• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.42.2-42.2
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• 2011

$TiO_2$ films were modified by adding a glass frit as a light scattering particle and applied to an anode electrode in dye-sensitized solar cells (DSSCs) to enhance the adhesion between $TiO_2$ and fluorine doped transparent oxide (FTO). Low melting point glass frits at contents of (3 to 7wt%) were added to the nano crystalline $TiO_2$ films. The light scattering properties, photovoltaic properties and microstructures of the photo electrodes were examined to determine the role of the low glass transition temperature ($T_g$) glass frit. Electrochemical impedance spectroscopy, Brunauer-Emmett-Teller method and scratch test were conducted to support the results. The DSSC with the $TiO_2$ film containing 3wt% low Tg glass frit showed optimal performance (5.1%, energy conversion efficiency) compared to the $TiO_2$-based one. The photocurrent density slightly decreased by adding 3wt% of the frit due to its large size and non conductivity. However, the decrease of current density followed by the decrease of electron transfer due to the large frit in $TiO_2$ electrode was compensated by the scattering effect, high surface area and reduced the electron transfer impedance at the electrolyte-dye-$TiO_2$ interface. The stability of the photo electrodes was improved by the frit, which chemically promoted the sintering of $TiO_2$ at relatively low temperature ($450^{\circ}C$).

• Journal of the Institute of Convergence Signal Processing
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• v.21 no.4
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• pp.177-182
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• 2020

Interest in heat pumps is increasing as an eco-friendly and energy-saving heating method. In particular, in order to develop a heat pump capable of heating in a low-temperature area, research to prevent frost on the surface of the outdoor unit is increasing. In other words, when heating through a heat pump in a low-temperature area, a frost layer is formed on the surface of the outdoor unit, which lowers the heat transfer performance, thereby reducing the heating capacity. Therefore, in this study, an adsorption-type dehumidification system is attached to remove the moisture vapor of the air into the outdoor unit of the heat pump. It is believed that this study can suggest the most effective dehumidification method in low temperature regions. In addition, it is expected that a heat pump with high energy efficiency can be developed by attaching an adsorption dehumidifying system to the front of the outdoor unit of the heat pump.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.2
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• pp.27-37
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• 2019

The shell and tube heat exchangers installed in the propulsion system test complex (PSTC) at the Naro Space Center heats cryogenic helium to 500 K with a heat transfer oil. As the experimental helium outlet temperature was lower than expected (less than 100 K), the boundary layer effect of the heat transfer oil is predicted to be the cause of the performance deterioration. A computational fluid dynamics (CFD) analysis was performed to verify where the boundary layer effect exists; however, the boundary layer effect has no significant impact on the performance of the heat exchanger. An alternative method to improve the performance of the heat exchanger by changing the heat transfer oil has been discussed in this paper. The low viscosity and high thermal conductivity at high temperature (~500 K) of heat transfer oil at the shell-side are required to improve the thermal performance of the heat exchanger. The experimental performance of the heat exchanger, used to exchange heat between the cryogenic helium and hot heat transfer oil at the PSTC are summarized in this paper.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.4
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• pp.561-575
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• 1996

The interaction of turbulent mixed convection and surface radiation in a three-dimensional channel with the heated blocks is analyzed numerically. Two blocks are maintained at high temperature and the other bottom and horizontal walls are insulated. S-4 method is employed to calculate the effect of the radiative heat transfer. The low Reynolds number k-$\varepsilon$ model proposed by Launder and Sharma is used to estimate the turbulent influence on the heat transfer enhancement. From above modeling, the effects of various channel specifications on the flow and heat transfer characteristics are investigated. The variables used for the present study are Reynolds number, block spacing, the channel height spacing for block and the emissivity. Average Nusselt numbers along the block surfaces are correlated and presented in terms of Reynolds number, emissivity and dimensionless geometric parameters. For the range of conditions in this study, average Nusselt numbers along the block surfaces are strongly influenced by the Reynolds numbers and channel height spacing for block but weakly influenced by the block spacing and the emissivity of the adiabatic walls.

• Journal of the Korean Society of Visualization
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• v.17 no.2
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• pp.58-66
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• 2019

This study investigated heat transfer and flow characteristics of a sweeping jet issued from a rectangular nozzle with a thin plate. A thin vertical aluminum plate was attached on outlet of fluidic oscillator to increase velocity of central area with Coanda effect and enhance heat transfer performance. From visualization and PIV experiments, sweeping jet with a thin plate has larger velocity distribution in center region than that of the normal sweeping jet while oscillating frequency is similar as the normal one. Thermographic phosphor thermometry method was used to visualize the temperature field and Nu distribution of plate with impinging sweeping jet with thin plate. Four Reynolds numbers and three jet-to-wall distances were selected as parameters. It is found that heat transfer performance in the low jet-to-wall spacing was enhanced as the cooled area was expanded. However, when the jet-to-wall spacing became greater than 8dh, heat transfer performance became similar due to reduced impinging velocity.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.5
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• pp.713-723
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• 1986

The purpose of this research was to study the heat transfer characteristics of heat pipe which used non-metallic(SiO$_{2}$), circumferential wick and meshed slab wick as ADI method and experimental results. Compared wick experimental data and results by ADI method showed the good agreement and ADI method was utilized in pridicting the performance of heat pipe. Also, ADI method was applied to predict heat pipe performance according to the various volume ratios of metallic bond. The heat transfer characteristics of heat pipe could be predicted by heat flux and superheat term below the maximum heat flux limit. According to the addition ratio of metallic bond, heat transfer ratio could be improved as 2-3 times and when heat conductivity ratio(K$_{b}$/K$_{a}$) was increased at 4-12 ratio, heat transfer was in creased as 1.7-2.4 times, and the prediction of heat transfer could be show as exponential type. In producting non-metallic wick used to low heat pipe, metallic bond which is the conductivity of good quality and enduring for high temperature will be improved as in important problem.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.3
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• pp.223-231
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• 2005

When test tubes for PCM with melting point lower than a room temperature are installed vertically as the T-history method proposes, there exists a temperature distribution in the longitudinal direction by natural convection, which lowers the precision of measured heat-of-fusion. The purpose of the present work is to improve the precision by arranging the test tubes horizontally, while maintaining the simplicity and convenience. Assuming that the amount of heat transfer is very small through the vapor space formed in the upper part of the tubes by volumetric change, the obtained value by the T-history method using the latent heat period bounded by two inflection points is in good agreement with that of the literature. Also, the scattering of measured values by the proposed method decreases markedly compared to that of vertical positioning.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.5
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• pp.653-659
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• 2001

This paper is concerned with the development of a new method for making and separating ice in-water and saving floated ice by installing an evaporation panel in an ice storage tank. The new method shows very good heat transfer efficiency than that of the convectional method. It is because the evaporation panel is directly contacted with water in the storage tank. The experiments were performed by varying inlet and outlet refrigerant temperatures of its evaporator. From the experimental results, the operating characteristics of in-water harvest-type ice storage system were investigated by measuring temperature and pressure at each point of the ice storage system and power required to operating compressor respect to the changes of the inlet and outlet refrigerant temperature of evaporator. It can be think that defrost frequency decreased and heavy ice created as the refrigerant temperature of evaporator outlet and defrost setting temperature is low so gotten result can effect to release efficiency. Also, consumption power, condensing heat quantity, refrigerating capacity and performance efficiency decreased as time goes by. Therefore, these results provide the basic data for system optimization, performance improvement and the possibility of application to other fields.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.290.2-290.2
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• 2016

Recently, organic thin-film transistors have been widely researched for organic light-emitting diode panels, memory devices, logic circuits for flexible display because of its virtue of mechanical flexibility, low fabrication cost, low process temperature, and large area production. In order to achieve high performance OTFTs, increase in accumulation carrier mobility is a critical factor. Post-fabrication thermal annealing process has been known as one of the methods to achieve this by improving the crystal quality of organic semiconductor materials In this paper, we researched the properties of pentacene films with X-Ray Diffraction (XRD) and Atomic Force Microscope (AFM) analyses as different annealing temperature in N2 ambient. Electrical characterization of the pentacene based thin film transistor was also conducted by transfer length method (TLM) with different annealing temperature in Al- and Ti-pentacene junctions to confirm the Fermi level pinning phenomenon. For Al- and Ti-pentacene junctions, is was found that as the surface quality of the pentacene films changed as annealing temperature increased, the hole-barrier height (h-BH) that were controlled by Fermi level pinning were effectively reduced.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 1999.02a
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• pp.173-176
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• 1999

Vacuum insulated pipes (VIP) are one of the important equipments for cryogenic fluids' transfer. Flange type of VIP, which can easily be installed at the site, uses a set of male and female bayonet with very small gap between them. In order to prevent leakage of liquid from inner pipe to bayonet. Teflon or Kel-F is located outside both the inner pipe of male and the guide of female. Even though liquid may leak at room temperature, it cannot leak at cryogenic temperature since Teflon shrinks much more than pipes and adheres closely to the inner pipe and guide. Teflon seal method has the advantage of easy fabrication, low cost and effective sealing compared to the conventional method.