• Applied Chemistry for Engineering
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• v.9 no.6
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• pp.901-906
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• 1998

Gas and liquid flow characteristics were investigated in an internal circulation airlift reactor using a single nozzle for a gas distributor. In three reactors with different diameters of the downcomer and heights of the riser, the gas holdup in the individual flow zone and the impulseresponse curve of tracer for an air-water system were measured for various gas velocities and reactor heights. Experimental results showed that the flow behavior of bubbles in the riser was the slug flow due to strong coalescences of bubbles and that the bubble flow pattern in the downcomer was the transition bubble flow for the smaller diameter of the downcomer, however, it was the homogeneous bubble flow for the larger one. And mean gas holdups in the individual flow zone and the reactor were greatly increased with decreasing the diameter of the downcomer for the equal ratio of height of the top section to that of the riser. Also, the mixing time was much effected by the height of the top section of reactor and for the equal ratio of height of top section to that of the riser, it was increased with increasing the diameter of the downcomer and the height of the riser. Flow characteristics of liquid were mainly varied with the bubble flow pattern in the downcomer and the size of the top section of reactor. And circulation velocities of liquid in the riser were increased with increasing gas velocities and the size of the top section of reactor, and for the equal ratio of height of top section to that of the riser, they were increased with increasing the diameter of the downcomer and the height of the riser.

• Journal of Korean Society of Steel Construction
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• v.21 no.5
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• pp.505-514
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• 2009

This paper describes the structural behavior and the ultimate strengths of circular hollow steel (CHS) sections based on a series of compression tests. The ultimate strengths of CHS section columns are mainly dependent on both diameter-thickness ratio and column slenderness ratio. For the CHS sections with a high diameter-thickness ratio, an elastic or an inelastic local buckling may occur prior to the overall buckling, and it may decrease the column strength. Test sections were fabricated from SM400 steel plate of 2.8 mm and 3.2 mm in thickness and were tested to failure. The diameter-thickness ratios of the test sections ranged from 45 to 170 to investigate the effect of local buckling on the column strength. The compression tests indicated that the CHS sections of lower diameter-thickness ratio than the yield limit in the current design specifications showed an inelastic local buckling and a significant post-buckling strength in the local mode. Their ultimate stresses were larger than the nominal yield stress. It was known that the allowable stresses of the sections predicted by the Korean Highway Bridge Design Specifications (2005) were too conservative in comparison with test results. The Direct Strength Method which was newly developed was calibrated for application to the CHS sections by the experimental and numerical results. The Direct Strength Method proposed can predict properly the ultimate strength of CHS section columns whether a local buckling and an overall buckling occur nearly simultaneously or not.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.4
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• pp.274-281
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• 2015

Thermal and nuclear power plants on shore commonly use the sea water for cooling facility. Discharged cooling water has the high kinematic energy potential due to amount of water flux. Numerical analysis was made to find the suitable combinations between the arrangement of tidal turbines and the overall dimensions of the discharged channel. Several parameters such as the turbine diameter to inlet size, and the axial distance to turbine size were investigated. Power coefficients for various test conditions were also compared to see the effect of inlet configurations such as single inlet and dual inlet. For the single inlet, the mean power coefficient appeared to be gradually decreased with increasing distance, and the maximum power was obtained when the turbine diameter was same as the inlet diameter. For the dual inlet, the tendency was similar so that the better result when the turbine diameter was same as the inlet diameter. It is expected that the present methodology can be extensively utilized to harness the high kinetic energy flow of the discharge channel of power plant.

• Journal of Korean Society of Forest Science
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• v.96 no.3
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• pp.362-368
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• 2007

This study was conducted to estimate merchantable volume and yield per diameter (DBH) class of Pinus koraiensis and Larix kaempferi. Stem volume of trees in each diameter class was calculated using the existing equations for taper and height curve. Saw logs and pulpwood volume were then estimated from the stem volume in each diameter class. The final step was to estimate merchantable volume and yield from saw logs, assuming saw logs were used for lumber (boards or dimension products) production only. The results showed that the stem volume of Larix kaempferi was 23~38% higher than that of Pinus koraiensis at the same diameter classes. Both species were able to produce saw logs from the diameter class of 18 cm. Saw logs and pulpwood yield for both species rapidly increased due to the size limitation on small end diameter. This yield reached a maximum of 90% and 88% at 26 cm and 38cm diameter class, respectively, for Pinus koraiensis and Larix kaempferi. Lumber yield estimated for board products ranged from 23% to 56%. In the case of dimension products, Lumber yield became significantly smaller as saw logs were used for larger dimension products. These results can be used for calculating merchantable volume and economic value of trees, as well as determining final lumber products.

• Journal of Energy Engineering
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• v.24 no.1
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• pp.97-103
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• 2015

Natural convection heat transfer rates in vertical pipes were measured varying the diameter, length, and roughness of vertical cylinder. To achieve high Rayleigh number with relatively small test rig, mass transfer experiments instead of heat transfer were performed based on the analogy. Prandtl number was 2,014. The length of vertical cylinder was 0.1m, 0.3m, and 0.5m, which correspond to GrL $4.2{\times}10^7$, $1.1{\times}10^9$, and $5.5{\times}10^9$. To each length of vertical cylinder, the heat transfer rates were measured varying the iameter 0.005m, 0.01m, and 0.03m. The heat transfer rate for a short length pipe(0.1m) agreed with the prediction from Le Fevre correlation developed for a vertical plate for all diameter. The heat transfer rate decreases as the diameter and the length of the pipe increases. The heat transfer rate inside of vertical cylinder is affected by roughness only for a laminar flow regime.

• Journal of Dental Rehabilitation and Applied Science
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• v.32 no.3
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• pp.194-201
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• 2016

Purpose: The purpose of this study was to evaluate of Zirconium Nitride (ZrN) coating on shear bond strength with denture base resin in Co-Cr and Ti-6Al-4V alloy. Materials and Methods: Co-Cr and Ti-6Al-4V alloy disks (10 mm in diameter, 2.5 mm in thickness; each other: n = 14) were prepared and divided with 2 groups each other by ZrN coating. After primer was applied to disks surface, denture base resin with diameter 6 mm, height 5 mm was bonded on metal disk surface. After surface roughness was measured by Profiler, shear bond strength was determined with Universal testing machine and analyzed with two-way ANOVA. The specimen surfaces and failure mode were examined using a scanning electron microscope. Results: ZrN coated groups showed significantly higher rough surface than non-coated groups (P < 0.05). Irrespective of alloy materials, shear bond strength of ZrN coated groups were lower than non-coated groups (P < 0.001). The scanning electron microscope (SEM) of ZrN coated groups showed mixed and adhesive fractures. Conclusion: ZrN coating weakened bonding strength between denture base resin and Co-Cr, Ti-6Al-4V alloy.

• Journal of Korea Foundry Society
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• v.21 no.3
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• pp.187-191
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• 2001

가스분무장치를 이용하여 제조된 304 stainless steel 분말의 미세응고조직 특성을 투과전자현미경으로 관찰하였다. 분말이 sandwich 현상으로 존재하도록 구리로 전기도금한 후 tripod jig 를 이용하여 기계적 연마하여 TEM 시편을 제작하였다. 이 방법으로 제조된 TEM 시편은 넓은 지역에서 200KV 로 가속된 전자가 투과하기에 충분히 얇았으며, 작은 분말의 경우에는 분말 전체를 관찰할 수 있었다. 제한시야회절법(SADP)을 이용하여 100 ${\mu}m$ 이하 분말의 결정구조를 조사한 결과에 따르면 가스분무법으로 급냉응고된 대부분의 분말은 austenite 상으로 응고되었으며, 모든 austenite 분말은 크기에 관계없이 쌍정조직 (twinstructure)이 발견되었으며 그 밀도 역시 아주 높았다. 그러나 직경이 2 ${\mu}m$ 이하의 분말에서는 큰 과냉 (supercooling) 효과에 의하여 준결정상인 bcc 상으로 응고됨을 발견하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.6
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• pp.1529-1538
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• 1995

In this study, a liquid sheet type co-axial nozzle has been used to investigate the turbulent atomization characteristics which could result in the experimental data to be used in designing a jet nozzle with high performance. Image processing technique and immersion sampling method were employed to measure droplet size. In atomizing characteristics, droplet size distributions and absolute droplet sizes, SMD(Sauter Mean Diameter) have been investigated in the wide ranges of flow field depending upon the air-water mass ratios. And the comparisons between the present data and the semi-empirical curves have been conducted semi-empirical correlation for SMD has been derived in the present analysis.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.395-398
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• 2009

전기도금 방법을 사용해 각기 다른 환원 전압과 전기도금시간에서 Pd 수지상 나노와이어(Pd DNWs) 전극이 합성 되었으며 그 성장 기작을 논의하였다. 전기화학적인 도금 공정 동안 Pd DNWs 이<111>방향으로 성장하는 것을 확인할 수 있었는데, 이것은 전해질 속의 황산음이온들이 Pd 의 (111)면에 흡착하기 유리하기 때문이라고 사료된다. 가해준 환원전압이 증가함에 따라, 단 결정 수지상의 나노와이어의 가지는 길어지고 얇아지는 경향을 보였다. 이것은 전기도금 시간이 아니라 환원전압에 의해서만 나노와이어 가지의 직경이 조절됨을 보여준다

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.2
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• pp.68-71
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• 2008

AlN crystals were grown by the sublimation process. As grown AlN crystals were the polycrystalline boule in the form of the agglomerate of small AlN single crystalline AlN. As-grown AlN boule has a length about 2${\sim}$3 mm long and a diameter of 1 inch. The carbon impurities were observed on the surface and inside of the grown AlN crystals and the growth behavior was investigated by optical microscopy and SEM observation.