• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.5
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• pp.856-866
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• 1987

In the present paper a statistical method using probability density function has been applied to investigate experimentally the flow patterns and fluctuations of time-averaged local void fraction in air-water two-phase mixtures which flow vertically upwards in concentric annuli. This study was carried out using three vertical concentric annuli. The annular test section consists of a lucite outer tube whose inside diameter is 38mm and a stainless steel inner rod. The rod diameter is either 12mm, 16mm or 20mm. The two-phase flow patterns observed in the experiment were bubbly, slug, annular and each transition patterns. It was first demonstrated that the variance, coefficients of skewness and kurtosis calculated from probability density function on time-averaged local void fraction can be used to identify the flow patterns in the annular passage, and the fluctuation of time-averaged local void fraction varies with the radial position in annular gap and the flow pattern.

• Journal of Energy Engineering
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• v.9 no.4
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• pp.334-341
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• 2000

회전 히트파이프의 열 전달 특성은 내부 관벽에 형성되는 응축 액막 두께와 증발부로 귀한되는 응축액의 유동율에 의해 결정된다. 본 연구는 축 방향으로 그루브(groove)를 갖는 회전 히트파이프의 열 전달 성능에 대한 실험 연구로써, 그루브에 의한 효과를 파악하기 위해 2종류의 히트파이프를 제작하고 작동성은 시험을 수행하였다. 회전 히트파이프가 작동시, 원심력에 의해 그루브로 응축액의 유동을 촉진시키며, 따라서 응축부 벽면에 형성되는 액막 두께가 얇게 된다. 응축부에 그루브를 갖는 히트파이프의 열전달 계수는 풀 유동에서 2000~4000W/$m^2$$^{0}$ C, 환상 유동 영역에서 1500~2500W/$m^2$$^{0}$ C로써, 전체 원형단면을 갖는 히트파이프와 비교하여 약 1.5배 정도의 열저달 향상을 볼 수 있었으며, 열전달 한계는 약 40% 정도 향상되는 것으로 나타났다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.12
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• pp.1796-1804
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• 1998

A numerical investigation has been performed to discuss the radiation-affected steady-laminar natural convection induced by a hot inner cylinder under a large temperature difference in the annuli filled with a gray gas. To examine the effects of thermal radiation on thermo-fluid dynamic behaviors in the eccentric geometry, the generalized body-fitted coordinate system is introduced while the finite volume method (FVM) is used for solving the radiative transport equation. After validating the numerical results for the case without radiation, the detailed radiation effect has been discussed. Based on the results of this study, when there exists a large temperature difference between two cylinders, the existence of radiatively participating medium is found to incur a distinct difference in fluid dynamic as well as thermal behavior.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.2
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• pp.338-348
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• 1988

This study presents an analysis of periodic heat diffusion in an annular fin with uniform thickness. When the temperature of the fin base is changed in the form of a sinusoidal function, the exact temperature solution can be obtained by Laplace transformation in terms of the dimensionless parameters in the infinite series. Local heat flux and average heat flux, local fin efficiency and average fin efficiency were obtained. Particularly, the table of eigenvalues that are the indispensable condition in solving the heat transfer problem of annular fin in a transient state with convection phenomena at the fin edge is provided. The tables of heat fluxes and average heat fluxes, fin efficiencies and average fin efficiencies are also provided from the computed results. Also, substituting the variations of dimensionless parameters into the these exact solutions, the characteristics of these response are investigated.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.6
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• pp.763-772
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• 1998

The effects of an inserted coil on flow patterns and heat transport performance for a horizontal rotating heat pipe have been studied experimentally. Especially, the present study is to see an internally inserted helical coil inside a RHP would lead to the same kind of results as internal fins. Visualization test conducted for an acryl tube, charged water with at a volumetric rate of 20%. When the flow kept pool regime at a low RPM(less than 1,000 RPM), the movement of coil forced the water to flow in axial direction. But this pumping effect of coil disappeared, when the pool regime changed to annular one which could be created by increasing RPM. The pumping effects for RHP with an inserted coil resulted enhancement both in condensation heat transfer coefficient and heat transport limitation, as obtained in case of using internal fins. But all these effects became negligible in the range of higher RPM(above 1,000∼1,200) with the transition of flow regime to annular flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.9
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• pp.1217-1228
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• 1998

In order to elucidate the operational characteristics of rotating heat pipes, the internal flow patterns and heat transfer performance are investigated. Flow patterns and its transition are studied with various rotational speeds by visualizing flows established inside a rotating tube. To verify those results of analysis, 2 heat pipes of the same geometries but fill charge rates of 7, 30% were manufactured and submitted to operating tests. Comparison of experimental results on heat transfer rate show a fairly good agreement with the analytical results. The analysis reveals that the optimum charge ratio is ranged in 4~7% depending on the quantity of thermal loads. but the heat pipe with 7% of fill charge ratio reached dry-out limitation at heat flux of $q^{{\prime}{\prime}}=6.2kW/m^2$ lower than that of analytic results. Transition of flow regime was well related to the correlation by Semena & Khmelev on transient centrifugal Froude Number Frc. But hysteresis phenomenon was observed in transition of flow regime, when the rotational speed was stepwisely changed in the way to undergo 1 cycle.

• Journal of the Korean Society of Mechanical Technology
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• v.13 no.2
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• pp.85-91
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• 2011

Computational results with pseudoplastic fluid flows for fully developed non-Newtonian laminar flows have been obtained. Those consist of the product of friction factor and Modified Reynolds number and Nusselt numbers with respect to the shear rate parameter in an annular pipe. The numerical results of the product of friction factor and Reynolds numbers and the Nusselt numbers for both Newtonian region and the power law region were compared with previously published asymptotic results, respectively. In the present calculations, the product of friction factor and Newtonian Reynolds numbers for pseudoplastic fluid at power law region in annular pipe is 180% less than that for Newtonian fluid. For power law fluids with different power law flow indices, the difference of the product of friction factor and power law Reynolds number between previous and the present results at the power law region is within 0.20%. The solutions also show the effect of the shear rate parameter on the Nusselt number and about 11% increase of Nusselt number at the power region.

• The Korean Journal of Pharmacology
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• v.24 no.2
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• pp.217-220
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• 1988

At present, the treatment of the radiation-induced diseases are only performing by the palliative treatment technique. Moreover, radioprotective drugs are a little toxic for human being and this seriously limits their application with various complication in clinical uses. Accordingly, new radioprotectors need developing. In our Lab., we synthesized trithioformaldehyde (TTFA), containing three sulfur atom, and examined the effect on mouse jejunal crypt cells after irradiation. Mice treated with TTF A (2.0 g/ kg) showed 78% survival ratio at 30 day after 800 rad irradiation. 1.0 g/kg and 2.0 g/kg of TTF A increased resistance of jejunal crypt cells to single doses of radiation by protection factors of 1.17 and 1.23, respectively.

• Polymer(Korea)
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• v.27 no.5
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• pp.429-435
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• 2003

Vinyl addition copolymerizations of norbornene (NB) and 5-vinyl-2-norbomene (VNB) were carried out using a cationic η$^3$-allyl palladium catalyst in the various mole ratio of comonomers. The copolymers could be obtained in good yield (65∼85%) with high weight-average molecular weights (M$_{w}$ > 760,000). Depending on increasing VNB contents, the molecular weight and yield of the copolymers decreased. FT-IR analysis confirmed that actual contents of VNB in polymer were proportional to the feeding content of VNB. From $^1$H-NMR spectroscopy, we found that both exo and endo VNB isomer were copolymerized with NB. Thermal stabilities of NB-VNB copolymers were independent on the VNB content and their initial decomposition temperatures were about 300 C. The NB-VNB copolymers were followed by epoxidation by using m-CPBA and hydroxylation by 9-BBN, respectively, and these post-polymers were characterized by FT-IR spectroscopy and $^1$H-NMR analysis..

• Korean Journal of Ichthyology
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• v.10 no.1
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• pp.115-127
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• 1998

The digestive tract of the rockfish, Sebastes schlegeli composed of pharynx, esophagus, stomach, intestine, anus and ten or eleven pyloric caeca. Pyloric caeca is blind sac of banana shape, and that is originated from pyloric portion of the stomach. The relative length of gut(RLG), that is length of digestive tract to standard length, is about 1.56(n=10). Esophageal muscularis consists of thin outer layer of longitudinal muscle and thick inner layer of circular muscle. Mucosal epithelium consists of columnar epithelium with short microvilli and contains numerous mucous secretory cell. The mucosal folds of the stomach are regular, and the muscularis consists of longitudinal, oblique and circular muscle layer. The chief cell of the gastric gland have a tubular mitochondria, endoplasmic reticula and numerous secretory granules in electron-dense. However, parietal cell contains small mitochondria, endoplasmic reticula and vacuoles in low electron density. Mucosal epithelium of the pyloric caeca and intestine composed of columnar epithelium, goblet cell, rodlet cell and dark cell. Columnar absorptive cell in the pyloric caeca and intestine contains well developed mitochondria, endoplasmic reticula, vesiculated granules in high electron density, pinocytotic vesicles and multivesicular body. Rodlet cell have a well developed cytoplasmic capsule and the endoplasmic reticula in the cytoplasm. Dark cell showing a high electron density in the cytoplasm and contains well developed mitochondria. Columnar epithelium of the intestine have a well developed intercellular junction and the microvilli which contains actin filament originated from the cytoplasm. Mucosal epithelium of the intestine have a longer microvilli and more abundant goblet cells than in the pyloric caeca.