• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.8
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• pp.640-647
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• 2014

Infrared signature of aircraft exhaust plume is the critical factor for aircraft survivability. To improve the military aircraft survivability, the accurate prediction of infrared signature for the propulsion system is needed. The numerical analysis of thermal fluid field for nozzle inflow, free stream flow, and plume region is conducted by using the in-house code. Weighted Sum of Gray Gases Model based on Narrow Band with regrouping is adopted to calculate the spectral infrared signature emitted from aircraft exhaust plume. The accuracy and reliability of the developed code are validated in the one-dimensional band model. It is found that the infrared radiant intensity is relatively more strong in the plume through the analysis, the results show the different characteristic of the spectral infrared signature along the temperature, the partial pressure, and the species distribution. The continuous spectral radiant intensity is shown near the nozzle exit due to the emission from the nozzle wall.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.6
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• pp.59-64
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• 2010

Building a firebreak against surface forest fire is a typical indirect suppression method that stops spread of flame by removing surface fuel, such as fallen leaves and bushes. In the sense of fire dynamic, building a firebreak is to set a section which will block thermal energy from igniting on virgin fuel. This study suggests and evaluates a calculation method for width of firebreak against surface fire for variant wind and slope conditions by applying the Point Source Model (PSM) to fallen leaves of Pinus densiflora. Width of firebreak was measured based on the distance the threshold radiant heat igniting Pinus densiflora fallen leaves at the heat flux of $4.9\;kW/m^2$ reaches. As a result, at the wind velocity of 0~5 m/s and on the slope of $0{\sim}50^{\circ}$, the appropriate width of a firebreak was 0.35~0.65 m for the mean flame height and 0.75~1.05 m for the maximum flame height. Accordingly, considering the factor of safety, the most appropriate width of a firebreak is 1.05 m based on the maximum flame height. Additional comparative analyses through experiments and field surveys are deemed necessary to determine appropriate widths of firebreak for different types of surface fuel.

• Magazine of the Korean Society of Agricultural Engineers
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• v.32 no.3
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• pp.31-38
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• 1990

The power water flowed out from the multipurpose darn influences the ecosystem approximately because of the low water temperature. An appropriate counter measure to the rising water temperature is needed for growing crops especially when the temperature is below 18˚C in the source of the irrigation water This observational study is practiced in Yong-Doo water warming canal and pond in the down stream of Choong-Ju multipurpose dam and is practiced for analyse and compare the rising effects in actural water temperature by actual measurement with the rising effects of planned water temperatuer by the basic theoritical method and for the help to present the direction in plan establishment through investigate the results afterwards. The results are as follows. 1.The degree of the rise of the water temperature can be decided by $\theta$x=$\theta$o +K L--v.h (T-$\theta$˚)Then, K values of a factor representing the characteristics of the water warming canal were 0.00002043 for the type I. and 0.0000173 for the type II. respectively. 2.A variation of water temperature which produced by the difference effective temperature and water temperature in the water warming canal was $\theta$x1 = 16.5 + 15.9(1-e -0.00018x), $\theta$x2 =18.8 + 8.4( 1-e -0.000298x)for the type I. and $\theta$x, = 19.6 + 12.8 ( 1-e -0.00041x) for the type II. 3.It was shown that the effects of the rise of water temperature for the type I. water warming canal were greater than that of type II. as a resultes of broadening the surface of the canal compared with the depth of water, coloring the surface of water canal and installing the resistance block. 4.In case of the type I. water warming canal, the equation between the air temperature and the degree of the rise of water temprature could be made ;Y= 0.4134X + 7.728 In addition, in case of the type II. water warming canal, the correlation was very low. 5.A monthly variation of the water temperature in the water warming canal was the highest in August during the irrigation period and the water temperature rose with the air temperature until August. However, it was blunted after then. 6.A rising degree of water temperature of the practical value in the water warming pond was higher than that of the theoritical equation by 69% for the type I. and 57% for the type II. Accordingly, it was possible to acquire the result near the practical value.$\theta$w-$\theta$o=[1-exp{ -h(1+2$\psi$) . X($\theta$w-$\theta$0)XC Here, C values are 1.69 for the type I. and 1.57 for the type II. 7.It was shown that the effect of the rise of water temperature was favorable when the thermal absorption was to be good by coloring the surface of the water warming pond and removing the bottom osmosis. 8.By enlarging the surface of water in comparison with the depth, and by having dead area of water in the water warming pond, this structure in the water warming pond is helpful for the rise of water temperature.

• Journal of Biosystems Engineering
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• v.43 no.1
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• pp.21-29
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• 2018

Purpose: The objective of this study is to evaluate the performance of the conical solar concentrator (CSC) system, whose design is focused on increasing its collecting efficiency by determining the optimal conical angle through a theoretical study. Methods: The design and thermal performance analysis of a solar concentrator system based on a $45^{\circ}$ conical concentrator were conducted utilizing different mass flow rates. For an accurate comparison of these flow rates, three equivalent systems were tested under the same operating conditions, such as the incident direct solar radiation, and ambient and inlet temperatures. In order to minimize heat loss, the optimal double tube absorber length was selected by considering the law of reflection. A series of experiments utilizing water as operating fluid and two-axis solar tracking systems were performed under a clear or cloudless sky. Results: The analysis results of the CSC system according to varying mass flow rates showed that the collecting efficiency tended to increase as the flow rate increased. However, the collecting efficiency decreased as the flow rate increased beyond the optimal value. In order to optimize the collecting efficiency, the conical angle, which is a design factor of CSC, was selected to be $45^{\circ}$ because its use theoretically yielded a low heat loss. The collecting efficiency was observed to be lowest at 0.03 kg/s and highest at 0.06 kg/s. All efficiencies were reduced over time because of variations in ambient and inlet temperatures throughout the day. The maximum efficiency calculated at an optimum flow rate of 0.06 kg/s was 85%, which is higher than those of the other flow rates. Conclusions: It was reasonable to set the conical angle and mass flow rate to achieve the maximum CSC system efficiency in this study at $45^{\circ}$ and 0.06 kg/s, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.7
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• pp.3252-3260
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• 2012

2,2'-Bipyridinium chlorochromate[$C_{10}H_8N_2HCrO_3Cl$] was synthesized by the reaction of 2,2'- bipyridine with chromium(VI) trioxide in 6M HCl. The structure was characterized by IR and ICP analysis. The oxidation of benzyl alcohol using 2,2'-bipyridinium chlorochromate in various solvents showed that the reactivity increased with the increase in the order of the dielectric constant(${\varepsilon}$), in the order: cyclohexene< chloroform$p-CH_3$, H, m-Br, $m-NO_2$) in N,N'-dimethylformamide. Electron-donating substituents accelerated the reaction, whereas electron acceptor groups retarded the reaction. The Hammett reaction constant(${\rho}$) was -0.64(303K). The oxidation reactivity of alcohols can be a useful factor to study about physical properties such as thermal stability, when the polysilsesquioxane solution is ready for an applying coating agent. The observed experimental data was used to rationalized the hydride ion transfer in the rate-determining step.

• Korean Chemical Engineering Research
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• v.48 no.1
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• pp.58-67
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• 2010

Combustion of the Korean Anthracite and wood-pellet was characterized in air atmosphere with variation of heating rate(5, 10, 20 and $30^{\circ}C/min$) in TGA. The results of TGA have shown that the combustion of the wood-pellet occurred in the temperature range of $200{\sim}620^{\circ}C$ which is much lower than that of Korean anthracite. Activation energies of the wood-pellet and Korean anthracite, determined by using Friedman method were 44.12, 21.45 kcal/mol respectively. Also, their reaction orders(n) and pre-exponential factors(A) were 5.153, 0.7453 and $4.01{\times}10^{16}$, $1.39{\times}10^6(s^{-1})$ respectively. In order to find out the combustion mechanism of the wood-pellet and Korean anthracite, twelve solidstate mechanisms defined by Coats Redfern Method were tested. The solid state combustion mechanisms of the woodpellet and Korean anthracite were found to be sigmoidal curve A3 type and a deceleration curve F1 type respectively. Also, from iso-thermal combustion($300{\sim}900^{\circ}C$) of their char, the combustion characteristics of their char was found. Activation energies of the their char were 27.5, 51.2 kcal/mol respectively. Also, pre-exponential factors(A) were $2.55{\times}10^{12}$, $1.49{\times}10^{10}(s^{-1})$ respectively. Due to the high combustion reactivity of wood-pellet compared with Korean anthracite, combustion atmosphere will be improved by co-combustion with Korean anthracite and wood-pellet.

• Korean Chemical Engineering Research
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• v.52 no.4
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• pp.530-537
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• 2014

Moisture is a major factor causing the deteriorative physical change, microbial growth, and chemical reaction of the products. In this study, the moisture absorbing composite films have been prepared with moisture absorbing material of polyacrylic acid partial sodium salt (PAPSS) impregnated on LLDPE polymer for the functional packaging applications. The results showed that PAPSS impregnated film illustrated uniformly dispersed PAPSS particles in the LLDPE polymer matrix. The transparency of the PAPSS impregnated film decreased slightly at higher PAPSS concentrations. An increase in the PAPSS content for moisture-absorbing films showed a similar decrease in tensile strength, percent elongation at break, and tear strength. Their values of films impregnated with PAPSS of 0.5, 1, and 2% showed no significant difference. Meanwhile, 4% PAPSS films significantly decreased the values of mechanical properties compared to the films impregnated with different PAPSS levels. Values of the oxygen permeability and water vapor permeability for PAPSS impregnated films decreased significantly with greater PAPSS. The results indicate that 4% PAPSS impregnated in LLDPE films had high affinity of moisture absorbencies compared to the other films. The mathematical equation that best described the moisture sorption isotherm of each film sample was the GAB equation at $25^{\circ}C$. The crystallization and melting temperatures of PAPSS films were influenced by the addition of PAPSS material, but showed good thermal stability.

• Journal of Korea Water Resources Association
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• v.43 no.10
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• pp.911-920
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• 2010

The closed water bodies, such as reservoirs and lakes, could be contaminated by an inflow of pollutants in the upstream as well as a stratification caused by seasonal natural phenomena. The vertical circulation particularly plays an important role in reduction of environmental pollutants. The factors of the vertical circulation are the temperature, wind, thermal diffusivity and sunlight. The wind is probably the most significant factor among them. Thus, it is necessary to describe the validation and application of a three-dimensional numerical model of wind-induced circulation in a thermally stratified flow. In this paper, a three-dimensional numerical model for the thermally stratified flows is presented. The model is conducted in three steps to calculate the velocity components from the momentum equations in x- and y- axis directions, the elevations from the free surface equation and the temperature from the scalar transport equation. Numerical predictions are compared with available analytical solutions for the sloshing free surface movement in a rectangular basin. The numerical results generally show a reasonable agreement with analytical solutions. And the model is applied to the circulation for the wind induced flow in a thermally stratification. Consequently, the developed model is validated by two verifications and phenomena of the internal flow.

• Membrane Journal
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• v.9 no.3
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• pp.157-162
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• 1999

In the crosslining reaction of poly(vinyl alcohoJ)(PVA) with sulfur-succinic acid which had been established in our previous work, reaction temperature, 15$0^{\circ}C$, was so high to collapse the pore struc¬tures in support membrane for the preparation of composite membrane. Therefore, the efforts have been focused on lowering of the reaction temperature to 100$^{\circ}$C by using a catalysis, HC!. The newly established crosslinking reaction was characterized through the analysis of the chemical and thermal properties. From these results, the optimum conditions for the membrane preparation couId be drawn as followings : (i) reac¬tion temperature, 100 $^{\circ}C$,(ii) reaction time, 90 min, (iii) the concentration of the catalysis (HCD, 1.5%. Com¬posite membranes were fabricated by coating a casting solution containing PYA, sulfur-succinic acid and HCl on a support membrane followed by crosslinking it at 10$0^{\circ}C$. The resulting membranes were applied to the pervaporation separation of methyl-tert-butyl ether(MTBE)/methanol (MeOH) mixtures at 30, 40, and 5O$^{\circ}C$. The flux of 5.09 g/$m^2$hr at 5O$^{\circ}C$ and the highest separation factor of 1622 were obtained, respectively.

• Journal of the Korean Magnetics Society
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• v.18 no.5
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• pp.195-199
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• 2008

Composites of $Fe_{93.5}Si_{6.5}$ powder and epoxy were prepared using a thermal curing process. Scanning electron microscope (SEM), vibrating sample magnetometer (VSM) and network analyzer were used to analyze the structure, electromagnetic properties and microwave absorption of the composites. Results show that the saturation magnetization depends on the fraction of the $Fe_{93.5}Si_{6.5}$ powder in the composite, which affects initial permeability. It is believed that the eddy current loss is a dominant factor over 1 GHz and that the resonance frequency of the composite decreases with increasing fractions of $Fe_{93.5}Si_{6.5}$ powder. Finally, reflection loss was calculated from the permeability and permittivity of these composites. Composite with 50 wt.% $Fe_{93.5}Si_{6.5}$ powder fractions and 5 mm thickness showed reflection loss below -20 dB from 3.66 GHz to 4.16 GHz. Therefore, it is believed that thin Fe-Si/epoxy composites may be a good candidate for microwave absorption application.