• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.7
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• pp.477-485
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• 2009

The study of nitrogen dilution effect on the flame stability was experimentally investigated in a non-premixed turbulent lifted hydrogen jet with coaxial air. Hydrogen gas was used as a fuel and coaxial air was used to make flame liftoff. Each of hydrogen and air were injected through axisymetric inner and outer nozzles ($d_F=3.65\;mm$ and $d_A=14.1\;mm$). And both fuel jet and coaxial air velocity were fixed as $u_F=200\;m/s$ and $u_A=16\;m/s$, while the mole fraction of nitrogen diluents gas was varied from 0.0 to 0.2 with 0.1 step. For the analysis of flame structure and the flame stabilization mechanism, the simultaneous measurement of PIV/OH PLIF laser diagnostics had been performed. The stabilization point was selected in the most upstream region of the flame base and defined as the point where the turbulent flame propagation velocity was equal to the axial component of local flow velocity. We found that the turbulent flame propagation velocity increased with the decrease of nitrogen mole fraction. We concluded that the turbulent flame propagation velocity was expressed as a function of turbulent intensity and axial strain rate, even though nitrogen diluents mole fraction was changed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.12
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• pp.2196-2201
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• 2007

Materials used at microwave are usually used as a dielectric with a manufacturing purpose of printed circuit boards, etc. Complex permittivity of them can be measured from attenuation constant or propagation constant of a transmission line using a microstrip line with bulk type. But as the technique recently which can manufacture to have complex permittivity and permeability demanded using nonferrous metals for powder-type grows up, we need sensors and methods which can measure characteristics of powder-type materials. So far measuring methods of permittivity and permeability with waveguide or coaxial cable are used but they have faults which have a complex measurement method and are difficult to simultaneously measure permittivity and permeability. In this paper, a simultaneous measuring method of permittivity and permeability with 2-port coaxial cable and a new proposed calculation. The proposed 2-port coaxial cable is designed to be easy to insert materials and to have a wideband. We measure permittivity and permeability of magnetic powder(Ni-Fe-Mo, Ni-Fe) which reveal its characteristic at $0.3{\sim}1.3GHz$ to identify the proposed sensor.

• Journal of ILASS-Korea
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• v.10 no.3
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• pp.29-37
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• 2005

The spray and acoustic characteristics of a gas/liquid swirl coaxial injector are studied experimentally. The self-pulsation is defined as a pressure and flow rate oscillations by a time-delayed feedback between liquid and gas phase. Self-pulsation has strong influences on atomization and mixing processes and accompanies painful screams. So. the spray and acoustic characteristics are investigated. Spray patterns are observed by shadow photography technique in order to determine the onset of self-pulsation. And self-pulsation boundary with Injection conditions and recess length is get. To measure the frequency of the spray oscillation. oscillation of the laser intensity which passes through spray is analyzed by Fast Fourier Transform. For acoustic tests, a PULSE System was used. Acoustic characteristics of a swirl coaxial injector are investigated according to the injection conditions. such as the pressure drop or the liquid and gas phase. and injector geometries. such as recess length and gap size between the inner and outer injector. Front the experimental results. the increase of recess length leads to the rapid increase of the sound pressure level. And as the pressure drop of the liquid phase increases. the frequency of the self?pulsation shifts to the higher frequency. The frequency of spray oscillations is the same as that of the acoustic fields by self-pulsation.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.3
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• pp.1-8
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• 2006

The influences of injection conditions and recess configuration of liquid-liquid swirl coaxial injectors on spray characteristics were investigated. The characteristics of the coaxial spray in internal mixing injection region were mainly controlled by the merging phenomenon and momentum balance between two liquid sheets, but those in internal mixing injection region were influenced by the impingement phenomenon as well as momentum balance between two liquid sheets.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1234-1243
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• 1990

Double coaxial are jets(annular and coaxial air jets) between which propane gas is fed was selected to study the structure of diffusion flames in turbulent shear flow. Schlieren and direct photographs are taken to visualize the flame structure. Mean and fluctuating temperatures and ion currents were measured to investigate the macroscopic and the instantaneous flame structure. The objective of this study is to understand the interaction between combustion and mixing process especially in the transition region of turbulent shear flow. The investigation reported in this paper focuses on the macroscopic and the instantaneous structures of three flames obtained. The increased mixing effect resulting from increase of Reynolds number of central air jet makes the flame bluish and short. When the velocity of surrounding air stream is higher than that of central air jet, the instantaneous flame structure is composed of coherent structure. It is considered that the flame structure of transitional region of mixing layer depends on the structure of mixing layer of non-reacting conditions.

• Journal of the Institute of Convergence Signal Processing
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• v.5 no.4
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• pp.317-324
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• 2004

Electromagnetically coupled coaxial dipole (ECCD) array antenna with and without short-ended termination is investigated theoretically. The integral equations are derived for the structure by use of the Fourier transform and mode expansion of radial waveguide. The integrals appearing in the integral equations are evaluated along the branch cut instead of real axis for a faster convergent integral. The effects of slots and dipoles, short-ended termination length, and dielectric coating on the radiation characteristics are presented. Radiation pattern of the structure is also investigated. The results of the present method are compared with those of the commercial EM simulator and good agreement is found.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.4
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• pp.79-83
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• 2018

An accurate method to measure shielding effectiveness(SE) of EMI spray coating film is presented. After high frequency simulating, Circular coaxial standard test fixture is fabricated. A sample of EMI spray coating film was fabricated for insertion into a circular coaxial standard test fixture. The measuring instrument used an Agilent 8722ES vector network analyzer for the SE measurement. The exact SE of copper and silver mixed spray coating sample was measured by the composition of the measuring instrument and the measuring sample. The SE of copper sample was measured at 70 dB and the SE of copper and silver mixed spray coating sample was measured at 60 dB. As a result of the measurement, the reliability of the circular coaxial standard test fixture was confirmed.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.8
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• pp.19-26
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• 1999

umerical simulations are performed to estimate how strongly the manufacturing error of an open-ended coaxial probe affects its measured complex permittivity of a contacted medium. The reflection coefficients of several dielectric materials contacted with an open-ended coaxial probe are calculated by employing the FDTD method. And then those complex permittivities are reconstructed by applying the calculated reflection coefficients into a new imaginary transmission-line model, which reveals more physically meaningful than the conventional model. It is found that the reconstructed complex permittivities suffer from significant error in spite of a slight imperfection of open-ended coaxial probe.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.7
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• pp.823-830
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• 2010

This paper deals with a coaxial-to-waveguide transition generating circularly polarized wave to be connected with horn antennas. By combining vertical coaxial fed structure, back-short and the polarization twisting structure, the circular polarization is successfully generated in the waveguide. The designed and implemented transition shows that the present structure can significantly reduce the size of the antenna part at X-band.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.6
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• pp.72-83
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• 2018

In this study, a series of CFD analyses were carried out for a hydrogen rocket combustor with a single shear coaxial injector. A hybrid RANS/LES approach was used for the turbulent combustion analysis with a two-dimensional axisymmetric configuration. Three reaction mechanisms, three spatial discretization methods, and three levels of grid resolution were compared to determine an appropriate CFD approach. The performance of the CFD prediction were investigated by comparing the wall heat flux with experimental data. Investigation of the flow field results provides an insight into the characteristics of the turbulent reacting flow of a rocket combustor with a shear coaxial injector.