• Journal of Power System Engineering
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• v.4 no.2
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• pp.17-24
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• 2000

직경비가 0.26, 0.39, 그리고 0.56인 경우 거칠기를 내벽면에, 외벽면에, 그리고 양벽면에 각각 설치한 동심환형관에서 완전히 발달된 난류유동에 대한 거칠기 효과를 실험과 이론으로 해석하였다. 그리고 거칠기 효과를 정량적으로 파악하기 위해 양벽면 모두 매끈한 환형관의 경우도 포함하였다. 실험에서 마찰계수를 구하는데 필요한 속도분포와 전단응력들은 피토튜브와 X-형 열선풍속계를 사용하였다. 이론 해석은 수정대수 난류모델을 사용하였고 그 결과를 이론값과 비교하여 아래의 결론을 얻었다. 1) 무디다이어그램 (Moody diagram)은 거칠기가 설치된 이중관에는 적용할 수 없음을 보였다. 2) 경우(c) 와 (d)에서는 반경비가 클수록 반드시 마찰계수가 증가하지 않았다. 3) 4개의 경우중 거칠기로 인해 마찰계수가 증가하는 크기의 순서는 경우(d)가 가장 컸고 경우(a)가 가장 작았다.

• Journal of Power System Engineering
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• v.1 no.1
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• pp.61-69
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• 1997

본 연구는 동심환형관에서 거칠기가 없이 매끈한 경우, 내측벽에 만, 외측벽에 만, 그리고 양측 모두에 거칠기가 있는 4경우에 대해 직경비가 0.26, 0.39, 그리고 0.56일 때 벽면에 설치된 거칠기 위치들이 난류유동장에 미치는 효과를 실험적으로 조사하고자 한다. 최대속도와 전단응력이 0인 지점들, 시간평균속도의 구배들, 그리고 와확산계수들을 X형 열선풍속계와 이중 피토튜브를 사용하여 측정하였다. 본 연구를 통하여 동심환형관에 설치된 거칠기들이 난류유동에 미치는 효과에 대한 정량적자료를 제시할 수 있었다.

• Journal of Advanced Marine Engineering and Technology
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• v.21 no.2
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• pp.136-143
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• 1997

직경 비가 0.56인 이중동심관에 내외측모두 매끈한 벽면, 벽면 거칠기를 안측, 외측, 그리고 양측 모두의 4경우에 대한 난류 유동과 열전달특성을 실험과 이론으로 연구하였다. 시간평균속도분포, 마찰계수, 그리고 최대 속도 지점과 전단응력이 0인 지점들을 피토튜브와 X형 열선 풍속계로 측정하였다. 이중동심관내에서 4가지 경우에 따른 사각돌출형 거칠기효과가 난류 유동과 열전달에 미치는 영향을 수정난류모델을 기초로 하여 연구하였다. 직경비, 거칠기 위치, 레이놀즈수, 그리고 프란틀수 등의 여러 변수에 의해서 난류 유동과 열전달을 고찰하였다. 본 연구는 전체적 효율 측면에서 유리하게 열전달율을 향상시킬수 있는 거칠기 구조를 밝혔다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1294-1303
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• 1993

The fully developed turbulent momentum and heat transfer induced by the square-ribed roughness elements on the inner wall surface in concentric annuli is studied analytically based on a modified turbulence model. The analytical results of the fluid flow is verified by experiment. The resulting momentum and heat transfer are discussed in terms of various parameters, such as the radius ratio, the relative roughness, the roughness density, fluid Reynolds number and for heat transfer, fluid Prandtl number. The study demonstrates that certain artificial roughness elements may be used to enhance heat transfer rates with advantages from the overall efficiency point of view.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.83-89
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• 2000

This paper presents a pressure drop correlation for evaporation and condensation of alternative refrigerant with oil in micro-fin tubes. The correlation was developed from a data base consisting of oil-free pure and mixed refrigerants in micro-fin tube; Rl25 R134a. R32 R410a(R32/R125 50/50% mass), R22, R407c(R32/R125/R134a, 23/25/52% mass) and R32/R134a(25/75% mass). The micro-fin tube used in this paper had 60 0.2mm high fins with a 18 helix angle. The cross sectional flow area $(A_c)$ was $60.8 mm^2$ giving an equivalent smooth diameter$(D_e)$ of 8.8mm. The hydraulic diameter $(D_h)$ was estimated to the 5.45mm. The new correlation was obtained by replacing the friction factor and the tube-diameter in Bo Pierre correlation by a friction factor derived from pressure drop data for a micro-fin tube and the hydraulic diameter, respectively. This correlation was also used to predict some pressure data with a lubricant after using a mixing viscosity rule of lubricants and refrigerants. As a result, the new correlation was also well predicted to the measured data within a mean deviation of 19.0%.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.314-322
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• 2003

Pipe cooling method is widely used for reduction of hydration heat and control of cracking in mass concrete structures. However, in order to effectively apply pipe cooling systems to concrete structures, the coefficient of flow convection relating the thermal transfer between inner stream of pipe and concrete must be estimated. In this study, a device measuring the coefficient of flow convection was developed. Since a variation of thermal distribution caused by pipe cooling has a direct effect on internal forced flows, the developed testing device is based on the internal forced flow concept. Influencing factors on the coefficient of flow convection are mainly flow velocity, pipe diameter and thickness, and pipe material. Using experimental results from the developed device, the coefficient of flow convection was calculated. Finally, a general prediction model was proposed by theoretical procedures. The proposed prediction model is able to estimate the coefficient of flow convection with flow velocity and material properties of pipe. From comparison with experimental results, the coefficient of flow convection by this model was well agreed with those by experimental results.

• Applied Microscopy
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• v.35 no.2
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• pp.65-72
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• 2005

The ultrastructure of submandibular gland was examined in the lesser white-toothed shrew, Crocidura suaveolens. The submandibular gland of C. suaveolens was a mixed gland composed of serous and mucous acinar cells. Secretory granules from the acini were discharged through the salivary ducts into the oral cavity. Serous and mucous acinar cells had well developed rough endoplasmic reticulum and mitochondria and large amount of granules. In case of serous acinar granules, an immature granule was formless and had only dense specks, and a matured granule was a complete round type delimiting by a single membrane and had a homogeneous dense center with dense specks on the border. In case of mucous acinar granules, while an immature granule was a round type and had an only homogeneous matrix and an indistinct limiting membrane, a mature granule was an even round type having a variety of pattern with several dense bands into the homogeneous matrix and had a distinct membrane. Therefore, a mature mucous acinar granule of C. suaveolens was not only distinct from those of the other mammalian species to have a variety of pattern but also from those of C. lasiura to have an even round type. A great serous-like secretory granules and Myelin-like body were observed in the cytoplasm and lumen of granular duct cells. Myelin-like body, a characteristic structure only reported in salivary gland of three shrews, was discharged from secretory cell into lumen by the manner of exocytosis which has little differences from discharging manner of secretory granules.

• Journal of Chest Surgery
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• v.31 no.7
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• pp.725-729
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• 1998

Endobronchial leiomyoma is extremely rare and accounts for less than 2% of benign tumors of the lower respiratory tract. Leiomyomas are predominantly found in the young and the middle aged : of the average age being 35 years for bronchial and lung parenchymal lesions and 40.6 years for tracheal lesions. The symptom depends on the location of the tumor, its size, and changes in the lung distal to the lesion. A 37-year-old woman was admitted to our hospital complaining of coughing. Bronchoscopy revealed complete obstruction of the right main bonchus at the carina by an oval-shaped, nonulcerative, smooth, and pinkish-tan tumor with a broad margin and extended to the left main bronchus. A biopsy was performed and showed a benign spindle cell tumor. A right pneumonectomy was performed because of chronic infection, and the lung could not expanded during aeration. The histological diagnosis of the resected specimen was leiomyoma. The postoperative course was uneventful.

• Journal of Energy Engineering
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• v.7 no.2
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• pp.194-201
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• 1998

In electric commuter trains using AC motors, lots of GTO thyristors and diodes are needed for power controls. These semiconductors generate heat about 1~2 kW, and for cooling which perfluorocarbon(PFC) heat pipes have been in use for the last two decades. The present study was investigated on the effects of such important design parameters as structure of internal surface (grooved or smooth), fill charge ratio, and inclinating angle from a vertical on heat transfer coefficients at both evaporators and condensers. To obtain experimental data, several heat pipes of the same geometry of 520 mm long and diameter of 15.88 mm but different in fill charge ratio and internal surface structure were designed and fabricated. For prediction of the heat transfer coefficients, related expressions were examined and the results of calculations were compared with experimental data. Performance tests were conducted while heat pipes operated at mode of thermosyphons. High enhancements of heat transfer coefficient were obtained internal grooves. In these cases, the evaporating heat transfer coefficients distributed in the range of 2~5.5 kW/$m^2$K, with an increase of heat flux from 15~45 kW/$m^2$. These experimental data were in good agreement with Rohsenow's expression based on nucleate boiling when correction factor $C_R$=1.3 was encountered. In addition, the condensation heat transfer coefficients were distributed from 1.5 to 3.5 kW/$m^2$K, and the data were in good agreements with Nusselt's correlation, based on filmwise condensation on vertical plate, when choosing a correction factor $C_N=4$. A fill charge ratio of 40~100% were recommended, and the in clination angle effects were negligible when the angle was higher then 30$^{\circ}$.

• Journal of the Korean Wood Science and Technology
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• v.41 no.3
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• pp.247-257
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• 2013

This study was to investigate the antifungal activity of Larix kaempferi essential oil against dermatophytes, Epidermophyton floccosum, Trichophyton mentagrophytes and Trichophyton rubrum. The active components of L. kaempferi against dermatophytes were determined (characterized by GC-MS), and the morphological changes of the dermatophytes exposed to the L. kaempferi essential oil were observed by electron microscope. Main component of L. kaempferi essential oil was (-)-bornyl acetate. In antifungal activity tests, MIC of L. kaempferi crude oil was 125 ppm on every fungi and 100% (agar dilution method) at more than 500 ppm. By using SEM and TEM, the fungal morphology of E. floccosum exposed to the L. kaempferi essential oil was different from that of normal hyphal morphology. Hyphae exposed to the L. kaempferi essential oil was damaged with distorted and collapsed surfaces. In addition, there were destruction and disorganization of organelles in cytoplasm and collapse of cell membrane. Active antifungal components from L. kaempferi essential oil were identified as terpene alcohol compounds like (-)-${\tau}$-muurolol, (+)-terpinen-4-ol, ${\alpha}$-terpineol, and ${\alpha}$-cadinol.