• 설비공학논문집
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• 제8권1호
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• pp.88-98
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• 1996

The present study is concerned with the flow friction and heat transfer characteristics of the combination of various regenerator materials, using the different Darcy number and porosity, which is filled uniformly and partially in a tube under oscillating flow condition. The poros medium is adopted as Brinkmann-Forschheimer extended Darcy model. Numerical results are obtained or the flow and temperature fields and described the effect of the combination of various regenerator materials and Womersley number on the pressure drop, the heat transfer and the regenerator efficiency. The results obtained indicate that not only heat transfer between the tube wall and oscillating flow but also the pressure drop at both ends of the regenerator are increased, while the regenerator efficiency is decreased in the increase of womersley number. It is also found that the friction factor is increased as Reynolds number is increased. The comparison between the combination of the various regenerator materials and the homogeneous regenerator material shows that the regenerator efficiency can be enhanced with the proper combination of various regenerator materials even though the averaged porosity of the regenerator is same.

• 에너지공학
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• 제26권1호
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• pp.9-22
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• 2017

A combined thermal and flow analysis was carried out to study the behavior and performance of a small, commercial LTD (Low-Temperature-Differential) heat engine. Laminar-flow solutions for annulus and channel flows were employed to estimate the viscous drags on the piston and the displacer and the pressure difference across the displacer. Temperature correction factors were introduced to account for the departure from the ideal heat transfer processes. The analysis results indicate that the work required to overcome the viscous drags on engine moving parts and to move the displacer is much smaller than the moving-boundary work produced by the power piston for temperature differentials in the neighborhood of $20^{\circ}C$ and engine speeds below 10 RPS. A comparison with experimental data reveals large degradations from the ideal heat transfer processes. Thus, heat-transfer devices inside the displacer cylinder are recommended.

• Design & Manufacturing
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• 제13권1호
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• pp.19-24
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• 2019

Currently, the world is paying keen attention to the production of renewable energy along with environmental issues, and the share of renewable energy in the world is rising above that of nuclear power. Especially when Korea, which is heavily dependent on foreign countries, needs to reconsider its national competitiveness due to the recent high oil prices, the government's energy policy is to develop and use renewable energy that replaces fossil fuels. In particular, solar energy, the most actively studied and commercialized field of renewable energy, is the main research for solar energy and is commercialized and used. However, the efficiency of solar energy has already reached saturation. Studies are also focusing on increasing the reflectivity of solar energy to increase efficiency. Therefore, this paper proposes a solar collection system that can utilize solar energy rather than solar energy. The proposed solar heat collection system uses solar tracking systems to effectively collect solar energy, particularly those that can be easily produced using single-modular reflectors and have price competitiveness. In addition, temperature measurement experiments with temperature measuring sensors were conducted to ensure reliability in order to verify the results interpreted.

• Nuclear Engineering and Technology
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• 제54권4호
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• pp.1482-1494
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• 2022

Power conversion cycles (Subcritical Steam, Supercritical Steam, Open Air Brayton, Recuperated Air Brayton, Combined Cycle, Closed Brayton Supercritical CO₂ (sCO₂), and Stirling) are evaluated for land-based nuclear microreactors based on technical maturity, system efficiency, size, cost and maintainability, safety implications, and siting considerations. Based upon these criteria, Air Brayton systems were selected for further evaluation. A brief history of the development and applications of Brayton power systems is given, followed by a description of how these thermal-to-electrical energy conversion systems might be integrated with a nuclear microreactor. Modeling is performed for optimized cycles operating at 3 MW(e) with turbine inlet temperatures of 500 ℃, 650 ℃ and 850 ℃, corresponding to: a) sodium fast, b) molten salt or heat pipe, and c) helium or sodium thermal reactors, coupled with three types of Brayton power conversion units (PCUs): 1) simple open-cycle gas turbine, 2) recuperated open-cycle gas turbine, and 3) recuperated and intercooled open-cycle gas turbine. Aeroderivative turboshaft engines employing the simple Brayton cycle and two industrial gas turbine engines employing recuperated air Brayton cycles are also analyzed. These engines offer mature technology that can facilitate near-term deployment with a modest improvement in efficiency.

• Nuclear Engineering and Technology
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• 제54권12호
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• pp.4743-4750
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• 2022

Heat pipe cooled nuclear reactor has been a very attractive technical solution to provide the power for deep space applications. In this paper, a 200 kWe space nuclear reactor power design has been proposed based on the combination of an integrated UN ceramic fuel, a heat pipe cooling system and the Stirling power generators. Neutronics and thermal analysis have been performed on the space nuclear reactor. It was found that the entire reactor core has at least 3.9 $ subcritical even under the worst-case submersion accident superimposed a single safety drum failure, and results from fuel temperature coefficient, neutron spectrum and power distribution analysis also showed that this reactor design satisfies the neutronics requirements. Thermal analysis showed that the power in the core can be successfully removed both in normal operation or under one or more heat pipes failure scenarios.

• 대한기계학회논문집A
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• 제34권5호
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• pp.605-609
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• 2010

적외선 센서를 사용하는 최신 관측용 장비들을 저온으로 유지하기 위해서는 극저온 컴프레서를 센서에 연결한다. 그러나 컴프레서 진동원으로부터 발생한 외란 힘에 의해 취득 영상 품질이 저하된다. 따라서 고품질의 영상을 얻기 위해 극저온 쿨러에 대한 진동 절연 설계가 필요하다. 본 논문은 수동 진동 절연 방법의 장점을 사용하면서 컴프레서 외란 진동에 대한 높은 절연 성능이 있는 시스템을 연구 및 설계하는 것이다. 수동 진동 흡수기는 컴프레서의 구동 주파수를 고려하여 설계했다. 또한, 특정 외란 진동과 고주파수의 진동도 절연되는 쿨러 절연 브래킷을 설계하였고, 성능 분석을 위한 실험을 수행하였다.

• 한국어류학회지
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• 제11권2호
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• pp.134-138
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• 1999

피부흡충인 Entobdella hippoglossi가 숙주인 Atlantic halibut의 피부에 기생할 때 기생 부위별 밀도와 숙주의 피부 점액세포 밀도를 조사하여 E. hippoglossi의 기생이 피부점액 세포의 밀도와 관계가 있는가를 조사하였다. 숙주인 Atlantic halibut 복측과 배측에 기생하는 E. hippoglossi의 밀도는 비슷하였으나 기생충의 크기는 복측이 배측보다 더 컸으며, 배측내에서는 배측의 머리부분에 기생하는 E. hippoglossi의 밀도가 배측의 중앙부나 꼬리부분에서보다 높았다. 숙주의 점액세포 크기, 밀도 그리고 표피 점액층의 두께는 대체로 기생충의 밀도와 비례하였고, 숙주내에서 기생충의 선택적 기생은 점액세포의 밀도와 관계가 있었다.

• 천문학회보
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• 제35권1호
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• pp.39.2-39.2
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• 2010

In this paper, I present the domestic development of near infrared camera systems for the ground telescope and the space satellite. These systems are the first infrared instruments made for astronomical observation in Korea. KASINICS (KASI Near Infrared Camera System) was developed to be installed on the 1.8m telescope of the Bohyunsan Optical Astronomy Observatory (BOAO) in Korea. KASINICS is equipped with a $512{\times}512$ InSb array enable L band observations as well as J, H, and Ks bands. The field-of-view of the array is $3.3'{\times}3.3'$ with a resolution of 0.39"/pixel. It employs an Offner relay optical system providing a cold stop to eliminate thermal background emission from the telescope structures. From the test observation, limiting magnitudes are J=17.6, H=17.5, Ks=16.1 and L(narrow)=10.0 mag at a signal-to-noise ratio of 10 in an integration time of 100 s. MIRIS (Multi-purpose InfraRed Imaging System) is the main payload of the STSAT-3 in Korea. MIRIS Space Observation Camera (SOC) covers the observation wavelength from $0.9{\mu}m$ to $2.0{\mu}m$ with a wide field of view $3.67^{\circ}{\times}3.67^{\circ}$. The PICNIC HgCdTe detector in a cold box is cooled down below 100K by a micro Stirling cooler of which cooling capacity is 220mW at 77K. MIRIS SOC adopts passive cooling technique to chill the telescope below 200K by pointing to the deep space (3K). The cooling mechanism employs a radiator, a Winston cone baffle, a thermal shield, MLI of 30 layers, and GFRP pipe support in the system. Opto-mechanical analysis was made in order to estimate and compensate possible stresses from the thermal contraction of mounting parts at cryogenic temperatures. Finite Element Analysis (FEA) of mechanical structure was also conducted to ensure safety and stability in launching environments and in orbit. MIRIS SOC will mainly perform the Galactic plane survey with narrow band filters (Pa $\alpha$ and Pa $\alpha$ continuum) and CIB (Cosmic Infrared Background) observation with wide band filters (I and H) driven by a cryogenic stepping motor.

• 천문학회보
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• 제35권1호
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• pp.40.2-40.2
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• 2010

MIRIS 우주관측카메라는 과학기술위성 3호의 주탑재체로서 $0.8{\sim}2.0{\mu}m$의 근적외선영역에서 우주배경복사와 우리은하 평면의 Pa-$\alpha$ survey 관측을 목적으로 한다. 이러한 임무를 수행하기 위해 MIRIS 우주관측카메라에는 MCT(HgCdTe) IR 검출기가 사용되고 6개의 필터를 장착할 수 있는 필터휠이 설계되었으며, 열잡음을 줄이고 원하는 SNR을 얻기 위해 모두 100K 이하로 냉각이 요구된다. 효과적인 냉각 및 저온유지를 위해서 외부의 열을 1차적으로 차단하는 Cryostat 외부용기와 100K 이하로 냉각되는 내부 Cold Box의 이중구조를 가지는 Dewar가 설계 되었다. 내부 Cold Box의 냉각은 소형 stirling cooler로 이루어지고 외부의 열 유입량이 Cooler의 냉각용량을 넘지 않도록 설계하였다. Cryostat 외부용기는 radiation cooling으로 냉각되어 200K 이하의 온도를 유지하며 내부 Cold Box로의 열유입을 최소화하기 위해 GFRP(Glass Fiber Reinforced Plastic) 단열 지지대와 MLI(Multi Layer Insulation)가 사용된다. 또한 100K으로 냉각시 필터고정부와 Cold Box 구조에서 일어날 수 있는 구조적인 피로도를 줄이고 열변형에 의한 문제를 방지하기 위한 고려가 설계에 포함되었다. FM(Flight Model)은 고진공 환경의 우주공간에서 문제가 발생하지 않도록 설계되었다. 또한 EQM 진동시험결과를 토대로 발사환경에서 발생하는 강한 진동을 견딜 수 있도록 FEM(Finite Elements Method) 구조해석을 통하여 필터고정부에 flexible structure 설계와 완충제를 추가하고 필터휠 구동부와 harness 고정부 및 cooler 지지부를 비롯한 전체 구조물에서 충분히 진동을 극복할 수 있도록 설계하였다.

• 한국양식학회지
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• 제19권2호
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• pp.99-108
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• 2006

Sex of the Nile tilapia Oreochromis niloticus is mainly determined by an XX/XY system. However, accumulating evidences suggest the existence of additional sex modifying factors including environmental, autosomal and parental influences. In order to investigate the possibility of parental effects on sex ratios of tilapia progenies, in this study, a series of crosses was carried out using gynogenetic clonal fish, neomales, normal males and females, and YY fish. Crosses between clonal XX male and clonal female have yielded only female progenies and no parental influences were observed. However, in the crosses between clonal males and normal females, female parents were significantly associated with the progeny sex ratios ($X^2$=20.046, 7 d.f., p<0.01). Progeny sex ratios from the crosses between neomales and normal females ($X^2$=60.491, 5 d.f and $X^2$=28.072, 2 d.f.) also showed significant association with female parents (P<0.001). The stability of progeny sex ratios from repeated spawns were confirmed by using 6 different parental pairs. In 16 crosses between normal males and normal females, sex ratios of progenies showed clear maternal influences, and further analysis of the results revealed a negative correlation ($r^2$=0.7718, p<0.05) between the sex ratios of progenies from two different males, indicating a strong paternal influence. No statistically significant relationship between survival rates and sex ratios of progenies was observed in any genotypic groups. Taken together, the influence of parental pairs on progeny sex ratios in this species is evident although the cause of this influence is not clear.