• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.9
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• pp.799-805
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• 2013

An analytical study is conducted to assess the efficiency of a flat-plate solar collector using nanofluids. The nondimensionalized 2D heat diffusion equation is solved by assuming a wavelength-independent extinction coefficient and intensity to obtain the analytical solution of the temperature distribution in the flat-plate solar collector. The dimensionless temperature distribution is investigated as functions of the volume fraction of the nanofluids, magnitude of heat loss, and collector's depth based on the analytical solution when using water-based single-walled carbon nanohorn (SWCNH) nanofluids as a working fluid. Finally, the efficiency of the flat-plate solar collector using the nanofluids is predicted and compared with that of the conventional solar collector. The results indicate that the efficiency of the nanofluid solar collector is better than that of the conventional solar collector under specific geometrical conditions.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.377-382
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• 2001

Mechanical behavior and electrical resistance change of CPDP (carbon particle dispersed plastic) composite consisting of epoxy resin and conductive carbon particle were investigated under monotonic loading and repeated loading-unloading. The electrical resistance almost linearly increased with increasing strain during loading and the residual electrical resistance was observed even after removing load. The value of the residual electrical resistance was dependent on the maximum strain under the applied stress. This result suggests that the estimation of maximum strain (i.e., damage) is possible by the measuring electrical resistance of composite. The behavior of electrical resistance change during and after loading was discussed on the basis of the results of microscopic deformation and fracture observation. Moreover, the relationship between the volume fraction of carbon particle and the electrical resistivity of CPDP was investigated in relation to the percolation theory. Simulation model of percolation structure was established by Monte Carlo method and the simulation result was compared to the experimental results. The electrical resistance change under applied loading was analyzed quantitatively using the percolation equation and a simple model for the critical volume fraction of carbon particle as a function of the mechanical stress. It was revealed that the prediction was in good agreement with the experimental result except in the region near the failure of material.

• Korean Journal of Materials Research
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• v.5 no.7
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• pp.858-868
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• 1995

Texture development and martensitic phase transformation, on rolling, are compared in two Hadfield's steels, one having low carbon content(0.65wt% C), the other high carbon content(1.35wt%). In spite of small difference in stacking fault energy(about 2 mJm$^{-2}$ ) between two Hadfield's steels, the differences in texture development are observed. In low carbon steel, the textures developed are similar to those of low stacking fault energy metals in low strain range. However, the abnormal textures such as {111} , {110} <001> are strongly developed at high strain, which are due to the disturbance of u martensite in the development of textures formed at the packets of shear bands or at the grain boundaries. In contrast to low carbon Hadfield's steel( LCHS), the texture development of high carbon Hadfield's steel(HCHS) is simitar to those of low stacking fault energy metals in the whole strain range. This may be due to the fact that the amount of deformation induced martensite was small, as observed by A.C. magnetic susceptibility and iron particle tests.

• Applied Chemistry for Engineering
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• v.27 no.6
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• pp.573-576
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• 2016

In this study, hydrogenation of 1,2,3,3,3-pentafluoropropene was performed to produce R-1234yf as an environmentally friendly refrigerant. Palladium based carbon was prepared as a catalyst in the hydrogenation reaction. The effect of reaction conditions including the weight hourly space velocity (WHSV), reaction temperature and ratio of hydrogen and reactants on the catalytic performance was investigated. Under the identical reaction conditions, the effect of WHSV on the main product selectivity was insignificant, but a high reaction temperature was essential for the good product selectivity. A high product selectivity was also obtained when the ratio of hydrogen and reactants kept less than 1.5. Moreover, a correlation model involving the statistical approach to predict product yields was developed.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.5
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• pp.134-142
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• 2011

Although combustion is essential in most energy generation processes, it is one of the major causes of air pollution. Exhaust pipes with circular fin were designed to study the effect of cooling the recirculated exhaust gases (EGR) of Diesel engines on the chemical composition of the exhaust gases and the reduction in the percentages of pollutant emissions. The gases examined in this study were oxides of nitrogen (NOx), carbon dioxide ($CO_2$) and carbon monoxide (CO). In addition, $O_2$ concentration in the exhaust was measured. The designs adopted in this study were about exhaust pipes with solid and hollow fins around them direct surface force measurement in water using a nano size colloidal probe technique. The direct force measurement between colloidal surfaces has been an essential topic in both theories and applications of surface chemistry. As particle size is decreased from micron size down to true Carbon nano Colloid size (<10 nm), surface forces are increasingly important. Nano particles at close proximity or high solids loading are expected to show a different behavior than what can be estimated from continuum and mean field theories. The current tools for directly measuring interaction forces such as a surface force apparatus or atomic force microscopy (AFM) are limited to particles much larger than nano size. This paper use Water and CNC fluid at normal cooling system of EGR. Experimental result showed all good agreement at Re=$2.54{\times}10^4$ by free convection and Re=$3.36{\times}10^4$ by forced air furnace.

• Korean Chemical Engineering Research
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• v.55 no.1
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• pp.68-73
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• 2017

The removal of particulate matter ranging from $0.01{\mu}m{\sim}10{\mu}m$ can be performed by using membrane filters composed of fibers. Electrospinning techniques offer the production of very thin fibers with a uniform fiber diameter over conventional techniques including template synthesis, melt-blown, phase separation, etc. Air filtration will be improved with electrospun membranes due to the open pore structures, high porosity, and large surface area of the membranes. In the present study, filtration efficiency increased with pore size decrease and fiber density increase induced by carbon nanotube and the increased CA (cellulose acetate) concentration during electrospinning process.

• Polymer(Korea)
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• v.37 no.4
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• pp.470-477
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• 2013

Multi-walled carbon nanotube (MWCNT) based nano-composite pastes having a high filler content are prepared for the facile fabrication of a counter electrode (CE) of dye-sensitized solar cell (DSSC). A polystyrene-based functional block copolymer is prepared through a controlled "living" radical polymerization technique, affording a surface modifier for the dispersion control of MWCNT in the paste. Physical dispersion through a ball-milling method additionally confirms the importance of the dispersion control, providing DSSC with enhanced processibility and improved solar-to-electricity energy conversion efficiency (${\eta}$) values. The performances of the DSSCs are further improved through the incorporation of minor amount of platinum (Pt) nanoparticles into the MWCNT pastes. The DSSC with the Pt/MWCNT hybrid CE exhibits very high ${\eta}$ values, which is superior to that of DSSC with the standard Pt CE.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.12a
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• pp.96-100
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• 2006

A pulsed laser ablation deposition (PLAD) technique is an excellent method for the fabrication of amorphous carbon (a-C) films. This paper was focused on the understanding and analysis of the motion of carbon atom (C) and carbon ion ($C^+$) particles in laser ablation assisted by Ar plasmas. The simulation has carried out under the pressure P=10~100 mTorr of Ar plasmas. Two-dimensional hybrid model consisting of fluid and Monte-Carlo models was developed and three kinds of the ablated particles which are C, $C^+$ and electron were considered in the calculation of particle method. The motions of energetic $C^+$ and C deposited upon the substrate were investigated and compared.

• Applied Chemistry for Engineering
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• v.16 no.2
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• pp.180-186
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• 2005

This paper discusses the development of mixtures for silica fume as a stabilization/solidification agent and a binder for industrial wastewater residue containing organic and heavy metal contaminants. The UCS (unconfined compressive strength) gradually increased to 66.7% as the silica fume content increased to 15%. The leaching of TOC (total organic carbon) and chromium decreased as more OPC (Ordinary Portland Cement) was substituted with the silica fume. When a mixture had 5% silica fume, it retained about 85% TOC, and chromium leached out 0.76 mg-Cr/g-Cr in acidic solution. Also, microstructural studies of the solidified analysis showed that the silica fume caused an inhibition to the ettringite formation which did not contrilbute to setting but coated the cement particles and retarded the setting reactions. The results indicated that the incorporation of silica fume into the cement matrix minimized the detrimental effects of organic materials on the cement hydration reaction and the contaminant leachability.

• The Journal of the Convergence on Culture Technology
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• v.8 no.5
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• pp.749-754
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• 2022

High adhesion and water resistance of the skin surface are required for wearable and skin-attachable electronic patches in various medical applications. In this study, we report a stretchable electronic patch that mimics the drainable structure pattern of the hexagonal channels of frog's pads and the sucker of an octopus based on carbon-based conductive polymer composite materials. The hexagonal channel structure that mimics the pads of frogs drains water and improves adhesion through crack arresting effect, and the suction structure that mimics an octopus sucker shows high adhesion on wet surfaces. In addition, the high-adhesive electronic patch has excellent adhesion to various surfaces such as silicone wafer (max. 4.06 N/cm²) and skin replica surface (max. 1.84 N/cm²) in dry and wet conditions. The high skin-adhesive electronic patch made of a polymer composite material based on a polymer matrix and carbon particles can reliably detect electrocardiogram (ECG) in dry and humid environments. The proposed electronic patch presents potential applications for wearable and skin-attachable electronic devices for detecting various biosignals.