• Journal of Advanced Marine Engineering and Technology
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• 제31권2호
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• pp.145-151
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• 2007

The evaporation heat transfer coefficient of $CO_2$(R-744) in a horizontal tube was investigated experimentally. The main components or the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator(test section). The test section consists of a smooth, horizontal stainless steel tube of inner diameter of 4.57 mm. The experiments were conducted at mass flux of 200 to $500\;kg/m^2s$, saturation temperature of -5 to $5^{\circ}C$, and heat flux of 10 to $40\;kW/m^2$. The test results showed the heat transfer of $CO_2$ has a greater effect on nucleate boiling more than convective boiling. Mass flux of $CO_2$ does not effect nucleate boiling too much. In comparison with test results and existing correlations, the best fit of the present experimental data is obtained with the correlation of Jung et al. But existing correlations failed to predict the evaporation heat transfer coefficient of $CO_2$, therefore, it is necessary to develope reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.81-81
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• 2011

본 연구는 $CO_2$를 냉매로 하는 급탕용 히트펌프 성능특성을 평가하는 시험 평가법에 대하여 국내 실정에 맞는 시험평가법을 개발하기 위한 목적으로 기존 $CO_2$ 급탕용 히트펌프의 평가방법을 분석하고자 한다. 현재 $CO_2$ 급탕기 또는 급탕용 히트펌프 제품은 일본에서 2000년 초반부터 에코큐트라는 제품으로 일본 급탕용 난방기기로 판매되고 2009년을 기초로 누적판매 대수가 150만대에 이르고 있다. 국내에는 2008년 후반부터 공기열원 또는 폐열원 등을 이용한 급탕용 히트펌프 제품이 일부 수입되어 목욕탕, 찜질방과 같은 숙박업소용으로 판매되고 있는 추세이다. 국내에서는 급탕용 열펌프의 제품의 정의가 아직 정립되지 않고 이에 대한 시험평가방법이 전무한 실정이기 때문에 현재 일본의 가정용 열펌프 급탕기의 규격을 토대로 실제 급탕용 열펌프의 시험을 수행하여 급탕용 히트펌프의 급탕성능특성을 평가하는 방법을 개발하고자 한다. 시험시료는 일본에서 판매되고 있는 급탕용 히트펌프(D사) 제품을 이용하였으며, 현재 일본에서 사용하고 있는 JRA4050 규격에 의해 급탕성능평가를 진행하고 급탕성능평가 지표 등을 국내 유사조건과 급탕성능특성의 평가방법을 비교분석하였다.

• 한국자동차공학회논문집
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• 제16권1호
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• pp.121-126
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• 2008

The cooling heat transfer coefficient of $CO_2$ (R-744) in a horizontal and helically coiled tube was investigated experimentally. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater, evaporator and gas cooler (test section). The test section consists of a horizontal stainless steel tube and hellically coiled copper tube of 4.57 and 7.75 mm. The experiments were conducted at saturation temperature of 100 to $20^{\circ}C$, and mass flux of 200 to $500kg/m^2s$. The test results showed the variation of the heat transfer coefficient tended to decrease as cooling pressure of $CO_2$ increased. The heat transfer coefficient with respect to mass flux increased as mass flux increased. The experimental results were also compared with the existing correlations for the supercritical heat transfer coefficient, which generally underpredicted the measured data. However, the experimental data showed a relatively good agreement with the correlations of Pitla et al. except for the pseudo critical temperature.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 1993년도 Proceedings of International Conference for Agricultural Machinery and Process Engineering
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• pp.686-695
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• 1993

A flywheel-type, inclined axis chopper for small-area rice and livestock farmers, has been developed at IRRI Agricultural Engineering, The prototype is belt-driven by a 2.6kW engine and uses four angled blades rotating below a fixed counteredge. Manual feeding is facilitated by a convenient spout presenting the crop to the inclined blade housing and also suction created by the rotating blades . The distance between the rotating blades and the bottom of the housing determines the length of chops, set here for 25 cm. The unit would cost $200 without the engine. Tests with napier grass, corn stalks , and rice straw showed satisfactory performance within the acceptable clearance, speed and moisture content ranges of the material presented. Highest capacities were 1186, 1148 and 744kg/hr for napier grass, corn stalks and rice straw, respectively. Corn stalks required the highest power demand at 2.3kW engine would be adequate as power source. The chopper performance was comparable to higher cost commercial chippers in terms of capacity and specific energy.

• 한국농공학회논문집
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• 제54권2호
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• pp.55-65
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• 2012

In the winter season, when the ventilation system is operating, the fresh cold air from the slot-type openings of broiler house which directly reached the animal zone can cause various problems such as thermal stress, decreasing of feed and water consumption, occurrence of respiratory disease, and etc. Therefore it is very important to control the trajectory of aero-flow from the slot openings to induce an efficient thermal heat change. Jet-drop distance model was proposed to predict and control the jet-trajectory. However their study was restricted due to the small scaled model and difficulties of measuring the Jet-drop distance. In this study, CFD was applied to analyze qualitatively and quantitatively the jet-drop distance in a real broiler house. The various variables were considered such as installed slot-angle, designed ventilation rate, and the outdoor ambient temperature. From the present study, two linear-regression models using the Jet-drop factor and corrected Archimedes number, and their R-squared values 0.744 and 0.736, respectively, were used. From this study, the applicability of CFD on the analysis of Jet-drop distance model was confirmed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 추계학술대회 논문집 학회본부 B
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• pp.742-744
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• 1999

In this paper, a new precharge type PFD for fast locking time of PLL is suggested. It is realized by inserting NMOS transistor and inverter into the precharge part of PFD for isolating the reset of the Up signal from the feedback signal. The new precharge type PFD generates the Up signal while the feedback signal is fixed at a high level. Therefore the new PFD output is increased than the conventional precharge type PFD output. As a result of the increased PFD output, fast locking of PLLs is achieved. Additionally, with control the falling time of the inverter, the dead-zone is reduced and the jitter characteristics are improved. The whole characteristics of PFD and PLL are simulated by using HSPICE. Simulation results show that the dead-zone is 20ps and the locking time of PLL using the new PFD is 38ns at the 350MHz frequency of referecne signal. This value is quite small compared with conventional PFD.

• Structural Engineering and Mechanics
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• 제18권6호
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• pp.731-744
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• 2004

Modified virtual crack closure integral (MVCCI) technique has become very popular for computation of strain energy release rate (SERR) and stress intensity factor (SIF) for 2-D crack problems. The objective of this paper is to propose a numerical integration procedure for MVCCI so as to generalize the technique and make its application much wider. This new procedure called as numerically integrated MVCCI (NI-MVCCI) will remove the dependence of MVCCI equations on the type of finite element employed in the basic stress analysis. Numerical studies on fracture analysis of 2-D crack (mode I and II) problems have been conducted by employing 4-noded, 8-noded (regular & quarter-point), 9-noded and 12-noded finite elements. For non-singular (regular) elements at crack tip, NI-MVCCI technique generates the same results as MVCCI, but the advantage for higher order regular and singular elements is that complex equations for MVCCI need not be derived. Gauss numerical integration rule to be employed for 8-noded singular (quarter-point) element for accurate computation of SERR and SIF has been recommended based on the numerical studies.

• 한국수소및신에너지학회논문집
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• 제18권2호
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• pp.189-196
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• 2007

The evaporation heat transfer coefficient and pressure drop of $CO_2$(R-744) in a horizontal tube was investigated experimentally. The main components of the experimental apparatus are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and an evaporator(test section). The test section consists of a horizontal stainless steel tube of 4.57 mm inner diameter. The experiments were conducted at mass flux of $200{\sim}1000\;kg/m^2s$ saturation temperature of $0{\sim}20^{\circ}C$, and heat flux of $10{\sim}40\;kW/m^2$. The test results showed that the heat transfer coefficient of $CO_2$ has a greater effect on nucleate boiling more than convective boiling. Mass flux of $CO_2$ does not affect nucleate boiling too much. In comparison with test data and existing correlations, All of the existing correlations for the heat transfer coefficient underestimated the experimental data. However lung et al.'s correlation showed a good agreement with the experimental data. The evaporation pressure drop of $CO_2$ increases with increasing mass flux and decreasing saturation temperature. When comparison between the experimental pressure drop and existing correlations. Existing correlations failed to predict the evaporation pressure drop of $CO_2$.

• 한국해양공학회지
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• 제15권2호
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• pp.46-52
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• 2001

In this paper, the real-time prediction of high temperature creep life was carried out for the friction welded joints of dissimilar heat resisting steels (SUH3-SUH35). various life prediction method such as LMP (Larson_miller Parameter) and ISM (initial strain method) were applied. The creep behaviors of those steels and the welds under static load were examined by ISM combined with LMP at 500, 600 and $700^{\circ}C$, and the relationship between these two methods was investigated. A real-time creep lie (tr, hr) prediction equation by initial strain (${\varepsilon}_0$, %) under any creep stress ($\sigma$, MPa) at any high temperature (T, K) was developed as follows: $t_r={\alpha}{\varepsilon}_0^{\beta}{\sigma}^{-1}$ where, ${\phi}=16: {\alpha}=10^{51.412-0.104T+5.375{\times}10^5T^2}$, $ {\beta}=-83.989+0.180T-9.957{\times}10^{-5}T^2,{\phi}=20:$ ${\alpha}=10^{69.910-0.146T+7.744{\times}10^{-5}T^2$, ${\beta}=-51.442+0.105T-5.595{\times}10^{-5}T^2$ for SUH3-SUH35 friction weld of =16mm and 20mm, respectively.

• 한국정보처리학회논문지
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• 제3권4호
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• pp.733-744
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• 1996

내용을 기반으로 한 이미지 데이타 검색은 이미지로부터 자동적으로 특징값들을 추출하여 사용자가 원하는 이미지를 검색하는 방법이다. 본 논문에서는 이미지 데이타 로부터 형태적 특징과 컬러 특징을 자동적으로 추출하여 내용을 기반으로 이미지 데이타를 검색할 수 있는 방법을 제안한다. 이를 위하여 필요한 일련의 이미지 처리 과정을 소개하고 추출된 특징값들을 빠르게 검색하기 위해 변형된 트라이와 R 트리를 사용한 인덱싱기법을 제안한다. 제안하는 검색 방법은 형태와 컬러에 대한 특징값들을 모두 취급하므로 보다 신뢰성 있는 검색을 할 수 있다. 또한 본 논문에서는 이를 바탕으로 구현된 이미지 데이타베이스와 약 200여개의 이미지 데이타를 대상으로한 검색 실험 결과를 보이며, 검색 결과를 통해 형태적 특징과 컬러 특징이 이미지가 데이타 검색에 미친 영향을 고찰해 본다.