• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3051-3059
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• 2015

In this study, the effect of corrugation angle on thermal performance of corrugated plate is numerically investigated with an aim to develop humidifying element. Numerical analysis was conducted for a range of corrugation angle (from $0^{\circ}/0^{\circ}$ to $60^{\circ}/60^{\circ}$ for equal angle and from $15^{\circ}/0^{\circ}$ to $15^{\circ}/60^{\circ}$ for unequal angle). Results revealed that both j and f factor increased as corrugation angle increased. Especially, f factor increased significantly at high corrugation angles. j and f factors of unequal angle plates and those of equal angle (obtained by averaging unequal angles) plates were approximately the same. The largest $j/f^{1/3}$, which implies the largest heat transfer rate per consumed power, was obtained at $15^{\circ}/15^{\circ}$. Existing correlations under- or over-predicted the present numerical results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.551-560
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• 1988

Gas-particle two phase flow and heat transfer in a cavity receiving thermal radiation through selectively transparent walls have been analyzed by a finite difference method. Particles injected from the upper hole of the cavity are accelerated downward by gravity and exit through the lower hole while they absorb, emit and scatter the incident thermal radiation. Gas phase is heated through convection heat transfer from particles, and consequently buoyancy induced flow field is formed. Two-equation model with two-way coupling is adopted and interaction terms are treated as sources by PSI-Cell method. For the particulate phase, Lagrangian method is employed to describe velocities and temperatures of particles. As thermal radiation is incident upon horizontally, radiative heat transfer in the vertical direction is assumed negligible and two-flux model is used for the solution of radiative heat flus. Gas phase velocity and temperature distributions, and particle trajectories, velocities and temperatures are presented. The effects of particle inlet condition, particle size, injection velocity and particle mass rate are mainly investigated.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.170-170
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• 2017

기후변화 따른 스마트팜 돈사 외부 환경의 변화에 대응하고, 사육 환경을 능동적으로 개선하기 위한 연구가 수행 중이다. 돈사 내 열전달 요소 간 상호 역학성 분석을 위해서 고려해야할 사항은 입기구, 보온 등, 열풍기, 단열제, 위치, 방향, 돈사의 연평균 온도, 습도, 연중 일사량, 가축의 열복사 등 상호 복잡하게 연관되어 있는 물리량이다. 돈사 전체 열손실, 자연발생 에너지량, 강제발생 에너지량, 난방용량 등을 고려한 순간 열부하 산정을 위한 여러 방법 중 우선적으로 CFD(Computational Fluid Dynamics)를 이용하였다. 순간 열부하 산정을 위한 해석 도구 선정에 있어서 다양한 유체 및 기체 전산 유체역학 Solver(Fluent, Open-FOAM, Blender)를 고려하였다. 공간 Mech를 수행하기 위한 도구로는 공개 소프트웨어 인 FreeFem++ 3.51-4 (http://www.freefem.org)를 이용하였다. 이 과정에서 일부 기체 (암모니아)의 농도를 난수로 변화시키는 기법을 적용하여 가상적으로 돈사의 환경을 Pseudo 시뮬레이션 하였다. 결과적으로 Fluent에 비하여 OpenFOAM을 이용하여 얻은 열유동의 방향(속도)과 크기 백터가 상대적으로 크게 나타났다. Fluent가 시계열 상에서 혼합 기체 물리량 변화를 무시할 수 있는 안정되고 균일한 환경에 적합하기 때문인 것으로 판단되었다. Blender의 경우 Lattice Boltzmann methods 과 Smoothed-particle hydrodynamics 방법을 이용한 유체/입자 동력학 모델링을 제공함에 있어 시각적 효과를 강조하는 기능에 중점을 두었다. Fluent와 Blender에서 제공하는 해석 연산 모듈의 정확성 검증을 위해선 공간 분해능을 높인 정밀 계측 시스템을 이용하여 검증할 필요가 있다. Open-FOAM를 이용한 열부하 분석 수행이 상대적으로 높은 절대값을 보이는 특성은 열부하 제어 시스템의 Overshoot를 유발할 가능성이 있으므로 이에 대한 해석 모델의 보정이 추가적으로 필요할 것이다. CFD의 한계인 시간 복잡도를 낮추고 상대적으로 높은 시계열 분해능을 확보할 경우 돈사 내 환기시스템에 맞는 소요 환기량 실시간 산정이 가능해지고 외부기상 및 돈사내부 복사열을 활용함과 동시에 돈군 순환에 상응하는 실시간 열부하 관리 시스템 도출이 가능할 것이다.

• Journal of Energy Engineering
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• v.19 no.3
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• pp.163-170
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• 2010

The objective of this study is to investigate the combustion characteristics of dual type of sintering burner as a function of design parameters using lab-scale sintering burner through experimental and numerical approaches. Combustion characteristics were evaluated by the radical method. The numerical model was verified as a temperature using R type of thermocouple at the bed surface. The effect of nozzle distance and angle were performed through the CFD analysis, and the comparison of burner types. As a results, dual type burner has more wider and uniform flame distribution than single type burner. Asymmetry and 45 degree angle condition have been suggested as an optimal condition for the ignition of the sintering bed surface.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.10
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• pp.1963-1970
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• 1992

An oscillatory motion of the natural convection in a two dimensional, partially divided square enclosure heated from below, and fitted with a partition is investigated numerically. The enclosure was composed of the lower hot and the upper cold horizontal walls and the adiabatic vertical walls, and a partition was situated perpendicularly at the mid-height of the one vertical insulated wall. The governing equations are solved by using the finite element method with Galerkin method. The computations were performed with the variation of the length and the thermal conductivity of the partition, and Rayleigh number based on the temperature difference between horizontal walls and the enclosure height with water(Pr=4.95). also, the effect of the inclination angles was studied for the transition to the oscillating flow. As the results, it was found that the intensity and frequency of oscillatory motion were affected significantly by the Rayleigh number and the length of partition. The effect of oscillatory motion was weaken with the increase of the thermal conductivity of partition. The inclination angle for the transition was raised with the increase of Rayleigh number and the length of partition.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.3
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• pp.289-300
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• 2013

This study numerically considered the characteristic of smoke movement and the effect of hot smoke gas on tunnel wall surface temperature during road tunnel fire under boundary condition of fire growth curve that is applied to fire analysis in road tunnels. The maximum heat release rate were 20 MW and 100 MW and tunnel air velocities were 2.5 m/s and velocity induced by thermal buoyancy respectively, also the cooling effect of tunnel wall was considered. As results, when tunnel air velocity was constant at 2.5 m/s during tunnel fire, due to the cooling effect of tunnel wall, the smoke layer was rapidly descent after some distance and it flowed the same patterns at the downstream. When heat release rate was 100 MW (and jet fan was not installed), the maximum temperature of tunnel wall surface has risen up to $615^{\circ}C$. The heat transfer coefficient of tunnel wall surface was varied from 13 to $23W/m^2^{\circ}C$ approximately.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.9
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• pp.1700-1710
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• 1992

The boundary element method is applied to determine thermal stress intensity factors for a cusp crack in transient state. In the steady temperature field, numerical values of thermal stress intensity factors for a Grifith crack and a symmetric lip cusp crack in a finite body are in good agreement within .+-. 5% with the previous solutions. In transient state, the numerical values of thermal stress intensity factors for the Griffith crack are also in good agreement with the pervious solutions. In both steady and transient states, those for the symmetric lip cusp crack with the crack surface insulated or fixed to the constant temperature are calculates for various effective crack lengths, configuration parameters and uniform heat flow angles. The variations of the thermal boundary conditions of the crack surface have a effect on stress intensity factors. The signs on the values of thermal stress intensity factors can be changed in time variation.

• Journal of Aerospace System Engineering
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• v.12 no.5
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• pp.8-15
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• 2018

The geostationary satellite uses a liquid apogee engine, to obtain a required velocity increment to enter a geostationary orbit. However, as the liquid apogee engine operates in the vacuum, a considerable disbursement of exhaust plume flow, from the liquid apogee engine can trigger a backflow. As this backflow may possibly collide with the satellite directly, it can cause adverse effects such as surface contamination, thermal load, and altitude disturbance, that can generate performance reduction of the geostationary satellite. So, this study investigated exhaust plume behavior of 400 N grade liquid apogee engine numerically. To analyze exhaust plume behavior in vacuum condition, the DSMC (Direct Simulation Monte Carlo) method based on Boltzmann equation is used. As a result, thermal fluid characteristics of exhaust plume such as temperature and number density, are observed.

• Tunnel and Underground Space
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• v.25 no.2
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• pp.155-167
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• 2015

The thermal-hydrological-mechanical (T-H-M) behavior of rock mass surrounding a high-temperature cavern thermal energy storage (CTES) operated for a period of 30 years has been investigated by TOUGH2-FLAC3D simulator. As a fundamental study for the development of prediction and control technologies for the environmental change and rock mass behavior associated with CTES, the key concerns were focused on the hydrological-thermal multiphase flow and the consequential mechanical behavior of the surrounding rock mass, where the insulator performance was not taken into account. In the present study, we considered a large-scale cylindrical cavern at shallow depth storing thermal energy of $350^{\circ}C$. The numerical results showed that the dominant heat transfer mechanism was the conduction in rock mass, and the mechanical behavior of rock mass was influenced by thermal factor (heat) more than hydrological factor (pressure). The effective stress redistribution, displacement and surface uplift caused by heating of rock and boiling of ground-water were discussed, and the potential of shear failure was quantitatively examined. Thermal expansion of rock mass led to the ground-surface uplift on the order of a few centimeters and the development of tensile stress above the storage cavern, increasing the potential of shear failure.

• Tunnel and Underground Space
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• v.31 no.3
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• pp.167-183
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• 2021

It is essential to understand the complex thermo-hydro-mechanical-chemical (THMC) coupled behavior in the engineered barrier system and natural barrier system to secure the high-level radioactive waste repository's long-term safety. The heat from the high-level radioactive waste induces thermal pressurization and vaporization of groundwater in the repository system. Groundwater inflow affects the saturation variation in the engineered barrier system, and the saturation change influences the heat transfer and multi-phase flow characteristics in the buffer. Due to the complexity of the coupled behavior, a numerical simulation is a valuable tool to predict and evaluate the THMC interaction effect on the disposal system and safety assessment. To enhance the knowledge of THMC coupled interaction and validate modeling techniques in geological systems. DECOVALEX, an international cooperation project, was initiated in 1992, and KAERI has participated in the projects since 2008 in Korea. In this study, we introduced the main contents of all tasks in the DECOVALEX-2023, the current DECOVALEX phase, to the rock mechanics and geotechnical researchers in Korea.