• 한국정보통신설비학회:학술대회논문집
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• 2009.08a
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• pp.54-58
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• 2009

In this paper, the ECT(eddy current testing) signal analysis of eddy current array probe for inspection of SG(steam generator) tube in NPP(nuclear power plant) using electromagnetic FEM(finite element method) was performed. To obtain the electromagnetic characteristics of probes, the governing equation was derived from Maxwell's equation, and the problem was solved by using the 3-dimensional FEM. The types of defects were FBH(flat bottomed hole) and OD groove, Spiral groove, natural defects(pitting, SCC, multiple SCC, wear). The depth of FBH defects were 20%, 40%, 60%, 80%, 100 of SG tube thickness, and it was assumed that the defects were located on the tube outside. And the operation frequency of 100kHz, 300kHz and 400kHz were used. Material of specimen was Inconel 600 which is usually used for SG tubes in NPP. The signal difference could be observed according to the variation of size and depth on FBH defects and operation frequencies. The results in this paper can be helpful when the ECT signals from EC array probe are evaluated and analyzed.

• Journal of Biomedical Engineering Research
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• v.39 no.3
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• pp.116-123
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• 2018

This study is a model experimental study using a phantom to propose an optimized brain CT scan protocol that can reduce the radiation dose of a patient and remain quality of image. We investigate the CT scan parameters of brain CT in clinical medical institutions and to measure the important parameters that determine the quality of CT images. We used 52 multislice spiral CT (SOMATOM Definition AS+, Siemens Healthcare, Germany). The scan parameters were tube voltage (kVp), tube current (mAs), scan time, slice thickness, pitch, and scan field of view (SFOV) directly related to the patient's exposure dose. The CT dose indicators were CTDIvol and DLP. The CT images were obtained while increasing the imaging conditions constantly from the phantom limit value (Q1) to the maximum value (Q4) for AAPM CT performance evaluation. And statistics analyzed with Pearson's correlation coefficients. The result of tube voltage that the increase in tube voltage proportionally increases the variation range of the CT number. And similar results were obtained in the qualitative evaluation of the CT image compared to the tube voltage of 120 kVp, which was applied clinically at 100 kVp. Also, the scan conditions were appropriate in the tube current range of 250 mAs to 350 mAs when the tube voltage was 100 kVp. Therefore, by applying the proposed brain CT scanning parameters can be reduced the radiation dose of the patient while maintaining quality of image.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.1
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• pp.63-67
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• 2016

We present a method of fabricating poly (lactic-co-glycolic acid) (PLGA) porous microfibers using a pore template. PLGA microfibers were synthesized using a glass capillary tube in a poly-(dimethylsiloxane) (PDMS) microfluidic chip. Gelatin solution was used as a porous template to prepare pores in microfibers. Two phases of PLGA solutions in different solvents-DMSO (dimethyl sulfoxide) and DCM (dichloromethane)-were used to control the porosity and strength of the porous microfibers. The porosity of the PLGA microfibers differed depending on the ratio of flow rates in the two phases. The porous structure was formed in a spiral shape on the microfiber. The porous structure of the microfiber is expected to improve transfer of oxygen and nutrients, which is important for cell viability in tissue engineering.

• International Journal of Air-Conditioning and Refrigeration
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• v.15 no.4
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• pp.163-168
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• 2007

The feature of six existing condensation heat transfer correlations for microfin tubes were evaluated with the consideration of vapor quality, mass flux, geometries, and various refrigerants. The Kosky and Staub [15] and the Jaster and Kosky [16] correlations for smooth tube were used for the evaluation of the heat transfer enhancement factor (EF). For the prediction of zeotropic mixtures, most correlations show discrepancy with previous measurements. The Yu and Koyama [4] and the Shikazono et al. [8] correlations do not consider spiral angle effect. The Han and Lee [10] correlation shows fin height growth deteriorates heat transfer. Experimental verification to develop reliable condensation heat transfer correlation for microfin tubes is still needed with the consideration of geometrical effects and working conditions.

• Applied Microscopy
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• v.33 no.4
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• pp.325-333
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• 2003

Fine structural characteristics of the heart tube and its cardiac muscle cells in spider, Araneus ventricosus are investigated by both of scanning and transmission electron microscopes. The heart tube of the spider is extended mid-dorsally along the anterior part of the abdomen, and is consisted of the thin outer layer of connective tissue (epicardium) and the thick muscle layer (myocardium). The myocardium in the spider has a typical fanlike spiral structure toward anterior part put across between the muscle fibers. Therefore, it did not give rise to the intima, and muscle cells are in direct contact to the hemolymph. The heart tube appeared to be three pairs of ostia and numerous hemocytes accumulated at the inner surface of the myocardial layer. Among several kinds of the hemocytes, the oenocytoids are the most predominant hemocytes accumulated along the myocardial folds which stretched toward heart lumen. The heart muscle cells are cross striated, branched, and multinucleated. They contain a lot of mitochondria, which provide for the continuous energy demands of the heart. Thread-like ganglion on the dorsal side of the heart tube gives off axons that innervate the heart muscle cells.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.9
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• pp.627-632
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• 2011

As an innovative effort to secure economically viable heat recovery system, various fin shapes for industrial fin-tube heat exchangers have been studied for better performance. In this study, the waste gas heat recovery from four different fin shapes was experimentally performed for heat transfer rate and pressure drop. According to the tested results, the twist and wavy shape fins of rectangular type show the superior performance in terms of Goodness factor and jH/f factor ratio, whereas the circular spiral fin shows the inferior values. Experimental results shows good comparison with the numerical results with a slight discrepancy of 5%, which is quite resonable.

• Applied Chemistry for Engineering
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• v.21 no.1
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• pp.71-75
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• 2010

The efficient performance of absorber is of great importance for the absorption heat pump cycle. The experimental study of absorber with spiral tube of tangential feeding of liquid phase has been investigated using methanol-glycerine as a working fluid. The effect of change in absorber operating conditions was analyzed to improve the performance. The increase in solution flow rate and cooling flow rate positively affects the absorber performance while an increse in the solution concentration negatively affects the absorber performance. The results showed that mass absorption flux was in the range of $0.2{\sim}0.6kgm^{-2}sec^{-1}$, the solution heat transfer coefficient between 1.6 and $4.2kwm^{-2}K^{-1}$, the absorber thermal load from 0.9 to 1.5kw and the mass transfer coefficient from 0.9 to 1.7 m/sec.

• Journal of the korean academy of Pediatric Dentistry
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• v.27 no.4
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• pp.490-493
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• 2000

Mesiodens are supernumerary teeth in the region of the maxillary central incisors, a condition which can lead to disorders of the dentition. Their presence may lead to disorders, such as delay in eruption of permanent teeth, development of dentigerous cysts, resorption of adjacent roots and eruption of a supernumerary tooth into nasal cavity. The optimal time for surgical intervention is controversial. Early diagnosis is important so as to enable good prognosis. Diagnosis primarily depends on x-ray films. Panorama film, occlusal film, periapical film have been used for detection of mesiodens. But, all of them have disadvantages. $SCANORA^{(R)}$ is a multimodal radiology system which utilizes the principles of narrow beam radiology and spiral tomography. Pre-programmed imaging procedure are provided for many dental situations An optional personal computer can be connected into the unit to help design the examination. We report two cases diagnosed by $SCANORA^{(R)}$. When compared with tube shift technique, it is simple and exact method of detecting mesiodens.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.2
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• pp.253-261
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• 1987

Thermoacoustic oscillation of an air column induced by heated wires is investigated analytically and experimentally. Acoustic power generation from a single heater wire is estimated based on the result of heat transfer analysis and expressed in terms of the efficiency factor indicating the conversion efficiency from heat to acoustic energy. It is shown that the efficiency factor becomes maximum when the wire radius is the order of the coustic boundary layer thickness and the flow velocity is close to the thermal diffusion velocity. Onset condition of the column oscillation is obtained by equating the acoustic power generation at the heater to the power loss due to thermoviscous dissipation at the tube wall and the convection and radiationloss at the open ends of the tube. In estimating the acoustic power generation, the heater is treated as a stretched single wire by correcting the flow velocity to take into account the interactions between adjacent heater wires. Experiment is performed by using a spiral heater of 1mm diameter in an air column of 37mm diameter. The heat input to drive the oscillation is measured and compared with the theoretical prediction. A good agreement is found between the theory and experiment, which is regarded as a substantial verification of the present analysis.

• The Journal of the Acoustical Society of Korea
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• v.29 no.8
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• pp.491-496
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• 2010

Thermoacoustic power generation by a spiral heater in the Rijke tube was analyzed numerically. In the analysis, variables were normalized by the angular frequency of the sound and the thermal diffusivity of the air. The effect of the heater wire diameter d, the spacing between wires P-d, and the air-current velocity $U_0$, upon the power generation was obtained and discussed. When the spacing is broad enough, the normalized velocity is $U_0{\approx}0.8$ and the diameter is $d{\approx}4$ for the maximum power generation. With decrease of the spacing, however, the power generation increases more than 5 times and becomes maximum around $d{\approx}2$, $P-d{\approx}3$. And the velocity $U_0{\approx}0.8$ for the maximum power generation is almost independent of the wire spacing.