• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.2
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• pp.101-109
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• 2005

The purpose of this study is to investigate the performance of outdoor heat exchanger for heat pump using carbon dioxide. Two types of fin and tube heat exchangers (2 rows for type A and 3 rows for B) are tested. Both heat exchangers have counter-cross flow and 1-circuit arrangement. Test results such as heat transfer rate, pressure drop characteristics and temperature distribution in the heat exchanger are shown with respect to mass flow rate of refrigerant and frontal air velocity For cooling mode, the minimum temperature difference between air and refrigerant of type B is smaller than that of type A by $1^{circ}C$, but the pressure loss of air side is much higher for type B by $29\%$. It is found that a large temperature gradient of carbon dioxide during gas cooling Process Promotes thermal conduction through tube wall and fins which results in degradation of heat transfer performance. For heating mode operation, type B heat exchanger shows higher heat transfer performance compared to type A. However, because pressure loss of refrigerant side of type B is much greater than that of type A, the refrigerant outlet pressure of type B becomes lower than that of type A.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.353-358
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• 2005

The heat transfer and pressure drop of supercritical $CO_2$ cooled in a helically coiled tube was investigated experimentally. The experiments were conducted without oil in the refrigerant loop. The experimental apparatus of the refrigerant loop consist of receiver, a variable speed pump, a mass flowmeter, a pre-heater, a gas cooler(test section) and an isothermal tank. The test section is a helically coiled tube in tube counter flow heat exchanger with $CO_2$ flowed inside the inner tube and coolant( water) flowed along the outside annular passage, It was made of it copper tube with the inner diameter of 4.55[mm]. the outer diameter of 6.35 [mm] and length of 10000 [mm]. The refrigerant mass fluxes were $200^{\sim}600$ [kg/m2s] and the inlet pressure of gas cooler varied from 7.5 [MPa] to 10.0 [MPa]. The main results are summarized as follows : The heat transfer coefficient of supercritical $CO_2$ increases, as the cooling pressure of gas cooler decreases. And the heat transfer coefficient increases with the increase of the refrigerant mass flux. The pressure drop decreases in increase of the gas cooler pressure and increases with increase the refrigerant mass flux.

• Journal of the Korean Institute of Gas
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• v.8 no.1 s.22
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• pp.1-6
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• 2004

In general, inlet temperature of cooling sea water for steam turbine condenser is about $25^{\circ}C$ and outlet temperature is about $60^{\circ}C$. For oil cooler, outlet temperature is about $40^{\circ}C$. Therefore corrosion heavily depends on the temperature of the coolant of a heat exchanger system. It is necessary to set the temperature of the cooling water to have maximum heat transfer efficiency. This paper was studied on the effect of temperature on SCC of Al-brass which is used as a tube material of vessel heat exchanger in $3.5\%$ NaCl + $0.1\%\;NH_4OH$ solution under flow by constant displacement tester. Based on the test results, the behavior of polarization characteristic, stress corrosion crack popagation and dezincification characteristic of Al-brass was investigated.

• Journal of the Korean Institute of Gas
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• v.16 no.3
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• pp.42-47
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• 2012

In this paper, alternative natural refrigerant R290(Propane), R600(Butane), R717(Ammonia), R1270(Propylene) for freon refrigerant R22 were used working fluids for 2-stage compression and 1-stage expansion refrigeration system. The operating parameters considered in this study included evaporation temperature, condensation temperature, subcooling degree, superheating degree, mass flow rate ratio of inter-cooler. The main results were summarized as follows : The COP of 2-stage compression and 1-stage expansion refrigeration system increases with the increasing subcooling degree and mass flow rate ration of inter-cooler, but decreases with the increasing evaporating temperature, condensing temperature and superheating degree. Therefore, subcooling degree, mass flow rate ratio of inter-cooler of 2-stage compression and 1-stage expansion refrigeration system using natural refrigerants have an effect on COP of this system. The COP of natural refrigerants was higher than the COP of freon R22 in this study, so points to be considered are the security, the attached facilities for natural refrigerants than COP.

• Journal of the Korean Institute of Gas
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• v.17 no.4
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• pp.1-8
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• 2013

The aim of this study is to assess thermal hazards of polystyrene polymerization process by bulk polymerization with accelerating rate calorimeter(ARC) and Multimax reactor system(MM). From this study, we found out that the polymerization process should be operated at reaction temperature of $120^{\circ}C{\sim}130^{\circ}C$. At reaction temperature over $130^{\circ}C$, there was a runaway reaction hazard due to the temperature control failure following a viscosity increase of reaction products. With a cooling failure of a reactor in the early stage of process operation at the reaction temperature ($120^{\circ}C{\sim}130^{\circ}C$), there was a high thermal hazard of burst of a reactor's rupture disk or explosion of a reactor caused by the rapid rise of temperature and pressure to $340^{\circ}C$, 5.3 bar respectively within 30 - 50 minutes.

• Journal of the Korean Institute of Gas
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• v.24 no.4
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• pp.56-61
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• 2020

For the hydrogen liquefaction, the large amount of energy is consumed, due to precooling, liquefaction and o-p conversion processes. The aim of this work is to improve the performance of hydrogen liquefaction process by introducing the new energy saving processes, that are the liquid nitrogen precooling process by using LNG cold energy, and the new design of cold box insulation using cold air circulation. The results show that the indirect use of LNG cold energy in precooling process enables not only to get energy saving, but to make safer operation of liquefaction plant. In new cold box, the energy loss of equipments could be reduced by nearly 35%~50% compared to the present perlite insulation, if insulation structure is organised as 3mm steel wall/20cm PUF/5cm air/20cm PUF/equipment. Additionally the equipments installed in cold box can get cooling effect, if the temperature is higher than the temperature of cold air. The application of this results can gives to increase the liquid yield of about 50% substantially in industrial hydrogen liquefaction plant.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.3
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• pp.20-28
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• 2007

The easiest way to see the phenomena of compressor surge is to show the static and dynamic operation characteristic on the map. Its operation zone will be restricted by the surge limit and, static and transient process must have some margin for it. Effect of rotor moment of inertia, air/gas volumes and heat transfer are factors to cause the transition from the static line. In case a large volume such as heat exchanger exists in the system it will exert a substantial influence to dynamic characteristics. In the present paper, influence of air volume bled from the compressor exit on transient process is investigated with an example of an auxiliary power unit micro-turbine engine. Turbine mass, pressure ratio, rotation speed, power and moment are calculated based on mass and work conservation. Result from the present study can give guidance to design the control system. A computer program is developed to calculate the dynamic process using the MathCAD commercial software.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.4
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• pp.81-88
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• 2013

It was designed and tested at the design point that an oxidizer rich preburner for a staged combustion liquid rocket engine propelled by kerosene and LOx. The oxidizer rich preburner was designed as some of LOx injected from the mixing head was burned with kerosene and the rest of LOx injected from injection holes in the regenerative cooling chamber was vaporized by combustion gas. The preburner is operated at OF ratio of 60 and combustion pressure of 20 MPa. The Preburner has a honey-comb type mixing head with simplex swirl injectors, a turbulence ring improving combustion stability and uniformity of product gas temperature distribution, and a nozzle simulating the duct. With the combustion test results at the design point, the oxidizer rich preburner showed high combustion stability and uniformity of product gas temperature distribution.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.306-313
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• 2019

Owing to the present problems of air pollution and fossil fuel exhaustion, ongoing research has been actively focused on developing an electric actuator system that can utilize diverse energy sources without producing any exhaust gas. Since the motors of such electric vehicles generally rotate at a high speed, the initial acceleration capability required for an automobile is insufficient. In this study, the motor output was decelerated by the transmission; the initial acceleration of the vehicle was increased, and the motor size and weight were reduced. The driving motor and transmission, which each form isolated structures, were integrated to simplify the connector for input and output. By reducing the cooling system's capacity, a vehicle was designed and manufactured that represents a structural change in effective technology.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.144.1-144.1
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• 2010

현재의 세계 자동차 시장은 석유 자원의 고갈과 전자화로 높은 연비의 기술적 성숙을 요구하고 있으며, 이는 미래 자동차 기술의 전동화를 가속시키고 있음에 따라 종래 엔진부하로 사용되는 시스템 및 유압시스템의 전동화 기술추이가 지속적으로 증가하고 있다. 이중 엔진 부하 메커니즘의 하나인 엔진 쿨링 팬 분야는 소비용량이 크고, 고 연비증감 기술증진의 전동화에 따른 차량 성능개선의 효과가 높아 실용 전동화 용의성에 의해 새로운 최우선 차량 전동부하로 나타나고 있다. 특히, 대형 차량(버스, 트럭)의 엔진 Cooling Fan 시스템은 차량 연비저감의 주요원 중에 하나로 대두되고 있으며, 도시 소음의 주된 요인이 되고 있어 전동화 기술개발의 필요성이 매우 높다. 전동 Cooling Fan 시스템은 종래 엔진 구동형 시스템에 비하여 엔진부하를 감소시킬 수 있고, 차량 연비향상 및 유해배출 가스를 저감시킴으로 기술적, 환경적 개발효과가 매우 높다. 본 연구에서는 쿨링팬 고출력 BLDC모터 설계제작에 관한 내용과, 최적 팬 블레이드 설계제작, 마지막으로 개발 전동 쿨링팬 성능평가에 관한 내용이 포함되어 있다.