• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.9
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• pp.745-751
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• 2012

Hybrid rocket shows interesting characteristics of complicated mixing layers developed by interactions between turbulent oxidizer flow and mass flow from surface due to fuel vaporization. In this study, compressible LES with a ring structure attached at the entrance of the combustor are performed. According to one recent report, adding a ring structure in the middle of the combustor helps increasing regression rate. From the numerical results, it is seen that vortex structures near the wall becomes stronger due to the interaction with surface mass injection, and the local heat flux increases due to the vortices. This phenomenon is obviously related to the generation of dimple structures which are seen in the number of experiments. Also, the ring structure at the entrance induces strong vortex flow which enhances heat transfer to the wall surface and mixing between fuel and oxidizer as well as reaction efficiency.

• Journal of ILASS-Korea
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• v.22 no.4
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• pp.210-217
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• 2017

A gasoline direct injection engine has an intake air temperature can be lowered by the fuel vaporization in the combustion chamber increase the volume efficiency is high compression ratio. Therefore, study for injection rate and characteristics which influence mixture formation in combustion chamber is important. Movement of the injector needle has a direct effect on the injection of the fuel, such as formation of cavitation, the fuel injection rate, etc. Therefore, recent studies on the dynamic characteristics of the injector considering the movement of the needle have been reported, but it takes a lot of time and cost to experimentally confirm the movement of the needle inside the injector. In this study, AMESim, a commercial 1-D code, and Star-CCM+, a 3-D CFD code, were used to predict the dynamic performance of the injector with needle motion. In order to predict the movement of the needle under the high pressure, the result of the surface pressure distribution according to the movement of the needle was derived by using the morphing technique of flow analysis. In addition, we predicted the injection rate of the injector considering the movement of the needle in conjunction with the 1-D code. The injection rate of the injector was measured by the BOSCH's method and the results were similar to those of the simulation results. This method can predict the injection rate and injection characteristics and this result is expected to be used to predict the performance of gasoline direct injection engines with low cost and time in the future.

• Journal of ILASS-Korea
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• v.14 no.4
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• pp.147-152
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• 2009

Since a liquid-phase LPG injection system allows accurate control of fuel injection and increase in volumetric efficiency, it has advantages in achieving higher engine power and lower emissions compared to the mixer type LPG supplying system. However, this system also leads to an unexpected event called icing phenomenon which occurs when moisture in the air near the injector freezes and becomes frost around the nozzle hole due to extraction of heat from surrounding caused by instant fuel vaporization. As a result, it becomes difficult to control air/fuel ratio in engine operation, inducing exacerbation of engine performance and HC emission. One effort to mitigate icing phenomenon is to attach anti-icing injection tip in the end of nozzle. Therefore, in this study, the effect of engine operation parameters as well as surrounding conditions on icing phenomenon was investigated in a bench test rig with commercially-used anti-icing injection tips. The test results show that considerable ice was deposited on the surface near the nozzle hole of the anti-icing tip in low rpm and low load operating conditions in ambient air condition. This is because acceleration of detachment of deposited ice from the tip surface was induced in high load, high rpm conditions, resulting in decrease in frost accumulation. The results of the bench testing also demonstrate that little or no ice was formed at surrounding temperature below a freezing point since the absolute amount of moisture contained in the intake air is too small in such a low temperature.

• Journal of Korea Water Resources Association
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• v.31 no.6
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• pp.667-674
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• 1998

Numerical models simulating the process of NAPL from contaminated soil or groundwater through steam injection can be a useful tool for designing and evaluating the cleanup strategy under various field conditions. One and two dimensional numerical analyses were conducted based on the governing equations describing the NAPL removal as a non-isothermal, multi-phase and multi component process. Relatively good agreements were obtained between the numerical results and the observations from one-dimensional laboratory experiment, except some discrepancy due to experimental difficulties. Simulation effectively identified the steam displacement process of xylene floating on the water table and TCE sinking on the aquifer bottom in a two-dimensional analysis. Overall, simulation models have a high potential in the design/appraisal of a system for field application of the technique as well as in the examination of complex processes such as vaporization which is hard to identify experimentally.

• Macromolecular Research
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• v.12 no.4
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• pp.399-406
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• 2004

Glass-like carbon precursors shrink significantly during curing and carbonization, which leads to crack formation and bending. Cured furan resin powder and ethanol were added to furan resin to diminish the weight loss, to suppress the shrinkage and bending, and to readily release the gases evolved during polymerization and curing. Curing and carbonization were controlled by pressure and slow heating to avoid damage to the samples. The effect of the filler and ethanol on the fabrication process was examined by measuring the properties of the glass-like carbon, such as the specific gravity, bending strength, electrical resistivity, and microstructural change. The specific gravities of the filler-added glass-like carbons were higher than those of the ethanol-added samples because of the formation of macropores from the vaporization of ethanol during the curing and polymerization processes. Although the ethanol-added glass-like carbons exhibited lower bending strengths after carbonization than did the filler-added samples, the opposite result was observed after aging at 2,600$^{\circ}C$. We found that the macropores created from ethanol were contracted and removed upon heat treatment. The electrical resistivity of the glass-like carbon aged at 2,600$^{\circ}C$ was lower than those of the samples carbonized at 1,000$^{\circ}C$. We attribute this phenomenon to the fact that aging at high temperature led to well-developed microstructures, the removal of macropores, and the reduction of the surface area.

• 한국태양에너지학회:학술대회논문집
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• 2011.04a
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• pp.204-209
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• 2011

According to the environment report of UN, korea was classified as potable water shortage countries. Approximately 71% of the Earth's surface is covered by ocean. However, it is difficult to use for industry of residential purpose without a certain processing. The development of solar and waste-heat used absorption desalination technology have been examined as a viable option for supplying clean energy. In this study, the modelling of the main devices for solar and waste-heat used and adsorption desalination system was introduced. The design is divided into three parts. First, the evaporator for the vaporization of the top water is designed, and then the reactor for the adsorption and release of the steam is designed, followed by the condenser for the condensation of the fresh water is designed. In addition, new features based on the energy balance are also included to design absorption desalination system. In this basicresearch, One-bed(reactor) adsorption desalination plant that employ a low-temperature solar and waste energy was proposed and experimentally studied. The specific water yield is measured experimentally with respect to the time controlling parameters such as heat source temperatures, coolant temperatures, system switching and half-cycle operational times.

• Journal of the Korean Chemical Society
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• v.7 no.2
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• pp.96-105
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• 1963

The weight decrease curves of 18 kinds of polymers have been measured by thermobalance at the same condition where temperature is increased $1^{\circ}C$ per minutes under nitrogen or air atmosphere. The curves are further differentiated to obtain rate curve of weight decrease. Those curve offer a method to compare relative thermal stability, effects of oxygen or modes of thermal degradation of polymers qualitatively. The curves could be classified into following four types: Polystyrene, polymethylmethacrylate and acetal polymer belong to the first type. Those polymers depolymerize mainly into corresponding monomers, weight decrease curves are steepy up to perfect vaporization of polymers and rate curves show a relatively sharp peak. (Type I) Polyvinyl chloride represents the second type. This polymer decomposes with splitting off of hydrogen chloride. The thermogravimetric curve rises rapidly at first, then level off at the moderate weight decrease and gradually rises. Polyvinyl acetate also belongs to this class. (Type II) The modification of the second type is represented by polyester. The curve at the early stage is less steep, the leveling off at the next stage is less clear and the final rising of the curve is steeper than the normal second type. Polyamide, polyurethane, and polycarbonate belong to this type. (Type II') The thermal decomposition of the third type polymers is more complex than that of others. Various irregular chain scissions including side chain splitting and depolymerization to monomers occur simultaneously. The weight of the polymer decreases gradually and the rate curve does not show sharp peaks. Polyvinyl alcohol and diene polymers belong to this type. (Type III) Generally, polycondensation polymers are more stable toward heat than addition polymers and polymers having aromatic nucleus show good thermal stability. Polymers having tertiary carbon atoms such as polystyrene or polypropylene and acetal resin start decomposition under airatmosphere at the temprature below $50^{\circ}C$ or more of the temperature where the polymers start decomposition under nitrogen atmosphere.

• Korean Journal of Materials Research
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• v.14 no.4
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• pp.293-299
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• 2004

Transition metal ions doped $TiO_2$ nanostructured powders were prepared with simply heating aqueous $TiOCl_2$ solutions, contained various metal ions (Ni, Al, Fe, Zr, and Nb) of 1.47 mol% added as metal-chlorides, at $100^{\circ}C$ for 4 hrs by homogeneous precipitation process under suppressing conditions of water vaporization. The characterizations for prepared $TiO_2$ powders were carried out to observe doping of metal ions, their concentrations and microstructures using XRD, UV-VIS (DRS), XPS, SEM, TEM and ICP. Also, photo-oxidative abilities were evaluated by decomposition of 4-chlorophenol (4CP) under ultraviolet light irradiations. No secondary oxide phases were formed in all the $VTiO_2$ powders, showing doping with various transition metal ions. When adding ions ($Ni^{2+}$ or$ Al^{3+ }$ and $Zr^{4+}$ ) having valance states or ionic radii greatly different from those of $Ti^{4+}$ , the $TiO_2$ powders of mixed anatase and rutile phases were formed, whereas in the case of additions of $^Fe{3+ }$ and $Nb^{ 5+}$ as well as no addition of metal ion the powders with pure rutile phase alone were formed. Among the prepared $TiO_2$ powders, Ni$^{2+}$ doped $TiO_2$ powders, containing a small amount of anatase phase, showed excellent photo-oxidative ability in 4CP decomposition because of relative decreases in electron-hole recombination and poisoning of $TiO_2$ surface during the photoreaction.n.

• Journal of the Korean Society of Tobacco Science
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• v.25 no.1
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• pp.59-69
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• 2003

The adsorption characteristics of H$_2$S, NH$_3$and $CH_3$SH on the graphite carbon have been investigated using Grand Canonical Monte Carlo(GCMC) method with universal force field (UFF) and dreiding force field. Most of the activated carbons used in vapor phase adsorption have the micropore of 6$\AA$ to 20$\AA$ and the specific surface area of ca. 1000 m$^2$/g, as the result of $N_2$ adsorption by BET method. For the more efficient comparison, the activated carbons have been manipulated with different pore sizes. The adsorption characteristics of H$_2$S, NH$_3$and $CH_3$SH have been considered at various temperatures and pressures. The adsorption amount using Dreiding force field is predicted to be lower than that using UFF. As the temperature is going to high, the adsorption amount of adsorbates is decreased due to their vaporization. Considering the pore size effect, the adsorption characteristic depends on the adsorbate size, polarity and interaction between adsorbates, etc. At all cases employed in this study, NH$_3$ is barely adsorbed and $CH_3$SH is preferentially adsorbed on the graphite carbon. Our theoretical result is qualitatively good agreement with the experimental observation. However, there are some quantitative discrepancies depending on the functional groups and pore size distribution on the real activated carbons used in experiment.

• Current Photovoltaic Research
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• v.2 no.3
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• pp.115-119
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• 2014

$Cu(In,Ga)Se_2$ (CIGS) thin films have been used as a light absorbing layer in high-efficiency solar cells. In order to improve the quality of the CIGS thin film, often selenization step is applied. Especially when the thin film was formed by non-vacuum powder process, selenization can help to induce grain growth of powder and densification of the thin film. However, selenization is not trivial. It requires either the use of toxic gas, $H_2Se$, or expensive equipment which raises the overall manufacturing cost. Herein, we would like to deliver a new, simple method for selenization. In this method, instead of using a costly two-zone furnace, use of a regular tube furnace is required and selenium is supplied by a mixture of selenium and ceramic powder such as alumina. By adjusting the ratio of selenium vs. alumina powder, selenium vaporization can be carefully controlled. Under the optimized condition, steady supply of selenium vapor was possible which was evidently shown by large grain growth of CIGS within a thin powder layer.