• Journal of Hydrogen and New Energy
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• v.10 no.1
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• pp.19-26
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• 1999

The effectiveness of a double-tube heat exchanger has been investigated experimentally. This problem is of particular interest in the design of the heat exchanger in a hydrogen liquefaction system. Temperature, pressure, and mass flow rate for hydrogen were measured both in inner tube and in annulus of a double-tube heat exchanger. The effectiveness could be evaluated from the measured temperature and mass flow rate. It is found that the effectiveness increases with an increase in the heat transfer area of a double-tube heat exchanger and with a decrease of the heat capacity ratio. But the increase rate of the effectiveness decreased with a decrease of the heat capacity ratio. Therefore, it is presented that a criterion for selecting the heat exchanger length and heat capacity ratio to obtain the effectiveness required in a hydrogen liquefaction system.

• Journal of Bio-Environment Control
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• v.9 no.4
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• pp.212-222
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• 2000

This study was performed to investigate the performance of heat recovery device attached to exhaust gas flue connected to combustion chamber of greenhouse heating system. The experimental heat recovery system is mainly consisted of LPG combustion chamber and two heat recovery units; unit-A is attached directly to the exhaust gas flue, and unit-B is connected with unit-A. Heat recovery performance was evaluated by estimating total energy amounts by using enthalpy difference between two measurement points together with mass flow rate of gas and/or air passing through each heat recovery unit depending on 5 different flow rates controlled by voltage meter. The results of this experimental study, such as heat exchange behavior of supply air tubes and exhaust air passages crossing the tubes, pressure drop between inlet and outlet, heat recovery performance of exchange unit, etc., will be used as fundamental data for designing optimum heat recovery device to be used for fuel saving purpose by reducing heat loss amounts mostly wasted outside of greenhouse through flue.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.11
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• pp.6412-6418
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• 2014

This paper performed a numerical study of an air-liquid ejector. An ejector is a fluid-transportation device that spouts high-pressure fluid from driving pipes using the kinetic energy of the spouted fluid and increases the pressure through the exchange of momentum with the surrounding gases of the lower pressure. The air-liquid ejector was investigated through steady three-dimensional multiphase CFD analysis using commercial software ANSYS-CFX 14.0. Water as the primary fluid is driven through the driving nozzle and air is ejected as the second gas instead of ozone in real applications. The difference in performance according to the shape of the diffuser of the ejector was examined. The results provide deep insight into the influence of various factors on the performance of the air-liquid ejector. The proposed numerical model will be very helpful for further design optimization of the air-liquid ejectors.

• The Journal of the Korea Contents Association
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• v.5 no.3
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• pp.19-28
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• 2005

It is true that internet provides consumers with an efficient way to search information with minimal effort and cost, which facilitates better decision making. Especially, previous studies revealed that the online word-of-mouth marketing is widely used as a source of consumers' information seeking and purchase decision making. Even with this importance of the online word-of-mouth communication on internet few researches have systematically addressed the issue. This study investigates the effect of consumers' motives on perceived usefulness of word-of-mouth marketing in online shopping mall contents. The results are as follows: First, choice uncertainty, perceived sacrifice, and social pressure play an important role for perceived usefulness of word-of-mouth marketing. Second, perceived usefulness has directly affected consumers' quality perception. Thus, it is essential for internet companies to find ways to encourage their customers to engage in word-of-mouth communication on their websites.

• The Korean Journal of Air & Space Law and Policy
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• v.5
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• pp.207-264
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• 1993

항공사의 외국인 소유는 이것으로 인하여 전체 항공운송 시스템이 변화될 수 있는 핵심적인 개념이다. 작금 항공운송산업을 둘러싼 환경은 급격하게 변화하고 있어서 많은 국가들이 항공사의 외국인 소유와 관련한 기존의 법제나 정책변경을 심각하게 고려하기 시작하였다. 항공기 및 항공사의 국적과 관련한 전통적인 개념은 양자사이에 '진정한' 또는 '효파적인' 관계가 있어야 한다는 것이다. 특별히 항공사의 '실질적인 및 효과적인 통제'조항은 양자 및 다자간 항공운송 협정에서 가장 핵심적인 역할을 해오고 있다. 그러나 변화의 바람이 거세게 일고 있다. 항공운송산업에서 이러한 변화는 미국에서 시작되고 미국의 국제항공관계에 적용되고 있는 규제완화에서 비롯되었다. 미국의 규제완화정책은 합병 및 흡수를 통한 항공사의 집중이라는 결과를 가져와서 항공운송 시장은 궁극적으로 소수의 거대 항공사에 의해 지배될 것이라는 우려를 낳고 있다. 이러한 새로운 추세에 대응하여 많은 국가틀이 다양한 형태의 지역협력체를 형성하고 있다. (예, EC, 아세안, 안데안 그룹, 야마스크로 선언 등) 또한 다수 국가들은 정치.경제적인 이웃에서 정부의 소유주식을 외국인 및 외국회사를 포함한 민간부문에 매각함으로써 사유.사영화를 추진하고 있다. 한편 제조업 분야에서 다국적기업 (IBM, 코카콜라 등)은 별 어력움이 없이 성립될 수 있다. GATT의 주관하에 열리고 있는 우루과이 협상에 참여하고 있는 국가들은 최혜국 대우, 내국인 대우, 시장접근 같은 상품교역의 개념및 원리를 항공운송서비스를 포함한 서비스교역에 적용하는데 기본적으로 합의하였다. 급격히 변화하는 환경에서 항공운송 산업만이 국가의 영공 주권, 항공사의 공익기업 개념, 상업적 이익의 균형교환 같은 자기류의 논리에 집착하여 언제까지나 홀로 고립될 수는 없을 것이다. 더구나 세계 항공운송 산업은 1980년 후반부터 큰 시련에 직면해 있다. 몇몇을 제외한 대부분의 항공사는 세계경제의 불황속에서 초과공급 및 운임전쟁으로 인한 엄청난 적자를 기록하고 있다. 모든점을 미루어볼 때 세계의 항공사들은 과거 어느 때보다도 외국인 투자를 필요로 하고 있으며 항공사가 속해 있는 정부는 외국인 소유에 관한 법제를 개정하고 나아가 전체 항공운송시스템을 개편하도록 압력을 받고 있다. 많은 국가에서 외국인 소유에 관한 법규의 개정은 현존 항공운송 시스템에 다각적인 영향을 가져올 것이다. 다시말하면 양자협상, 반독점및 경쟁볍규의 적용, 고용 및 카보타지등을 포함한 제반분야가 영향을 받을 것이다. 결국 외국인 소유에 관한 법제의 완화는 항공사의 세계화 또는 다국적화의 과정을 촉진시킬 것이고, 항공사간 다양한 형태의 제휴가 이러한 방향에서 계속될 것이다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.11
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• pp.1056-1062
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• 2008

The interaction between thrust plume and satellite base region was investigated by using direct simulate Monte-Carlo calculations. For the accurate simulation of N2 and H2 collisions and rotation-translation transition, a variable soft-sphere model and a recent rotational relaxation model of N2 and H2 were used. For the investigation of the interaction between thrust plume and base region, the number density distribution for each species, translational and rotational temperature distributions, heat flux, and pressure were examined by direct simulation of Monte-Carlo calculations. It was found that most of the surface properties are affected by H2 collisions and a strong non-equilibrium state is observed at the base region. It was demonstrated that an accurate model is needed to simulate H2 collisions and the rotation-translation transition. The results by the present calculation are more accurate than previous direct simulation Monte-Carlo calculations because more accurate rotational relaxation models were used in simulating the inelastic collisions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.8
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• pp.1059-1065
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• 2010

An analysis was conducted to predict the hydraulic performance of a reactor coolant pump (RCP) of SMART at the off-design as well as design points. In order to reduce the analysis time efficiently, a single passage containing an impeller and a diffuser was considered as the computational domain. A stage scheme was used to perform a circumferential averaging of the flux on the impeller-diffuser interface. The pressure difference between the inlet and outlet of the pump was determined and was used to compute the head, efficiency, and break horse power (BHP) of a scaled-down model under conditions of steady-state incompressible flow. The predicted curves of the hydraulic performance of an RCP were similar to the typical characteristic curves of a conventional mixed-flow pump. The complex internal fluid flow of a pump, including the internal recirculation loss due to reverse flow, was observed at a low flow rate.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.4
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• pp.470-476
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• 2010

The thermodynamic performance of closed ocean thermal energy conversion (OTEC) cycle with 1 MW gross power was evaluated to obtain the basic data for the optimal design of OTEC. The basic thermodynamic model for OTEC is Rankine cycle and the thermal effluent from power plant was used for the heat source of evaporator. The cycle performance such as efficiency, heat exchanger capacity, etc. was analyzed on the temperature variation of thermal effluent. The saturated pressure of evaporator increased with respect to the increase of thermal effluent temperature, so the cycle efficiency increased and necessary capacity of evaporator and condenser decreased under 1 MW gross power. As the thermal effluent temperature increases about $15^{\circ}C$, the cycle efficiency increased approximately 44%. So, it was revealed that thermal effluent from power plant is important heat source for OTEC plant. Also, if there is an available waste heat, it can be transferred heat to the working fluid form the evaporator through heat exchanger and cycle efficiency will be increased.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.4
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• pp.425-431
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• 2011

Thermal energy generated because of the friction between the disc and pad is transferred to both sides and causes thermal expansion of the material, which affects the contact pressure distribution. This phenomenon, which is called thermoelastic instability (TEI), is affected by the natural mode of a disc. TEI results in the formation of a hot spot and causes hot judder vibrations. In this study, three-dimensional analysis of the hot judder of a ventilated disc for automotives was performed by using the commercial finite element analysis program, SAMCEF. The intermediate processor based on a staggered approach was used to exchange the result data of the mechanical and thermal model. The hot spot was formed on the surface of the disc, and the number of hot spots was compared with the natural mode of the disc.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1343-1349
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• 2011

In this study, the power enhancement potential of a Rankine power cycle by transcritical operation was investigated by comparing the power of an HFC-134a subcritical cycle with that of an HFC-125 transcritical cycle, for a low-grade heat source with a temperature of about $100^{\circ}C$. For a fair comparison using different working fluids, each cycle was optimized by three design parameters from the viewpoint of power. In contrast to conventional approaches, the working fluid's heat transfer and pressure drop characteristics were considered in the present approach, with the aim of ensuring a more realistic comparison. The results showed that the HFC-125 transcritical cycle yields 9.4% more power than does the HFC-134a subcritical cycle under the simulation conditions considered in the present study.