• 설비공학논문집
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• 제20권2호
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• pp.87-96
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• 2008

Flow condensation heat transfer coefficients(HTCs) of R123 and R245fa are measured in a horizontal plain tube. The main test section in the experimental flow loop is made of a plain copper tube of 9.52 mm outside diameter and 530 mm length. The refrigerant is cooled by passing cold water through an annulus surrounding the test section. Tests are performed at a fixed saturation temperature of $50\;{\pm}\;0.2\;^{\circ}C$ with mass fluxes of 50, 100, $150\;kg/m^2s$ and heat flux of $7.3{\sim}7.7\;kW/m^2$. Heat transfer data are obtained in the vapor quality range of $10{\sim}90%$. Test results show that the flow condensation HTCs of R245fa are overall 7.9% higher than those of R123 at all mass fluxes. The pressure drop of R245fa is smaller than that of R123 at the same heat flux. In conclusion, R245fa is a good candidate to replace ozone depleting R123 currently used in chillers from the view point heat transfer and environmental properties.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.286-288
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• 2003

The physical model considered here is a horizontal layer of fluid heated below and cooled above with a periodic array of evenly spaced square cylinders placed at the center of the layer, whose aspect ratio here varies from unity to six. Periodic boundary condition is employed along the horizontal direction to allow for lateral freedom for the convection cells. Two-dimensional solution for unsteady natural convection is obtained using an accurate and efficient Chebyshev spectral multi-domain methodology for a given Rayleigh numbers of $10^6$

• Journal of Advanced Marine Engineering and Technology
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• 제30권5호
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• pp.597-607
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• 2006

This paper presents a numerical simulation of the behavior of the LiBr solution droplets and falling films in horizontal tube banks of absorber. The model developed here accounts for the details of the droplets formation and impact process for absorption on horizontal tubes including the heat transfer from solution film to the tube wall. Especially. the characteristic of unsteady behavior of solution flow has been investigated. Flow visualization studies shown that the solution droplets and falling films have some of the complex characteristics. It is found that. with the numerical conditions similar to the operating condition of an actual absorption chiller/heater, the outlet solution temperature and heat flux from solution film to the tube wall have a stable periodic behavior with time. The solution droplets and falling films in horizontal tube banks of absorber is a periodic unsteady flow. The results from this model are compared with previous experimental observation taken with a high-speed digital video camera and shown good agreement.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 1995년도 춘계학술발표회 초록집
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• pp.69-76
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• 1995

The horizontal thermal storage tank with heat pipe which is suitable for the sensible heat storage system is able to store a hot water from the heat source such as heating pad efficiently and to supply a hot water to load rapidly. Therefore Arrangement of heating pad affects thermal flow and thermal storage efficiency. So, if effective arrangement is decided for condition of constant number of heating pad, the more rapid thermal flow effect and higher thermal storage efficiency is obtainable by active heat transfer. In this experiments, number of heating pad is ranged from three, five and nine, and when number of heating pad is constant, arrangement are two types of concentration-type and dispersion-type. As a result, for the case of concentration-type of heating pad, strong entrainment take place in horizontal thermal storage tank with heat pipe by active heat transfer and in the constant number of heating pad, the concentration-type has the higher efficiency with about 5∼6% than the dispersion-type. Therefore, when heating pad is equipted to horizontal thermal storage tank with heat pipe, concentration-type of heating pad is an efficient design in constant number. of heating pad.

• 설비공학논문집
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• 제7권3호
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• pp.528-537
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• 1995

Natural convective flow and heat transfer characteristics in a partially opened enclosure fitted with a horizontal divider are investigated numerically. The enclosure is composed of a lower hot and a upper cold horizontal walls and adiabatic vertical walls. A divider is attached perpendicularly to the vertical insulated wall. The governing equations are solved by using the finite element method with Galerkin method. The computations have been carried out by varying the length of divider, the opening size, and the Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height for air(Pr=0.71). As result, when the opening size is fixed, the intensity of the secondary flow is weaken as the length of divider increases. The maximum heat transfer rate over the upper cold wall occurs at a position bounded on the opening. However, when the length of divider is increased considerably, its maximum occurs at the right wall. The stability and frequency of oscillation are affected by the Rayleigh number and length of divider. The Nusselt number is increased with the increase of the opening size and the increase of Rayleigh number.

• 기술경영경제학회:학술대회논문집
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• 기술경영경제학회 2001년도 제19회 하계학술발표회 논문집
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• pp.133-143
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• 2001

Technology transfer from universities and research institutes to industries is recognized as a critical issue to strengthen industrial competitiveness, and the roles of technology transfer intermediaries are becoming one of the most important factors for successful technology transfer In today's global and knowledge-based economies, technology transfer services are started shifting to Internet and vertical transfer of technology from R&D labs to industries is becoming more emphasized than horizontal company-to-company transfer of commercialized technology. And the need of comprehensive technology transfer services necessitates cooperation among technology transfer intermediaries and networks offering complementary services. In order to respond to these changes, it is required to construct a new type of technology transfer system. But there are few researches on technology transfer system configuration for design and realization of technology transfer intermediaries. This paper presents the configuration models of technology transfer from universities and research institutes to industries. The configuration models are classified and described from the viewpoint of flows of information, technology and knowledge.

• 한국지반환경공학회 논문집
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• 제24권1호
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• pp.5-14
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• 2023

본 연구에서는 설계 대상인 현장타설말뚝기초에 대하여 상사율을 고려한 하중전이 대형토조 모형시험과 3차원 수치해석을 수행함으로써 현장타설말뚝 선단부와 주면부의 하중전이 특성을 분석하고 하중분담율을 산정하였다. 대형토조 모형시험 및 3차원 수치해석 결과에서 나타난 현장타설말뚝의 선형적 거동으로부터, 본 연구의 설계 조건에 대한 주면하중전이곡선은 Baquelin 등의 제안식, 선단하중전이곡선은 Baquelin 등의 제안식, 수평하중전이곡선은 Reese 등의 제안식이 적정한 것으로 확인되었다. 암반근입부에서 축하중은 시험값이 수치해석값보다 약간 크게 측정되었지만 암반 근입부에서 하중분담율은 연직하중이 증가함에 따라 평균적으로 약 27.8%의 분담율을 나타내었다. 연직재하 시에 말뚝두부의 침하량은 해석값이 시험값보다 약간 작게 평가되었으며, 모형시험 및 해석 최대 연직하중에서 말뚝두부의 최대 침하량은 시험치 10.6mm, 해석치 10.0mm 이고, 말뚝선단에서 최대 침하량은 시험치 2.0mm, 해석치 1.9mm로 나타났다. 수평재하 시에 기둥 두부(지표)와 말뚝 두부에서 수평변위는 시험값과 해석값이 비교적 잘 일치하는 것으로 나타났고, 모형토조시험 결과 최대 수평변위 38.0mm에서 측정된 수평하중은 24,713kN, 수치해석에서의 수평하중은 26,073kN으로 평가되었다.

• 대한토목학회논문집
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• 제39권5호
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• pp.613-621
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• 2019

지하철역사의 일반적인 환승통행은 노선간환승과 역사환승을 의미한다. 노선간환승은 다른 두 노선의 열차를 갈아타기 위하여 환승통로와 같은 수평보행시설을 통해 이동한다. 역사환승은 스마트카드 진출입 단말기노선과 승하차 열차노선이 다른 상황에서 발생하는 보행통행으로 계단, 에스컬레이터와 같은 수직보행시설을 이용하면서 환승통로를 함께 이용하는 통행이다. 이러한 환승의 가정은 지하철 네트워크를 운행하는 모든 노선은 완행 또는 급행의 단일노선에 한정되었다는 한계를 포함하고 있다. 따라서 완행과 급행이 동일노선으로 운영되는 상황에서 노선내에서 발생되는 환승에 대한 검토가 수행되지 않았다. 노선내환승은 메트로9호선과 같이 급행 및 완행 정차역이 동일노선에서 운행되는 상황에서 발생한다. 본 연구는 스마트카드 자료기반의 급행 및 완행열차가 동일노선에 존재하는 지하철네트워크를 대상으로 노선내환승을 분석하는 방법론을 구축한다. 이를 위해 급행 및 완행열차를 분리하기 위한 네트워크확장기법을 구축하고 최소시간경로를 선택하는 과정에서 동일 노선의 내부 환승이 재현되는 경로선택모형을 제안한다.

• 설비공학논문집
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• 제18권11호
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• pp.906-914
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• 2006

The present paper dealt with an experimental study of boiling heat transfer characteristics of R-290. Pressure gradient and heat transfer coefficient of the refrigerant flow inside horizontal smooth minichannel were obtained with inner tube diameter of 3.0 mm and length of 2,000 mm. The direct electric heating method was applied for supplying a heat to the refrigerant uniformly. The experiments were conducted with R-290 purity of 99.99%, at saturation temperature of 0 to $10^{\circ}C$, a mass flux range of $50{\sim}250kg/m^2s$, and a heat flux range of $5{\sim}20kW/m^2$. The heat transfer coefficients of R-290 increased with increasing mass flux and saturation temperature, wherein the effect of mass flux was higher than that of the saturation temperature. Heat flux has a low effect on the increasing of heat transfer coefficient. The heat transfer coefficient was compared with six existing heat transfer coefficient correlations. The Zhang et al.'s correlation (2004) gave the best prediction of heat transfer coefficient. A new correlation to predict the two-phase flow heat transfer coefficient was developed based on the Chen correlation. The new correlation predicted the experimental data well with a mean deviation of 11.78% and average deviation of -0.07%.

• 태양에너지
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• 제19권2호
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• pp.45-56
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• 1999

The performance of vertical and horizontal tubes with extended surface of rectangular and triangular cross section was investigated theoretically for boiling heat transfer. A simple method for numerical program assuming one-dimensional heat flow was used to predict the performance of these extended surface tubes. The object of this study was to predict the effects of the height, thickness, numbers and, clearance of the extended surface on boiling heat transfer. The results showed that extended surfaces are quite effective as compared to plane surfaces especially near the bum-out point and to promote heat flux in boiling heat transfer.