• Journal of Advanced Marine Engineering and Technology
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• 제38권9호
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• pp.1021-1026
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• 2014

본 논문에서는 hot-gas를 이용한 다양한 바이패스 제어 방식 중에서 증발기 흡입부 방식에 대해 각각의 성능에 영향을 미치는 외기온도, 출수온도, 과열 및 과냉도 등에 대해서 알아보았다. 그 주요 결과를 요약하면 다음과 같다. 우선, 증발기 흡입부로 hot-gas를 바이패스 하였을 경우에 냉동장치의 성능은 외기온도, 출수온도, 과열 및 과냉도 등에 영향을 받는 것을 알 수 있었다. 따라서 이러한 변수에 대한 최적화를 통해 본 냉동장치의 기초 설계 자료를 제공할 수 있다. 그리고 증발기 흡입부 hot-gas 바이패스 방식의 운전특성을 고찰하여 본 논문에서 제안하는 냉동장치에 대한 적용 가능성을 확인할 수 있었다.

• 대한안전경영과학회:학술대회논문집
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• 대한안전경영과학회 2010년도 춘계학술대회
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• pp.81-95
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• 2010

Gas turbines generating power operate in high temperature condition and use natural gas as fuel. For that reason, there are many cases where damage is done to the hot gas parts caused by the high temperature and many accidents occur like gas explosions, then various efforts are needed to maintain the hot gas parts and prevent accidents. It is difficult to find the root causes of damage to the hot gas parts from the gas explosion caused by gas leakage through rotor cooling air line from fuel gas heat exchanger during the shut down. To prevent gas turbine from damage, removal of gas leakage inside of gas turbine is required by purging the turbine before firing, improving the fuel gas heating system and installing alarm systems for detecting gas leakage from stop valve to turbine while the gas turbine has shut down.

• 대한안전경영과학회지
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• 제12권2호
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• pp.75-82
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• 2010

Gas turbines for power generating operate in a very high temperature condition and use natural gas for fuel. For this reason, many cases of damage happen at hot gas parts which are severely affected by high temperature gas and many cases of explosion occur by fuel gas. So a lot of efforts should be made to prevent hot gas parts damage and gas explosion accidents. Though there are many damage cases and explosion accidents, it is very difficult to find out the root causes of hot gas parts damage caused by gas explosion due to gas leakage in the heat exchanger for air cooling and gas heating. To prevent gas turbine from damage caused by gas explosion, removal of leakage gas from gas turbine is inevitably required before firing the gas turbine and installing alarm systems is also required for detecting gas leakage at stop valve to turbine while shut down.

• 설비공학논문집
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• 제14권6호
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• pp.493-502
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• 2002

During the defrosting process, the temperature in the cabinet of a showcase becomes high as compared to the setting point, which is not desirable for stored foods or materials. It is necessary to develop a more efficient defrosting method to prevent large temperature fluctuation. In this study, the performance of a showcase refrigeration system with three evaporators is investigated by employing a hot-gas bypass defrosting technology in the system under frosting and defrosting conditions. The operating characteristics are compared with those for the on-off defrosting method that has been widely used in current products. As a result, the hot-gas bypass defrosting method shows higher refrigerating capacity and less temperature fluctuation than the on-off method under frosting/defrosting conditions, while the power input is relatively high for the hot-gas bypass method.

• 동력기계공학회지
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• 제18권5호
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• pp.48-54
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• 2014

In this paper, three refrigeration systems bypassing hot-gas to compressor outlet, compressor and condenser outlet and evaporator inlet are theoretically compared to offer basic design data for performance depending on cooling load using a HYSYS program. The main results are summarized as follows : First, the COP of third system is the highest. Next, the COP of second system is higher than first one. And, the temperature of compressor inlet of third system is constant for all cooling load. Compared to first and second system, the compressor inlet temperature of the first system is higher than second one for all cooling loads. From the above results, third system, which is bypassing hot-gas to evaporator inlet, is more advantageous when considering the precise temperature control and excellent performance of oil and water cooler of industrial machine.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.539-543
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• 2009

When the suction pressure of compressor decreases under its limit, the compression ratio is increased causing the malfunctions of compressor. As the method to decrease the compression ratio, hot gas bypass system is usually adopted in heat pump system. In the hot gas bypass system, the discharged gas from the compressor is bypassed into the compressor suction, which causes the increase of suction pressure and the decrease of compression ratio. In this study, the characteristics and performances of the hot gas bypass system in heat pump was investigated experimentally with a variation of the bypass flow rate ratio. With the increase of the bypass rate ratio, the compressor suction pressure was increased, even though the total capacity and COP was decreased. From the analysis of the experimental results, the optimum pressure control algorithm was suggested in this study.

• International Journal of Air-Conditioning and Refrigeration
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• 제15권4호
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• pp.175-181
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• 2007

A computer model of a high efficiency refrigeration system equipped with heat storage for reverse cycle-hot gas defrost (the stored heat is used during defrost cycle of the system) is presented. The model was developed based on both theoretical and empirical equations for the compressor, evaporator, condenser and the heat storage equipment. Simulations of the prototype system were carried out to investigate refrigeration system performance under various operating conditions during refrigeration cycles. The simulations of the evaporator during defrost cycles at 30 and $40^{\circ}C$ hot gas refrigerant temperature were also performed which resulted on shorter defrost time but only slight increase in defrost efficiency. These information on energy efficiency and the defrost time required are important in order to avoid excessive parasitic load and temperature rise of the refrigerated room.

• 한국정밀공학회지
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• 제26권3호
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• pp.73-80
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• 2009

In accordance with the trend for high-speed multi-axes, and the increasing technical sophistication of machine tools, thermal deformation has become an important factor in the accuracy of machine tools. It was analyzed that thermal deformation error accounts for about 70% of all errors made with machine tools. For precise temperature control, both cooling and heating should be implemented. A hot gas bypass type cooling cycle method has a simplified structure and temperature control accuracy to with in ${\pm}0.1^{\circ}C$. In this study, the performances of oil cooler system, including temperature controllability according to hot gas floe and preset temperature sustainability according to temperature load, were tested. It is expected that this study will contribute to the development and performances of oil cooler system, which could minimize thermal errors and improve the quality of precision machine tools.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.50-53
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• 2008

It's so difficult to obtain simultaneously both product quality and improvement of the productivity of which products are in hot aluminum extrusion process. But significant improvements in productivity and extrudate quality result from die cooling system using nitrogen gas injection during aluminum hot extrusion. These benefits are due primarily to cooling effect nitrogen gas and removal of excess heat in the extrudate temperature. This investigation is carried out hot extrusion experiment, also compared cooling system with non-cooling system to inspect cooling effects on hot aluminum extrusion. The purpose of this investigation is estimated the grain growth fur the extrudate quality, and the ram speed for the improvement of the productivity.

• 한국산학기술학회논문지
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• 제10권9호
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• pp.2189-2194
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• 2009

부분 부하운전시 냉동공조장치의 능력을 조절하기 위해서 핫가스 바이패스 기술을 적용한다. 이 개념은 압축기에서 나온 고온의 냉매증기를 증발기 입구측으로 보내는 것이다. 본 논문에서 질량과 에너지 보존법칙을 근거로 CO2에 대한 핫가스 바이패스 개념을 적용하여 분석한다. 본 논문에서 고려된 운전 변수는 냉동장치의 압축효율, 과열도, 가스냉각기 냉매 출구온도, 증발온도 등이다. 주요결과를 요약하면 다음과 같다. 과열도, 가스냉각기 출구온도, 증발온도는 냉동장치의 COP와 냉동능력에 영향을 미치는 것을 알 수 있다. 따라서 이러한 결과의 면밀한 분석을 통해 R744용 냉동장치를 설계할 필요가 있다.