 450°C and by 59% at 500°C compared with the levels seen for the alumite catalyst (Ni/γ-Al₂O₃/Al). A silica-coating time of 20 h was found to be the best for reducing ethylene formation. A temperature programmed desorption analysis with ammonia desorption also showed that the number of acidic sites per apparent surface area of the silica-coated alumite support (silica/Al₂O₃/Al) and the silica-coated alumite catalyst (Ni/silica/Al₂O₃/Al) was smaller than that of the alumite support (γ-Al₂O₃/Al) and the alumite catalyst (Ni/γ-Al₂O₃/Al) without any silica coating, respectively. These results suggest that the low level of ethylene formation with the silica-coated alumite support and silica-coated alumite catalyst was due to the smaller number of acidic sites. It is concluded that the silica-coating method is preferable for improving the properties of alumite supports and alumite catalysts for use in ethanol steam reforming.

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It was found that in a volatile organic compound (VOC) catalytic combustion reaction, the dispersion of the platinum catalyst that was supported on an anodized aluminum plate by the electrolysis supporting method, decreased with the reaction time. The sintering of the catalysts was explored by the respective catalytic combustion of benzene, toluene, and ethylbenzene. The dispersions of platinum varied with reaction atmospheres during the reaction. The results of activity tests showed that catalytic activity was promoted with sintering of platinum particles. From the analysis of temperature-programmed desorption (TPD), the surface characteristics of catalysts were studied. It was found that the amount of chemisorbed aromatic hydrocarbons increased along with the sintering of platinum particles. This was applied to elucidate the activating effect of sintering.

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Induced air flotation (IAF) was developed using a rotating-flow microbubble generator for water treatment. This newly-developed generator can produce fine microbubbles with diameters on the order of micrometers, whereas it has to use a large quantity of water as propulsion, especially when surfactant-free water is used. That is to say, if the microbubble generator is utilized in flotation, the recycle ratio in IAF will be very high. To overcome this problem, we applied a centrifugal pump and altered the air-induced way of the generator. Microbubble size, microbubble concentration and particle removal efficiency of the improved microbubble generating method were compared with those of traditional ones.
The best performance occurred in the improved method where gas and water were simultaneously induced and mixed by the pump, and dispersed through the rotating-flow microbubble generator. Microbubble size was decreased, while microbubble concentration was increased by the improved method. Particle removal efficiency of over 95% was achieved by recycling only 10% of treated water.
Batch experiments were carried out under various flocculation and flotation conditions to evaluate the improved IAF process. A slight overdose achieved better removal efficiency and no or less flocculation time performed very well. Lower water flow rates achieved better removal efficiency due to the increase of the bubble concentration and the decrease of the bubble size. The air flow rate showed little effect on removal efficiency.

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