• 한국전산유체공학회:학술대회논문집
• /
• 1999.11a
• /
• pp.139-144
• /
• 1999

There have been many studies for heat transfer enhancement. Particularly, the study of flow in heat exchangers which have fin device has been main theme in heat transfer area. Practically, the circular tube which has internal fins is widely used for developing heat transfer rate. In this study, flow and heat transfer analysis of the circular tube with fins are investigated. The height and the number of fins are arbitrary. The flow field is assumed to be laminar. The conformal mapping is used for analytic solution of the laminar flow field. Discretization of governing equation, namely, FDM was used for numerical analysis. The velocity field, flow rate and shear stress are calculated for some numbers of fins in circular tube and for some heights of fin. Temperature fields are plotted along the tube length. It can be shown that the numerical solution agrees with the analytical solution.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.11 no.1
• /
• pp.10-17
• /
• 1999

The present work presents condensation heat transfer and pressure drop data for the flow of R-12 in flat extruded aluminum tubes with small hydraulic diameters. The tube outside dimensions are $18mm(width){\times}1.7mm(height)$. Three types of internal geometry with the same outside dimensions are tested : sample 1 (7 tube holes), sample 2 (13 tube holes) and sample 3 (7 tube holes, micro-fin). The overall heat transfer coefficient is obtained for air-to-refrigerant heat transfer, and the Wilson plot method is used to determine the heat transfer coefficient for refrigerant flow. The sample 2 and sample 3 show significantly higher performance than sample 1. The heat transfer rates for the sample 2 and sample 3 are 9% and 12% higher, respectively, than sample 1. The friction factors for the sample 2 and sample 3 are 11.9% and 2.4% higher, respectively, than sample 1.

• Transactions of Materials Processing
• /
• v.17 no.1
• /
• pp.52-58
• /
• 2008

Tube hydroforming process is generally consisted with pre-bending, preforming and hydroforming processes. Among forming defects which may occur in tube hydroforming such as buckling, wrinkling and bursting, the wrinkling and bursting by local instability under excessive tensile stress mode were mainly caused by thinning phenomenon in the manufacturing process. Thus the accurate prediction and suitable evaluation of the thinning phenomenon play an important role in designing and producing the successfully hydroformed parts without any failures. In this work, the formability on hydroformed part for automobile, i.e. engine cradle, was evaluated using finite element analysis. The initial tube radius, loading path with axial feeding force and internal pressure, and preformed configuration after preforming process were considered as the dominant process parameters in total tube hydroforming process. The effects on these process parameters could be confirmed through the numerical experiments with respect to several kinds of finite element simulation conditions. The degree of enhancement on formability with each process parameters such as initial tube radius, loading path and preform configuration were also compared. Therefore, it is noted that the evaluation approach of the formability on hydroformed parts for lots of industrial fields proposed in this study will provide one of feasible methods to satisfy the increasing practical demands for the improvement of the formability in tube hydroforming processes.

• The Journal of the Korea Contents Association
• /
• v.22 no.4
• /
• pp.479-487
• /
• 2022

This study divided video content of current representative YouTube channels on Chinese language education into internal and external elements for analysis. By examining these channels, this study found that they have various external and internal elements. In addition, YouTube classes also have certain distinct characteristics that are non-existent in traditional classroom or face-to-face classes, and show potential to serve as a new educational medium that can fill the gaps in existing classroom classes. However, a large number of these channels still have problems with their internal and external elements, which seem to require not only the effort and attention of the instructors creating the videos, but also considerable time and human and material resources.

• Tuberculosis and Respiratory Diseases
• /
• v.72 no.5
• /
• pp.416-425
• /
• 2012

Background: The sensitivities and specificities of interferon-gamma release assays (IGRAs) vary among different population studies, and the data on the routine use of IGRAs are limited. The aim of this study was to evaluate the role of QuantiFERON-TB Gold In-Tube (QFT-GIT) test in the diagnosis of active tuberculosis. Methods: We conducted a prospective study, enrolling 77 patients with suspected pulmonary tuberculosis (TB), at a secondary care teaching hospital in Seoul. Results: In total, 12 (15.6%) patients showed indeterminate results due to positive control failure on the QFT-GIT test. Indeterminate results were significantly associated with the elderly, history of the intensive care unit stay, lymphocytopenia, especially low CD4 count, increased C-reactive protein and decreased protein levels. Of the 77 patients, 44 (57.1%) were diagnosed with active pulmonary tuberculosis, and the percentage of false negative results of the QFT-GIT was 36.4% (vs. 31.8% with TST). In the TB group with >65 years old (n=12), the proportions of the indeterminate (33.3% vs. 3.1%) and the false negative results (58.3% vs. 25.0%) of the QFT-GIT were significantly higher than in the younger TB group (n=32). Conclusion: Indeterminate and false negative results of QFT-GIT test were not infrequent in tuberculosis, especially in the elderly. Care should be considered for the interpretation with the elderly, immunocompromised, chronic and severely diseased patients.

• Journal of Advanced Marine Engineering and Technology
• /
• v.36 no.5
• /
• pp.618-626
• /
• 2012

Suppression of abnormal flow phenomena in the Francis hydro turbine is very important to improve the turbine performance. Especially, as cavitation and cavitation surge makes serious problems when the turbine is operated in the range of partial flow rate, optimum method of suppressing the abnormal flow characteristics is required necessarily. Moreover, as swirl flow in the draft tube of the Francis turbine decreases pressure at the inlet of the draft tube, suppression of the swirl flow can be an useful method of suppressing the occurrence of cavitation. In order to clarifying the possibility of suppressing the swirl flow by J-Groove in the draft tube, a series of CFD analysis has been conducted in the range of partial load, designed condition and excessive flow rate of a Francis turbine. A kind of J-Groove is designed and applied to the draft tube of the Francis hydro turbine model. The pressure contours, circumferential velocity vectors and vortex core regions in the draft tube are compared by the conditions with or without J-Groove. In addition, a group of data about the velocity in the draft is presented to show the influence of J-Groove.

• Journal of the Korean Society for Advanced Composite Structures
• /
• v.6 no.2
• /
• pp.32-39
• /
• 2015

So far, square concrete filled tubular(CFT) columns have been used in a limited width thickness ratio. The reason is that local buckling occurs in steel tube easily. Once the local buckling occurs, the confinement effect of steel tube on concrete disappears. In this study, we developed welded built-up square steel tube with reinforcement which are placed at the center of the tube width acts as an anchor. 3 specimens of slender welded built-up square CFT columns and 3 specimens of slender welded built-up square steel tube columns were manufactured with parameters of width(B) of steel tube, width thickness ratio(B/t). we conducted a experimental test on the 6 specimens under eccentric load, and evaluated the structural resistance and behavior of 6 specimens.

• Proceedings of the KSME Conference
• /
• 2000.04b
• /
• pp.96-103
• /
• 2000

In this study, evaporation heat transfer tests were conducted in flat aluminum multi-channel tubes using R-22. Two internal geometries were tested ; one with smooth inner surface and the other with micro-fins. Data are presented for the following range of variables ; vapor quality $(0.1{\sim}0.9)$, mass flux$(100{\sim}600kg/m^2s)$ and heat flux$(5{\sim}15kW/m^2)$. The micro-tin tube showed higher heat transfer coefficients compared with those of the smooth tube. Results showed that, for the smooth tube, the effects of mass flux, quality and heat flux were not prominent, and existing correlations overpredicted the data. For the micro-fin tube at low quality, the heat transfer coefficient increased as heat flux increased. However, the trend was reversed at high quality Kandlikar's correlation predicted the low mass flux data, and Shah's correlation predicted the high mass flux data. The heat transfer coefficient of the micro fin tube was approximately two times larger than that of the plain tube. New correlation was developed based on present data.

• Journal of Korean Society of Steel Construction
• /
• v.25 no.4
• /
• pp.347-357
• /
• 2013

Recently, In recognition of outstanding structural performance the use of Concrete Filled steel Tube(CFT) columns has been increased. Research is ongoing that effective use of cross-sectional because steel strength development and rising prices. In this Lab, suggests new shape by Thin steel plates bent to be L-channel welded to form square steel tube to maximize efficiency of the cross section. In addition, since the rib placed at the center of the tube width acts as an anchor; higher load capacity of buckling is acceptable. we have developed New shape welded built-up square tube for broader usability which were bent to be L-shaped and thin Plate each unit member were welded. In order to apply the new shape built-up square columns, we predicted structure behavior, stress distribution with parameter Width thickness ratio. The experimental results presented in standards and even exceed the b/t of the rib anchors installed in the role due to exert enough strength and deformation to improve performance was favorable.

• Tunnel and Underground Space
• /
• v.25 no.1
• /
• pp.46-55
• /
• 2015

A water tube with detonating cord was devised to control the blast dust. Water diffusion experiments with different detonating cord positions were conducted during the series of experiments to optimize the design parameters of the tube. Images from high speed camera were analyzed to evaluate the results. AUTODYN program was adopted to simulate the diffusion process of water and compared with the images. Diffusion of water shows cross flow in case of external charge while the internal case shows radial flow. A bubble ring was formed during the numerical analysis of internal charge case as occurred in underwater blast. An additional bubble ring was formed by the reflection pressure from the ground. And the Weber number was determined as sufficient for spray atomization performance of the water tube.