• Journal of the Korean Society for Heat Treatment
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• v.9 no.2
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• pp.91-102
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• 1996

Microstructural control to produce multiphase structure has received much attention to improve the high temperature strength as well as low temperature ductility of intermetallics. Transmission electron microscopic investigation has been carried out concerning the effect of Cr-precipitation on the mechanical properties of B2-ordered NiAl containing 4 to 8 mol% of Cr. By aging at temperatures around 973 K after solution annealing, fine spherical precipitates took place homogeneously in the NiAl matrix and the alloys hardened appreciably. Selected area electron diffraction (SAED) patterns have not revealed any additional extra-spots during aging, because the Cr-particles show cube-cube orientation relationship and keep a perfect coherency with the ordered matrix lattice. Dislocations were confirmed to bypass the particles during deformation. Although the dispersion of Cr-particles increased the yield strength of NiAl at intermediate temperature, the strength decreased appreciably at higher temperatures.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.309-309
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• 2000

The main objective of this study is to understand the regeneration step of the PTSA(Pressure and thermal swing adsorption) process below the atmospheric pressure by rigorous dynamic simulation. This target process is to recover toluene using activated carbon as an adsorbent. To do this, the dynamic simulations for the regeneration step are performed at 360, 490, 590mmHg and at high temperature after the simulation of the adsorption step at latm and 298K. A mathematical model was developed to simulate the column dynamics of the adsorption systems. This model is based on non-equilibrium, non-isothermal and non-adiabatic conditions, and axial dispersion and heat conduction are also considered. Heat transfer resistances are considered in gas-solid, gas-column wall and column wall-outside air. The LDF(Linear Driving Force) approximation model describes the mass transfer rate between the gas and solid phase. This study shows that the recovery of toluene by PTSA is more preferable than that by general TSA.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.11
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• pp.949-956
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• 2007

Pool boiling critical heat flux (CHF) of nanofluids with oxide nanoparticles of $TiO_2$ or $Al_2O_3$ was experimentally investigated under atmospheric pressure. The results showed that a dispersion of oxide nanoparticles significantly enhances the CHF over that of pure water. Moreover it was found that nanoparticles were seriously deposited on the heater surface during pool boiling of nanofluids. CHF of pure water on a nanoparticle-deposited surface, which is produced during the boiling of nanofluids, was not less than that of nanofluids. The result reveals that the CHF enhancement of nanofluids is absolutely attributed to modification of the heater surface by the nanoparticle deposition. Then, the nanoparticle-deposited surface was characterized with parameters closely related to pool boiling CHF, such as surface roughness, contact angle, and capillary wicking. Finally, reason of the CHF enhancement of nanofluids is discussed based on the changes of the parameters.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.152-154
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• 2005

Austenitic stainless steel has good weldability but is sensitive to hot cracking such as solidification crack and liquation crack. In this study, the specimens of dissimilar metals made between austenitic stainless steel and Al-brass were welded by GTAW process using four different filler metals. Cracks were detected in the heat-affected zone of the stainless steel when welded with CuAl, CuSn and NiCu filler metals, but no cracks were detected a Ni filler metal was used. The cracks propagated along the grain boundary in the heat affected zone near the fusion line to base metal of 316L stainless steel. The cracks were located inside the weld bead with very fine hairline crack. All cracks initiated at the fusion line and moved forward in the base metal. From energy dispersion spectroscopy (EDS), Cu peak was detected only in the crack-opening area.

• Applied Chemistry for Engineering
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• v.18 no.3
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• pp.245-250
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• 2007

Adsorption characteristics of 1,2-dichlorobenzene on the surface of heat treated silica gel were determined by the moment analysis. The heat treatment of the silica gel was performed at temperatures of 150, 500, and $800^{\circ}C$ and pulse-response of 1,2-dichlorobenzene was measured in a gas chromatograph equipped with thermal conductivity detector (TCD) using the packed column. Equilibrium adsorption constants and isosteric heat of adsorption were recorded the highest value at $500^{\circ}C$. This might be due to the increase of interaction between silica surface and 1,2-dichlorobenzene as the decrease of OH concentration and moisture by increase of heating temperature. Axial dispersion coefficient calculated by the moment method was about $0.046{\times}10^{-4}{\sim}1.033{\times}10^{-4}m^2/sec$ and pore diffusivity of heat treated silica gel at $500^{\circ}C$ measured the lowest value. Because heat treating at $800^{\circ}C$ caused the specific surface area to reduce, equilibrium adsorption constants and isosteric heat of adsorption were decreased.

• Journal of Power System Engineering
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• v.17 no.5
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• pp.78-85
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• 2013

A high thermal conductivity material, namely graphene is treated by planetary ball milling machine to transport the heat by increasing the temperature. Experiments were performed to assess the heat transfer enhancement benefits of coating the bottom wall of copper substrate with graphene. It is well known that the graphene is unable to disperse into base fluid without any treatment, which is due to the several reasons such as attachment of hydrophobic surface, agglomeration and impurity. To further improve the dispersibility and thermal characteristics, planetary ball milling approach is used to grind the raw samples at optimized condition. The results are examined by transmission electron microscopy, x-ray diffraction, Raman spectrometer, UV-spectrometer, thermal conductivity and thermal imager. Thermal conductivity measurements of structures are taken to support the explanation of heat transfer properties of different samples. As a result, it is found that the planetary ball milling approach is effective for improvement of both the dispersion and heat carriers of carbon based material. Indeed, the heat transfer of the ground graphene coated substrate was higher than that of the copper substrate with raw graphene.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.1
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• pp.1-9
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• 2000

This study shows the defect detection and sizing capability of ultrasonic guided waves in the nondestructive inspection of heat exchanger and steam generator tubing. Phase and group velocity dispersion curves for the longitudinal and flexural modes of a sample Inconel tube were presented for the theoretical analysis. EDM(Electric Discharge Machining) wears in tubing under a tube support plate and circumferential laser notches in tubing were detected by an axisymmetric and a non-axisymmetric transducer set up, respectively. EDM wears were detected with L(0, 2), L(0, 3) and L(0, 4) modes and among them L(0, 4) mode was found to be the most sensitive. It was also found that the flexural modes around L(0, 1) mode could be used for the detection and sizing of laser notches in the tubing.

• Journal of the Korean Institute of Gas
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• v.18 no.3
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• pp.67-74
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• 2014

Buried natural gas pipelines in densely populated urban areas have serious hazards of property damages and casualties generated by release, dispersion, fire and explosion of gas caused by outside or inside failures. So as to prevent any accident in advance, managers implement danger management based on quantitative risk analysis. In order to evaluate quantitative risk about buried natural gas pipelines, we need calculation for radiant heat and pressure wave caused by calculation for release rate of chemical material, dispersion analysis, fire or explosion modeling through consequence analysis in priority, in this paper, we carry out calculation for release rate of pressured natural gas, radiant heat of fireball based in accident scenario of actual "San Bruno" buried high pressured pipelines through models which CCPS, TNO provide and compare with an actual damage result.

• The Journal of the Acoustical Society of Korea
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• v.22 no.7
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• pp.545-553
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• 2003

This paper is concerned with protecting piezoelectric transducers used in an ultrasonic flowmeter from the high temperature of hot fluid in a pipe by using a waveguide and with improving the propagation of ultrasonic longitudinal vibration in the waveguide. Waveguide material has been chosen for efficient insulation of heat transferred in the waveguide, and the minimum length of the waveguide for protecting piezoelectric transducer has been estimated. Forced response of the longitudinal vibration in a uniform circular rod has been obtained and the length of the waveguide has been selected for maximum amplitude. Longitudinal vibration response of a conically-tapered rod excited at a natural frequency has been obtained to confirm that wave motion is amplified as the cross-sectional size of the waveguide decreases along the axial direction. The fact that dispersion of a pulse wave in a waveguide is reduced as the cross-sectional radius is decreased has been examined theoretically and confirmed experimentally by using a single-rod waveguide. A bundle-type waveguide has proven to be a practical one through the evaluation of the wave propagation performance.

• Journal of the Korean Society for Heat Treatment
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• v.20 no.2
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• pp.65-71
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• 2007

Microstructural changes and hardness variations in STS 304 steel have been investigated during the processes of carbide dispersion (CD) carburization; carburization, austenitization, subzero treatment and tempering. The carbon content of the surface layer increased up to maximum 4.0% after carburization, and the content was homogenized with the value of 2.3% to the $95{\mu}m$ from the surface after austenitization. The carbide appeared during CD carburization process was $Cr_7C_3$ type, which was composed network carbides along the austenite grain boundaries, square type carbides in the interior of the grain and fine nano-sized carbides. The fine nano-sized carbides precipitated at the austenitization stage and possibly subzero treatment stage were coarsened after tempering at $200^{\circ}C$, resulting the hardness decrease. The tempered steel without subzero treatment increased hardness with increasing time due to the continuous precipitation of fine carbides during tempering. The nano-sized carbide appeared square type morphology.