• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.3
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• pp.408-418
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• 1986

본 연구에서는 표면은 단단하고 내면은 강인한 조직을 얻기위하여 대형 성형 탄 로울에 대하여 노에서의 급속가열 및 대기 상태에서의 자연냉각의 열처리가 수행 되어진다. 급속가열 및 냉각시 성형탄 로울 내부의 온도 분포 예측을 위하여 대류 및 복사 열전달 경계조건을 가지는 1차원 비정상 열전도 방정식이 유한 차분법을 사 용하여 해석되어졌다. 여기서 급속가열시 연소가스로 부터 기체복사에 의하여 성 형탄 로울의 바깥표면을 통하여 흡수되는 열량은

• Publications of The Korean Astronomical Society
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• v.15 no.spc2
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• pp.65-71
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• 2000

We have investigated the numerical methods to calculate model atmosphere for the analysis of spectral lines emitted from the sun and stars. Basic equations used in our calculations are radiative transfer, statistical equilibrium and charge-particle conservations. Transfer equation has been solved to get emitting spectral line profile as an initial value problem using Adams-Bashforth-Moulton method with accuracy as high as 12th order. And we have calculated above non linear differential equations simultaneously as a boundary value problem by finite difference method of 3 points approximation through Feautrier elimination scheme. It is found that all computing programs coded by above numerical methods work successfully for our model atmosphere.

• Publications of The Korean Astronomical Society
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• v.22 no.1
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• pp.21-33
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• 2007

Ever since the identification of 6830 and 7088 features as the Raman scattered O VI 1032, 1038 resonance doublets in symbiotic stars by Schmid (1989), Raman scattering by atomic hydrogen has been a very unique tool to investigate the mass transfer processes in symbiotic stars. Discovery of Raman scattered He II in young planetary nebulae (NGC 7027, NGC 6302, IC 5117) allow one to expect that Raman scattering can be an extremely useful tool to look into the mass loss processes in these objects. Because hydrogen is a single electron atom, their wavefunctions are known in closed form, so that exact calculations of cross sections are feasible. In this paper, I review some basic properties of Raman scattered features and present detailed and explicit matrix elements for computation of the scattering cross section of radiation with atomic hydrogen. Some astrophysical objects for which Raman scattering may be observationally pertinent are briefly mentioned.

• Journal of the Korean Society of Tobacco Science
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• v.17 no.2
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• pp.160-169
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• 1995

A mathematical model for the pyrolysis processes during unforced smoldering of cigarette was proposed in this study by analyzing the physical model of the smoldering cigarette (including the establishment of burning front between burning zone and pyrolysis zone, and analyzing the involvement of main factors such as pyrolysis of virgin tobacco, evaporation of water, and internal heat transport in the processes). Thermal conduction of cigarette paper and convective and radiative heat transfer at the outer surface were also considered via the thermal resistance law for the competitive heat transfer mechanisms. The governing partial differential equations were solved using an integral method. Model predictions of smoldering speed, or linear burn rate, as well as temperature and density profiles in the pyrolysis zone for different kinds of cigarettes were found to be close to the experimental data in the literature (Muramatsu, 1981). The model provides a relatively fast and efficient way to simulate the pyrolysis processes and offers a practical tool for exploring important parameters for a smoldering cigarette, such as blended tobacco composition, properties of cigarette paper, and heat flux from the burning zone to the pyrolysis zone.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.2
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• pp.271-276
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• 1989

Flame spreading over a hydrocarbon fuel surface has been investigated for liquid fuels such as kerosene and diesel, using thermocouple. Without forced convection, it was clearly found that the flame spreading was mainly controlled by the liquid fuel surface flow. Furthermore, the radiative heat transfer was dominant over a conductive heat transfer in kerosene. But in diesel the latter was found to be more influential than the former, when the direction of windflow was the same as that of flame spreading. The oscillation period and amplitude of the flame spreading velocity increase if the windflow is blowing in the direction of the flame spreading velocity, and decrease if the direction of windflow is blowing against the flame spreading direction.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2001.11a
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• pp.61-67
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• 2001

Hybrid propulsion systems provide many advantages in terms of stable operation and safety. However, classical hybrid rocket motors have lower fuel regression rate and combustion efficiency compared to solid propellant rocket motor. The recent research efforts are focused on the improvement of volume limitation and regression rate in the hybrid rocket engine. The present study has numerically investigated the combustion processes in the hybrid rocket engine. The turbulent combustion is represented by the eddy breakup model and Hiroyasu and Nagle and Strickland-Constable model are used for soot formation and soot oxidation. Radiative heat transfer is modeled by finite volume method. To reduce the uncertainties for convective heat transfer near solid fuel surface having strong blowing effect, the Low Reynolds number k-$\varepsilon$ turbulent model is employed. Based on numerical results, the detailed discussion has been made for the turbulent combustion processes in the vortex hybrid rocket engine.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.50.1-50.1
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• 2016

The incorporation of radiation from massive stars is essential for modeling the dynamics and chemistry of star-forming clouds, yet it is a computationally demanding task for three-dimensional problems. We describe the implementation and tests of radiative transfer module due to point sources on a three-dimensional Cartesian grid in the Eulerian MHD code Athena. To solve the integral form of the radiation transfer equation, we adopt a widely-used long characteristics method with spatially adaptive ray tracing in which rays are split when sampling of cells becomes coarse. We use a completely asynchronous communication pattern between processors to accelerate transport of rays through a computational domain, a major source of performance bottleneck. The results of strong and weak scaling tests show that our code performs well with a large number of processors. We apply our radiation hydrodynamics code to some test problems involving dynamical expansion of HII regions.

• Journal of The Korean Astronomical Society
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• v.36 no.3
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• pp.145-148
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• 2003

P-Cygni type Ly$\alpha$ from starburst galaxies, either nearby galaxies or Lyman Break galaxies, are believed to be formed by galactic outflows such as galactic supershells or galactic superwinds. We develope a Monte Carlo code to calculate the Ly$\alpha$ line transfer in a galactic supershell which is expanding and formed of uniform and dusty neutral hydrogen gas. The escape of Ly$\alpha$ photons from the system is achieved by a number of back-scatterings. A series of emission peaks are formed by back-scatterings. When we observe P-Cygni type Ly$\alpha$ emissions of starforming galaxies, we can usually see merely singly-peaked emission. Hence the secondary and the tertiary emission humps should be destroyed. In order to do this, dust should be spatially more extended into the inner cavity than neutral supershell. We find that the kinematic information of the expanding supershell is conserved even in dusty media. We discuss the astrophysical applications of our results.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.1
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• pp.1-9
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• 2002

The thermal response of electronic components during infrared reflow soldering is studied by a two-dimensional numerical model. The convective, radiative and conduction heat transfer within the reflow oven as well as within the card assembly are simulated. Parametric study is also performed to determine the thermal response of electronic components to various conditions such as conveyor velocities, exhaust velocities and emissivities. The results of this study can be used in selecting the oven operating conditions to ensure proper solder melting and minimization of thermally induced card assembly stresses.

• Solar Energy
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• v.12 no.2
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• pp.28-42
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• 1992

This investigation is carried out numerically for the two dimensional natural convection and surface radiation heat transfer in a square enclosure. The bottom wall is a constant heat flux at hot temperature and also top wall is isothermal at cold temperature whereas the left and right side walls are adiabatic except a transparent window on the right side partially. The exchange of radiant energy is obtained by the net radiation method and the shape factor by the crossed string method. The change in temperature and Nusselt number distributions of the walls due to the effect of the wall emissivity for various emissivities and for various dimensionless insolation energies are investigated. The dimensionless local convective heat flux and local radiative heat flux distributions in the wall except an adiabatic wall are also compared.