• The KSFM Journal of Fluid Machinery
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• v.14 no.3
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• pp.33-38
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• 2011

Medicated water electrolysis apparatus, which electrolyzes water into acidic water and alkaline water, was in the spotlight as becoming known the effect of alkaline water. It is known as good for health as removing active oxygen in the human's body and promoting digestion. But, the customers could not get that desired water temperature because these apparatuses are directly connected with a water pipe. So, the cooling system was developed for controlling the temperature of the alkaline water. One of the typical way is to store water in water tank and control the temperature. But, in this way, storing water can be polluted impurities coming from outside. For protecting this pollution, the cooling system based on indirect heat exchange method through phase change between water and ice was developed. In this study, we have calculated efficiency of the cooling system with phase change by experiment and commercial CFD(Computational Fluid Dynamics) code, ANSYS CFX. To consider the effect of latent heat that is generated by melting ice, we have simulated two phase numerical analyses used enthalpy method and found the temperature, velocity, and ice mass distribution for calculating the efficiency of cooling. From the results of numerical analysis, we have obtained the relationship between the cooling efficiency and each design factor.

• KIEE International Transactions on Electrophysics and Applications
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• v.3C no.3
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• pp.77-80
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• 2003

An innovative ozonizer has been developed using a high frequency, surface discharge and a high purity Ti-Si-AI ceramic catalyst as a dielectric component. Using a type of thin film, a thin cylindrical compound ceramic catalyst layer was adhered to the outside surface of its inner electrode. An alternating current (AC) exciting voltage with frequencies from 0.6 KHz to 1.0 KHz and peak-to-peak voltages of 4-6 ㎸ was applied between the electrodes to produce a stable high-frequency silent discharge. A substantial reduction of the exciting voltage was also enabled by means of a thin Ti-Si-Al ceramic catalyst tube. As a result, the ozonizer can effortlessly obtain the required ozone concentration (50-60 g/$m^2$ for oxygen) and high ozone efficiency consumption power (180 g/kWh for oxygen) with-out the assistance of any particular methods. For purposes of this experiment, oxygen gas temperature was set at 2$0^{\circ}C$, with an inner reactor pressure of 1.6 atm at 600 Hz and a flow rate of 2 l/min.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.1
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• pp.55-60
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• 2017

Capacitor Charging Power Supply(CCPS) is one of the most important components of a pulsed power system. The CCPS is widely used in source of lasers, accelerators and plasma generators. This paper presents design of a dead time control circuit and operation characteristics for stable high repetition rate of high voltage CCPS. The CCPS consists of battery, high voltage transformer and controller with a dead time control circuit. A dead time control circuit was simulated by PSpice. The performance test of the CCPS was carried out with a 7[nF] load capacitor at output voltage of 50[kV] and a pulse repetition frequency of 100[Hz]. As a result, we can verify that charging and discharging waveform is stable at 100[Hz]. The experiment results indicate that 3[ms] dead time made it possible for stable high repetition rate of 100[Hz]. This paper paves the way for designing an advanced CCPS which is more applicable outside experiments.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.28-29
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• 2006

When photovoltaic module is used for a long time, its performance decreases due to several reasons. In this paper, we focus on the possibilities mainly contributing to the degraded efficiency of the polycrystalline silicon photovoltaic modules. The analysis is based on the modules that have been used for 15 years. These are two main reasons that cause the efficiency degradation, the corrosion and thermal decomposition. The former phenomenon of electrode is mainly due to the moisture from damaged back sheet in some module. However the other reason of the degraded efficiency comes from the thermal decomposition, which can not be observed from the outside but only by experiment. In this study, the comparison between the efficiency of normal modules and degradation modules is presented. Module having degraded cell was seen to cause increase of series resistance by about 80%, in comparison to normal samples efficiency which reduce by about 20%. This study shows that the effects of series resistances on module performance are critical. These effects must be understood and taken into consideration when analyzing performance degradation.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.12
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• pp.943-949
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• 2002

The propagation of the impulse wave discharged from the Inclined exit of a pipe is investigated through shock tube experiment and numerical computations. The pressure histories and directivities of the impulse wave propagating outside from the exit of pipe with several different configurations are analyzed for the range of the incident shock wave Mach number between 1.1 and 1.4. In the shock tube experiments, the impulse waves are visualized by a Schlieren optical system for the purpose of validation of computational work. Computations using the two-dimensional. unsteady, compressible, Euler equations are carried out to represent the experimented impulse waves. Computed Schlieren images predict the experimented impulse waves with a good accuracy. The results obtained show that for the radial direction the peak pressure of the impulse wave discharged depends upon the Inclined angle of the exit of the pipe. but for the axial direction it is almost constant regardless of the inclined angle of the pipe exit.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.10
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• pp.5153-5170
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• 2016

The benefit of the scalability and flexibility inherent in cloud computing motivates clients to upload data and computation to public cloud servers. Because data is placed on public clouds, which are very likely to reside outside of the trusted domain of clients, this strategy introduces concerns regarding the security of sensitive client data. Thus, to provide sufficient security for the data stored in the cloud, it is essential to encrypt sensitive data before the data are uploaded onto cloud servers. Although data encryption is considered the most effective solution for protecting sensitive data from unauthorized users, it imposes a significant amount of overhead during the query processing phase, due to the limitations of directly executing operations against encrypted data. Recently, substantial research work that addresses the execution of SQL queries against encrypted data has been conducted. However, there has been little research on top-k join query processing over encrypted data within the cloud computing environments. In this paper, we develop an efficient algorithm that processes a top-k join query against encrypted cloud data. The proposed top-k join processing algorithm is, at an early phase, able to prune unpromising data sets which are guaranteed not to produce top-k highest scores. The experiment results show that the proposed approach provides significant performance gains over the naive solution.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.11a
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• pp.66-67
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• 2019

Insulated buildings are exposed to the external environment due to aging and construction problems, resulting in a decrease in building energy efficiency. Therefore, the purpose of this paper is to provide a material for the change in thermal conductivity of the insulation when it is exposed to various external environments. In the experiment, five types of heat insulating materials were selected, stored under different environmental conditions, and the thermal conductivity was measured periodically to confirm the change in thermal conductivity. As a result, the thermal conductivity of all the insulating materials except the PF board increased with the passage of time. This is because thermal insulation absorbs atmospheric moisture under all environmental conditions and the thermal conductivity increases, and in the case of thermal insulation stored indoors in environmental conditions, the temperature differs from the thermal insulation stored outside. It is considered that there is little evaporation of moisture absorbed constantly, and the change in thermal conductivity is large.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.2
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• pp.227-232
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• 2021

In this paper, the narrow-band characteristic, which is the disadvantage of the existing the PD sensor, was improved by transforming the sensor shape into a trapezoidal shape to improve the characteristics of the dipole-shaped conventional PD(Patial Discharge) sensor. In addition, by applying a cavity structure, which is a structure that can fundamentally block the electromagnetic wave signal from the outside as it is used for an external sensor, it is a partial discharge sensor that takes advantage of the structural advantages of low cost and convenience of installation. As a result of the experiment, it was shown that there is a broadband characteristic of about 70.5%(1.59~3.32GHz) at the center frequency of 2.45GHz, and the broadband characteristic was confirmed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.5
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• pp.23-29
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• 2018

This study is about the distribution of heat transfer in air conditioning ducts used for marine vessels and oil drilling platforms. As the convective heat transfer coefficient increased, heat transfer was conducted dynamically to inside as it exited to the outlet of duct. The experiment was to determine if the amount of heat transfer generated at the duct exit increased as the convective heat transfer coefficient increased. When the convective heat transfer coefficient was low, the temperature of the duct showed a relatively high temperature difference between the outside and inside of the duct due to the temperature influence of the internal fluid. In case of temperature distribution generated the volume of the duct along the change of the convective heat transfer coefficient, the temperature descended as heat transfer was promoted and the convective heat transfer coefficient increased.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.5
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• pp.123-130
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• 2018

In this study, the optimum design of mold feed systems is determined for plug cover housing (PCH), which is a cover-assembly product that protects the wiring of automobile connectors. The design goal is to achieve the filling balance of the resin in the left and right covers while avoiding the occurrence of weld lines in the hinge as much as possible. For the optimization, an orthogonal array experiment and a main effect analysis of the design factors are performed, and the factors that cause the interactions with the two design characteristics are selected as the design variables. We present some design alternatives, i.e., some combinations of the design variables, and analyze the filling-simulation results, expected molding risk, and cost economics to select an optimum design solution among the design alternatives. In the optimal solution, the weld line is generated at a position outside the hinge, and the filling balance is also acceptable, showing that both design goals can be satisfied simultaneously despite conflicting with each other.