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))
Shin Mukai (Hokkaido University)
Akinori Muto (Osaka Prefecture University)
Nobuyoshi Nakagawa (Gunma University)
Hiroyasu Ogino (Osaka Prefecture University)
Naoto Ohmura (Kobe University)
Mitsuhiro Ohta (Muroran Institute of Technology)
Hiroshi Ooshima (Osaka City University)
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))

Editorial office:
The Society of Chemical Engineers, Japan
Kyoritsu Building, 4-6-19, Kohinata, Bunkyo-ku
Tokyo 112-0006, Japan
journal@scej.org

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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Polymer blends and composite materials are often produced by a melt-mixing process using equipment specially designed to mix high-viscosity fluids during laminar flow. The melt-mixing process can be classified into distributive and dispersive mixing. Distributive mixing includes stretching and folding of fluid elements and re-arrangement of dispersed materials. Dispersive mixing is the size reduction of filler aggregates and/or liquid droplets in a matrix fluid. In order to optimize the design of a melt-mixing equipment, the evaluation of distributive and dispersive mixing is essential. In this paper, we consider fundamental aspects of melt-mixing, and experimental and computational approaches that have been reported in the literatures. Experimental observation of melt-mixing, by and large, provides rather limited information on the mixing process inside of equipment. Although a mixed material can be obtained under specified conditions and its physical properties can be directly measured, it is difficult for the mixing mechanism behind the final result to be inferred. Computational fluid dynamics complements this situation. Numerical simulation of a mixing process provides a non-invasive and detailed data in a equipment so that the quantitative measures for distributive and dispersive mixing can be obtained. We consider various quantitative measures that have been previously proposed to characterize distributive and dispersive mixing.

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Power numbers in a baffled stirring tank with paddle-type impellers were measured over a range of Reynolds numbers, from laminar- to turbulent-flow regions. The impellers studied included a two-blade flat-paddle impeller, a 45° two-blade pitched-paddle impeller, a 45° four-blade pitched-blade turbine, and a two-stage pitched-blade turbine. The impeller-diameter-to-tank-diameter ratio was 0.5 to 0.6. The measured power numbers were compared with those derived from two other methods: prediction by using correlations and computational fluid dynamics (CFD). Power number correlations showed that the values estimated from the empirical correlations proposed by Nagata agreed closely with those measured in the laminar-flow region but deviated significantly in the transitional- and turbulent-flow regions. The power numbers derived from the correlation proposed by Kamei and Hiraoka agreed well with the experimental results in the laminar- and turbulent-flow regions. The power number in a stirring tank was also simulated by the CFD method. The numerical results showed satisfactory agreement with the experimental data over a wide range of Reynolds numbers.

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In the present study, isolated mixing regions (IMRs) in an agitated vessel using a paddle or disk-turbine impeller have been visualized experimentally, and their structural properties and formation mechanism are investigated in detail. A set of thin filaments spirally wrapping around the core of a toroidal isolated mixing region is observed under laminar-flow conditions, where the Reynolds number is smaller than 60. This filament rotates in both directions of horizontal and vertical circulating flows. The three-dimensional geometrical structure of a filament in an IMR depends on the periodical perturbations caused by the rotating impeller. We have succeeded in the determination of the three-dimensional geometrical structure of a filament in an IMR based on the relationship between the movement of a fluid particle and filament numbers and/or wire turns. Interestingly, the wire turns of filaments are opposite to movement of fluid particles.

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Recently, several investigations for unsteady agitation in an agitated vessel has been carried out because it is useful for laminar mixing but rarely been for pitched paddle. Laminar mixing is often inefficient because of the formation of segregated regions. Two unsteady stirring approaches, co-reverse periodic rotation and time-periodic fluctuation of rotational speed, are adopted to eliminate the unmixed regions, which are two doughnut rings formed above and below the impeller in an agitated vessel equipped with a pitched paddle or a flat paddle. It is well known that the pitched paddle creates upward or downward flow according to rotational directions, which may result in an unique effect on mixing performance especially when co-reverse periodic rotation was conducted. The relationship between mixing time, t_m, measured by the decolorization method with Reynolds number, Re, is used as a quantitative method to compare the mixing performance under an unsteady stirring with that obtained under a steady one for pitched paddle in addition to for flat paddle. The experimental results show that the mixing time can be drastically reduced in an agitated vessel equipped with pitched paddle when both unsteady stirring approaches adopted in this work are used. However, it is also found experimentally that for the method of time-periodic fluctuation of rotational speed, only when Re is smaller, can significant enhancements in mixing be obtained. In contrast to this, for the case of co-reverse periodic rotation, denoting improvements are observed in the range of all Re covered in this work. These results were explained by the precise measurements of positions of doughnut rings at different impeller speeds and different rotational directions.

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The high performance of a large impeller can be combined with the advantages of an eccentric mixer by using the impeller at an eccentric position. In this study, the power consumption, mixing time, and dispersion performance of an eccentrically located Hi-F mixer, which is a type of large impeller, were investigated. Furthermore, the sloshing phenomenon was investigated. The power consumption, P, and mixing time, θ_M, were measured under various eccentric conditions. The relation between the power number (N_p) and Reynolds number (Re) and that between the dimensionless mixing time (n · θ_M) and Re were investigated. The curves representing these relations were similar to curve that is characteristic of concentric mixing with baffles. Equations for estimating N_p and n · θ_M were proposed. To investigate the dispersion performance for low- and medium-viscosity liquids, the suction rotational speed, n_s, and the dispersion rotational speed, n_d, were measured. The dispersion performance of eccentric mixing was higher than that of concentric mixing without baffles. In the medium-viscosity liquids, the performance of eccentric mixing was higher than that of concentric mixing with baffles. When the Hi-F mixer was used under eccentric conditions, rotary sloshing was generated at a specific rotational speed. The sloshing rotational speed, n_slosh, was independent of the eccentric length, liquid properties, etc. An equation for estimating the n_slosh from D and d_L was obtained.

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It is difficult to determine the representative apparent viscosity of a pseudoplastic liquid in a stirred vessel because the viscosity of the liquid varies with on the shear rate in the vessel. Until now, the method proposed by Metzner and Otto has exclusively been applied to the determination of this value. In this study, we proposed a new method for determining the representative viscosity, η_a, by averaging the viscosity distribution in the vessel using a weight of dissipation function on the basis of numerical simulation results, without any power correlation with a Newtonian liquid. Further, we calculated the representative shear rate, Γ, from η_a using a rheological equation presenting the pseudoplasticity; then, we found that Metzner's constant, B, can be expressed as the function of the impeller Reynolds number, Re_d. The reliability of this method was ascertained by comparing the results with those obtained when using the conventional Metzner's method: better conservation of flow similarity was achieved when scaling up the vessel using the proposed method than when employing the conventional method.

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Horizontal mechanically agitated vessels are widely used in mining enterprises. However, there is insufficient information about any direct relationship between the solid suspension and the impeller geometric parameters in a horizontal vessel. This paper presents a study on the effects of blade pitch angle on solid suspension in a horizontal vessel. The critical speed of solid suspension, N_c and power, P_c, were observed by independently varying both off-bottom clearance, C, and the blade pitch angle, θ to, give two correlations for each of the variables. Particle suspension experiments were also performed in a horizontal vessel with baffles and without baffles, and in a vertical vessel. The superior performance of a horizontal reactor without baffles is illustrated, comparing with a classical flat bottomed cylindrical reactor and a horizontal reactor with baffles.

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There are a number of operations that are carried out in the process industries by a small impeller in an agitated vessel in which particles are suspended, and thus, the possible abrasion of the particles should be considered precisely to understand the operation. To investigate the abrasion of particles in an agitated vessel, an aggregated spherical silica particle, whose diameter was set at about 2.0 mm or 1.0 mm, was prepared purposely, put into a vessel, and agitated by a Rushton turbine impeller (RT) or an edged turbine impeller (ET). The change in the particle diameter with time elapse was measured as an area-equivalent diameter by using a CCD camera. The frequency of the particle passing through the impeller-swept region was also measured by the 3-D PTV method. As a result, it was found that an ET is superior to a RT for the abrasion of particles at the same power input per unit volume. For both the impellers, the power efficiency of particle abrasion at a very high impeller speed was less than that at a low impeller speed. However, it was also found that with increasing impeller speed, the particle abrasion rate per circulation of the particle passing through the impeller-swept region, R_ω, increased, especially at a high tip velocity in the case of an ET. At the same maximum impact energy, R_ω in the case of an ET was more than that in the case of a RT.

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In crystallization processes, measurements and estimations of nucleation in a stirred vessel are important in the quality control of the crystal product. However, primary nucleation in a crystallizer is a very complicated and sensitive phenomenon, so much that obstacles such as impellers and temperature sensors in the crystallizer affect primary nucleation. The effects of the operation parameters on primary nucleation have not been well characterized. Herein, we attempted to establish a non-intrusive on-line measurement method for the initial dynamic behavior of a series of primary nucleation based on the detection of laser light scattering induced by small particles. Firstly, properties of laser-scattered light by particles suspended in a stirred vessel were investigated under various size and mass conditions for polystyrene particles. Secondly, with these results for model particles, we attempted to apply the measurement method to the quantification of the initial dynamics of a series of primary nucleation of batch cooling crystallization of glycine. The results show that there are cases in which the super-saturation of solution increases in spite of increases in crystal precipitation mass.

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The feasibility of antisolvent crystallization by means of gas–liquid slug flow in curved microchannels is examined in this study. The present flow regime and channel design are employed to avoid the stratified flow of a solution and antisolvent where sufficient mixing cannot be expected. DL-Threonine in water is crystallized with ethanol (antisolvent) as a model study on high-value amino-acid crystallization. Air is used as the carrier fluid, since ethanol is soluble in organic liquids, which were used as the carrier fluids for salting-out proteins in microchannels in the literature. It is found that a sudden increase in the channel width after the confluent point of gas and liquid streams results in the stable formation of slugs, but the length of the slugs varies to some extent. However, it seems that effective mixing is achieved in the slugs regardless of their length. The degree of supersaturation is adjusted by changing the ratio of threonine aqueous solution to ethanol flow rates such that the total flow rate remains constant. It is shown that antisolvent crystallization in curved microchannels is feasible and effective in controlling the crystal shape and size. The characteristics and potential for antisolvent microcrystallization is discussed, and it is compared with crystallization without mixing in microchannels.

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Micromixing has been studied in a semi-batch reactor agitated by a Rushton turbine using two different reaction schemes. With one scheme, the selectivity was similar at the same mean specific energy dissipation rate and feed location at the 3.6 L scale to that found earlier at the 25 L scale. Also, at the 3.6 L scale, a study of backmixing at different feed locations showed that it was greatest when feeding into the trailing vortex, which is also the best feed location to improve micromixing. At that location, all pipes gave a similar selectivity at the same exit velocity. Comparison with the limited literature showed that one of the two criteria for predicting backmixing fitted the present results quite well but the other was out by two orders of magnitude. The other reaction scheme was used to compare micromixing in a 3 L vessel under baffled conditions with that without them. Such a comparison has only been made once before at a larger 25 L scale and with a different reaction scheme. The earlier surprising result was confirmed, namely that the mean specific energy dissipation rate required for equivalent selectivity without baffles was less than that required with them.

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With the object of developing a new measuring method of the heat transfer coefficient at the inside wall of an agitated vessel in high Reynolds number region, extensive investigation has been conducted using a model tank that holds two types of thermocouples attached on the surface wall of a test piece. This new method is verified experimentally by the confirmation on the linearity of temperature slope in the test piece, suitability of setting method of the thermocouples on the surface of the test piece and the correspondence between this new method and the extrapolation method. Then, this new method is practically applied to determine the heat transfer coefficient at the inside wall of an agitated vessel. The impellers used are a 3-bladed propeller, a 4-bladed pitched paddle, a 6-bladed flat turbine and Satake Supermix MR210 as a large scale impeller. The characteristics of each impeller are clarified by investigating the effects of the impeller speed, baffling conditions, and the clearance between the impeller and the vessel bottom on the heat transfer coefficient. Moreover, new information concerning the relations between the flow pattern and the flow velocity distribution on the heat transfer coefficient are also clarified. Finally, this new method is confirmed to provide beneficial information for new designs of mixing devices.

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