• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.6
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• pp.814-821
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• 2000

The Discrete Ordinates Interpolation Method (DOIM) is tested in three-dimensional enclosures. The radiative transfer equation (RTE) is solved for a linear source term and the DOIM is formulated for a gray medium. Several interpolation methods can be applied to the DOIM scheme. Among them, the interpolation method applicable to an unstructured grid system is discussed. In a regular hexahedron enclosure, radiative wall heat fluxes are calculated and compared with exact solutions. The enclosure has an absorbing, emitting and nonscattering medium and a constant temperature distribution. These results are obtained with varying optical depths (xD = 0.1, 1.0, 10.0). Also, the same calculations are performed in an irregular hexahedron enclosure. The DOIM is applied to an unstructured grid system as well as a structured grid system for the same regular hexahedron enclosure. They are compared with the exact solutions and the computational efficiencies are discussed. When compared with the analytic solutions, results of the DOIM are in good agreement for three-dimensional enclosures. Furthermore, the DOIM can be easily applied to the unstructured grid system, which proves the reliability and versatility of the DOIM.

• Journal of Animal Science and Technology
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• v.61 no.6
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• pp.313-323
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• 2019

The interactive effect of dietary fat supplementation and milk yield level on dairy cows performance under heat stress has not been thoroughly investigated. The purpose of this study was to evaluate the effect of production level, the source of fat supplements and their interaction on dairy cows performance under heat stress. In this study, 64 Holstein multiparous cows were divided into 2 groups and received one of two rations having either calcium salts of fatty acids (Ca-FA) or high-palmitic acid (PA) supplements (2.8% of DM; dry matter). After completing the experiment and based on maturity-equivalent milk, cows were divided into two groups of high-yielding (14,633 kg) and medium-yielding (11,616 kg). Average temperature humidity index (THI) was 71 during the trial period. Apparent digestibility of dry matter (p = 0.04), organic matter (p = 0.05), and neutral detergent fiber (NDF; p = 0.04) for cows fed Ca-FA were greater than cows fed PA. The milk fat content in high-producing cows was 0.3% greater than medium-producing cows (p = 0.03). The milk protein content in cows fed Ca-FA was greater than cows fed PA (p < 0.01). High-producing cows had greater serum cholesterol (p = 0.02) than medium-producing cows. The cows fed PA tended to have a greater BUN than cows fed Ca-FA (p = 0.06). Alanine aminotransferase and aspartate aminotransferase tended to be increased by PA, which indicates that cows in PA treatment may have experienced more adverse effect on the liver function than cows on Ca-FA. Therefore, under heat stress and in 90 d trial, milk production level does not affect the cows' response to PA or Ca-FA. Although cows fed Ca-FA received lower energy than those fed PA, they compensated for this shortage likely with increasing the digestibility and produced a similar amount of milk.

• Plant Journal
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• v.12 no.1
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• pp.29-36
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• 2016

It is becoming increasingly important to make use of alternative energy source. because It is not able to rely on only fossil fuel for the recent increasing demand of energy consumption. With this situation, lots of studies for utilizing low grade energy such as industrial waste heat, solar energy, and geothermal energy have been conducted. The aim of this study is to predict the operation characteristics of working fluid by using performance analysis program (ThermoFlex) through the system analysis which is not mixing district return water but using ORC(Organic Rankine Cycle, hereinafter ORC) as a downstream cycle when accumulating district heating (hereinafter DH). In this study, We conducted the performance analysis for the case which has the district heating water temperature($120^{\circ}C$) and Flow rate of $163m^3/h$ (including District Heating return water flow), and examined several working fluid which is proper to this temperature. The case using R245fa (which is the best-case) showed 269.2kW power output, 6.37% efficiency. Additionally, Cut down on fuel was expected because of the boiler inlet temperature increase by being Formed $57.3{\sim}85^{\circ}C$ in a temperature of district heating return water, depending on a pressure change of a condenser in ORC system.

• Applied Chemistry for Engineering
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• v.34 no.3
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• pp.307-312
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• 2023

In this study, a catalytic oxidation-heat recovery system was designed that can remove unreacted with a concentration of about 1% to 6% in the exhaust gas of hydrogen fuel cells and recover heat to ensure safety in the hydrogen economy. The safety system was devised by filling hydrogen oxidation catalysts at room temperature that can remove unreacted hydrogen without any energy source, and an exhaust-heat recovery device was integrated to efficiently recover the heat released from the oxidation reaction. Through CFD analysis, variations in pressure and fluid within the system were shown depending on the filling conditions of the hydrogen oxidation system. In addition, it was found that waste heat could be recovered by optimizing the temperature of the exhaust gas, flow rate, and pressure conditions within the heat recovery system and securing hot water above 40 ℃ by utilizing the exhaust gas oxidation heat source above 300 ℃. Through this study, it was possible to confirm the potential of utilizing hydrogen processes, which are applied in small to medium-sized systems such as hydrogen fuel cells, as a safety system by evaluating them at a pilot scale. Additionally, it could be a safety guideline for responding to unexpected hydrogen safety accidents through further pilot-scale studies.

• Journal of the Korea Organic Resources Recycling Association
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• v.28 no.1
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• pp.83-95
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• 2020

The economic issue of the period of return versus investment has emerged to efficiently utilize the thermal energy of public resource recovery facilities using waste and private thermal source facilities using BIO-SRF. Accordingly, the optimum temperature and pressure facilities are required beyond the traditional designed, constructed and operated. In this study, we analyzed current energy output by different heat and pressure model in domestic facilities, and calculated the characteristics of green-house gas emission. In order to, utilize the thermal energy producing facilities using waste and biomass fuel more efficiently, it is temperature and pressure, which will lead to more lucrative investment and return as well.

• Korean Chemical Engineering Research
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• v.57 no.5
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• pp.730-734
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• 2019

Thermophoresis is a transport phenomenon of particles driven by a temperature gradient of a medium. In this paper, we discuss the thermophoresis of particles in microfluidic channels. In a non-fluidic, stagnant channel, the thermophoretic transport of micro-particles was found to be larger in proportion to the voltage applied to the platinum wire heat source installed in the channel. The variation of the temperature around the platinum wire depending on the voltage was estimated, by using the Callendar-van Dusen equation. The thermophoretic behavior of nano-particles in the same system was observed, which is similar to that of the microparticles. Finally, we fabricated a Y-shaped microfluidic channel with a platinum wire heat source installed in the channel, to realize the thermophoretic phenomenon of the particles in the suspension flowing through the channel. It is shown that the flow of the suspension can be controlled based on the thermophoretic principle.

• Structural Engineering and Mechanics
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• v.76 no.1
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• pp.17-26
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• 2020

The objective of this paper is to study the deformation in transversely isotropic thermoelastic solid using new modified couple stress theory subjected to ramp-type thermal source and without energy dissipation. This theory contains three material length scale parameters which can determine the size effects. The couple stress constitutive relationships are introduced for transversely isotropic thermoelastic solid, in which the curvature (rotation gradient) tensor is asymmetric and the couple stress moment tensor is symmetric. Laplace and Fourier transform technique is applied to obtain the solutions of the governing equations. The displacement components, stress components, temperature change and couple stress are obtained in the transformed domain. A numerical inversion technique has been used to obtain the solutions in the physical domain. The effects of length scale parameters are depicted graphically on the resulted quantities. Numerical results show that the proposed model can capture the scale effects of microstructures.

• Structural Engineering and Mechanics
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• v.77 no.3
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• pp.315-327
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• 2021

Here, in this research we have studied a two dimensional problem in a homogeneous orthotropic magneto-thermoelastic medium with higher order dual-phase-lag heat transfer with combined effects of rotation and hall current in generalized thermoelasticity due to time harmonic sources. As an application the bounding surface is subjected to uniformly distributed and concentrated loads (mechanical and thermal source). Fourier transform technique is used to solve the problem. The expressions for displacement components, stress components and temperature change are derived in frequency domain. Numerical inversion technique has been used to obtain the results in physical domain. The effect of frequency has been depicted with the help of graphs.

• Tunnel and Underground Space
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• v.34 no.2
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• pp.127-142
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• 2024

The robustness of a numerical method means that its computational performance is maintained under various modeling conditions. New numerical methods or codes need to be assessed for robustness through benchmark testing. The TOUGH-FLAC modeling approach has been applied to various fields such as subsurface carbon dioxide storage, geological disposal of spent nuclear fuel, and geothermal development both domestically and internationally, and the modeling validity has been examined by comparing the results with experimental measurements and other numerical codes. In the present study, a benchmark test of the TOUGH-FLAC approach was performed based on a coupled thermal-hydro-mechanical behavior problem with an analytical solution. The analytical solution is related to the temperature, pore water pressure, and mechanical behavior of a fully saturated porous medium that is subjected to a point heat source. The robustness of the TOUGH-FLAC approach was evaluated by comparing the analytical solution with the results of numerical simulation. Additionally, the effects of thermal-hydro-mechanical coupling terms, fluid phase change, and timestep on the computation of coupled behavior were investigated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.7
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• pp.711-719
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• 2012

A thermodynamic analysis and a feasibility study on the organic Rankine cycle (ORC) as a waste heat recovery system for a marine diesel engine were carried out. The ORC and its combined cycle with the engine were simulated, and its performance was estimated theoretically using R245fa. A parametric study on the performance of the ORC system was carried out under different temperature conditions of the heat transfer loop and specification of the heat exchanger. According to the thermodynamic analysis, ~10% of the thermal efficiency of the cycle was able to be realized with the low temperature heat source below $250^{\circ}C$. The electric power output of the ORC was estimated to be about 4% of the mechanical power output of the engine, considering additional pumps for cooling water and circulation of the heat transfer medium. According to the present study, the electric power generated by the ORC is about 59%-69% of the required power, and it is possible to reduce the fuel consumption under normal seagoing conditions.