• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.115-116
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• 2002

This study was carried out as one of efforts to overcome difficulties in air bearing design due to low stiffness and low damping. Hydrodynamic effects on hydrodynamic stiffness of a fluid film in a high speed air bearing with tow-row air sources are investigated. The hydrodynamic effects by the high speed over DN 1,000,000 and eccentricity of a proceeding which are not considered in conventional design of an air bearing need to be reconsidered. The hydrodynamic effects, which dominantly influence on the load capacity of air bearing, are caused mainly by proceeding speed, eccentricity, and the source positions. The two-row source arrangement in the air bearing produces quite unique hydrodynamic effects with respect to pressure distribution of the air film. Optimal arrangement of the two-row sources improves performance of an air bearing in film reaction force and loading capacity of high speed spindles. This study compares the pressure distribution by numerical simulation as a function of eccentricity of proceeding and the source positions. The air source position 1/7L form one end of an air bearing was found to be superior to source position of 1/4L. The dynamic stiffness were obtained using a two-dimensional cutting method which can directly measure the cutting reaction forces and the displacements of the spindle in two directions using a tool dynamometer and transducer sensors. Heat generation in the air film can not be negligible over the speed of DN 2,000,000. In order to analysis effects of heat generation on the characteristics of air bearing, high cooling bearing spindle and low cooling bearing spindle were tested and compared. Characteristics of the frequency response of shaft and motion of run out errors were different for the spindle. The test results show that, in the case of low cooling bearing spindle, the stiffness became smaller due to heat generation. The results, which were obtained for high speed region, may be used as a design information for spindle which can be applied to precision devices such as ultra precision grinding and ultra high speed milling.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.4
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• pp.245-251
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• 2008

The cooling load in winter is significant in buildings and hotels because of the usage of office equipments and the high efficiency of wall insulation. Hence, the development of a multi-heat pump that can cover heating and cooling simultaneously for each indoor unit is required. In this study, the operating characteristics and performance of a simultaneous heating and cooling heat pump in the heating-main operating mode were investigated experimentally. The system adopted a variable speed compressor with four indoor units and one outdoor unit with R-410A. In the heating-main mode, the cooling capacity was lower than the design cooling capacity due to the reduction of the flow rate in the indoor unit for the cooling, with the increase of the heating capacity. To solve these problems, the performance characteristics of the simultaneous heating and cooling heat pump in the heating-main mode were investigated by varying the flow rate to the indoor unit for the cooling and the compressor rotating speed. In addition, the adequate control methods were suggested to improve the system efficiency.

• Plant Journal
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• v.15 no.4
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• pp.36-42
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• 2019

In recent, according to the tightening of environment regulation policy, the height of the site of the power plant is increased and the length of the cooling water pipe is increased. This has a serious impact on the stability of the plant. This study analyzes the transient phenomenon using LIQT 7.2, an unsteady state one-dimensional analysis software, to secure the stability of 1,000 MW high-capacity coal-fired power plant cooling water system with high head. To prevent water hammer, The effects on performance characteristics were predicted by individual and combination application. The surge pressure of the cooling water which occurs when the pump was stopped without installing the anti-surge devices was the largest at the pump outlet side. The most effective and simple way to reduce surge pressure in these cooling water systems is to combine a vacuum breaker with a hydraulic non-return valve, which is an essential device for pump protection.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.1063-1066
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• 2002

An equivalent circuit for the superconductor flux flow transistor(SFFT) was combined with high temperature cooling device, based on the analogy between thermal and electrical variables using the high-temperature superconductor(HTS), is proposed. The device is composed of parallel weak links with a nearby magnetic control line. A model has been developed that is based on solving the equation of motion of Abrikosov vortices subject to Lorentz viscous and pinning forces as well as magnetic surface barriers. The use of thermal models the global performance of thermal cooling circuit and signal system to be checked by using electrical circuit analysis programs such as SPICE.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.7 no.1
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• pp.51-58
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• 2011

Due to enhanced sealing and insulation of buildings, extensive use of glasses for building envelopes and increased use of heat generating office equipments, energy consumption of modem buildings for cooling is steadily increasing. With outdoor air cooling(ODAC) system, cooling load can be reduced by exchanging indoor air with the cold outdoor air during spring and fall seasons. If ODAC is operated based only on temperature, total cooling load may virtually increase if the outdoor humidity is high. To overcome this problem, ODAC should be controlled based on enthalpy. In this work energy saving characteristics of enthalpy controlled ODAC is studied using dynamic simulation. The result shows that cooling load can be reduced by 27% by adopting ODAC.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.8
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• pp.1122-1130
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• 2001

Film cooling performance from two rows of holes with opposite orientation angles is evaluated in terms of heat flux ratio. The film cooling hole has a fixed inclination angle of 35°and orientation angle of 45°for the downstream row and -45°for the upstream row. Four film cooling hole arrangements including inline and staggered configurations are investigated. The blowing ratio studied was 1.0. Boundary layer temperature distributions are measured to investigate injectant behaviors and mixing characteristics. Detailed distributions of the adiabatic film cooling effectiveness and the heat transfer coefficient are measured using TLC(Thermochromic Liquid Crystal). For the inline configuration, there forms a downwash flow at the downstream hole exit to make the injectant well attach to the wall, which gives high adiabatic film cooling effectiveness and heat transfer coefficient. The evaluation of heat flux ratio shows that the inline configuration gives better film cooling performance with the help of the downwash flow at the downstream hole exits.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.7
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• pp.623-629
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• 2004

Rapid development of electronic technology requires small size, high density packaging and high power of electronic devices, which result in more heat generation by the electronic system. Present cooling technology may not be adequate for the thermal management in the current state-of-the-art electronic equipment. Forced convective heat transfer in a channel filled with pin-fin array is studied experimentally in this paper as an alternative cool-ing scheme for a high heat-dissipating equipment. Various configurations of the pin-fin array are selected in order to find out the effect of spacing and diameter of the pin-fin on the heat transfer and pressure drop characteristics. In the low porosity region, interfacial heat transfer and pressure drop seem to show different trend compared to the conventional heat transfer process.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1130-1137
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• 1988

Heat transfer characteristics of evaporative transpiration cooling was investigated experimentally in the range of coolant mass flux, 0.002kg/m$^{2}$.sec~0.015m$^{2}$.sec. Glass beads, sand and copper particles were used as porous media and distilled water was used as a conant. The existence of evaporation zone was confirmed on this experimental conditions and its length increases with increasing article size and with decreasing mass flux. In order to get the low surface temperature, porous materials with high thermal conductivity is preferred when the panicle sizes are same, and small particles with low porosity is effective in case of the same material. Due to the relatively small coolant mass flux, evaporative transpiration cooling system could be stable by the capillary effect.

• Journal of Fisheries and Marine Sciences Education
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• v.17 no.1
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• pp.18-25
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• 2005

We have researched 10,811 schools to evaluate the characteristics of school buildings and the conditions of heating and cooling systems at the elementary, middle and high school levels. Air conditioning systems in school buildings are related to school scale, and 35% of the researched schools have less than 10 air conditioned classrooms among all of the schools in Korea. The LOADSYS is used to grasp the characteristics of school buildings heating and cooling load. From the results of this work, the heating load differs by nearly 24% between Seoul and Busan, but other than that there are not so many serious regional differences. Almost 85.4% of the classrooms are equipped with heating facilities and 6.9% of them are equipped with heating and cooling facilities. As a result, it is necessary to make improvements in 31.8% of the classrooms using only heaters and 14.6% of the classrooms not equipped with HVAC. The survey shows that there is a wide gap in the heating equipment status of the classrooms according to the region and school district.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3294-3299
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• 2007

These days the exhaustion of petroleum resources and environmental problems are getting serious. Many researchers are focused on low emission and high performance vehicles. Therefore, we should concern about emission regulation when we design a new car. In this study, we investigated the characteristics of the traditional mechanical engine cooling systems which control the engine temperature using engine speed and wax type thermostat. This experiment used three components which are Radiator fan, water pump and water valve controlled by an electronic system based on the engine status (load, speed). We elucidated how different between traditional mechanical cooling system and electronic cooling system which control coolant temperature and coolant flow rate in a DI diesel engine in this paper. The results revealed a fuel saving and an emission (CO, HC) reduction on NEDC cycle.