• 한국재난정보학회 논문집
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• 제9권4호
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• pp.400-412
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• 2013

CFT 구조는 내부의 콘크리트와 강관의 합성거동을 위한 전단연결재를 필요로 한다. 하지만, 현행 설계기준에서는 통상적으로 무근콘크리트로 채워지는 CFT 구조에 적용할 수 있는 전단연결재에 대한 설계기준을 제시하고 있지 않다. 본 연구는 강-콘크리트 합성구조에 널리 사용되는 스터드 전단연결재를 CFT 구조에 적용하기 위한 설계기준 즉, CFT 구조에 적용된 스터드 전단연결재의 전단강도를 제안하기 위한 연구의 일환으로 수행되었다. 본 연구에서는 CFT 구조에 적용된 스터드의 전단강도를 결정하는 주된 파괴모드를 검토하기 위하여 무근콘크리트를 적용한 직접전단실험체를 이용하여 실험을 수행하고 파괴모드를 분석하기 위한 유한요소해석을 실시하였다. 직접전단실험 및 유한요소해석결과로부터 CFT 구조에 적용된 스터드 전단연결재의 주된 파괴모드는 콘크리트의 쪼갬파괴이며, 이러한 파괴모드로 인하여 철근콘크리트에 적용된 스터드에 비해 전단강도가 감소한다는 사실을 확인할 수 있었다.

• Steel and Composite Structures
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• 제18권4호
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• pp.1023-1044
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• 2015

Concrete-filled tubes (CFT), formed by an outer steel tube filled with plain or reinforced concrete inside, have been increasingly used these recent decades as columns or beam-columns, especially for tall buildings in seismic areas due to their excellent structural response. This improved behavior is derived from the effect of confinement provided by the tube, since the compressive strength of concrete increases when being subjected to hydrostatic pressure. In circular CFTs under compression, the whole tube is uniformly tensioned due to the radial expansion of concrete. Contrarily, in rectangular and square-shaped CFTs, the lateral flanges become subjected to in-plane bending derived from this volumetric expansion, and this fact implies a reduction of the confinement effect of the core. This study presents a numerical analysis of different configurations of CFT stub columns with inner stiffening plates, limited to the study of the influence of these plates on the compressive behavior without eccentricity. The final purpose is to evaluate the efficiency in terms of strength and ductility of introducing stiffeners into circular and square CFT sections under large deformation axial loading.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.489-492
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• 2006

The present work was performed to investigate the thermal and hydraulic characteristics of flow inside the plain and turbulator flat tubes for the automobile application. The pressure drop and heat transfer coefficient at laminar, transition and turbulent regimes were studied experimentally and numerically. The flow transition was confirmed by flow visualization and quantitative data. It is proposed equations for the friction and heat transfer coefficient in the fully developed laminar flow inside rectangular tube as function of aspect ratio.

• International Journal of Advanced Culture Technology
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• 제3권2호
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• pp.124-131
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• 2015

Computational fluid dynamics (CFD) has been employed for the Heat exchanger efficiency of a counter flow heat exchanger. The Heat exchanger efficiency has been assessed by considering the computed Nusselt number and flow friction characteristics in the double pipes heat exchanger equipped with two types twisted-tapes: (1) single clockwise direction and (2) alternate clockwise and counterclockwise direction. Cold and hot water are used as working fluids in shell and tube side, respectively. Hot and cold water inlet mass flow rates ranging are between 0.04 and 0.25 kg/s, and 0.166 kg/s, respectively. The inlet hot and cold water temperatures are 54 and $30^{\circ}C$, respectively. The results obtained from the tube with twisted-tapes insert are compared with plain tube. Nusselt number and friction factor obtained by CFD simulations were compared with correlations available in the literature. The numerical results were found in good agreement with the results reported in literature.

• 대한방사선기술학회지:방사선기술과학
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• 제3권1호
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• pp.43-48
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• 1980

An experimental study was carried out to make a comparison between tube voltage and density of barium sulphate in the stomach radiography. The results were summarized as follows: 1. The percentage of density on concentrations of barium sulphate as contrast media could not show in differences with changes of voltages applied X-ray tube. 2. The changes of density visualized on X-ray film mainly depend upon with thickness of stomach filled barium sulphate than the ratio of barium sulphite and plain water volume. 3. The lesions positioned in upper part within stomach exhibited their best discrimination performanance with depth in the low tube voltage, followed in order by the middle part and lower part. However, the discrimination performanance at the high tension radiography uniformly visualized over X-ray film without density in change.

• 대한기계학회논문집B
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• 제22권7호
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• pp.980-991
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• 1998

In this study, nucleate pool boiling heat transfer coefficients of alternative refrigerants on a plain, low fin, and two enhanced tubes were measured and compared against each other. To obtain data at conditions similar to the actual evaporator, a fluid heating method was employed instead of an electric heating method in the experiments. R123, R134a, R22 and R410a were used as working fluids and data were taken at 7 deg.C ar heat fluxes of 20 ~ 100 kW/m$\^$2/. Comparison of the plain tube data against some correlations showed that the simplest correlation of Cooper based on reduced pressure predicted the data for all fluids tested with a 10% deviation. For all refrigerants, enhanced tubes composed of subsurface and subtunnels, especially Thermoexcel-E tube, showed the highest heat transfer coefficients among the tubes tested with one exception that the low fin tube's performance was better than those of enhanced tubes for high vapor pressure fluid such as R410a at high heat flux. Finally, a low fin and enhanced tubes showed higher heat transfer enhancement for low vapor pressure of R123 than for high vapor pressure fluisd. For R123, the enhancement factors for Turbo-B and Thermoexcel-E tubes were 2.8 ~ 4.8 and 4.6 ~ 8.1 respectively.

• 보험의학회지
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• 제3권1호
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• pp.90-102
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• 1986

The gallbladder is a pear-shaped, thin walled sac located on the inferior surface of the liver between the right and quadrate lobe, in a recess called fossa vesicae felleae. It is 7.5cm-12.5 cm in length, 3.5 cm in the largest width, and has a volume of about 45 ml with a remarkable capacity for expansion. There are many kinds of diagnostic methods to evaluate diseases of biliary tract including gallbladder-Plain abdomen, Oral cholecystography. Intravenous cholangiography, Percutaneous transhepatic cholangiography(PTC), Endoscopic retrograde cholangiography(ERCP), Operative or T-tube cholangiography, Ultrasonography, Radioisotope study, Computed tomography, and Angiography. Especially, ultrasonography is the most effective and noninvasive study in these days. Plain abdomen, oral cholecystography, intravenous cholangiography, and ultrasonography have been performed in our clinic. Methods and findings of above mentioned study are discussed with consideration of references.

• 태양에너지
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• 제18권4호
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• pp.49-57
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• 1998

In this study, thin film evaporation of water on a horizontal plain tube is experimentally investigated. At a high heat flux, boiling of water is noticed inside the film. Once boiling occurs, evaporation heat transfer coefficient increases as the heat flux increases. In the non-boiling region, however, the heat transfer coefficient remains uniform irrespective of the heat flux. In this region, the heat transfer coefficient increases as the film flow rate increases. Comparison with existing correlations is also provided.

• International Journal of Air-Conditioning and Refrigeration
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• 제10권2호
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• pp.79-87
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• 2002

In this study, flow boiling experiments were performed using R-134a on a plain tube bundle. Tests were conducted for the following range of variables; quality from 0.1 to 0.9, mass flux from 8kg/$m^2$s to 26 kg/$m^2$s and heat flux from 10kW/$m^2$ to 40kW/$m^2$. The heat transfer coefficients were strongly dependent on the heat flux. However, they were almost independent on the mass flux or quality. The data are compared with the modified Chen model, which predicted satisfactorily ($\pm$30%) the data. The Original Chen model, however, did not adequately predict the effect of quality. The reason may be attributed to the flow pattern of the present test, where the bubbly flow prevailed for the entire test range. The heat transfer coefficients of the tube bundle were 6~40% higher than those of the single tube pool boiling.

• Steel and Composite Structures
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• 제31권3호
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• pp.291-301
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• 2019

Pure torsion loading conditions were not frequently occurred in practical engineering, but the torsional researches were important since it's the basis of mechanical property researches under complex loading. Then a 3D finite element model with precise material constitutive models was established, and the effectiveness was verified with test data. Parametric studies with varying factors as steel yield strength, concrete strength and sectional height-width ratio, were performed. Internal stress state and the interaction effect between encased steel tube and the core concrete were analyzed. Results indicated that due to the confinement effect between steel tube and core concrete, the torsional strength of CFT columns was greatly improved comparing to plain concrete columns. The steel ratio would greatly influence the torque share between the steel tube and the core concrete. Then the torsional strength calculation formulas for core concrete and the whole CFT column were proposed. The proposed formula could be simpler and easier to use with guaranteed accuracy. Related design codes were more conservative than the proposed formula, but the proposed formula presented more satisfactory agreement with experimental results.