Editor-in-Chief:
Hiroyuki Honda (Nagoya University)

Associate Editors-in-Chiefs:
Manabu Shimada (Hiroshima University)
Takao Tsukada (Tohoku University)

Editors:
Ryuichi Egashira (Tokyo Institute of Technology)
Jun Fukai (Kyushu University)
Choji Fukuhara (Shizuoka University)
Takayuki Hirai (Osaka University)
Masahiko Hirao (The University of Tokyo)
Jun-ichi Horiuchi (Kitami Institute of Technology)
Eiji Iritani (Nagoya University)
Yoshinori Itaya (Gifu University)
Hideo Kameyama (Tokyo University of Agriculture and Technology)
Masahiro Kino-oka (Osaka University)
Toshinori Kojima (Seikei University)
In-Beum Lee (Pohang University of Science and Technology (POSTEC))
Kouji Maeda (University of Hyogo)
Shin Mukai (Hokkaido University)
Akinori Muto (Osaka Prefecture University)
Nobuyoshi Nakagawa (Gunma University)
Hiroyasu Ogino (Osaka Prefecture University)
Naoto Ohmura (Kobe University)
Mitsuhiro Ohta (The University of Tokushima)
Yuji Sakai (Kogakuin University)
Noriaki Sano (Kyoto University)
Masahiro Shishido (Yamagata University)
Richard Lee Smith, Jr. (Tohoku University)
Hiroshi Suzuki (Kobe University)
Shigeki Takishima (Hiroshima University)
Yoshifumi Tsuge (Kyushu University)
Tomoya Tsuji (Nihon University)
Da-Ming Wang (National Taiwan University)
Yoshiyuki Yamashita (Tokyo University of Agriculture and Technology)
Miki Yoshimune (National Institute of Advanced Industrial Science and Technology (AIST))

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AIMS AND SCOPE:

Journal of Chemical Engineering of Japan, an official publication of the Society of Chemical Engineers, Japan, is dedicated to providing timely original research results in the broad field of chemical engineering ranging from fundamental principles to practical applications. Subject areas of this journal are listed below. Research works presented in the journal are considered to have significant and lasting value in chemical engineering.

Physical Properties and Physical Chemistry
Transport Phenomena and Fluid Engineering
Particle Engineering
Separation Engineering
Thermal Engineering
Chemical Reaction Engineering
Process Systems Engineering and Safety
Biochemical Food and Medical Engineering
Micro and Nano Systems
Materials Engineering and Interfacial Phenomena
Energy
Environment
Engineering Education

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In most of the bubble column designs, it is assumed that the liquid phase is well mixed and spatial distributions of molar concentrations of all components are uniform. However, liquid mixing occurs in actual bubble columns. The performance of a bubble column strongly depends on the liquid mixing induced by bubbles in the column. The above-mensioned assumptions therefore lead to errors in the optimum column design. However, only a few quantitative investigations have been carried out on two-phase turbulence and liquid mixing. In this study, numerical simulations of liquid mixing in a bubble column were carried out and the results obtained were compared with those of experiments. Time-dependent tracer concentrations were measured for test columns 0.3 m in diameter. The height of the columns was 1 m. Bubbles were supplied by using two types of spargers, ring spargers and a perforated plate. A hybrid method, NP2-3D, that is based on a combination of multi-fluid and interface tracking models was used to simulate the flow. In a two-phase turbulence model, the linear superposition of bubble-induced turbulence and shear-induced turbulence was assumed. Numerical were found to be good predictions of the effects of the column diameter and gas inlet on the liquid mixing in the column.

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To reduce the release of greenhouse gas from massive emission sources into atmosphere, a slurry bubble column suspending lithium silicate is proposed to remove hot CO₂ from flue gas or pre-combustion effluent gas. As the liquid phase, the molten salt consisting of binary carbonates was used. The slurry suspending solid particles of lithium silicate in the molten salt promoted to mix gas and slurry in the column so that the absorption rate of CO₂ was improved. In this study, the effects of some important operating conditions such as superficial flue gas velocity, the concentration of lithium silicate powder in the slurry and the height of the slurry on CO₂ absorption were investigated to optimize the system. The CO₂ absorption increased with increasing superficial gas velocity and decreasing slurry concentration. Fractional CO₂ recovery increased with increasing the height of the slurry. The apparent rate constant and the apparent activation energy were determined in the reaction system. Moreover, an endurance test was conducted to confirm stable recovery capacity, in which the proposed CO₂ recovering system performance was repeatedly maintained.

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Catalase-bound liposome containing glucose oxidase (CLG) has been used to catalyze the oxidation of glucose in an external loop airlift bubble column. In a static liquid system suspending CLG, glucose was steadily oxidized at 40°C at the initial pH of 7.4 for 73 h, although the oxidation rate is significantly small because of strong permeation resistance of the CLG membrane to glucose. In the airlift, the rate of oxidation catalyzed by the CLG with initial mean diameter D_P of 324.9 nm significantly increases at superficial gas velocity U_G of 0.5–3.0 cm/s compared to that in the static liquid. The gas–liquid flow has thus been found to induce permeabilization of the CLG. The reactivity of CLG in the airlift is influenced by the interaction between catalase (CA) and the membrane. Furthermore, the structural stability of CLG in the airlift is dependent on its initial D_P. The CLG with D_P of 168.8 nm remains practically unchanged in its size in the airlift at U_G of 1.0 cm/s. On the other hand, the CLG with D_P of 269.5 nm shows to be partly disrupted with deactivation of CA under the above condition. The reactivity and stability of CLG have also been elucidated in catalyzing the fed-batch oxidation of glucose for 34 h in the airlift.

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To promote the production of useful substances such as polysaccharide and trehalose from Flammulina velutipes mycelium in submerged culture, F. velutipes was exposed to stress caused by a sudden change in temperature. The production of polysaccharide doubled when the temperature was changed once and tripled when it was changed twice. The production of trehalose was promoted only when the temperature was changed from high to low during the exponential growth phase.

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This work investigates a mechanism and degree for bubble interactions such as bubble clustering, coalescence and breakup to affect the liquid phase mass transfer coefficient k_L. Our previous k_L data for a normal bubble column (NBC), internal loop airlift (ILBC) and external loop airlift (ELBC) are compared with k_LS for single bubbles and k_L,BF in the bubble flow (BF) at a fixed mean bubble diameter d_B. Our correlations of k_L∝ε_G^0.1 (NBC and ILBC) and k_L∝ε_G^0.2 (ELBC) have been found to arise from the relationship for gas holdup ε_G=0.5(d_B/l)³, where l is the mean distance between the adjacent bubbles. The reported k_L,BF values were reproduced by the Higbie model with the average bubble slip velocity of (gd_B/2)^0.5. A factor F=k_L,CTF/k_L,BF is defined to quantify an effect of the bubble interactions on k_L,CTF in the churn-turbulent flow (CTF). The reported correlation gives F=0.5Eo^3/8, where Eo=gd_B²ρ_L/σ. Eo<6.4 and Eo>6.4 have been found to give the clustering regime and the coalescence and breakup regime, respectively. Our k_L,CTF data (NBC and ILBC) satisfied F=0.5Eo^3/8. F=k_L,ELBC/k_L,BF for the ELBC roughly correlates as F=1.3.

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The liquid phase mass transfer coefficient k_L for an external loop airlift has been investigated to elucidate a mechanism and degree for the gas–liquid concurrent, circulating liquid velocity u_L to affect it. The approach is based on the Higbie model, i.e. k_L∝u_S^0.5 at a fixed average bubble diameter d_B, where the average bubble slip velocity u_S is derived from the drift flux model. The u_S and k_L values have been deduced to decrease in the order of the gas–liquid concurrent flow, batch liquid and countercurrent flow. The result is elucidated by variation of the bubble wake development with the turbulent liquid flow direction and rate, in addition to variations of liquid inertia and drag on individual bubbles. The observed k_L, surpassing k_LS for the single bubble and k_L,BF for the bubble flow (BF), increases from the enhancement effect of concurrent u_L on k_L through its preventing bubbles from clustering, coalescence and breakup. The k_L values could reasonably be reproduced by the Higbie model in which the terminal rise velocity u_BS is replaced by u_S,BF=(gd_B/2)^0.5 for the BF. A factor F=k_L/k_L,BF derived from the above u_S,BF-based equation for k_L well reproduces the observed F.

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We measured gas holdup, bubble size distribution, volume-surface mean diameter, and specific surface area for oxygen micro-bubbles issuing from a high-speed rotation and compression-dissolution-type micro-bubble generator into a bubble column with a 150 mm i.d. and a height of 1000 mm containing pure water saturated with oxygen at 25.0°C in up-flow and down-flow operations. We also measured the apparent volumetric mass transfer coefficient, k_La, in the micro-bubble column using the transient physical absorption of oxygen. The dependence of the values of k_La on the superficial gas velocity was interpreted and correlated by a complete absorption model. Furthermore, the oxygen absorption efficiency, which was defined as the percentage of the ratio of the absorbed amount of oxygen to the introduced amount of oxygen, was found to be within the range of 40–98%, decreasing with increasing volume-surface mean diameter. The differences in the physical and mass transfer properties between the up-flow and down-flow operations were also compared and interpreted. The values of the gas holdup and the volume-surface mean diameter in the up-flow mode were greater than those in the down-flow mode at the same superficial gas velocity. On the other hand, the values of the specific surface area, those of k_La, and those of oxygen absorption efficiency for the down-flow operation were greater than those for the up-flow operation.

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Melanoidin containing wastewater is generated from the distillation process in bioethanol production system. In this study, the melanoidin in water was decomposed by ozone microbubbles and the effect of operation conditions on the decolorization and the total organic carbon (TOC) was investigated. A rectangular tank was made from transparent acrylic resin. A microbubble generator utilizing liquid shear stress, consisting of a liquid pump and a special line mixer, was set at the side of the tank. For comparison, a sintered glass gas sparger was used to generate millimeter sized bubbles. A melanoidin aqueous solution was prepared from glycine and glucose using an autoclave. Compared with ozone millibubbles, the melanoidin in water was effectively decomposed by ozone microbubbles. The volumetric mass transfer coefficient of ozone for microbubbles was much higher than that for millibubbles. The decomposition of melanoidin in water was enhanced by incrementing ozone concentration and flow rate of sparging gas. In the case of decolorization, the reaction rate obeyed a pseudo-first order reaction and the apparent rate constant became higher at pH=4.0 with a radical trap agent. The decolorization of melanoidin was mainly attributed to direct ozone oxidation. The apparent decolorization rate constant increased with decreasing temperature and the rate-controlling step of decolorization was the ozone dissolution into water. On the other hand, the TOC reduction rate increased by the hydroxide radical generated by ozone self-decomposition. The TOC reduction rate increased with increasing temperature. The combination of ozone microbubbles and biological treatment was effective in the treatment of melanoidin containing wastewater.

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We performed experiments on the risk-free degradation of p-chlorophenol dissolved in water, by using micro-bubbles or milli-bubbles of ozonated oxygen in a 1 L bubble column reactor. The micro bubble dispersion showed superior phenolic degradation performances as compared to the millibubble dispersion system. When using ozonated-oxygen microbubbles, the ozone absorption efficiency was found to be very high when the volumetric flow rates of supplied ozonated oxygen were low. Owing to their high specific surface area and self-compression effects, the microbubble dispersion could achieve very high ozone absorption performances. Even though the microbubble methodology leads to low volumetric flow rate of ozonated oxygen, the degradation rate of phenolic compounds was maintained high during the course of the experiments, and the produced organic acid components were further decomposed quickly to maintain their concentrations at low levels. The apparent first-order-reaction rate constant for the ozone-degradation of p-chlorophenol correlated well with a linear function of the liquid-phase ozone concentration attained, regardless of the bubble flow mode utilized. With the aim to enhance the ozone degradation of the phenolic compound in the microbubble dispersion, we further investigated the effects of addition of NaOH.

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Packed and bubble columns represent important multiphase contactors utilized for reaction and separation in chemical engineering. The analysis of the hydrodynamic behavior of such multiphase apparatuses is usually done by assessing important hydrodynamic parameters such as superficial liquid and gas flow velocities and gas/liquid hold-up. However, those parameters are not capable to explain the real behavior, since interactions between phases are very complex. As a consequence, a large variety of probe technologies have been developed in the last decade. However, all these methods have the disadvantage that only few of the probes could be implemented in a cross section to avoid a significant influence on the interaction of the gas and liquid phases. Other non-intrusive techniques like tomography avoids these restrictions, but experiments using such methods are in most cases limited in terms of a temporal and/or spatial resolution of small diameters and thus are not representative for production scale dimensions. The local liquid and gas hold-up and their distribution were measured with the wire-mesh sensor (WMS) technology applied in bubble columns as well as in packed columns. The sensor can be used to measure transient phase fraction distributions in cross-sectional flow and is able to discriminate fluids having different relative permittivity (dielectric constant) in multiphase flow.

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It is expected that fine bubbles increase the rate of gas dissolution into a liquid phase. To disperse the submilli-bubbles whose diameter is less than 1 mm, a novel gas distributor was developed. By scaling up a single slit orifice that generates submilli-bubbles, previously proposed by the authors, a multislit submilli-bubble distributor was developed for practical use. The distributor generated smaller bubbles, and realized higher gas holdup and higher volumetric mass transfer coefficient than the conventional distributors did. The bubbles distributed from each slit were hardly affected by the number of slits. The gas holdup in the case of submilli-bubble aeration was higher than those in the case of conventional gas distributors. The multislit submilli-bubble distributor showed fast gas dissolution rate.

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When both a gas and liquid are simultaneously introduced from an injector into a vertical mini-channel, the hydrodynamic pattern in the channel depends on the construction of the injectors. To evaluate the effect of the injector on the two-phase flow pattern, direct injection has been compared to a co-flow pre-injection and a cross-flow pre-injection in recent study. For the three different injections, the flow pattern regime maps, which are described as the relation between the superficial liquid velocity and superficial gas velocity, were developed. The direct injector realized better dispersion of uniform bubble flow, various flow patterns and stable slug flow than the other injections. To clarify the two-phase flow dynamics in a vertical mini-channel attached to a direct injector, the frictional pressure drop has been measured and illustrated by a contour. The frictional pressure drop through a mini-channel was correlated using the equation of Chisholm. The two-phase friction multiplier was plotted versus the Lockhart–Martinelli parameter. The constant of the Chisholm equation has been evaluated for the two-phase flow such as bubbly flow and slug flow. By using the equation, the frictional pressure drop through a mini-channel can be well predicted.

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Dynamic pulse experiments for cell analysis require rapid and precise preparation of probes, which is often not possible in a macro-laboratory environment. Lab-on-a-Chip technology can offer new ways of probe preparation for both chemical and biochemical processes. A passive microfluidic mixer (micromixer) is presented in this contribution, which is designed for the preparation of cells. The micromixer is based on the method of split-and-recombination. Two alternating channel layers result in a three-dimensional pathway. Mixing in the laminar flow regime not only relies on molecular diffusion but is also enhanced by chaotic advection. The mixer was fabricated in a glass-silicon-glass sandwich technology, and mixing was characterized by chemical and biological probes. The contribution of chaotic advection, which appears in repeated 90° turns of the channel geometry, could be confirmed in computational fluid dynamics (CFD) analysis and laser-induced fluorescence images. Mixing performance was characterized by chemical iodometry. This method is based on the chemical reaction of Lugol’s solution and sodium thiosulfate. The resulting solution changes its color such that mixing becomes visible in a fluidic channel. Experiments were conducted for flow rates between 20 µL/min and 1000 µL/min corresponding to Reynolds numbers from 0.9 to 62. The experiments showed that fewer mixer units are necessary at higher flow rates because vorticity increases at higher Re in the recombination regions of the mixer. A mixing time of approximately 5 ms was achieved at a flow rate of 1000 µL/min at both inlets, which corresponds to a Re of 62 in this channel geometry. Biological pulse experiments were performed with the mixer, showing its suitability for preparing biological particles as eukaryotic cells.

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The impact of local phenomena on mass transfer from single free-rising gas bubbles with and without a superimposed chemical reaction was investigated using laser-induced fluorescence and particle image velocimetry. This paper discusses a novel calculation method for mass transfer rates using local concentration and velocity fields. Qualitative and quantitative results for the impact of a superimposed sulfite–sulfate reaction on oxygen mass transfer are also presented.

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The dynamic motion of a bubble rising through a shear-thickening fluid is numerically simulated. The simulations are carried out on a three-dimensional, dynamic, block-structured adaptive grid. The deforming bubble boundary is captured using the coupled level-set/volume-of-fluid (CLSVOF) method, which combines some of the advantages of the volume-of-fluid (VOF) method with those of the level-set (LS) method. The viscosity profile around the rising bubble is derived from numerical data, and it facilitates the determination of the shear-thickening effects as a function of the power-law exponent n. In general, as n increases, the bubble rise speed decreases and the amount of deformation of the bubble shape decreases. For different values of n, the effective viscosity and the associated effective physical dimensionless numbers are determined in order to quantify the shear-thickening effect of the continuous phase fluid on the bubble rise motion. One can analyze non-Newtonian bubble morphology by considering a non-Newtonian system with a specific effective viscosity.

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In this paper, we present a numerical investigation of various types of drops detaching from an axisymmetric, laminar compound jet of immiscible fluids. The compound jet flows in a co-flowing immiscible outer fluid. We use a front-tracking/finite difference method to track the unsteady evolution and breakup of the compound jet which is governed by the Navier–Stokes equations for incompressible and Newtonian fluids. Numerical results show that depending on flow parameters, the compound jet can break up into different types of drops: simple drops, single-core compound drops and multi-core compound drops.

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Interfacial properties play an increasingly important role in gas/liquid devices as the characteristic dimensions become smaller. This contribution describes the application of microstructured devices to gas/liquid systems being studied at the Institute for Micro Process Engineering. In microstructured reactors, good wettability is desired to maximize the gas/liquid interfacial area. In this work, the material wettability is demonstrated to impact the flow pattern as well as reaction conversion. Using a membrane to stabilize a gas/liquid interface for the purpose of gas/liquid separation requires a robust and poorly wettable membrane. A Gore PTFE membrane is able to achieve a stable interface and separate CO₂ from water. Since the material wettability has a decisive impact on the operation of gas/liquid reactors and separators, controlling this property could improve the performance of microstructured devices. Thin films of silicon and carbon have been deposited with PECVD. The films demonstrate a promising method to alter and control surface properties.

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In this study, two oil–water systems of oleic acid–water and chloroform–water are used as samples. Ultrasound is sequentially irradiated using five ultrasonic transducers at 20 kHz, 0.5 MHz, 1.6 MHz, 2.4 MHz and 4.8 MHz to produce emulsion. The distribution of droplet diameter is measured. The effects of ultrasonic frequency and oil kind on the emulsion characteristics are experimentally examined. For the oleic acid–water system, the droplet diameter decreases and the stability of emulsion increases as the step number and the frequency of tandem acoustic emulsification increase. The emulsion formed by tandem acoustic emulsification at 4.8 MHz is still stable after 7 months. The stability of emulsion decreases with increasing oil volume fraction. For a chloroform–water system, the diameter and polydispersity of droplet become drastically small by tandem acoustic emulsification. Compared with the oleic acid–water system, the stability of emulsion was low.

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Absorption of pure carbon dioxide into aqueous emulsions of three different n-alkanes (n-heptane, n-dodecane and n-hexadecane) has been studied at 0 to 100% oil volume fraction in a stirred tank at a high stirring speed (1000 min⁻¹). Phase inversion (o/w to w/o) occurs for n-dodecane and n-hexadecane at 60–65% oil volume fraction; for n-heptane, there is no clear inversion point. The volumetric mass transfer coefficient k_La was evaluated from the pressure decrease during saturation under isochoric and isothermal (298.2 K) conditions. The o/w emulsions of both n-dodecane and n-hexadecane show the same trends: k_La first increases to a maximum at 2% oil fraction, then decreases towards the phase inversion region. The maximum might indicate an additional transport mechanism; the decrease at higher oil fractions is expected based on the increase in emulsion viscosity. Differently, the o/w emulsions of n-heptane always show higher k_La values compared to pure water. The increase in k_La (by +280% at 25% n-heptane) might be explained by a bubble covering mechanism enabled by the high spreading coefficient. In w/o emulsions of n-hexadecane, from 100% oil to the phase inversion region, k_La monotonously decreases with increasing fraction of the dispersed water phase as expected due to the viscosity effect. Surprisingly, for both n-heptane and n-dodecane, k_La does not decrease, but rather increases substantially. At the phase inversion region, the relative k_La increase compared to pure oil is by +107% for n-dodecane, and even +143% for n-heptane.

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One of the most frequently used microorganisms in industrial bioprocesses is the filamentous fungus Aspergillus niger with not easily controllable morphology, ranging from dense spherical pellets to viscous mycelia depending on culture conditions. The main parameter which influences the morphology is the mechanical stress induced by either stirring or aeration. The well-established computational fluid dynamics (CFD) facilitates the quantification of the stress due to turbulent fluctuations, namely the Reynolds stress, and characterization of the flow pattern throughout the reactor by using appropriate turbulence models (Reynolds Stress Model; RSM). In order to refer the numerical simulation to the cultivation process in a multi-phase stirred tank bioreactor (STBR), a parallel research has been undertaken concerning the distinct pellet morphology of A. niger. The characterization of Reynolds stresses is based on the magnitude and the direction of tensor elements. Using CFD delivers the so-called hot spots in the reactor with respect to positioning and magnitude of various stress tensor components, respective velocity of phases and kinetic energy dissipation. For instance, in this case, the discharge zones of the air sparger and the two impellers are the regions in which cells are prone to deform or be damaged. Furthermore, the normal stress can cause more cell damage and possibly cell comminution.

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This study investigates drip pyrolysis in a fluidized bed (DPFB) applied to the continuous production of anatase-type N–F-codoped titanium oxide photocatalysts with oxygen vacancy under a reducing atmosphere for the development of a more compact reactor with fewer operating steps. The effects of bed temperature, precursor sol concentration and superficial gas velocity on the particle properties of the product powder and the photocatalytic activity of gaseous acetaldehyde degradation have been investigated. Although the photocatalysts produced by DPFB showed very small N-doping as compared to F-doping, they showed higher absorbance in both visible and ultraviolet regions than those by an electric furnace (EF). The surface atomic ratio of F to Ti increased with increasing the precursor sol concentration and superficial gas velocity. The BET surface area of product photocatalyst sample prepared at 773 K by DPFB was three times larger than that by an electric furnace, and its photocatalytic activity was higher than any other photocatalysts prepared in this study.

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The hydrodynamics of three multiphase reactors (spouted beds, fluidized bed and bubble column) have been studied in order to identify the main transition velocities U_trans. The Kolmogorov entropy (KE) algorithm is applied to gauge pressure fluctuations as a universal method for U_trans identification. The local KE minima are used as transition indicators. It has been found that the boundaries of the main hydrodynamic regimes (packed bed, stable spouting and unstable spouting) in two spouted beds (0.076 and 0.152 m i.d.) could be identified easily by this method. In the smaller bed the U_trans values (0.783 and 0.885 m·s⁻¹) tend to be higher than the ones (0.563 and 0.631 m·s⁻¹) in the bigger bed. In the case of the fluidized bed (0.14 m i.d.), the minimum fluidization velocity was identified at U_G=0.121 m·s⁻¹. At U_G=0.151 and 0.377 m·s⁻¹, both the fast bubble and slow bubble sub-regimes of bubbling fluidization were identified. At U_G=0.83 m·s⁻¹, the turbulent fluidization regime was established. The KE values in a bubble column (0.14 m i.d.) are capable of identifying four U_trans values (0.016, 0.03, 0.04 and 0.046 m·s⁻¹). The boundaries of a gas maldistribution zone, bubbly flow regime, two transition sub-regimes and churn–turbulent flow regime are thereby delineated.

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The documented hydrodynamic analogies in the behavior of churn–turbulent bubble columns (BC) and bubbling fluidized beds are further supported by the existence of so-called chaotic analogies. It has been found that the Kolmogorov entropy (KE) values monotonously decreased in both reactors, corresponding to the growth of large bubbles. The KE values have been extracted from the absolute pressure fluctuations measured in three different BCs (0.19, 0.38 and 0.8 m i.d.) as well as gauge pressure fluctuations measured in a BC (0.44 m i.d.). In addition, the same declining KE trend has been derived from gamma-ray densitometry (GD) scans performed in a churn–turbulent BC (0.1 m i.d.). An air–water system was always used. Decreasing KE values derived from computed tomography scans in an air–therminol BC (0.162 m i.d.) are also presented. Gauge pressure fluctuations have also been performed in a bubbling fluidized bed (0.14 m i.d.) operated with an air–glass beads system. The same declining KE trend was obtained. Such a trend is also extracted from GD scans performed in a bubbling fluidized bed (0.44 m i.d.) operated with an air–polyethylene system and gas–solids riser (0.152 m i.d.) operated with an air–glass beads system.

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The holdups of two kinds of bubbles such as relatively large and small bubbles have been discriminated and investigated in a viscous three-phase (gas/liquid/solid) fluidized bed having a diameter of 0.102 m (i.d.) and height of 2.5 m, respectively. Effects of gas (U_G) and liquid (U_L) velocities, particle size (d_P), and liquid viscosity (μ_L) on the holdups of relatively large and small bubbles are determined. The holdups of two kinds of bubbles are estimated by means of the dynamic gas disengagement method combining with the static pressure drop method. The increase in the slope of pressure drop with a variation of elapsed time was quite different from each other between the two kinds of bubbles. It has been found that the holdup of relatively large bubbles increased with increasing gas velocity but decreased with liquid velocity and liquid viscosity. However, the holdup showed a local minimum with a variation of fluidized particle size. The holdup of relatively small bubbles increased with an increase in the gas velocity or solid particle size, but decreased with an increase in the liquid velocity or viscosity. The holdups of two kinds of bubbles are well correlated in terms of operating variables within these experimental conditions, respectively.

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Filtration is an important industrial production processes to treat particle dispersion systems. In this paper we show the filtration characteristics of suspensions of agglomerated streptobacteria (chain bacteria), Bacillus amyloliquefaciens, by asymmetric depth filter membranes of poly(L-lactic acid) (PLLA). The permeation flux was higher in the filtration with the depth filter membrane than in that with a screen filter membrane at a transmembrane pressure of 50–150 kPa. The bacterial cell layer had a high compressibility index of the specific resistance (0.60) in the filtration with the screen filter membrane. However, the cell layer formed in the internal structure of the depth filter membrane of PLLA showed a low apparent compressibility index (0.11). Scanning electron micrographs revealed that the agglomerated cells were captured on the depth filter membrane at 10 kPa while those cells were captured within the membrane at 150 kPa. Thus the filtration performance with the depth filter membrane increased at higher transmembrane pressures. The biodegradable PLLA membrane showed high performance in the filtration of bacterial cell suspensions and has an advantage in disposal after use because it can be compostable with bacterial cells clogged in the membrane.

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In this study, four kinds of porous glass beads were synthesized. Hydrogen-producing bacteria were immobilized in the porous glass beads. The effect of the pore size of the porous glass beads on the hydrogen yield was examined by using a batch-type fermenter. The hydrogen-producing bacteria were screened by heat-shock treatment of the anaerobic sludge containing the bacteria in a wastewater treatment plant. The heat-shock treatment was conducted at 343 K for 30 min. When the pore size was 10 µm or more, the porous glass beads prevented the washout of bacteria from the fermenter. Continuous hydrogen production was realized by using porous glass beads with a pore size of about 20 µm. The hydrogen yields obtained with porous glass beads were much higher than those obtained without porous glass beads. In the absence of porous glass beads, lactic acid fermentation occurred.

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Water-soluble Au nanoparticles were prepared using the phase transfer method, and their dispersion properties were investigated. Using mercaptocarboxylic acids having various alkyl chain lengths as stabilizing agents, Au nanoparticles stably dispersed in aqueous solutions were obtained. The Au core size of the nanoparticles decreased with increasing alkyl chain length of mercaptocarboxylic acid. Dynamic lightscattering measurements showed that the size of dispersed Au nanoparticles coated with 6-mercaptohexanoic acid remained almost constant with changing solution pH, while Au nanoparticles coated with 15-mercaptopentadecanoic acid increased with decreasing solution pH, and completely precipitated at pH 5. These observations indicate that the dispersion behavior of the Au nanoparticles depends on the alkyl-chain length of the stabilizing agent, and that is sensitive to the solution pH in the case of the particles with longer alkyl chains.

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Direct numerical simulations of fully-developed gas–particle flows in a rectangular channel have been done using a point force method to calculate the forces exerted by particles on the gas. Particle transport in two flow configurations, i.e., (1) gas–solid flow in which particles bounce on the walls and (2) gas–liquid disperse flow of an annular pattern in which particles are injected from wall sources and are removed when they hit a wall are examined. The particles are represented by solid spheres with a density ratio of 1000. The effect of gravity is ignored. A volume fraction, α=1×10⁻⁴, which is sufficiently small to ignore inter-particle collisions, is assumed. A significant effect of particle–wall interaction is observed in the near-wall region of the concentration field and of the particle velocity field. Large concentrations in the near-wall region of the gas–solid flow are due to the particles that lose their momentum by slipping against the gas flow after bouncing on the wall. Damping of gas turbulence, which is caused by decreases in the gas Reynolds shear stresses to accommodate the particle stresses, shows to be larger in the gas–liquid flow than is observed in the gas–solid flow. The injection and deposition mechanisms that decrease concentrations in the near-wall region show to be effective in drag reduction.

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