• Nuclear Engineering and Technology
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• v.41 no.8
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• pp.1015-1024
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• 2009

The presence of a non-condensable gas can considerably reduce the level of condensation heat transfer. The non-condensable gas effect is a primary concern in some passive systems used in advanced design concepts, such as the Passive Residual Heat Removal System (PRHRS) of the System-integrated Modular Advanced ReacTor (SMART) and the Passive Containment Cooling System (PCCS) of the Simplified Boiling Water Reactor (SBWR). This study examined the capability of the Multi-dimensional Analysis of Reactor Safety (MARS) code to predict condensation heat transfer in a vertical tube containing a non-condensable gas. Five experiments were simulated to evaluate the MARS code. The results of the simulations showed that the MARS code overestimated the condensation heat transfer coefficient compared to the experimental data. In particular, in small-diameter cases, the MARS predictions showed significant differences from the measured data, and the condensation heat transfer coefficient behavior along the tube did not match the experimental data. A new method for calculating condensation heat transfer coefficient was incorporated in MARS that considers the interfacial shear stress as well as flow condition determination criterion. The predictions were improved by using the new condensation model.

• Journal of Chest Surgery
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• v.17 no.4
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• pp.753-761
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• 1984

Most patients having annuloaortic ectasia are associated with marked dilatation of the sinuses of Valsalva and the aortic annulus as well as the huge aneurysm of the ascending aorta. A 19 year old male patient complaining of tightness on left posterior chest wall underwent cardiac angiography in which demonstrated annuloaortic ectasia with ascending aortic aneurysm and aortic insufficiency. The patient had corrective operation replacing the ascending aorta and aortic valve with a composite graft[Dacron prosthesis containing a Bjork-Shiley aortic valve] within the aneurysmal sac. The coronary orifices were anastomosed to the tubular Dacron prosthesis [30 mm in diameter] by means of a second smaller Gore-Tex tube [8mm in diameter]. The aneurysmal sac was trimmed by removing the redundant wall and then wrapped outer wall of the Dacron prosthesis. Postoperatively, mediastinal bleeding was temporarily observed in the operative day and satisfactory blood pressure was maintained with small dose of dopamine. One week later, large amount of serous effusion was drained out of the retrosternal space making partial disruption of the skin which was healed well by daily local dressing. The patient discharged in good condition on postoperative 29th day with no residual complications and is doing very well on the 4 months follow-up.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.7
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• pp.915-922
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• 2004

A stent is small tube-like structure expanded into stenotic arteries to restore blood flow. The stent expansion behaviors define the effectiveness of the surgical operation. In this paper, finite-element method was employed to analyze expansion behaviors and fatigue life of a typical diamond-shaped balloon-expandable stent. Beyond safety considerations, this type of analysis provides mechanical properties that are often difficult to obtain by experiments. Mechanical properties of the stent expansion pressure, radial recoil, longitudinal recoil and foreshortening were simulated using commercial FEM code, ANSYS and fatigue life were estimated using NISAII ENDURE. The FEM results showed that the pressures necessary to expand the stent up to a diameter of 3mm, 4mm and 5mm were 0.75MPa, 0.82MPa and 0.97MPa. The fatigue lifes according to expansion diameter were 114${\times}$10$^{7}$cycles, 714${\times}$$^{6}$cycles and 163${\times}$10$^{6}$cycles. As a result, a finite element model used in this study can simulate expansion behaviors of stents and should be useful to design new stents or analyze actual stents.

• Journal of the Korean Society of Safety
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• v.35 no.3
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• pp.43-48
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• 2020

It is considered that most of reusable pipe supports, which are used as formwork support posting at construction sites, do not meet the performance standard. Due to the use of reusable pipe supports that do not meet such performance standard the potential risk of collapse accident is increasing. Therefore, this study identifies the status of compliance with performance standard, and presents the requirements for improving quality control to prevent the collapse of pipe supports reused at the construction site. First, if the female thread of the product with no clearance and new support pin with the diameter of 12mm are replaced at the same time for use, it is considered that the performance will be improved. Second, as the quality performance during use can be improved in the case of larger thickness of inner diameter compared to the case of larger thickness of outer diameter, it is necessary to increase the inner pipe thickness greatly than the current thickness. Based on the results of this study, it is expected that the performance the reusable pipe support (V4) can be improved, if the diameter of the support pin is 12mm, the female thread has a small clearance, and the inner tube thickness is 2.3 ~ 2.7mm. In addition, it is considered that other performance improvement factors included in the study results could be used as important data for improving the performance of reusable pipe support.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.9
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• pp.613-620
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• 2016

In order to scrutinize the fluid conductivity effects on the electromagnetic flowmeter(EMF) characteristics, a small scale EMF was designed and fabricated. The measuring tube has a $3mm{\times}4mm$ rectangular cross-section, 9 mm length, and a $2mm{\times}3mm$ plate electrode and a ${\Phi}1.5mm$ point electrode. The design parameters, such as the magnetizing frequency and the number of coil turns, and the diameter were optimized. The EMF was tested with a gravimetric calibrator and showed good linearity in the range of 0 to $1.17{\times}10^{-5}m^3/s$. The fluid conductivity was varied between 3 and $11{\mu}S/cm$, and the magnitude of the flow signal was proportional to the fluid conductivity and the wetted area of the electrode. The design information and the test results provide flow measurement techniques for very low flowrate.

• Journal of the Korean Society of Radiology
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• v.4 no.1
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• pp.19-24
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• 2010

A cone-beam computed tomography (CT) system for a small animal has been widely used in the bio-medical application. This paper introduced simple methods for evaluating a cone-beam CT system using a simple tungsten wire phantom of 10{$\mu}m$ diameter and a water phantom. Slice images and three-dimensional tomography images were obtained through 360 projection views per one sample rotation under stable X-ray tube conditions for a long running time. The cone-beam CT system at a position of a 1.07 magnification showed a spatial frequency of 13.78 lp/mm ($36.2{\mu}m$ spatial resolution) and gave a CNR of 10.33 and a S/N of 5.87 under a tube voltage of 80kV.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.27.2-27.2
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• 2009

Grinding characteristics for aluminium and carbon nanotubes (CNTs) powder during traditional and planetary ball milling investigated from the viewpoint of particle behaviour with the aimat developing CNT-dispersed samples ground based on powder metallurgy routes.In this work, a comparison between the pure aluminium and CNT input aluminium grinding was carried out to determine grinding time effect on size reduction.We observed that the use of the curly small-diameter multi-walled carbon nanotubes (MWCNTs) attributed to the beneficial role of the MWCNTs as grinding aids. It is suggested that careful choices of the sizes of CNTs and Al powders would allow fine-grinding of composite particles with uniformly distributed CNT reinforcements thereby ensuring improved properties of the final composites produced by low-temperature compacting.

• Journal of the Korean Ceramic Society
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• v.29 no.12
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• pp.919-925
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• 1992

Continuous synthesis process for monodispersed zirconia powders with ultrasonic wave mixing was developed. Reactant solutions were flowed through a T-tube with small diameter and then mixed in a microscale with ultrasonification. Reaction and aging were followed during the mixed solution of reactants is in plug flowing through a narrow long teflon tubing. Zr(n-OC4H9)4 in ethanol and H2O in ethanol were used as reactants. From this process monodispersed, spherical, non-agglomerated, singlet hydrated zirconia powders with 0.6 $\mu\textrm{m}$ average size were obtained. Geometrical standard deviation of the particle size distribution was less than 1.2 with ultrasonic mixing, and the geometrical standard deviation was not affected by the flow rate of the reactants.

• Journal of the Korean Society for Heat Treatment
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• v.33 no.4
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• pp.185-192
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• 2020

In this study, materials characterization of pure copper and copper based carbon nano-tube composite prepared by powder metallurgy method were investigated. Prior to evaluate materials characterization, spark plasma sintering processing variables such as sintering temperature, pressure, thickness and diameter of compacts was optimized to ensure the microstructure and materials property of pure Cu and Cu-CNT composite. In addition, corrosion behavior of Cu-based CNT composite produced by powder sintering method was investigated. It was confirmed from this study that the corroded surfaces of the composite shows less dissolution compared with pure copper in 3.5 wt% NaCl solution. The measured corrosion current density (I_corr) indicates improved corrosion property of Cu based composite containing small additions of CNTs in chloride containing media. Micro-galvanic activity between Cu and CNT was not observed in given sintering condition.

• Proceedings of the KIEE Conference
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• 2003.11c
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• pp.871-874
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• 2003

The T-5 Lamps developed in 1996 is the high efficiency fluorescent lamps, the lamps voltage is high, and the lamps current small because the lamps are slender tube of 16mm diameter. And so, the electrical characteristics of the Ballast for the lamps are different from of the Ballast for T-10 or T-8 lamps. Therefore, the know-how of the exclusive Ballast for the T-5 fluorescent lamps should be as soon as possible. We described the electrical and optical characteristics of the Electronic Ballast for T-5 Circular Fluorescent lamps. The developed Electronic dimming Ballast for T-5 Circular Fluorescent lamps has the 45% energy saving effects than the T-10 lamps. And it has the promotion of the THD less than 10%, CF less than 1.5%, Flickering less than 5% and 99% power factor. And it is available for two T-5 Circular fluorescent Lamps dimming, 22W and 40W.