• Progress in Superconductivity and Cryogenics
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• v.13 no.2
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• pp.29-32
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• 2011

The thermal properties of insulation material are essential to develop a high-temperature superconducting (HTS) power cable to be operated at around liquid nitrogen temperature. Unlike metallic materials, nonmetallic materials have a high thermal resistance; therefore special attention needs to be paid to estimate heat flow correctly. Thus, we have developed a precise instrument for measuring the thermal conductivity of insulating materials over a temperature range from 40 K to near room temperature using a cryocooler. Firstly, the measurement of thermal conductivity for Teflon is carried out for accuracy confirmation. For a supplied heat flux, the temperature difference between warm and cold side is measured in steady state, from which the thermal conductivity of Teflon is calculated and compared with published result of NIST. In addition, the apparent thermal conductivity of Polypropylene laminated paper (PPLP) is presented and its temperature dependency is discussed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.524-527
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• 2004

Hybrid rocket had many advantage with compared to solid and liquid rockets. However, the engines have not yet been used in practical rocket systems, due mainly to the disadvantage of hybrid combustion, such as low fuel regression rate. In this study, lab-scale hybrid motor was designed and manufactured. And the methods of regression rate improvement were considered. Test firings with thrusts up to 300 N were conducted with GOX and transparent PMMA. Thrust was calculated with the pressure of the combustion chamber and the regression rate was measured in with variation of oxidizer flow rate. The regression rates showed a strong dependency on GOX mass flux. The frequency analysis technique of the bulk-mode oscillation of motor was applied to a hybrid rocket motor and was based on the principle that this frequency was inversely proportional to the square root of the chamber volume. Several problems and solutions of operating hybrid rocket were presented.

• Journal of the Korean Vacuum Society
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• v.9 no.1
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• pp.24-29
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• 2000

MgO thin films were deposited on soda lime glass substrates by rf magnetron sputtering using a MgO target at various oxygen flow ratios in order to probe the relationship between MgO film properties and discharge characteristics. MgO films have a tendency to form microstructures with a preferred growth orientation of (200) with increasing oxygen flo ration up to 0.1 $O_2$/(Ar+$O_2$). MgO film obtained at 0.1[$O_2$/(Ar+$O_2$)] was found to be fully stoichiometric. The stoichiometric MgO film was observed to have relatively very clean surface and grains of large size and contain almost no hydroxyl group. The AC PDP with fully stoichiometric MgO film showed lower firing and sustain voltages than those with magnesium-rich or oxygen-rich MgO films, being largely attributed to the larger grain size and the minimized hydroxyl group.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.7
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• pp.907-915
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• 2000

The preconditioned Krylov subspace methods were applied to the incompressible Navier-Stoke's equations for convergence acceleration. Three of the Krylov subspace methods combined with the five of the preconditioners were tested to solve the lid-driven cavity flow problem. The MILU preconditioned CG method showed very fast and stable convergency. The combination of GMRES/MILU-CG solver for momentum and pressure correction equations was found less dependency on the number of the grid points among them. A guide line for stopping inner iterations for each equation is offered.

• Bulletin of the Korean Chemical Society
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• v.12 no.5
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• pp.468-473
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• 1991

Viscoelastic properties of PET filament fibers on stress relaxation were investigated in the solvents of $H_2$O, 0.05% NaOH and 50% DMF using an Instron (UTM4-100 Tensilon) with solvent chamber. The theoretical stress relaxation equation derived by applying the Ree-Eyring's hyperbolic sine law to dashpot of three element non-Newtonian model was applied to the experimental stress relaxation curves, and the model parameters $G_1,G_2$, ${\alpha}$ and ${\beta}$ were obtained. By analyzing temperature dependency of the relaxation time, the values of activation entropy, activation enthalpy and activation free energy for flow in PET filament fiber were evaluated, the activation free energy being about 25.7 kcal/mol. The self diffusion coefficient and hole distance were obtained from parameters ${\alpha}$, ${\beta}$ and crystallite size in order to study the self diffusion and the orientation of crystallites in amorphous region and the effect of solvent.

• Korean Journal of Food Science and Technology
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• v.19 no.2
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• pp.81-88
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• 1987

Rheological properties of rehydrated suspensions of two kinds of freeze dried Kochujang powders, processed at different freezing rates, were compared with raw Kochujang using Brookfield wide-gap rotational viscometer at $25^{\circ}C-60^{\circ}C$. Shear rates ranged from $0.1965\;sec^{-1}$ to $1.9650\;sec^{-1}$ and solid content ranged from 47% to 56%. Rehydrated suspensions of quickly frozen Kochujang powder and slowly frozen Kochujang powder, and raw Kochujang exhibited pseudoplastic behaviors with yield stress and presented thixotropic properties which followed the second-order kinetic behavior proposed by Tiu. Suspensions of Kochujang powders exhibited considerably higher decaying rates than raw Kochujang. The dependency of the equilibrium structure parameter on the shear rate was weak, and there were no significant differences among the values of structure parameters of three samples. The temperature dependency of the apparent viscosity of Kochujang suspension was fully expressed by Arrhenius equation and activation energies of suspensions of quickly frozen Kochujang powder and slowly frozen Kochujang powder, and raw Kochujang were 2.21, 2.18, and 2.32 Kcal/g.mole respectively. Consistency indices of three samples increased with solid content and decreased with temperature. Flow behavior indices of three samples showed no considerable dependency on the temperature and solid content. There were no significant differences in the rheological properties between two Kochujang powders.

• Bulletin of the Society of Naval Architects of Korea
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• v.25 no.4
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• pp.7-12
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• 1988

The Resistance Committee of Korea Towing Tank Conference extended the Cooperative Experimental Study Program(1985)[1] to perform the geosim tests by exchanging the five different scaled Series 60, $C_B=0.60$ models between the participating organizations and 13 sets of resistance data have been obtained. The test results are compared among the participating towing tanks and also with the results given in the report of the Resistance and Flow Com-identify the mittee of 18th ITTC. The form factor of each model is derived by Prohaska's method to investigate its dependency on $R_n$. On the other hand, at each $F_n$, form factors are also derived by Telfer's method to relation between $F_n$ and form factor. For this hull form, form factors show relatively weak dependency on $R_n$ and strong dependency on $F_n$. And it is also found that dependencies on both have a cross relation. It seems that further study should be continued to understand more clearly the physical phenomena involved in this problem.

• Journal of Global Scholars of Marketing Science
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• v.17 no.4
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• pp.201-221
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• 2007

Recently price as an information clue on online shopping has become important and price dependency has been also increased. This study suggests the flow which customers experience on online shopping plays a leading role in a matter of revisiting intention, but price sensitivity has a possibility to decrease the flow on the basis of literature investigation. While telling the differences in types of shopping malls, this study also examines relationship verifications with price sensitivity, flow of internet shopping mall and revisiting intension. The results show the flow experience through temporal dissociation makes increase a revisiting intention. To the contrary, this study presents a price search dimension in price sensitivity has negative influence to each dimension of temporal dissociation, heightened enjoyment and curiosity and also the relationship between price importance and flow is rejected. In addition, this influence gets different results by internet auction, pure internet shopping mall, shopping mall which can show price comparisons. In the case of shopping mall which can show price comparisons, more price researches become less curiosities and more heightened enjoyments and curiosities get more revisiting intentions. In the internet auction's case, price search decreases a temporal dissociation and heightened enjoyment and improves a revisiting intention when a temporal dissociation and heightened enjoyment are increased. Price research reduces three types of flow dimensions such as a temporal dissociation, heightened enjoyment, and curiosity in the pure internet shopping mall. In addition, only heightened enjoyment affects to a revisiting intentions.

• Applied Chemistry for Engineering
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• v.18 no.3
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• pp.239-244
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• 2007

For the simultaneous methane recovery and $CO_2$-stripping, we have been developed dual vent auto circulation bubble lift column reactor, and evaluate optimum conditions for monoethanolamine (MEA) solutions as a $CO_2$ absorbent. At the 5 wt% MEA solution, we investigated the pH change during $CO_2$-stripping and absorption reaction, $CO_2$-stripping rate with reaction time, methane recovery efficiency for various inflow rates of air, $CO_2$-stripping rate for flow liquid over flow height, and $CO_2$-stripping dependency on the temperature of absolvent solutions. The suggested optimum conditions for $CO_2$ recovery with MEA in the dual vent auto circulation bubble lift column reactor were 40 mm over flow liquid height, 1.5 L/min of air inflow rate, and $25^{\circ}C$ of absorbent solution temperature.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.2
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• pp.1-11
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• 2002

In the present study, a parallel DSCM technique based on a cell-based data structure is developed for the efficient simulation of rarefied gas flows especially od PC clusters. Dynamic load balancing is archieved by decomposing the computational domain into several sub-domains and accounting for the number of particles and the number cells of each domain. Mesh adaptation algorithm is also applied to improve the resolution of the solution and to reduce the grid dependency. It was demonstrated that accurate solutions can be obtained after several levels of mesh adapation starting from a coars initial grid. The method was applied to a two-dimensioanal supersonic leading-edge flow and the axi-symmetric Rothe nozzle flow to validate the efficiency of the present method. It was found that the present method is a very effective tool for the efficient simulation of rarefied gas flow on PC-based parallel machines.