• Journal of Powder Materials
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• v.10 no.2
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• pp.123-128
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• 2003

$TiO_2$ nanopowder was synthesized by chemical vapor condensation (CVC) process and its photocatalytic property depending on microstructure was considered in terns of decomposition rate of organic compound. In order to control microstructure of $TiO_2$ nanopowder such as particle size and degree of agglomeration, precursor flow rate representing number concentration was changed as a process variable. In TEM observation, spherical $TiO_2$ nanoparticles with average size of 20 nm showed gradual increases in particle size and degree of agglomeration with increase of precursor flow rate. Also decomposition rate of organic compound increased with decreasing precursor flow rate. Thus, it was concluded that photocatalytic property was enhanced by targe surface area of disperse $TiO_2$ nanoparticles synthesized at lower precursor flow rate condition in CVC process.

• Restorative Dentistry and Endodontics
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• v.4 no.1
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• pp.29-34
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• 1978

The purpose of this study was to measure penetration of dye stuff(5% Methylene blue, Hematoxylin, Crystal violet and Safranin-O) on silicate cement, Adaptic, Hi-pol and unfilled resin. Each filling material was mixed on the mixing pad and the mixed material was inserted with condensation force of 500gr, 1000gr and 2000gr and without condensation force into preformed glass tube (10mm in diameter and 10mm in height). The specimen was stored in the air for 24 hours, then specimen was immersed in various dye solution (5% methylene blue, hematoxin, crystal violet and safranin-O) for different period of time (l hour and 24 hours). These dye-treated specimen was cut horizontally at the middle portion and the dye penetration in cut surface was measured. Following results were obtained. 1. Pentration of various dye was excessive in silicate cement with and without Condensation force. 2. There has been no evidence of dye penetration in unfilled resin. 3. Dye penetration occurced with in 1 hour period and the extending time didn't affect the dye penetration.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.1
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• pp.99-106
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• 2021

This study explores the improvement of storage environment of igloo-shaped magazine using forced ventilation. Conjugate heat transfer analysis of forced convection and conduction are performed to calculate the flow, temperature, and relative humidity field in igloo-shaped magazine. Through the conjugate heat transfer analysis, the effects of inlet vent, volume flow rates of jet, and jet angles on the condensation and relative humidity are numerically investigated. The area of condensation in igloo-shaped magazine and relative humidity at the surface of ammunitions are then calculated.

• Journal of computational fluids engineering
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• v.11 no.2 s.33
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• pp.8-18
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• 2006

A CFD benchmark calculation for a steam blowdown test was performed for 30 seconds to develop the methodology of numerical analysis for the thermal mixing between steam and subcooled water. In the CFD analysis, the grid model simulating the sparger and the IRWST pool were developed by the axisymmetric condition and then the steam condensation phenomena by a direct contact was modelled by the so-called condensation region model. Thermal mixing phenomenon in the subcooled water tank was treated as an incompressible flow, a free surface flow between the air and the water, a turbulent flow, and a buoyancy flow. The comparison of the CFD results with the test data showed a good agreement as a whole, but a small temperature difference was locally found at some locations. The commercial CFD code of CFX4.4 together with the condensation region model can simulate the thermal mixing behavior reasonably well when a sufficient number of mesh distribution and a proper numerical method are adopted.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.11
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• pp.573-577
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• 2013

An external window directly affects the energy performance of its building. In modern well-insulated buildings, U-values for walls of 0.36 $W/m^2K$ or even lower can be realized. In such buildings, glazing with typical U-value of 2.1 $W/m^2K$ or higher creates thermal weak spots on the facade. The performance of the existing triple glass window has been limited to energy savings and condensation prevention. In this study, the performance of condensation prevention of a vacuum multi-layer glass was analyzed. The final conclusion through mock-up experiments is as follows. The surface temperature of the vacuum multi-layer glass was $2^{\circ}C$ higher, and the temperature difference ratio (TDR) was 0.07 lower, than the corresponding values of the triple glass.

• Journal of Mechanical Science and Technology
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• v.19 no.10
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• pp.1957-1963
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• 2005

In this study, external condensation heat transfer coefficients (HTCs) of six flammable refrigerants of propylene (RI270), propane (R290), isobutane (R600a), butane (R600), dimethylether (RE170), and HFC32 were measured at the vapor temperature of $39^{\circ}C$ on a 1023 fpm low fin and Turbo-C tubes. All data were taken under the heat flux of $32\~116\;and\;42\~142kW/m^2$ for the low fin and Turbo-C tubes respectively. Flammable refrigerants' data obtained on enhanced tubes showed a typical trend that external condensation HTCs decrease with increasing wall subcooling. HFC32 and DME showed up to $30\%$ higher HTCs than those of HCFC22 due to their excellent thermophysical properties. Propylene, propane, isobutane, and butane showed similar or lower HTCs than those of HCFC22. Beatty and Katz' correlation predicted the HTCs of the flammable refrigerants obtained on a low fin tube within a mean deviation of $7.3\%$. Turbo-C tube showed the best performance due to its 3 dimensional surface geometry for fast removal of condensate.

• Nuclear Engineering and Technology
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• v.33 no.2
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• pp.241-253
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• 2001

Under severe accidents, the pressure and temperature response has an important role for the integrity of a nuclear power plant containment. The history of the pressure and temperature is characterized by the amount and state of steam/air mixture in a containment. Recently, the heat transfer rate to the structure surface is supposed to be increased by the wavy interface formed on condensate film. However, in the calculation by using CONTAIN code, the condensation heat transfer on a containment wall is calculated by assuming the smooth interface and has a tendency to be underestimated for safety. In order to obtain the best- estimate heat transfer calculation, we investigated the condensation heat transfer model in CONTAIN 1.2 code and adopted the new forced convection correlation which is considering wavy interface. By using the film tracking model in CONTAIN 1.2 code, the condensate film is treated to consider the effect of wavy interface. And also, it was carried out to investigate the effect of the different cell modelings - 5-cell and 10-cell modeling - for KNGR(Korean Next Generation Reactor) containment phenomena during a severe accident. The effect of wavy interface on condensate film appears to cause the decrease of peak temperature and pressure response . In order to obtain more adequate results, the proper cell modeling was required to consider the proper flow of steam/air mixture.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.7
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• pp.607-616
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• 2002

This study has been conducted to evaluate the applicability of the control method in the dehumidification-integrated radiant floor cooling system in terms of stability of the room air temperature and the control variables through experiments. To do this, the relationship between the control variables in preventing floor surface condensation is first analyzed and the control method is predetermined through simulations. The results are as follows. First, it is necessary to determine the operation status of the dehumidification system according to the relationship between floor surface temperature and dew point temperature in the conditioned space. Second, outdoor reset with indoor temperature feedback control is better than on/off bang-bang control with respect to temperature stability in controlling the room air temperature and the possibility of energy savings. Finally, the humidity sensor can be located with the current thermostat in that there are small differences in absolute humidity in vertical distribution.

• Journal of Environmental Science International
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• v.16 no.6
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• pp.689-698
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• 2007

Mesoporous silicas for heavy metals adsorption were prepared by co-condensation of surfactant as a template and Ludox HS-40 as a silica precursor. Various mesoporous silicas with the introduction of chelating ligands (mercaptopropyl and aminopropyl groups) were synthesized to remove heavy metal ions from aqueous solutions. The surface modification was conducted with a co-condensation process using the sequential or simultaneous addition of mesoporous silica and high concentration of the organosilane(3-mercaptopropyltrimethoxysilane and 3-aminopropyltriethoxysilane). These materials have been characterized by elemental analysis, XRD, SEM and TEM analysis. Adsorbents synthesized with 3-mercaptopropyltrimethoxysilane and 3-aminopropyltriethoxysilane shows a high loading capacity for Hg(II), Pb(II), Cd(II) and anion Cr(VI). Especially the one synthesized with a mercaptopropyl function has the highest adsorption capacity for Hg(II) and Cd(II).

• Carbon letters
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• v.27
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• pp.42-49
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• 2018

A citric acid functionalized graphene oxide nanocomposite was successfully synthesized and the structure and morphology of the nanocatalyst were comprehensively characterized by Fourier transform infrared spectroscopy, energy-dispersive X-ray analysis, X-ray diffraction patterns, atomic force microscopy images, scanning electron microscopy images, transmission electron microscopy images, and thermogravimetric analysis. The application of this nanocatalyst was exemplified in an important condensation reaction to give imidazole derivatives in high yields and short reaction times at room temperature. The catalyst shows high catalytic activity and could be reused after simple work up and easy purification for at least six cycles without significant loss of activity, which indicates efficient immobilizing of citrate groups on the surface of graphene oxide sheets.