KAGAKU KOGAKU RONBUNSHU
Online ISSN : 1349-9203
Print ISSN : 0386-216X
ISSN-L : 0386-216X
Volume 43 , Issue 1
Showing 1-10 articles out of 10 articles from the selected issue
Editorial Note
Transport Phenomena and Fluid Engineering
  • Kenjiro Kanazawa, Hidehiro Kamiya
    Type: Research Paper
    2017 Volume 43 Issue 1 Pages 1-15
    Published: January 20, 2017
    Released: January 20, 2017
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    The cylindrical-wall revolving mixer (CRM) is a high velocity revolution mixer used in industry to produce emulsions with uniform droplet size. However, fundamental verification data and the mechanism by which this mixer imparts size uniformity have not been clarified. In this study, we compared the droplet size distributions of emulsions produced by a CRM and a general rotor-stator mixer. We also conducted an impulse response experiment and analyzed mixer flow using flow visualizations and computational fluid dynamics (CFD) simulations. The preparation results showed that the CRM produces more uniform emulsions than the general rotor-stator mixer operated with a clearance of 0.5–2.0 mm between the rotor and stator. The impulse response results showed that the holding time distribution of processing liquid is approximately the same for the CRM and the general rotor-stator mixer. The flow visualization results near the clearance showed a uniform steady flow state in the CRM but a turbulent flow state with unsteady flow in the general rotor-stator mixer. The CFD simulations indicated that the CRM had a significant supply of the processing liquid in the high velocity gradient region, and that the velocity gradient tended to be uniformly even. These results suggested that the flow state near the clearance and the velocity gradient are important factors for generating a uniform emulsion.

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Particle Engineering
  • Shiro Kitajima, Masatoshi Yasuda, Shuji Matsusaka
    Type: Research Paper
    2017 Volume 43 Issue 1 Pages 16-21
    Published: January 20, 2017
    Released: January 20, 2017
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    Experiments were carried out on the electric charging of particles continuously fed on a dielectric plate using charges generated by an atmospheric pressure plasma jet. The jet was generated by supplying 1 SLM (standard liter per minute) of helium gas and by applying AC voltage (6 kHz, 5 kV) and DC bias voltage (range: −5 to +5 kV). By varying the DC bias voltage, positive or negative charges could be extracted at a certain ratio from the plasma; the charges were homogeneously deposited onto the dielectric plate. The surface charge density of the dielectric plate was evaluated using surface potential. When the particles moved on the inclined dielectric plate, the particles were charged according to the amount of charge on the dielectric plate. It was found that the material of the dielectric plate and the external electric field do not affect the particle charging, although the initial charge does.

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Separation Engineering
  • Kazuhisa Sato
    Type: Research Paper
    2017 Volume 43 Issue 1 Pages 22-28
    Published: January 20, 2017
    Released: January 20, 2017
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    Experiments were carried out to concentrate lactic acid by means of electrodialysis. Under certain operating conditions, the process was hindered by an increase in the volume of the concentrated solution as a result of water permeation across the membranes due to electro-osmosis and the difference in osmotic pressures. A necessary operating condition for successful concentration of lactic acid was that the concentration difference between the concentrated and dilute solutions should not be too large. The highest concentration of lactic acid economically achieved by electrodialysis was 50 wt%. This upper limit was related to an acute increase in the electrical resistance of lactic acid solution. In successive operations, it was found possible to concentrate lactic acid solution from 7 to 50 wt% through 13 cycles of electrodialysis.

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Process Systems Engineering and Safety
  • Koji Inagaki, Yoshiyuki Yamashita
    Type: Research Paper
    2017 Volume 43 Issue 1 Pages 29-36
    Published: January 20, 2017
    Released: January 20, 2017
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    Real-time moisture monitoring of crystal powder in a pilot-scale fluidized-bed dryer was examined in the conversion of lactulose trihydrate crystal powder into lactulose anhydride crystal powder. Two types of in-line near-infrared spectroscopy (NIRS) were investigated as means to estimate moisture content. Of these, a simplified filter type spectroscopy with 3 wavelengths showed poor accuracy in estimating moisture content, while a method using Fourier-transform spectroscopy showed high accuracy, notably when the moisture content less than 1.00%. This technique allowed real-time monitoring of the moisture content in the crystal powder and was applicable to automatic endpoint determination in the fluidized-bed dryer.

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Materials Engineering and Interfacial Phenomena
  • Hironobu Imakoma, Hiroshi Taki, Minako Sokai, Takafumi Horie
    Type: Research Paper
    2017 Volume 43 Issue 1 Pages 37-44
    Published: January 20, 2017
    Released: January 20, 2017
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    Exact and approximate models were proposed for the convective drying of a slurry coating with low particle concentration in polymer solution, and particle exposure on the dried surface (surface coverage) was estimated. The exact model was derived from the Maxwell–Stefan equation of ternary component coating, and the approximate model was derived by assuming a rectangular profile of moisture content. A critical value of moisture content uAC was assumed in both models. The particle component, which is stagnant in the high moisture content region, begins to move with the same velocity as the polymer component at uAC. The surface coverage estimated by computer simulation based on the strict model was compared with the measured value of the coverage published in a previous study, and the validity of the assumption of uAC was shown. This result suggests a new mechanism of particle movement, namely, that particles move with tangled polymer molecules in concentrated polymer solution. A series of computer simulations based on the two convective drying models was performed. The simulated result showed that the coverage increased with increasing initial moisture content and with decreasing uAC. For particles of 1.6 µm or more in diameter, the coverage shows a constant value of less than 1 when the dried polymer is over 10 µm in thickness only in the case of the strict model, while the approximate model is suggested to be useful only in limited conditions. When particle diameter is under 1.6 µm, however, the coverage shows a constant value of about 1 in the case of the strict model, and the results of both models agree well.

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Energy
  • Hikaru Tsuchida, Zairan Cheng, Kiyoharu Nakagawa, Hirokazu Oda
    Type: Research Paper
    2017 Volume 43 Issue 1 Pages 45-49
    Published: January 20, 2017
    Released: January 20, 2017
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    The performance and stability in long-term charge/discharge of a mesoporous resorcinol-acetaldehyde carbon cryogel as an electrode in an electric double-layer capacitor were evaluated with an organic electrolyte of 0.5 M LiClO4/PC (C4H6O3). Capacitance was found to increase as mesopore volume increased, and at all scan rates, the capacitance of mesoporous carbon CG-74 (74 indicates the concentration of catalyst at pH 7.4) was higher than that of commercial microporous activated carbon. CG-74 showed higher stability than microporous activated carbon, although performance decreased over the course of long-term charge/discharge measurement. The cause of this decline was examined by evaluating surface characteristics and pore structure. Deposition of lithium was seen at the cathode of microporous activated carbon, though no functional group was generated. Pore structure showed no decrease in pore volume due to deposition of lithium, and micropore volume was remarkably decreased in all samples. However, mesopore volume was not decreased, indicating that mesoporous carbon material CG-74 has better long-term stability. In terms of ionic diffusion and long-term stability, mesoporous carbon material CG-74 is superior to microporous activated carbon as an electrode material for use in an organic electrolyte.

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  • Shumpei Murayama, Takuya Ito, Toshiyuki Iwasaki, Seiichi Suzuki, Toshi ...
    Type: Research Paper
    2017 Volume 43 Issue 1 Pages 50-56
    Published: January 20, 2017
    Released: January 20, 2017
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    In our previous studies, CO2 gasification characteristics of char produced by rapid pyrolysis were evaluated for various biomass samples of softwoods and hardwoods, which were pyrolyzed at 1000°C in a small-scale fluidized bed with porous alumina as bed material under N2 flow (regular gasification). The characteristic curve of conversion rate dX/dt versus conversion obtained from the gas evolution rate revealed a sharp peak the gasification at conversion of around X=0.05 in the case of softwoods, which was suggested to be affected by the bed material. In the present study, the effects of the type of bed material on the gasification characteristics were examined using bed materials of alumina, silica sand and pulverized brick for the gasification of cypress. It was found that the characteristic peak in gasification was observed only with alumina as bed materials. To elucidate the cause of this phenomenon, the char and bed materials were together cooled to room temperature under a nitrogen flow, separated by sieving, and then independently gasified. The char produced in the alumina bed was found to have a low conversion rate, while the alumina bed material was gasified more rapidly and showed the characteristic peak in gasification. While the ratios of hydrogen production to carbon monoxide production in the gasification of separated char and bed materials were always lower than those of regular gasification, the decrease in the case of char gasification was much greater than in the case of bed materials. The decrease in the ratio in the gasification of char was the biggest for alumina followed by brick, while the decrease in the gasification of bed materials was the smallest for alumina and the largest for silica sand. The present results indicate that the reactive carbonaceous material with high hydrogen content was easily moved to alumina and hold, which showed rapid gasification at the first stage of gasification.

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  • Kazuhiro Itoh, Takuji Yamamoto, Kouji Maeda, Hiroshi Tachikawa
    Type: Research Paper
    2017 Volume 43 Issue 1 Pages 57-62
    Published: January 20, 2017
    Released: January 20, 2017
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    The effectiveness of vacuum degassing and steam treatment was examined as a means to reduce waste and increase energy recovery in the treatment of sewage sludge. Equipment using a steam ejector was constructed to apply these treatments consecutively and was able to operate continuously for more than 15 min in an experiment sucking the digestive sludge. The methane component ratio in the bio-gas generated from the treated sludge increased by 11 points. Both the removal of VTS, CODcr and BOD and the digestive efficiency also increased. Further, the use of a water ejector in combination with the steam ejector and reduction of the pressure of degassing was found to promote the solubilization of digestive sludge.

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  • Koji Nakui, Takahiro Nomura, Tomohiro Akiyama
    Type: Research Paper
    2017 Volume 43 Issue 1 Pages 63-73
    Published: January 20, 2017
    Released: January 20, 2017
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    A method to evaluate the efficiency of hydrogen transportation systems is proposed. Three major types of long-distance hydrogen carrier, organic chemical hydride, ammonia, and liquid hydrogen, are evaluated with the exergy efficiency as a criterion. In addition, exergy loss resulting from gas compression for road haulage is examined. Efficiency is expressed in terms of the ratio of net reserved exergy in the carrier to chemical exergy of hydrogen. The examined carriers would be normally expected to lose around 40 to 50% of exergy during modification processes (hydrogenation, dehydrogenation, and liquefaction) and to lose 2.5 to 10% during long-distance transportation. With the exergy consumption accruing from compression for local delivery and filling included, which comprise another 17% of losses, depending on the type of carrier, around half or more of the chemical exergy is found to be lost in the whole transportation system, based on the current technologies. In order for hydrogen to be an efficient medium as an energy carrier, it is necessary to recover unused exergy generated in the system, which would improve efficiency by 10% to more than 30%.

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