• 한국산업융합학회 논문집
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• 제5권4호
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• pp.379-384
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• 2002

As automotive diesel engines adopt the direct injection method for a lower level of the exhaust emission and a higher fuel efficiency, the maximum temperature of engine coolant decreases. Consequently, the total available heat source from the engine coolant decreases over 35%. However, the heating source of air-conditioning system in automobiles depends on the hot engine coolant completely, so that it is nearly impossible to control air conditioning in heating season. Therefore, the present study has been carried out to develop the air conditioning system for the high efficient heat pump type using the HFC-134a. Especially, the air conditioning system of heating has been developed at a beginning stage, when it has low heat source from small and medium sized diesel recreation vehicles. To develop a control logic system for air conditioning system which is a heat pump type with a heat recovery exchanger, its cycle characteristics has been investigated according to the opening of LEV at a bench system.

• 한국지열·수열에너지학회논문집
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• 제14권4호
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• pp.27-34
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• 2018

This study compared constant water bath performances of conventional water-cooled refrigerator and electric heater with an air-cooled VRF chiller and electric heater equipped with optimal control algorithm. In heating mode, the air cooled VRF chiller and electric heater combination reduced the set temperature arrival time by an average of 42 minutes, and energy was also reduced by 18%. In cooling mode, the two systems took 70 minutes to reach the set temperature and showed no difference. Energy was reduced by 33.5% with the new system. For constant temperature maintaining experiment, after reaching the set temperature of $15^{\circ}C$, $20^{\circ}C$ and $22^{\circ}C$, temperature deviations were all in the range of $-0.2^{\circ}C$ to $+0.1^{\circ}C$. Energy was reduced by an average of 84.9%. Through this study, possibility of precise temperature control by an air cooled VRF chiller system was confirmed.

• 한국산학기술학회논문지
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• 제20권7호
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• pp.353-362
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• 2019

그간 캐스케이드 냉동 시스템에 대해서 열역학적 해석은 다수 수행되었으나 증발기, 응축기, 인터쿨러 등 부품 해석을 통한 시스템 평가는 미진한 상태이다. 본 연구에서는 냉방 및 냉동 열교환기가 별도로 장착되어 있고 하부 사이클에 공랭식 응축기와 인터쿨러가 직렬로 연결되어 있는 캐스케이드 냉동 사이클에 대해 성능 해석을 수행하였다. 우선 증발기, 응축기, 인터쿨러 등 요소부품에 대해 모델링을 수행하고 R-410A를 사용하는 냉방 능력 8 kW, 냉동 능력 15 kW의 캐스케이드 냉동 사이클의 요소 부품의 - 상부 응축기, 하부 응축기, 냉방 증발기, 냉동 증발기, 인터쿨러, 압축기, 전자팽창변 - 설계를 수행하였다. 설계 사양에 대하여 외기 온도를 $26^{\circ}C$에서 $38^{\circ}C$로 변화시키며 해석을 수행한 결과 냉각 열량은 하부 증발기에서는 거의 일정하고 상부 증발기에서는 9% 감소, 인터쿨러에서는 63% 증가하였다. 한편 COP는 외기 온도의 증가에 따라 감소하였다. 인터쿨러가 작동하지 않는 사이클 대비 인터쿨러 사이클이 COP 측면에서 우위를 보였다. 또한 상부 응축기의 크기를 당초 설계치의 2배 증가시키면 하부 증발기 열량은 변함이 없는 반면 상부 증발기 열량은 4% 증가하였다. 한편 상부 응축기의 크기 증가에 따라 상부 사이클의 COP는 증가하는 반면 하부 사이클의 COP는 큰 변화가 없다. 또한 하부 응축기 크기를 2.8배 증가시키면 상하부 증발기의 열량 변화는 거의 없고 인터쿨러의 열량만이 8% 감소하였다. 아울러 하부 사이클의 COP는 응축기의 크기가 증가함에 따라 다소 증가하였으나 상부 사이클의 경우는 그 변화가 미미하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제33권8호
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• pp.1129-1136
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• 2009

본 논문은 EEV를 이용한 냉각시스템의 성능특성에 관한 논문이다. 산업용냉각기는 고속으로 운전하는 공작기기의 열 변형을 줄이기 위해 사용되었으며, EEV는 냉각기의 용량조절을 위해 사용되었다. 본 장치는 압축기 출구에서 나온 핫가스를 증발기 입구로 보내는 핫가스 바이패스 시스템을 위해 설계되었다. 본 실험은 PID제어를 통한 고정도 온도제어 연구의 중간결과물이다. 실험의 결과로 핫가스 바이패스의 EEV스텝 조절을 통하여 증발압력의 상승과 냉동능력의 감소를 알 수 있었다. 본 실험의 결과를 통하여 효율적인 냉각기의 설계에 있어 기초 자료로 이용할 예정이다.

• Journal of Advanced Marine Engineering and Technology
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• 제40권7호
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• pp.563-568
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• 2016

본 연구는 연료전지 자동차용 공기조화기의 난방성능평가를 위하여 기존의 전반적인 히트펌프 시스템 중 공기열원 히트펌프 시스템의 증발기를 판형열교환기로 교체하여 시스템에 흐르는 냉매와 연료전지 스택 폐열을 직접 열교환이 가능한 수열원 이용이 가능한 난방시스템의 성능실험을 수행하였다. 실험결과에서 압축기의 회전수가 높을수록 소비동력이 증가하였다. 공기열원 이용방식의 경우 압축기 회전수가 1,200rpm이고 EEV개도가 25%인 경우 $COP_h$가 2.03으로 가장 높게 나타났고, 같은 압축기의 회전수에서 수열원 시스템은 EEV개도가 75% 및 스택 폐열의 온도가 $50^{\circ}C$인 경우 $COP_h$가 9.42로 가장 높게 나타났다.

• Tuberculosis and Respiratory Diseases
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• 제81권2호
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• pp.106-115
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• 2018

Chest tube insertion is a common procedure usually done for the purpose of draining accumulated air or fluid in the pleural cavity. Small-bore chest tubes (${\leq}14F$) are generally recommended as the first-line therapy for spontaneous pneumothorax in non-ventilated patients and pleural effusions in general, with the possible exception of hemothoraces and malignant effusions (for which an immediate pleurodesis is planned). Large-bore chest drains may be useful for very large air leaks, as well as post-ineffective trial with small-bore drains. Chest tube insertion should be guided by imaging, either bedside ultrasonography or, less commonly, computed tomography. The so-called trocar technique must be avoided. Instead, blunt dissection (for tubes >24F) or the Seldinger technique should be used. All chest tubes are connected to a drainage system device: flutter valve, underwater seal, electronic systems or, for indwelling pleural catheters (IPC), vacuum bottles. The classic, three-bottle drainage system requires either (external) wall suction or gravity ("water seal") drainage (the former not being routinely recommended unless the latter is not effective). The optimal timing for tube removal is still a matter of controversy; however, the use of digital drainage systems facilitates informed and prudent decision-making in that area. A drain-clamping test before tube withdrawal is generally not advocated. Pain, drain blockage and accidental dislodgment are common complications of small-bore drains; the most dreaded complications include organ injury, hemothorax, infections, and re-expansion pulmonary edema. IPC represent a first-line palliative therapy of malignant pleural effusions in many centers. The optimal frequency of drainage, for IPC, has not been formally agreed upon or otherwise officially established.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.310-315
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• 2008

In this study, experimental study on the heating performance of a $CO_2$ heat pump water heater with a variation of operating conditions such as refrigerant charge amount, outdoor temperature, compressor frequency, EEV opening and water mass flow rate. Based on the test results, the optimum charge amount was 1800 g. At the water mass flow rates of 75, 85, 95 kg/hr, the water heating temperature was 62, 67, $74^{\circ}C$ and COP was 2.6, 2.8, 3.0, respectively. Besides, the water mass flow rate and compressor frequency were varied to maintain above the water heating temperature of $60^{\circ}C$ with the decrease of outdoor temperature. So, The compressor frequency increased beyond 65 Hz and the water mass flow rate was 45 kg/hr at the outdoor temperature of $-13^{\circ}C$, 65 kg/hr at $-8^{\circ}C$, 75 kg/hr at $-3^{\circ}C$ and 85 kg/hr at 2, $7^{\circ}C$. As the outdoor temperature decreased, the heating COP decreased by 2.5-39.8%.

• 설비공학논문집
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• 제23권2호
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• pp.111-119
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• 2011

Recently, the performances of speed and accuracy are enhanced in machine tools. The high speed of the machine tools usually causes harmful thermal displacements on the objects. To reduce the thermal displacements, machine tools generally adopt oil coolers with precise temperature control function. This study aims at precise control of oil outlet temperature in the oil coolers with hot-gas bypass manner based on PI control logic. The control system was designed for obtaining steady state error within ${\pm}0.1^{\circ}C$ and maximum overshoot with 0.8% even though abrupt disturbances are added to the system. We showed that the PI gains could be easily decided by numerical simulations using practical transfer function which got experiments. Also, transient characteristics could be improved significantly by reflecting the inlet temperature of an evaporator to the output of a controller feedforwardly considering periodic abrupt disturbances. Through some experiments, excellent control performances were established by the suggested control.