Dong Wook Jerng

Toluene and acetaldehyde removal from air on to graphene-based adsorbents with microsized pores

Volatile organic compound (VOC) gases can cause harm to the human body with exposure over the long term even at very low concentrations (ppmv levels); thus, effective absorbents for VOC gas removal are an important issue. In this study, accordingly, graphene-based adsorbents with microsized pores were used as adsorbents to remove toluene and acetaldehyde gases at low concentrations (30ppm). Sufficient amounts of the adsorbents were prepared for use on filters and were loaded uniformly at 0.1-0.5g on a 50×50mm2 area, to evaluate their adsorption features with low gas concentrations. The morphology and chemical composition of the adsorbents were characterized using scanning electron microscopy, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and Raman spectroscopy. Microwave irradiation and heat treatment near 800°C under KOH activation resulted in enlargement of the pristine graphene surface and its specific surface area; maximum volume capacities of 3510m3/g and 630m3/g were observed for toluene and acetaldehyde gas. The high removal efficiency for toluene (98%) versus acetaldehyde (30%) gas was attributed to π-π interactions between the pristine graphene surface and toluene molecules.

Visual study of ex-pin phenomena for SFR with metal fuel under initial phase of severe accidents by using simulants

ABSTRACT In the present Korean sodium-cooled fast reactor (SFR) program, early dispersion of the molten metal fuel within a subchannel is suggested as an inherent safety strategy in the initiating phase of a hypothetical core disruptive accident (HCDA). This safety strategy provides a negative reactivity driven by the melt dispersion; therefore, it could reduce the possibility of occurrence of a severe recriticality event. In the initiating phase, the melt could be injected into the subchannel horizontally by the internal pressure of the fuel pin. Complex phenomena occur during intermixing of the melt with the coolant after the horizontal injection of the melt. It is rather difficult to understand the several combined mechanisms that occur that are related to the dispersion and fragmentation of the melt. Thus, it seems worthwhile to study the horizontal injection of melt at lower temperatures, which could help to observe the dispersion phenomenon and understand the fragmentation mechanism. In this work, for a parametric study, tests were performed under structural conditions, coolant void conditions, and boiling conditions. As a result, in some cases, the injected molten materials were stuck around the injection hole. On the other hand, the molten materials were dispersed upward sufficiently well under the boiling condition when R123 was used as the coolant. The built-up vapor pressure was found to be one of the driving forces for the upward dispersion of the molten materials.

Dynamic Leidenfrost temperature on micro-textured surfaces: Acoustic wave absorption into thin vapor layer

The dynamic Leidenfrost phenomenon is governed by three types of pressure potentials induced via vapor hydrodynamics, liquid dynamic pressure, and the water hammer effect resulting from the generation of acoustic waves at the liquid-vapor interface. The prediction of the Leidenfrost temperature for a dynamic droplet needs quantitative evaluation and definition for each of the pressure fields. In particular, the textures on a heated surface can significantly affect the vapor hydrodynamics and the water hammer pressure. We present a quantitative model for evaluating the water hammer pressure on micro-textured surfaces taking into account the absorption of acoustic waves into the thin vapor layer. The model demonstrates that the strength of the acoustic flow into the liquid droplet, which directly contributes to the water hammer pressure, depends on the magnitude of the acoustic resistance (impedance) in the droplet and the vapor region. In consequence, the micro-textures of the surface and the increased spacing between them reduce the water hammer coefficient ( kh) defined as the ratio of the acoustic flow into the droplet to total generated flow. Aided by numerical calculations that solve the laminar Navier-Stokes equation for the vapor flow, we also predict the dynamic Leidenfrost temperature on a micro-textured surface with reliable accuracy consistent with the experimental data.The dynamic Leidenfrost phenomenon is governed by three types of pressure potentials induced via vapor hydrodynamics, liquid dynamic pressure, and the water hammer effect resulting from the generation of acoustic waves at the liquid-vapor interface. The prediction of the Leidenfrost temperature for a dynamic droplet needs quantitative evaluation and definition for each of the pressure fields. In particular, the textures on a heated surface can significantly affect the vapor hydrodynamics and the water hammer pressure. We present a quantitative model for evaluating the water hammer pressure on micro-textured surfaces taking into account the absorption of acoustic waves into the thin vapor layer. The model demonstrates that the strength of the acoustic flow into the liquid droplet, which directly contributes to the water hammer pressure, depends on the magnitude of the acoustic resistance (impedance) in the droplet and the vapor region. In consequence, the micro-textures of the surface and the increased spa...

Prediction of creep crack initiation and growth for P91 at 600°C using MOD-NSW model

In this paper, predictions of creep crack initiation times and growth rates using the NSW-MOD model are compared with experimental data for the parent and weld metals of P91 at 600°C. For the weld metal, creep crack growth rates are found to be bounded by upper and lower bounds of the predictions, but creep crack initiation times are close to the upper bound. For the parent material, creep crack growth rates are bounded by upper and lower bounds of the predictions using the minimum creep rates, but creep crack initiation times are bounded by those using the average creep rates.

Experimental Study of Molten Wood's Metal Jet Breakup in Subcooled Water

Abstract The liquid jet breakup has been studied in the areas such as aerosols, spray and combustion. The breakup depends on sev-eral physical parameters such as the jet velocity, the nozzle inner diameter, and the density ratio of the water to the jet. Thispaper deals with characteristics of the jet breakup according to the jet velocity and the nozzle diameter. In order to consideronly hydrodynamic factors, all the experiments were conducted in non-boiling conditions. The jet behavior in the water poolwas observed by high-speed camera and PIV technique. For the condition of the inner diameter of 6.95 mm and the jetvelocity of 2.8 m/s, the debris size of 22 mm gave the largest mass fraction, 39%. For higher jet velocity of 3.1 m/s, thedebris size of 14 mm gave the largest mass fraction, 36%. For the nozzle with inner diameter of 9.30 mm, the debris sizedistribution was different. For jet velocity of 2.8 m/s and 3.1 m/s, the debris size with the largest mass fraction was foundto be 14 mm. It was identified that the debris size decreased as the diameter or the jet velocity increased.