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A method to intensify the mixing process of scalar components within shear-thinning fluids was proposed. A conical Taylor–Couette flow enabled fluid elements to circulate in the entire fluid column owing to the global circulation flow (i.e., meridional flow) for keeping good local mixing within Taylor cells. The global convection and mixing characteristics were numerically investigated. The meridional flow was found to be enhanced with increasing shear-thinning. In addition, ......

The present chapter provides an overview of vortex dynamics in complex fluids by taking examples of Taylor vortex flow. As complex fluids, non-Newtonian fluid is taken up. The effects of these complex fluids on the dynamic behavior of vortex flow fields are discussed. When a non-Newtonian shear flow is used in Taylor vortex flow, an anomalous flow instability is observed, which also affects heat and mass transfer characteristics. Hence, the effect of shear-thinning on vortex dynamics including heat transfer is mainly referred. This chapter also refers to the concept of new vortex dynamics for chemical process intensification technologies that apply these unique vortex dynamics in complex fluids in Conclusions.

The drying process of electrode slurry for LiB should be crucial to obtain higher electrochemical performance, but it has been a black box. Furthermore, the lack of sufficient information on slurry microstructure complicates solving this issue. In this study, the cathode slurries having different internal structures are prepared and characterized by rheological properties. The drying process of the coating layer is evaluated in terms of film shrinkage. When the coarse particles of active material and the network structure of acetylene-black particles are uniformly mixed, a low drying rate results in extensive particle segregation and poor cycle performance. On the other hand, it is found that insufficient dispersion of active materials causes poor rate performance. Under the optimal drying condition, the slurry microstructure is found not to affect battery performance. However, the optimization of drying conditions requires consideration of material mobility during drying.

This work experimentally investigated flow characteristics and mixing properties of the two-phase flow in a continuous Taylor-Couette flow reactor (CTCR) with narrow gap width. In the device with a gap width of 0.5mm, to the authors’ knowledge, the narrowest gap width device ever studied in CTCR systems, the present study revealed that slug flows with alternating gas and liquid phases, as observed in microchannels, appeared in a certain flow regime. This slug flow appeared mainly in the region of low rotational Reynolds and axial Weber numbers. The non-dimensional effective diffusion coefficient Deff/uL [-] of slug flow was also measured by a tracer response method. Deff/uL in the slug flow was on the order of 10⁻⁶ and it has been successfully found that ideal plug flow mixing characteristics could be achieved under this flow condition. Since the intensified and controllable mixing in the liquid phase due to Taylor vortex motion induced by the inner cylinder rotation is expected to be much better than the mixing in the liquid phase of slug flows in microchannels, this flow is expected to be one of the process intensification techniques that will outperform the performance of the conventional microreactors with microchannels.

The sedimentation and flow characteristics of micro-encapsulated phase change materials have been investigated. As a phase change material, trimethylolethane clathrate hydrate having 218 kJ kg−1 of latent heat was used and encapsulated in silica hard-shell microcapsules, which size distribution has two peak at 15 µm and 59 µm. A cationic surfactant, oleylbishydroxyethylmethylammonium chloride with a counter-ion, sodium salicylate was used as drag reducing additives and poly vinyl alcohol was used as a stabilizer. From the results, it was found that the combination additive prevents effectively the microcapsule sedimentation. The drag reduction was also observed to occur in the high Reynolds number region. Thus, the present additive was concluded to be promising for the latent heat transportation by use of silica hard-shell microcapsules containing phase change materials.

This study numerically investigates the heat transfer characteristics, including the fluid flow, of a Taylor vortex flow system with shear-thinning fluids. Governing equations were solved using OpenFOAM® 4.0 code. The Carreau model was utilized as the rheological model. The parameter (n) in the Carreau model, which describes the slope of a decrease in viscosity with an increase in shear-rate, was varied from 1 to 0.3. The local Nusselt number (NuL) decreased with the increase in shear-thinning property. Furthermore, a correlation equation between the effective Reynolds number (Reeff) and a global Nusselt number (NuG) was proposed. Using this equation, NuG was evaluated within a ± 10% error in the case of n = 1, 0.7, 0.5, and within a ± 20% error in the case of n = 0.3. The size of the Taylor vortices became axially larger with an increase in the shear-thinning property. Furthermore, the thickness of the boundary layer of velocity and temperature increased with an increase in shear-thinning property. The ratio of the thickness of velocity boundary layer to the temperature boundary layer monotonically decreased with an increase in Reeff.

The material deposition in a mixing tank agitated by the MAXBLEND impeller in a turbulent state was quantified and compared between cases with and without baffle clearance. Magnesium hydroxide formed from the chemical reaction between calcium hydroxide and magnesium chloride was used as a model of scale formation. Flow velocity in the tank was investigated by employing computational fluid dynamics simulation and experimentally validated by an ultrasonic velocity profiler method. Results showed that the amount of scale decreased with the increase in the rotational speed of the impeller due to the erosion effect on the tank wall. In the case without baffle clearance, the smaller weight of the scale was deposited on the front of the baffle plate due to the flow impingement, which enhanced the removal of the scale deposition. However, the lower-velocity magnitude behind the baffles resulted in an enhancement in the formation of scale. Installation of baffle clearance caused a contraction flow in between the tank wall and baffles, and consequently, the higher flow velocity reduced the amount and thickness of the scale. Measurement of the torque showed that the baffle clearance did not affect the power consumption, so the installation of baffle clearance can be a promising approach to reduce scale deposition in terms of saving operational costs and increasing process efficiency and safety.

Pressure-driven membrane filtration processes such as microfiltration and ultrafiltration are still hindered by concentration polarization and membrane fouling. Generally in these filtration processes, concentration polarization causes decline of permeate flux and rejection, and fouling leads to permeate flux decline with the increase of rejection. The use of high shear stress for cross flow filtrations has long been considered one of the most efficient methods for overcoming these problems. However, circumferential fluid motion of the hollow fiber membrane surface is also important to avoid formation of a high concentration layer on the surface. In this study, ultrafiltration of humic acid aqueous solution using a polyethersulfone hollow fiber membrane was selected as a model case, and a membrane module with a helical baffle installed around the membrane was used. With the insertion of the baffle, normalized permeate flux and rejection became higher than those without the baffle at the wide range of the feed flow rate. In order to identify the cause of the improvement, CFD simulation was conducted for different baffle geometries. Swirling flow motion generated by the helical baffle around the membrane became more dominant with the lower aperture ratio of the cross sectional area, and there existed the optimum value for the swirling flow generation in terms of the variation of the helical baffle pitch length. The intensity of this fluid motion was characterized by Swirl number and it was found out that high separation performance was obtained at the high Swirl number.

In this paper, thermal processing of starch slurry in a Couette-Taylor flow (CTF) apparatus was investigated. Gelatinized starch dispersion, after treatment in the CTF apparatus, was characterized using such parameters like starch granule diameters (or average diameter), starch granule swelling degree (quantifying the amount of water absorbed by starch granules) and concentration of dissolved starch. These parameters were affected mostly by the process temperature, although the impact of the axial flow or rotor rotation on them was also observed. Moreover, the analysis of results showed a relatively good correlation between these parameters, as well as, between those parameter and apparent viscosity of gelatinized starch dispersion. Meanwhile, the increase in the value of the apparent viscosity and in shear-tinning behaviour of dispersion was associated with the progress of starch processing in the CTF apparatus. Finally, the CTF apparatuses of different geometries were compared using numerical simulation of the process. The results of the simulation indicated that the apparatus scaling-up without increasing the width of the gap between cylinders results in higher mechanical energy consumption per unit of processed starch slurry.

In food industries, enzymatic starch hydrolysis is an important process that consists of two steps: gelatinization and saccharification. One of the major difficulties in designing the starch hydrolysis process is the sharp change in its rheological properties. In this study, Taylor–Couette flow reactor was applied to continuous starch hydrolysis process. The concentration of reducing sugar produced via enzymatic hydrolysis was evaluated by varying operational variables: rotational speed of the inner cylinder, axial velocity (reaction time), amount of enzyme, and initial starch content in the slurry. When Taylor vortices were formed in the annular space, efficient hydrolysis occurred because Taylor vortices improved the mixing of gelatinized starch with enzyme. Furthermore, a modified inner cylinder was proposed, and its mixing performance was numerically investigated. The modified inner cylinder showed higher potential for enhanced mixing of gelatinized starch and the enzyme than the conventional cylinder.

Biological Liquid Crystal, a rich set of soft materials with rod-like structures widely existed in nature, possess typical lyotropic liquid crystalline phase properties both in vitro (e.g. cellulose, peptides and protein assemblies), and in vivo (e.g. cellular lipid membrane, packed DNA in bacteria and aligned fibroblasts). Given the ability to undergo phase transition in response to various stimuli, numerous practices have been exercised to spatially arrange biological liquid crystals. In this mini-review, the fundamental understanding of interactions between rod-shaped biological building blocks and their orientational ordering across multiple length scales is addressed. Discussions are made with regard to the dependence of physical properties of non-motile objects on the first-order phase transition and the coexistence of multi-phases in passive liquid crystalline systems. This review also focuses on how the applied physical stimuli drives the reorganization of constituent passive particles for a new steady-state alignment. A number of recent progresses in the dynamics behaviours of active liquid crystals are presented, and particular attention has been given to those self-propelled animate elements, like the formation of motile topological defects, active turbulence, correlation of orientational ordering and cellular functions. Finally, future implications and potential applications of the biological liquid crystalline materials are discussed.

Background: The intensification of fermentation in stirred bioreactors is an attractive approach for commercial interests and industries that work with biochemical products. Alpha amylase is an enzymatic bio-products that is produced largely from Aspergillus oryzae. Using adaptable agitator can be an efficient way for stirred fermentation. Objective: This study, concentrated on enhancing the mixing process in order to intensify Aspergillus oryzae fermentation. A straight type of Maxblend® impeller was used as an agitator to investigate the incubation parameters compared with the use of a 6-blade double Rushton turbine. Method: Stirred fermentation was done in batch condition. Effect of flow pattern of mixing on fermentation parameters was investigated after each sampling. Results: The results showed that the Maxblend® significantly intensified both enzyme activity and growth rate at low and moderate rates of power consumption (P). The main reason for the decreases in the growth rate and the enzyme activity during agitation by the Rushton turbine at low and high Pv was the lack of oxygen and mycelial damage, respectively. Additionally, use of the Maxblend® significantly intensified the KLa at low and moderate rates of power consumption. Conclusion: Axial and uniform mixing by Maxblend® impeller was resulted in improving the fermentation characteristics and enzyme activity.

This study investigated the effect of pretreatment of ultrasonic irradiation on emulsion polymerization of styrene to propose a process intensification method which gives high conversion, high reaction rate, and high energy efficiency. The solution containing styrene monomer was irradiated by a horn mounted on the ultrasonic transducer with the diameter of 5 mm diameter and the frequency of 28 kHz before starting polymerization. The pretreatment of ultrasound irradiation as short as 1 min drastically improved monomer dispersion and increased reaction rate even under the agitation condition with low rotational speed of impeller. Furthermore, the ultrasonic pretreatment resulted in higher monomer concentration in polymer particles and produced larger polymer particles than conventional polymerization without ultrasonic pretreatment.

In this study, a Taylor-Couette flow reactor (TCFR) was applied to starch hydrolysis accompanied with an intricate viscosity change during reaction for the purpose of process intensification. In industries, several reactors are used in starch hydrolysis, namely gelatinization, liquefaction, and saccharification. It was possible to conduct a continuous starch hydrolysis with one TCFR. In addition, a sufficient reducing sugar yield was obtained in the Taylor vortex flow regime. However, the yield decreased at a higher effective Reynolds number (Reeff) due to axial dispersion through a bypass flow generated by the wavy motion of Taylor cells. In order to immobilize Taylor vortex flow at this condition, a ribbed inner cylinder was employed which suppressed axial dispersion at the higher Reeff. As a result, a higher reducing sugar yield was successfully obtained than that by using a standard cylinder, demonstrating that the optimization of TCFR geometry has the potential for process intensification.

In this study, it was shown that how rheology and fluid dynamics effected the behavior of cell growth and L-Lactic acid productivity during cultivation of filamentous fungi (Aspergillus oryzae) in a stirred-tank. Submerged culture of A. oryzae was a shear-thinning fluid with complex rheology and morphology. It is a shear-sensitive fluid. The scope of this study, was enhancing the gas-liquid flow of fermentation fluid to improve the liquid-gas mass transfer, L-lactic acid production and stagnant zone reduction at low energy consumption by effective shear rate generation using multi-large blade agitator with global axial pattern of mixing. Due to this reason, the advantage of Fullzone® (FZ), and impeller was investigated. Experimental results when using multi-large and multi-radial impeller, showed that the same volumetric power consumption of the dissolved oxygen concentration, Re, macro and micro-morphology size, biomass and L-lactic acid production when using multi large impeller was higher and more stable than that of the multi radial impeller. Most of above positive properties were due to the reduction in viscosity and apparent consistence index of fermented fluid.

Membrane technology has been widely applied for environmental protection such as water treatment and CO2 reduction. Thus, there is increasing interest in the membrane field in Japan. The first membrane center (Center for Membrane and Film Technology, MaF Tech center) was established at Kobe University in 2007. This center is the only center focusing on membrane technology in Japan. In this paper, academic research activities and projects in Japan, and the cutting-edge research carried out at the MaF Tech center are briefly reviewed.

A Fullzone (FZ) impeller was used in the first study of the characteristics involved in the fermentation of Aspergillus oryzae. Both the experimental and simulation results of this study revealed novel findings into the positive relationship between the global-axial mixing patterns of a FZ impeller and fermentation efficiency. The mixing results when using the FZ impeller compared with a double Rushton turbine (DRT) impeller indicated that the culture mixed by the FZ resulted in a more homogeneous medium with higher values for oxygen mass transfer, cell growth rate, and alpha amylase activity. The simulation of fluid flow was done in a laminar regime using a two-fluid model. According to the simulation results, the maximum shear stress when using the DRT was higher than that with the FZ at the same power input (Pin). A high degree of local shear stress and the shear rate near the turbine blade of the DRT resulted in cell damage and a reduction in the enzyme activity, biomass, pellet diameter, and dissolved oxygen concentration. Calculations using the Brown equation showed that the maximum and average shear rates during mixing with the FZ impeller were lower than that when using the DRT. Therefore, the use of an FZ impeller, particularly at low Pin, enhanced the cultivation of A. oryzae.

A novel millimeter-sized reactor, named millireactor in the present study, is proposed for oil droplet formation aiming at heterogeneous enzymatic hydrolysis. The reactor consists of a circular ditch with a small stirring bar and a straight channel. To obtain optimal operation conditions and a reactor configuration for droplet formation, the stable droplet formation region was explored by mapping analysis, and the relationship between the specific interfacial area of droplets and other physical parameters were investigated by dimension analysis. It was found that the shear stress parameter and interfacial tension played important roles in the droplet formation. Considering parameters such as the length of the stirring bar, rotating speed, diameter of the stirring section, gap width, interfacial tension, viscosity and residence time in the stirring section, a correlation equation including three dimensionless numbers was obtained. The optimal design guide for obtaining high specific area of oil droplets involves increasing the volume of the stirring section and reducing the gap width as narrow as possible. The reactor performance was evaluated comparing the amount of fatty acid produced in the millireactor versus the batch reactor. The productivity of the millireactor was higher than the batch reactor for the first 10 min.

A yeast with the xylose isomerase (XI) pathway was constructed by the multicopy integration of XI overexpression cassettes into the genome of the Saccharomyces cerevisiae MT8-1 strain. The resulting yeast strain successfully produced ethanol from both xylose as the sole carbon source and a mixed sugar, consisting of xylose and glucose, without any adaptation procedure. Ethanol yields in the fermentation from xylose and mixed sugar were 61.9% and 62.2% of the theoretical carbon recovery, respectively. Knockout of GRE3, a gene encoding nonspecific aldose reductase, of the host yeast strain improved the fermentation profile. Not only specific ethanol production rates but also xylose consumption rates was improved more than twice that of xylose-metabolizing yeast with the XI pathway using GRE3 active yeast as the host strain. In addition, it was demonstrated that xylitol in the medium exhibits a concentration-dependent inhibition effect on the ethanol production from xylose with the yeast harboring the XI-based xylose metabolic pathway. From our findings, the combination of XI-pathway integration and GRE3 knockout could be result in a consolidated xylose assimilation pathway and increased ethanol productivity.

Particle dispersion in a stirred vessel with dual paddle impellers was numerically investigated by a commercial CFD code. The working fluid was assumed a weak shear-thinning non-Newtonian fluid or Newtonian fluid having low viscosity (ca. 4.0 Pa · s). Particles were initially set in the lower half region in the vessel. Numerical simulations were conducted by varying rheological property, location of the impellers and discharge flow rate of impellers. Numerical results showed that the viscosity was lower near the impeller in the non-Newtonian fluid than in the Newtonian fluid due to strong shear near the forefront of impeller. Consequently, the velocity of discharge flow from impeller was larger in the non-Newtonian. Larger velocity of the discharge flow took more particles to the tank wall as compared with Newtonian fluid. The present work adopted the mean value and the standard deviation of particle concentration as particle dispersion indexes. It has been found that the standard deviation depends on particle dispersion process.

This paper reports on an experimental study of mixing intensification using speed modulation of a six-blade Rushton turbine in a stirred vessel. Mixing times were measured using a non-intrusive technique based on direct visualisation of an acid-base reaction in a Newtonian fluid. The impeller speed modulation was achieved by using two waveforms: a square wave and a sine wave. The amplitude was fixed between a maximum Reynolds number of Remax = 60 and minimum Reynolds numbers of Remin = 40 or 30. The wave periods were varied (10, 20, or 40 s) in order to compare the effects of unsteady stirring on mixing performance. It was observed that a square wave protocol with the shortest wave period and the larger amplitude resulted in the shortest time to destroy the observed isolated mixing regions (IMRs), which are known to exist in stirred vessels operating at low Reynolds number. However, the sine wave protocol led to a slow diffusive mechanism in which IMR structures reached an asymptotic volume and remained visible even after several hours. The results are presented and discussed using digital photographs taken at different time intervals during experimentation.

A novel facilitated transport membrane consisting of 2,3-diaminopropionic acid (DAPA) as a selective carrier of CO 2 and PVA/PAA gel as support was developed for the removal of CO 2 from the water gas shift reactor in the hydrogen production plants. The membrane performance was tested by the experiments on the selective separation of CO 2 from a mixture of 3.65% CO 2 , 32.9% N 2 and 63.5% H 2 O at the temperature from 125 to 160 °C and the feed gas pressure from 100 to 650 kPa. Typical observed CO 2 permeances were 3.14 × 10 −4 mol/m 2 s kPa at 125 °C and 300 kPa, 1.71 × 10 −4 at 140 °C and the feed gas pressure of 450 kPa and 1.10 × 10 −4 at 160 °C and 600 kPa, and the CO 2 /H 2 selectivities at the respective conditions were 1070, 561 and 432, respectively. Obtained results showed that the water content in the membrane is one of the key factors, which determines the CO 2 permeance and CO 2 /N 2 selectivity. The CO 2 permeance as well as the CO 2 /N 2 selectivity increased with increasing the pressure, which might be mainly caused by increasing the water content in the membrane. It was also found that increasing the carrier concentration could significantly enhance the membrane performance, especially at elevated temperatures.

The stability of the helical flow in a system of coaxial rotating conical cylinders, the inner one rotating and the outer one stationary was experimentally investigated. The helical flow resulted from a Hopf bifurcation, which occurred only when the acceleration of the inner conical cylinder was smaller than 0.06 rad/s2. When the rotational speed of the inner conical cylinder was increased, the transition to turbulence occurred following a succession of flow states: (i) three-dimensional laminar flow (TDLF), (ii) laminar periodic helical flow (LPHF), (iii) doubly periodic wavy helical flow (DWHF), (iv) weakly turbulent helical flow (WTHF) and (v) fully turbulent helical flow (FTHF). Time series obtained by an electrochemical method permitted the identification and analysis of the fundamental frequencies and their evolutions associated with each time-dependent flow state, using Fourier and wavelet transforms. Phase space analysis revealed the associated attractors constructed from the embedded time series. In the FTHF flow state, the fundamental frequency of the helical flow was observed to have a ratio to the rotational frequency of almost twice that of the one measured in the LPHF regime.

The transient evolution and steady state analysis of Taylor vortex flow in a tapered annulus was conducted by numerical experiments in the case where the inner cylinder was rotated and the outer one fixed. The gap between the cylinders was linearly tapered from a supercritical value at the upper base to the critical value at the lower base. The wavelength adjustment depended on the variation of Reynolds number in the spatially ramped gap. The axisymmetric conservative governing equations were solved by the use of an simplified marker and cell (SMAC) algorithm. A coordinate transformation function allowed us to numerically solve the problem in a rectangular computational domain. The results have shown that Taylor vortices growth was sensitive to the spatial ramp of the gap even with tapering angle values less than one degree. The interaction between the inflow and outflow boundaries could be clearly seen as the taper angle was increased. The investigation of the transient dynamics related to the flow system also revealed a characteristic dependence on the taper angle.

Particle classification phenomenon in Taylor vortex flow with an axial flow was investigated experimentally and numerically. The flow-visualization experiment by a laser-induced fluorescence method clearly revealed that there existed two distinct mixing regions at low Reynolds numbers. The tracer near the vortex cell boundary was rapidly transported axially owing to the bypass flow effect. On the other hand, the fluid element was confined to the vortex core region without being exchanged with the outer flow region. In order to observe particle classification phenomenon, polymethyl methacrylate (PMMA) particles suspended in the same aqueous solution of glycerol as the working fluid were fed into the top of the apparatus. Particle size was initially ranging from 10 to 80 ?m. The ratio of the particle density to the fluid density was 1.04?1.05, which means the density difference between particle and fluid is very small. The suspended solution was withdrawn using a hypodermic needle every a certain time period at 30 mm above the bottom of apparatus. The fluid was sampled both near the outer wall and in vortex core. The particles sampled at 42 min having the size of 20?50 ?m were mainly observed in the vortex core region. On the other hand, a large population of particles having the size of about 50?80 ?m could be seen in the outer region of vortex. It was found that large particles located near the outer edge of vortices were quickly transported axially owing to the bypass flow effect. Numerical simulation also revealed that the loci of particles depended on the particle size.

Synthesis of thiol-capped gold nanoparticle is carried out by mixing of a THF solution of HAuCl4·4H2O and nC12H25SH with a THF solution of triethylsilane in a flow system that consists of polytetrafluoroethylene tubing. The effect of residence time and reaction temperature on the particle size is examined.

A combined numerical and experimental investigation was conducted to study mode selection in Taylor-vortex flow (TVF) between coaxial conical cylinders (truncated cones), where the inner cylinder rotates and the outer one is at rest. Simulations, using a finite-difference method with simplified marker and cell (SMAC) formulation, confirmed the same dependence of mode selection on the acceleration rate β of the inner conical cylinder as observed experimentally. Different TVF modes were obtained in the Reynolds number (Re) range studied. Three different modes corresponding to six, seven and eight pairs of steady Taylor vortices were obtained when the inner conical cylinder rotation speed was increased linearly at different acceleration rates. The transition diagram obtained by Re-β mapping successfully summarizes the various flow states and modes observed.

This work examined the controllability of the size of polymer particles and its distribution by taking advantage of the self-sustained oscillations of monomer conversion in continuous emulsion polymerization of vinyl acetate in a CSTR. The emulsifier concentration was primarily varied as a control parameter of the experimental condition below the critical micelle concentration. Regularly periodical oscillations in monomer conversion occurred with a long period as compared to the mean residence time of the CSTR. Time-dependent size distribution of polymer particles observed by TEM varied in form synchronously with the periodical oscillations of monomer conversion. These results suggest that particles can be formed intermittently owing to the temporal variation of the concentration of free emulsifier in the condition below CMC. It has also been confirmed that the particle size distribution (PSD) is made quite narrow in the condition for regularly periodical oscillations but considerably wide in the condition for irregular oscillations. It has been successfully indicated that the self-sustained oscillations in continuous emulsion polymerization will be profitable not only for controlling the size of latex particles but also for raising the monomer conversion.

Effective mass diffusion over cell boundaries in a Taylor-Couette flow system was investigated ranging from singly periodic wavy vortex flow to weakly turbulent wavy vortex flow by a salt-solution tracer technique. In order to determine experimentally the intercell mixing coefficient k CB between the neighbouring pairs of vortices, an appropriate model was formulated. As a result, k CB depends not only on Taylor number but also on axial wavelength with fluid viscosity. In the singly periodic wavy vortex flow region, the intermixing is enhanced by periodic fluctuations resulting from azimuthally travelling waves on the cell boundaries. With increasing Taylor number in the doubly periodic wavy vortex flow and weakly turbulent wavy vortex flow regions, the mixing characteristics go toward axial turbulent diffusion. In these two flow regions, the correlation between k CB and effective diffusion coefficient D z based on an axial diffusion model has been obtained as D z = 2 λk CB .

アスペクト比が3のテイラー・クエット流の渦発生と乱流遷移特性について, 数値計算, 電気化学的方法および流れの可視化法を用いて, 内円筒の回転加速度の効果を考慮に入れて調べた.SMAC法を基にした3次元数値計算により, 渦の発生機構と波動テイラー渦流の時空間特性を明らかにした.電気化学的方法と流れの可視化法を用いて, 波動, 準周期性波動および, 弱い乱流波動テイラー渦流の時空間特性を明らかにした.内円筒の回転加速度が小さい場合, 2つの渦セルをもつ主モードが発生する.一方, 回転加速度が大きい場合, 4つの渦セルをもつ二次モードとなる.波動テイラー渦流において, 速度および, 速度勾配変動のパワースペクトルに現れる単一の基本周波数は, 巡回する周方向波の移動周波数と一致し, 流れのモードに依存する.準周期性および, 弱い乱流波動テイラー渦流においても, 時空間特性は, この渦セルモードに大きく依存していることがわかった.これらの結果より, 渦セルの幾何学的構造が流れの特性に影響を及ぼしていることがわかった.

A continuous emulsion polymerization of styrene was tried in a Taylor vortex flow reactor which has characteristics of a plug flow reactor. The Taylor vortex flow reactor has the mixing characteristics appropriate for this reaction system. The steady-state conversion, the average molecular weight and the size distribution of latex particles can be controlled by the flow condition as well as by the reaction temperature.

Bifurcation phenomena in a finite-length Taylor-Couette flow system have been observed by an electrochemical technique. The axial wavelength was varied as the characteristic parameter of vortex cell structure by varying the aspect ratio of the annular flow space and controlling the inner cylinder acceleration up to a steady rotation speed. Multi-resolution analysis in wavelets was used not only for noise reduction, but also for extraction of low frequency components from the experimental time-series data. When the dimensionless axial wavelength λ/d < 1, the first fundamental frequency f 1 /f r of singly periodic wavy vortex flow was fixed at a unique value independent of the magnitude of λ/d. When λ/d ≥1, on the other hand, f 1 was not fixed uniquely but showed some variation, depending on the magnitude of λ/d. In the transition to doubly periodic wavy vortex flow, not only Hopf bifurcation but also two-cycle period doubling bifurcation occurred in some cases when λ/d < 1. The first and second fundamental frequencies, f 1 and f 2 have tendencies to increase with increasing λ/d in spite of some exceptions. In the process of a transition to weakly turbulent wavy vortex flow, two-torus motion in phase space broke up at all wavelengths without frequency locking.

Mixing has been one of essential unit operations for chemical engineering processes. Among a number of mixers, stirred tanks that are available in a wide variety of tank sizes and impeller shapes are the most frequently adopted to homogenize different substances and to conduct chemical reactions in industrial chemical processes. In addition, there are various technologies for fluid mixing: static mixer, micromixer, unsteady agitation, eccentric agitation, and so on. Recently in various industrial processes, a wide range of operation for stirred tank is required depending on purposes and conditions, and high efficiency on mixing has been strongly required. In addition, the techniques of computer simulation analyses by the use of CFD software have been dramatically developed, which is essential to analyze the mixing mechanism. The main goal of this special issue was to gather contributions dealing with the latest breakthrough of mixing techniques. There is a collection of twelve papers in this special issue focused on mixing fundamental (2 papers), multiphase mixing (3 papers), chemical reactive mixing for metallurgical industry, and biotechnology (4 papers), and new technology of mixing (3 papers) ranging in topic from laminar-to-turbulent mixing by means of both experimental analyses and numerical simulations. The highlights of each paper are introduced as follows.

The instabilities of the Belousov-Zhabotinskii reaction were studied in an isothermal CSTR by varying the space velocity as bifurcation parameter. The time-dependent concentration of bromide ion and redox potential were observed, respectively, by a Ag-AgBr electrode and a platinum-wire electrode under reaction-controlling conditions. The single-peak periodic and the chaotic oscillations occur alternately with increasing space velocity. The multipeak oscillations were also observed at higher space velocities. Two kinds of chaotic oscillations were observed, chaotic oscillations with amplitudes varying irregularly in the periodic-chaotic sequence region and chaotic mixing of large and small amplitude in the multipeak oscillations region. An analysis of the phase portraits for these chaotic oscillations indicates that they correspond to low dimensional and fractal structures.

Four kinds of transporters, HXT1 and HXY7 from Saccharomyces cerevisiae, and GXF1 and GXS1 from Candida intermedia, were overexpressed in xylose-metabolizing S. cerevisiae harboring a xyloseisomerase-based pathway. Overexpression of transporter enhanced sugar consumption and ethanol production, and GXF1 was efficient for ethanol fermentation from both glucose and xylose.