• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.8
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• pp.4809-4814
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• 2014

The aim of the present study was to estimate the prediction performance of a FDS (Fire Dynamic Simulator) to simulate the fire behaviors and suppression characteristics by operating a water-mist. Rosin-Rammler/log-normal distribution function was used to determine the initial droplet distribution of water-mist and the effects of its model constant were considered. In addition, the simulation models were validated by a comparison of the predicted fire suppression characteristics with water-mist injection pressures to the previous experiments, and the thermal flow behaviors and gaseous concentration variations were analyzed. The results showed that water-mists with the same mean diameter were affected by the characteristics of the droplet size distribution, which have different size and velocity distributions at the downstream location. The fire simulations conducted in this study determine the initial droplet size distribution tuned to the base of the spray characteristics measured by previous experiments. The simulation results showed good agreement with the previous measurements for temperature variations and fire suppression characteristics. In addition, it was confirmed that the FDS simulation with a water-mist operation supplies useful details on estimations of the thermal flow fields and gaseous concentration under water mist operation conditions.

• The Journal of Advanced Prosthodontics
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• v.4 no.3
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• pp.139-145
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• 2012

PURPOSE. To evaluate the shear bond strength of resin luting agent to dentin surfaces cleansed with different agents like pumice, ultrasonic scaler with chlorhexidine gluconate, EDTA and the influence of these cleansing methods on wetting properties of the dentin by Axisymmetric drop Shape Analysis - Contact Diameter technique (ADSA-CD). MATERIALS AND METHODS. Forty coronal portions of human third molar were prepared until dentin was exposed. Specimens were divided into two groups: Group A and Group B. Provisional restorations made with autopolymerizing resin were luted to dentin surface with zinc oxide eugenol in Group A and with freegenol cement in Group B. All specimens were stored in distilled water at room temperature for 24 hrs and provisional cements were mechanically removed with explorer and rinsed with water and cleansed using various methods (Control-air-water spray, Pumice prophylaxis, Ultrasonic scaler with 0.2% Chlorhexidine gluconate, 17% EDTA). Contact angle measurements were performed to assess wettability of various cleansing agents using the ADSA-CD technique. Bond strength of a resin luting agent bonded to the cleansed surface was assessed using Instron testing machine and the mode of failure noted. SEM was done to assess the surface cleanliness. Data were statistically analyzed by one-way analysis of variance with Tukey HSD tests (${\alpha}$=.05). RESULTS. Specimens treated with EDTA showed the highest shear bond strength and the lowest contact angle for both groups. SEM showed that EDTA was the most effective solution to remove the smear layer. Also, mode of failure seen was predominantly cohesive for both EDTA and pumice prophylaxis. CONCLUSION. EDTA was the most effective dentin cleansing agent among the compared groups.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.3
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• pp.1-7
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• 2003

In this research, it is intended to measure shape of the nozzle throat of the KL-3 engine, which is the main engine of the KSR-III rocket. For the purpose, an image-based method was invented to replace the 3D pointer, which is actually inaccessible to such large scale engines. As a result, our equipment showed satisfactory Performances. Analysing the results of experiments, we find that the pattern of ablation is determined by the spray pattern and that the process of thermal ablation phenomena can be categorized in three regimes - the first regime that the shape of nozzle throat is maintained and ablation is negligible, the second regime that saw-tooth form is developed and ablation is accelerated, and the third regime that the saw-tooth form is already established and the growth of ablation rate is reduced Also, we find that the ratio of area increase after 60 seconds combustion is +5.82% and conclude that the ratio is acceptable and satisfactory.

• Corrosion Science and Technology
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• v.19 no.2
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• pp.82-88
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• 2020

This work examined the corrosion protection performance of benzoate loaded hydrotalcite/graphene oxide (HT/GO-BZ) for carbon steel. HT/GO-BZ was fabricated by the co-precipitation method and characterized by infrared spectroscopy, X-ray diffraction, and scanning electronic microscopy. The corrosion inhibition action of HT/GO-BZ on carbon steel in 0.1 M NaCl solution was evaluated by electrochemical measurements. The benzoate content in HT/GO-BZ was determined by UV-Vis spectroscopy. Subsequently, the effect of HT/GO-BZ on the corrosion resistance of the water-based epoxy coating was investigated by the salt spray test. The obtained results demonstrated the intercalation of benzoate and GO in the hydrotalcite structure. The benzoate content in HT/GO-BZ was about 16%. The polarization curves of the carbon steel electrode revealed anodic corrosion inhibition activity of HT/GO-BZ and the inhibition efficiency was about 95.2% at a concentration of 3g/L. The GO present in HT/GO-BZ enhanced the inhibition effect of HT-BZ. The presence of HT/GO-BZ improved the corrosion resistance of the waterborne epoxy coating.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.66-70
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• 2006

Magnetite nanoparticles, which have been extensively used in many fields, were encapsulated with a natural polymer, chitosan, to improve their biocompatibility. We have synthesized magnetite $(Fe_3C_4)$ nanoparticles using chemical coprecipitation technique with sodium oleate as surfactant. Nanoparticle size can be varied from 1.2 to 7.4nm by controlling the sodium oleate concentration. Magnetite phase nanoparticles could be observed from X-ray diffraction. Magnetic colloid suspensions containing particles with sodium oleate and chitosan have been prepared. High magnetic property chitosan-microsphere particles were prepared from oleate-coated magnetite suspension using spray method. The surftce, and tile morphology of the magnetic chitosan microsphere particles were characterized using optical microscope and scanning electron microscope. Magnetic hysteresis measurement were performed using a superconducting quantum interference device (SQUID) magnetometer at room temperature to investigate the magnetic properties of the chitosan microspheres including magnetite nanoparticles. The SQUID measurements revealed superparamagnetism of nanoparticles.

• Korean Journal of Human Ecology
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• v.17 no.5
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• pp.1001-1013
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• 2008

The purpose of this study were to make clear the actual state of indoor air quality by cooling in private institute classrooms and to analyze influencing factors on indoor air quality. The measurements of physical elements and observations of architectural characteristics and living conditions were carried out in each 1 classroom of 5 private institutes. Measuring elements were indoor temperature, relative humidity, $PM_{10}$, HCHO, CO, and $CO_2$ concentration. As results, the averages of indoor temperature each classroom were $21.7\sim28.1^{\circ}C$. 3 classrooms were lower than the Maintenance standard($26\sim28^{\circ}C$) of School Health Law. The means of relative humidity were 48$\sim$63%, all classrooms were ranged within the standard(30$\sim$80%). The means of $PM_{10}$ concentration were 2.1 $\sim$ 17 $\mu g/m^3$, all classrooms were kept within the standard(100 $\mu g/m^3$). The means of HCHO concentration were 0.02$\sim$0.16 ppm, 2 classrooms were exceed the standard(0.1 ppm). The means of CO concentration were 1.4$\sim$3.6 ppm, all classrooms were kept within the standard(10ppm). The means of $CO_2$ concentration were 1,593$\sim$3,819 ppm, all classrooms were exceed the standard(1,000ppm). The results of analysis on influencing factors of the physical elements are as follow; the air conditioner set of temperature, personal necessities like hair spray, teacher's smoking in corridor, windows and doors opening time, the number of students, and volume of classroom.

• Journal of Environmental Health Sciences
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• v.36 no.3
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• pp.236-246
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• 2010

In preparative anti-corrosive coating experiments, polyaniline was obtained by reacting an oxidizing agent with the monomer aniline. Further, the primer coating was prepared using a variety of widely-used materials such as urethane resin. For the top coating, epoxy resin and acrylic urethane resin were used. Characteristics of the coatings were assessed according to KS and ASTM specifications, and the structure of the polyaniline was characterized using FT-IR and TGA. For analysis of anti-corrosive properties in salt-spray experiments, measurements of the oxidation state of iron and surface atomic analysis were conducted using XPS and SEM-EDX. Unlike general anti-corrosive coatings which exhibit anti-corrosive effects only as a primer coating, the anti-corrosive coatings using polyaniline as the anti-corrosive pigment showed a marked synergistic effect with the top coatings. In other words, the top coatings not only produce a fine view effect, but also increase, through interaction with the primer coatings, the resistance to diffusion of corrosive factors from the external environment. It was also found that, unlike the heavy metal oxide-forming layer of the passive barrier alone, the polyaniline anti-corrosive pigment oxidized iron at the interface with the iron substrate to form a passive barrier in the oxidic layer, and itself formed a potential barrier layer with anti-corrosive factors from the external environment. Although the passive layer was damaged, the damaged area did not become completely oxidized iron; on the contrary, it showed a tendency to reduction. This can be interpreted such that a passive layer is formed again on the damaged area, and that at the same time there is a tendency to self-healing.

• The Journal of Advanced Prosthodontics
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• v.7 no.2
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• pp.85-92
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• 2015

PURPOSE. This study aimed to investigate the efficacy of cleaning solutions on saliva-contaminated zirconia in comparison to air-abrasion in terms of resin bonding. MATERIALS AND METHODS. For saliva-contaminated air-abraded zirconia, seven cleaning methods)-no contamination (NC), water-spray rinsing (WS), additional air-abrasion (AA), and cleaning with four solutions (Ivoclean [IC]; 1.0 wt% sodium dodecyl sulfate [SDS], 1.0 wt% hydrogen peroxide [HP], and 1.0 wt% sodium hypochlorite [SHC])-were tested. The zirconia surfaces for each group were characterized using various analytical techniques. Three bonded resin (Panavia F 2.0) cylinders (bonding area: $4.5mm^2$) were made on one zirconia disk specimen using the Ultradent jig method [four disks (12 cylinders)/group; a total of 28 disks]. After 5,000 thermocycling, all specimens were subjected to a shear bond strength test with a crosshead speed of 1.0 mm/minute. The fractured surfaces were observed using an optical and scanning electron microscope (SEM). RESULTS. Contact angle measurements showed that groups NC, AA, IC, and SHC had hydrophilic surfaces. The X-ray photoelectron spectroscopy (XPS) analysis showed similar elemental distributions between group AA and groups IC and SHC. Groups IC and SHC showed statistically similar bond strengths to groups NC and AA (P>.05), but not groups SDS and HP (P<.05). For groups WS, SDS, and HP, blister-like bubble formations were observed on the surfaces under SEM. CONCLUSION. Within the limitations of this in vitro study, some of the cleaning solutions (IC or SHC) were effective in removing saliva contamination and enhancing the resin bond strength.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.2
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• pp.166-174
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• 2009

The liquid column trajectory and column breakup length characteristics have been experimentally studied in angled jets injected into subsonic crossflow. Pulsed shadowgraph photography and Planar Liquid Laser Induced Fluorescence measurements were used to determine the angled effects. And the main objectives of this research are to get a empirical formula of liquid column trajectory and breakup length with below the $90^{\circ}$ degree injection angle conditions, and were compared with previous results. It was also found that the empirical formula, which reversed injection conditions of air stream. As the result, This has been shown that liquid column trajectories and column breakup length were spatially dependent on various injection angle, normalized injector exit diameter, air-stream and fuel injection velocity. Furthermore, the empirical formula of liquid column trajectories and breakup length has been some different of drag coefficient results between normal angled injection and reversed injection in subsonic crossflow.

• International Journal of Automotive Technology
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• v.6 no.5
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• pp.437-444
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• 2005

Unburned hydrocarbon (UBHC) emissions from gasoline engines remain a primary engineering research and development concern due to stricter emission regulations. Gasoline engines produce more UBHC emissions during cold start and warm-up than during any other stage of operation, because of insufficient fuel-air mixing, particularly in view of the additional fuel enrichment used for early starting. Impingement of fuel droplets on the cylinder wall is a major source of UBHC and a concern for oil dilution. This paper describes an experimental study that was carried out to investigate the distribution and 'footprint' of fuel droplets impinging on the cylinder wall during the intake stroke under engine starting conditions. Injectors having different targeting and atomization characteristics were used in a 4-Valve engine with optical access to the intake port and combustion chamber. The spray and targeting performance were characterized using high-speed visualization and Phase Doppler Interferometry techniques. The fuel droplets impinging on the port, cylinder wall and piston top were characterized using a color imaging technique during simulated engine start-up from room temperature. Highly absorbent filter paper was placed around the circumference of the cylinder liner and on the piston top to collect fuel droplets during the intake strokes. A small amount of colored dye, which dissolves completely in gasoline, was used as the tracer. Color density on the paper, which is correlated with the amount of fuel deposited and its distribution on the cylinder wall, was measured using image analysis. The results show that by comparing the locations of the wetted footprints and their color intensities, the influence of fuel injection and engine conditions can be qualitatively and quantitatively examined. Fast FID measurements of UBHC were also performed on the engine for correlation to the mixture formation results.