Journal of Fluid Science and Technology
Online ISSN : 1880-5558
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Special Issue of the Thirteenth International Conference on Flow Dynamics (ICFD2016)
Papers
  • Ryan J. MILCAREK, Michael J. GARRETT, Jeongmin AHN
    Volume 12 (2017) Issue 3 Pages JFST0021
    Released: December 18, 2017
    JOURNALS FREE ACCESS

    Micro-tubular solid oxide fuel cells operating in fuel-rich combustion exhaust are explored in this work and their benefits in reducing the balance of plant in fuel cell systems is discussed. The current state of performance of these micro-tubular flame-assisted fuel cells operating with methane fuel is described and the benefits of operating in propane fuel are explored. An experimental investigation of propane combustion at different fuel/air equivalence ratios is conducted. Temperature measurements of the propane combustion are recorded with thermocouples while the gas species present in the exhaust are measured with a gas chromatograph. Propane is found to have advantages over methane due to a higher upper flammability limit and higher percentages of hydrogen and carbon monoxide, i.e. syngas, generated in the combustion exhaust. A micro-tubular flame-assisted fuel cell is tested using the four probe technique in model propane combustion exhaust at different equivalence ratios and temperatures. A method for comparing the performance of the fuel cell in the combustion exhaust to a hydrogen fuel baseline is developed and comparisons are made. The benefits of operating in propane compared to methane are explored with the potential for fuels like propane and butane being distinguished by their higher upper flammability limits and potential for higher concentrations of syngas in the combustion exhaust.

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  • Yutaro OZEKI, Tsuyoshi MATSUO, Manabu TANAKA, Takayuki WATANABE
    Volume 12 (2017) Issue 3 Pages JFST0022
    Released: December 18, 2017
    JOURNALS FREE ACCESS

    The purpose of the present work is to visualize the temperature fluctuation of water thermal plasma for biomass gasification. Another purpose is to investigate D-glucose decomposition mechanism in water thermal plasma because D-glucose is one of the main components in general biomass products. Arc temperature distributions of water thermal plasma with and without D-glucose injection were successfully visualized by high-speed camera. Two synchronized arc images in different wavelengths of Hα and Hβ were observed owing to appropriate optical band-pass filters with negligible other emissions from the arc. The arc temperature was measured based on Boltzmann-plot method. Measured arc temperature without D-glucose was 9000 K, and that with D-glucose was 7500 K. These temperatures were sufficiently high to decompose D-glucose completely. Furthermore, frequency analysis of arc fluctuation revealed that the time period of arc fluctuation was sufficiently shorter than that of the time constant of D-glucose decomposition. These results implied that the influence of arc fluctuation on D-glucose decomposition was negligible. In addition, the decomposition mechanism of D-glucose was discussed on the basis of the analyses of the products in vapor, liquid, and solid phases. They were converted from D-glucose through the water thermal plasma. Decomposition rate of D-glucose reached 99%. Gaseous product contains more than 86% of syngas, H2 and CO. This ratio is much higher than that in conventional gasification device. From these characteristics, water plasma system is suitable device for biomass utilization.

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  • Shinichiro OGAWA, Daisuke SASAKI
    Volume 12 (2017) Issue 3 Pages JFST0023
    Released: December 18, 2017
    JOURNALS FREE ACCESS

    Many countries in recent year have focused on small satellite launch. Therefore, Solid Rocket Motor (SRM) plays an important role in the development of small satellites. However, vortical flows sometimes occur from an inhibitor in the propellant, which causes the pressure oscillation. The basic research was carried out to compute various types of simplified SRM model. In this study, Cartesian mesh-based CFD solver, Building-Cube Method (BCM), was employed with the implementation of internal flow boundary condition, and applied for two Taylor Flow models, CDV nozzle and Simple SRM model with/without an inhibitor. According to two Taylor flow model result, the BCM was able to analyze the internal flow in the simplified SRM combustion chamber. The BCM is proved to be valid for nozzle model because the result of CDV nozzle was qualitatively agreed with theoretical solution. According to the result of the simple SRM model, the BCM was able to predict flowfield in the SRM combustion chamber, even with the existence of an inhibitor. Throughout the computations, BCM solver was able to reproduce flows in the SRM combustion chamber, thus it is expected the approach has a great potential to apply for the internal flows in the complicated SRM combustion chamber.

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  • Manabu TANAKA, Tomoyuki IMATSUJI, Taro HASHIZUME, Takayuki WATANABE, H ...
    Volume 12 (2017) Issue 3 Pages JFST0024
    Released: December 18, 2017
    JOURNALS FREE ACCESS

    The objective of the present study is to understand fluctuation phenomena in a multiphase AC arc as a heat source for material processing based on the high-speed visualization technique of the temperature field. The multiphase AC arc is one of the most attractive thermal plasmas which possess extremely high temperature, high chemical reactivity, rapid quenching capability, and selectivity of the reaction atmosphere in accordance with required chemical reaction. In particular, the multiphase AC arc has a strong advantage on higher energy efficiency compared with other thermal plasmas. Therefore, this heat source has been applied to innovative material processing such as in-flight glass melting. However, the temporal and spatial characteristics of the multiphase AC arc have not been clarified although these are essential to control the characteristics of the products such as particle size distribution, yields of the desired materials. The high-speed visualization of the temperature field of the multiphase AC arc was conducted at 1x104 fps as typical framerate to observe the dynamic behavior of the multiphase AC arc in millisecond time scale. An optical system including the band-pass filters was combined with the high-speed camera to observe particular line emissions from atomic argon with negligible emissions from thermal plasma. The obtained experimental results indicated that the temperature of the multiphase AC arc was around 1.0x104 K. The arc temperature fluctuated in the range from 0.6x104 to 1.3x104 K. Consequently, the arc temperature in the multiphase AC arc is sufficiently high to treat the refractory metals and/or ceramics powders. Furthermore, the obtained temperature was well-validated by the conventional spectroscopic method with high accuracy.

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  • Kazuyuki UENO, Yuko MATSUMOTO, Keiichi ISHIKO
    Volume 12 (2017) Issue 3 Pages JFST0025
    Released: December 18, 2017
    JOURNALS FREE ACCESS

    A decomposition method of a given two-dimensional incompressible flow field into a dipole sequence is developed. Necessary condition for dipole sequence is revealed using a wavelet transform of di-vorticity of the given flow. Subsequently, a practical way to extract dipole sequence by a recurrence formula is proposed. Each obtained dipole is characterized not only by the dipole moment but also by its own length scale. The reconstructed flow fields always give divergence-free fields even if the successive correction with the recurrence formula is truncated at a finite number. Typical two-dimensional flows are decomposed into dipoles, and graphical representations of extracted dipoles are shown. Many columns of dipoles and isolated dipoles in various length scale are found in a two-dimensional turbulent flow.

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  • Hidemi TAKAHASHI
    Volume 12 (2017) Issue 3 Pages JFST0026
    Released: December 18, 2017
    JOURNALS FREE ACCESS

    A conceptual study of a supersonic cruise aircraft employing an airframe-integrated linear aerospike propulsion system was conducted based on the evaluation of the thrust performance, propulsion efficiency, cruise performance, and flight attitude characteristics. The thrust performance was evaluated through physics-based performance prediction models established for linear aerospike nozzles by accounting for the freestream effect based on wind tunnel experiments. The airframe geometry was premised to be similar to that of the Concorde but was given only a minor alternation in the span geometry and on-design flight conditions. The airframe configuration, equipped with a boattail integrated upstream of the primary cell nozzle exit of the primary airbreathing engine, enabled the freestream effect to be utilized by increasing the surface pressure of the linear aerospike-type airframe aft-body, thus increasing the total thrust. The boattail configuration is beneficial as it prevents potential thrust loss that is anticipated for transonic flight conditions. The force balance analysis indicated that the proposed conceptual aircraft is feasible in terms of the aerodynamic center location. Results of the feasibility study showed that both the cruise performance and fuel consumption efficiency can be improved by employing the airframe-integrated aerospike propulsion system compared with those of some existing supersonic aircraft. Thus, the minor alternation in airframe design based on the existing supersonic aircraft offers significant improvement in performance and environmental concerns.

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  • Katsuyuki NAKAYAMA, Lucas DIAS MIZUSHIMA
    Volume 12 (2017) Issue 3 Pages JFST0027
    Released: December 18, 2017
    JOURNALS FREE ACCESS

    A numerical analysis, based on a novel physical quantity of the topology, is presented to specify the key flow leading into a vortex. This analysis traces the flow transition into a vortical flow in terms of local flow geometry (topology) specified by the velocity gradient tensor, and specifies the important flow component for the vortex transition. The transition where a non-vortical flow becomes vortical can be identified by swirlity that represents the unidirectionality and intensity of the azimuthal flow in a plane. The swirl plane after the vortex transition can be predicted by an eigenplane of real eigenvalues of the velocity gradient tensor. Then the tensor components are represented associating with the predicted plane, and their relations to the flow topology are clarified. The analysis of their transitions enables to specify the important flow components that lead the flow into a vortical flow. This numerical analysis can be applied to various turbulent flows in order to clarify the mechanism or feature of the vortex transition, or suppress a specific vortex in engineering fields.

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  • Ryan FALKENSTEIN-SMITH, Matthew RUSHBY, Hiroki NAGASHIMA, Takashi TOKU ...
    Volume 12 (2017) Issue 3 Pages JFST0028
    Released: December 18, 2017
    JOURNALS FREE ACCESS

    There is a rising pressure on industry to meet the steady climb of energy demand while concurrently reducing harmful emissions exhausted into the atmosphere. For the past decade, oxygen transport membrane reactors (OTMs), have been receiving growing attention due to their ability to provide high volumes of pure oxygen that react with incoming fuel at minimal energy costs. However, one significant concern is the OTM’s stability when exposed to high concentrations of CO2, a potentially harmful acidic gas. To preserve the integrity of the OTM in acidic environments, many have adapted dual-phase OTMs, combining the advantages of the perovskite-type material’s high oxygen permeation performance with a stable additive material’s tolerance of CO2. In this study, dual-phase OTMs comprised of varying weight ratios between SrSc0.1Co0.9O3-δ (SSC) and Sm0.2Ce0.8O1.9 (SDC) were successfully prepared and studied. Specifically, the dual-phase OTMs’ oxygen permeation flux and combustion performance are reported. The results show that the oxygen permeation flux through dual-phase OTMs decreases with the increase in SDC wt.% in the composition using a helium or methane sweeping gas. The highest oxygen permeation flux is found to be a pure SSC OTM at 5.27 ml.min-1.cm-2 using methane sweeping gas with a flow rate of 80 ml.min-1. Additionally, a pure SSC OTM exhibits a CO2 selectivity of 97.7% with a methane sweeping gas flow rate of 5 ml.min-1. Despite the SSC OTM’s higher oxygen permeation flux and CO2 selectivity, a dual-phase OTM exhibited a higher oxygen permeation flux and membrane stability compared to a pure SSC membrane after exposed to a CO2 sweeping gas for 60 hours. This suggests the potential for a highly stable dual-phase OTM design that can maintain an oxygen permeation performance in any environment and be potentially implemented in future carbon capture technologies.

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