• Progress in Superconductivity and Cryogenics
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• v.16 no.1
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• pp.36-41
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• 2014

Since glass microsphere has high crush strength, low density and small particle size, it becomes alternative thermal insulation material for cryogenic systems, such as storage and transportation tank for cryogenic fluids. Although many experiments have been performed to verify the effective thermal conductivity of microsphere, prediction by calculation is still inaccurate due to the complicated geometries, including wide range of powder diameter distribution and different pore sizes. The accurate effective thermal conductivity model for microsphere is discussed in this paper. There are four mechanisms which contribute to the heat transfer of the evacuated powder: gaseous conduction ($k_g$), solid conduction ($k_s$), radiation ($k_r$) and thermal contact ($k_c$). Among these components, $k_g$ and $k_s$ were calculated by Zehner and Schlunder model (1970). Other component values for $k_c$ and $k_r$, which were obtained from experimental data under high vacuum conditions were added. In this research paper, the geometry of microsphere was simplified as a homogeneous solid sphere. The calculation results were compared with previous experimental data by R. Wawryk (1988), H. S. Kim (2010) and the experiment of this paper to show good agreement within error of 46%, 4.6% and 17 % for each result.

• Membrane and Water Treatment
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• v.13 no.5
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• pp.235-243
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• 2022

The paper presents the effect of operating temperatures and flow rates on the distillate flux that can be obtained from a hydrophobic membrane having the characteristics: pore size of 0.15 ㎛; thickness of 130 ㎛; and 85% porosity. That membrane in the present investigation could be the direct contact (DCMD) or the air-gap membrane distillation (AGMD). To model numerically the membrane distillation processes, the two-dimensional computational fluid dynamic (CFD) is used for the DCMD and AGMD cases here. In this work, DCMD and AGMD models have been validated with the experimental data using different flows (Parallel and Counter-current flows) in non-steady-state situations. A good agreement is obtained between the present results and those of the experimental data in the literature. The new approach in the present numerical modeling has allowed examining effects of the nature of materials (Polyvinylidene fluoride (PVDF) polymers, copolymers, and blends) used on thermal properties. Moreover, the effect of the area surface of the membrane (0.021 to 3.15 ㎡) is investigated to explore both the laminar and the turbulent flow regimes. The obtained results found that copolymer P(VDF-TrFE) (80/20) is more effective than the other materials of membrane distillation (MD). The mass flux and thermal efficiency reach 193.5 (g/㎡s), and 83.29 % using turbulent flow and an effective area of 3.1 ㎡, respectively. The increase of feed inlet temperatures and its flow rate, with the reduction of cold temperatures and its flow rate are very effective for increasing distillate water flow in MD applications.

• Journal of the Korean GEO-environmental Society
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• v.17 no.2
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• pp.31-39
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• 2016

Vertical drain has usually been used to accelerate the consolidation of soft clay deposits with high moisture content. Busan thick clay deposits are subjected to artesian pressure from an aquifer in sand and gravel layers. However, effect of artesian pressure existing in drainage-installed soft ground on consolidation behaviors is not well known. This paper investigates the consolidation behavior of drainage-installed soft ground at the Nakdong river estuary with artesian pressure and without artesian pressure. A series of one-dimensional large size column test was carried out to find out the consolidation characteristics of clay. Test results indicated that total settlement of clay with artesian pressure was higher than that without artesian pressure because effective stress decreased due to upward flow. Dissipation rate of excess pore water pressure delayed and excess pore water pressure did not fully dissipate in clay layer with artesian pressure. Undrained shear strength of clay ground with artesian pressure was lower than that without artesian pressure.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.42 no.1
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• pp.7-12
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• 2010

Morphological characteristics of hemp fiber were investigated using a light microscope in order to provide fundamental data for the use of hemp as a papermaking law material. Phloem of hemp is composed of cortical parenchyma cells and bast fiber with thick walls while xylem is composed of vessel, wood fiber and ray parenchyma cells. Also there are solitary pore and radial pore multiple which exist in diffuse porous pattern. Ray cells consist of uniseriate rays and thin walled ray parenchyma cells. Wood fibers are composed of three types: a large diameter fiber with longer length; a large diameter fiber with shorter length; a small diameter fiber with medium length. Vessel elements are composed of: a medium length one; a longer length one; the one whose both end walls have ligules or tails. Parenchyma cells in xylem and pit parenchyma cells have completely different size and shape. For bast fiber, the average length is about 4.4 mm and the width is about $30.5\;{\mu}m$; for vessel element, $600.0\;{\mu}m$ in length and $493.6\;{\mu}m$ in width; for wood fiber, $1000\;{\mu}m$ and $38.9\;{\mu}m$; for parenchyma cell, $50\;{\mu}m$ and $26.4\;{\mu}m$.

• Journal of Microbiology and Biotechnology
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• v.16 no.12
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• pp.1968-1976
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• 2006

Recombinant E. coli ACV 1003 (recA:: lacZ) was used to measure low concentrations of DNA-damaging chemicals, which produce $\beta$-galactosidase via an SOS regulon system. Very low $\beta$-galactosidase activities of less than 0.01 unit/ml, $\beta$-galactosidase produced through an SOS response corresponding to the 10 ng/ml (ppb) of DNA damaging chemicals in the environment, can be rapidly determined by using an alternative interferometric biosensor with optically flat thin films of porous silicon rather than by the conventional time-consuming Miller's enzyme assay as well as the ELISA method. fu order to enhance the sensitivity in the interferometry, it needs to obtain more uniform distribution and higher biolinking efficiency, whereas interferometric sensing is rapid, cheap, and advantageous in high throughput by using a multiple-well-type chip. In this study, pore size adjusted to 60 nm for the target enzyme $\beta$-galactosidase to be bound on both walls of a Si pore and a calyx crown derivative was apllied as a more efficient biolinker. Furthermore, anti-$\beta$-galactosidase was previously functionalized with the biolinker for the target $\beta$-galactosidase to be specifically bound. When anti-$\beta$-galactosidase was bound to the calyx-crown derivative-linked surface, the effective optical thickness was found to be three times as high as that obtained without using anti-$\beta$-galactosidase. The resolution obtained was very similar to that afforded by the time-consuming ELISA method; however, the reproducibility was still unsatisfactory, below 1 unit $\beta$-galactosidase/ml, owing to the microscopic non-uniform distribution of the pores in the etched silicon surface.

• Journal of Electrochemical Science and Technology
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• v.6 no.4
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• pp.139-145
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• 2015

Capacitive deionization (CDI) process is a novel approach for desalination of an aqueous salt solution. In the present study, an activated carbon cloth (ACC) is proposed as effective electrode material. Initially the carbon cloth was activated in 1 M and 8 M HNO₃ for 9 hours at room temperature. The untreated and chemically activated carbon cloth (ACC) electrode materials were subjected to BET surface area measurements in order to get information about their specific surface area, average pore size, total pore volume and micropore area. The above materials were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM) also. The electrochemical studies for the electrodes were done using cyclic voltammetry (CV) in 0.1 M Na₂SO₄ medium. From the studies, it was found that resistivity of the activated carbon cloth electrodes (treated in 1 M and 8 M HNO₃) was decreased significantly by the chemical oxidation in nitric acid at room temperature and its capacitance was found to be 90 F/g (1 M HNO₃) and 154 F/g (8 M HNO₃) respectively in 0.1 M Na₂SO₄ solution. The capacitive deionization behavior of a single cell CDI with activated carbon cloth electrodes was also studied and reported in this work.

• Journal of Electrochemical Science and Technology
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• v.2 no.3
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• pp.131-135
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• 2011

It is, in general, believed that during the activation process, the proton conductivity increases due to wetting effect and the electrochemical resistance reduction, resulting in an increase in the fuel cell performance with time. However, until now, very scant information is available on the understanding of activation processes. In this study, dominant variables that effect on the performance increase of membrane electrode assemblies (MEAs) during the activation process were investigated. Wetting, pore restructuring and active metal utilization were analyzed systematically. Unexpectedly, the changes for both ohmic and reaction resistance characterized by the electrochemical impedance spectroscopy (EIS) after initial wetting process were much smaller when considering the degree of cell performance increases. However, the EIS spectra represents that the pore opening of electrode turns into gas transportable structure more easily. The increase in the performance with activation cycles was also investigated in a view of active metals. Though the particle size was grown, the number of effective active sites might be exposed more. The impurity removal and catalytic activity enhancement measured by cyclic voltammetry (CV) could be a strong evident. The results and analysis revealed that, not merely wetting of membrane but also restructuring of electrodeand catalytic activity increase are important factors for the fast and efficient activation of the polymer electrolyte fuel cells.

• Applied Chemistry for Engineering
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• v.22 no.2
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• pp.209-213
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• 2011

Hydrophobic silica aerogel beads with low thermal conductivity and high porosity were prepared using a cost-effective sodium silicate as a silica source via an ambient-pressure drying process. Monolithic wet gels were first prepared by adjusting pH (~5) of a diluted sodium silicate solution. The silica aerogel beads (0.5~20 mm) were manufactured by breaking the wet gel monoliths under a simultaneous solvent exchange/surface modification process and an ambient-pressure drying process without using co-precursors or templates. Dried silica aerogel beads exhibit a comparable porosity ($593m^2/g$ of surface area, 34.9 nm of pore size, and $4.4cm^3/g$ of pore volume) to that of the aerogel powder prepared in the same conditions. Thermal conductivity of the silica aerogel beads (19.8 mW/mK at $20^{\circ}C$) is also identical to the aerogel powder.

• Journal of the Korean Wood Science and Technology
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• v.38 no.2
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• pp.149-158
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• 2010

Organosolv pretreatments which utilized sulfuric acid, sodium hydroxide and ammonia as catalysts were conducted to screen the effective catalyst for organosolv pretreatment of Liriodendron tulipifera. The enzymatic hydrolysis was achieved effectively with sulfuric acid (74.2%) and sodium hydroxide (63.7%). They were thus considered as effective catalysts for organosolv pretreatment of L. tulipifera. The organosolv pretreatments with sulfuric acid and sodium hydroxide showed a different behavior on the reaction mechanism. The pretreatment with sulfuric acid increased the biomass roughness and pore numbers. On the other hand, the pretreatment with sodium hydroxide enhanced the surface area due to the size reduction and minor defiberization which were caused by hemicellulose degradation at an initial stage and more defiberization by lignin degradation at a later stage. The organosolv pretreatment with sodium hydroxide was performed at several different conditions to evaluate effectiveness of sodium hydroxide as a catalyst for organosolv pretreatment. According to the results of enzymatic digestibility, the changes of chemical composition and the morphological analysis of pretreated biomass, it was suggested that the pretreatment time impacted primarily on enzymatic hydrolysis. Increase in surface area during the pretreatment was a major cause for improvement in enzymatic digestibility when sodium hydroxide was used as a catalyst.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2142-2147
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• 2007

Experimental study was conducted to evaluate the performance of a miniature loop heat pipe (MLHP) with non-inverted meniscus type capillary structure. All parts of MLHP in this study were made of copper including the capillary structure and the distilled water was used as a working fluid of MLHP. The outer diameter of evaporator was 9 mm and its length was 119 mm. The effective pore size of the capillary structure was 30 micron and its porosity was 60%. The vapor transport line, the liquid transport line and the condenser were consisted of single 4.0 mm copper tube. The distance between the evaporator and the condenser region was 200 mm and the length of the loop was 969 mm. This MLHP was operated successfully at any orientation but the gravity highly influenced the thermal performance of the MLHP. The maximum thermal load was 130 watts at the bottom heat mode and the 20 watts at the top heat mode.