• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.1261-1266
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• 2008

Experimental study was performed to understand the operations of a showcase working in a discount store. Temperatures of evaporation, condenser were measured and also electric power consumption of compressor were measured. The purpose of this study is to application use of cold-heat storage systems operated the showcase. At the condition using ice storage system, the ice making process was operated during midnight being not needed the cooling of the showcase through the continuous running of the condenser unit. And then, the refrigerant was sub-cooled using stored cold-heat after being discharged from the air cooling condenser during the day time. The cooling performance was increased owing to the sub-cooling of refrigerant during day time, hence the running time of the compressor was effectively decreased. In other words, this study showed that power consumption during daytime can be transferred to the midnight for making use of the refrigerant sub-cooling. So the operating characteristics of the showcase system under various working conditions were analyzed and discussed.

• 대한기계학회논문집B
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• 제39권1호
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• pp.37-43
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• 2015

현열 뿐만 아니라 잠열을 이용하는 증발냉각은 배기열 회수에 매우 유용하게 사용될 수 있다. 본 연구의 목적은 증발냉각을 이용한 배기열 회수장치의 성능을 실험적으로 규명하는 것이다. 성능실험장치는 플라스틱 열교환기, 물 분무 노즐, 공기유동용 홴, 물 순환용 펌프, 수조, 온도 습도 유량 측정 센서 등으로 구성되었다. 증발이 없는 현열 회수에서의 유용도와 증발을 수반하는 전열 회수에서의 유용도를 여러가지 작동조건에서 측정하여 비교하였다. 현열냉각과 증발냉각의 유용도는 공기의 유량이 증가함에 따라 감소하고, 대향류에서의 유용도가 평행류에서의 유용도 보다 휠씬 높다. 증발냉각의 경우 물 유량이 증가함에 따라 유용도는 증가하고, 평행류가 대향류보다 물 유량에 더 민감함을 알 수 있다.

• KIEAE Journal
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• 제17권5호
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• pp.69-76
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• 2017

Purpose: This study aimed at developing an Artificial Neural Network (ANN) model for predicting the amount of cooling energy consumption of the variable refrigerant flow (VRF) cooling system by the different set-points of the control variables, such as supply air temperature of air handling unit (AHU), condenser fluid temperature, condenser fluid pressure, and refrigerant evaporation temperature. Applying the predicted results for the different set-points, the control algorithm, which embedded the ANN model, will determine the most energy efficient control strategy. Method: The ANN model was developed and tested its prediction accuracy by using matrix laboratory (MATLAB) and its neural network toolbox. The field data sets were collected for the model training and performance evaluation. For completing the prediction model, three major steps were conducted - i) initial model development including input variable selection, ii) model optimization, and iii) performance evaluation. Result: Eight meaningful input variables were selected in the initial model development such as outdoor temperature, outdoor humidity, indoor temperature, cooling load of the previous cycle, supply air temperature of AHU, condenser fluid temperature, condenser fluid pressure, and refrigerant evaporation temperature. The initial model was optimized to have 2 hidden layers with 15 hidden neurons each, 0.3 learning rate, and 0.3 momentum. The optimized model proved its prediction accuracy with stable prediction results.

• 한국수소및신에너지학회논문집
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• 제34권6호
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• pp.767-772
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• 2023

In this study, combustion experiments were conducted at various engine speeds under full-load conditions using a single-cylinder diesel engine by blending butanol, pentanol, and octanol with diesel at a volume ratio of 10%. Experimental results revealed that higher alcohol-diesel blends resulted in lower brake torque and brake power than pure diesel due to the lower calorific value and the cooling effect during evaporation. An evident improvement in the brake thermal efficiency of the blended fuels was observed at engine speeds below 2,000 rpm, with the butanol blend exhibiting the highest thermal efficiency overall. Furthermore, the brake-specific fuel consumption of the higher alcohol-diesel blends was lower than that of pure diesel at speeds below 2,200 rpm. When using blended fuels, the exhaust gas temperature decreased under lean mixture conditions due to heat loss to the air and the cooling effect from fuel evaporation.

• 한국정밀공학회지
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• 제34권4호
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• pp.247-251
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• 2017

Titanium alloy has been widely used in the aerospace industry because of its high strength and good corrosion resistance. During cutting, the low thermal conductivity and high chemical reactivity of titanium generate a high cutting temperature and accelerates tool wear. To improve cutting tool life, cryogenic machining by using a liquid nitrogen (LN2) jet is suggested. In cryogenic jet cooling, evaporation of LN2 in the tank and transfer tube could cause pressure fluctuation and change the cooling rate. In this work, cooling uniformity is investigated in terms of liquid nitrogen jet pressure in cryogenic jet cooling during titanium alloy turning. Fluctuation of jet spraying pressure causes tool temperature to fluctuate. It is possible to suppress the fluctuation of the jet pressure and improve cooling by using a phase separator. Measuring tool temperature shows that consistent LN2 jet pressure improves cryogenic cooling uniformity.

• Journal of Advanced Marine Engineering and Technology
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• 제35권5호
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• pp.576-581
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• 2011

본 논문은 $CO_2$ 히트펌프용 모세관의 기초 설계자료를 제공하기 위해서 모세관 길이 예측에 대해서 이론 및 실험적으로 조사하였다. 본 연구에서 고려된 작동변수로는 증발온도, 가스냉각기 냉각압력, 냉매유량, 모세관의 관경 등이다. 몇몇 연구자들의 자료를 바탕으로 $CO_2$ 모세관 길이를 예측할 수 있는 수학적 모델식을 작성하였다. 그리고 단열 모세관 팽창장치내 $CO_2$의 증발온도, 냉매유량, 냉각압력 등에 대해서 실험한 결과, 이들 모두는 식 (3)으로 예측한 값과 0.63~10.9%이내에서 좋은 일치를 보였다. 따라 서 본 연구에서는 $CO_2$ 열펌프 단열 모세관에 대한 기초설계 자료로서, 냉각압력, 증발온도, 모세관 직경, 냉매유량 등의 조건으로부터 모세관 길이를 계산해낼 수 있는 예측 상관식을 제안하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제36권4호
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• pp.437-444
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• 2012

본 논문은 지열을 이용한 코일 침적형 히트펌프 시스템의 운전변수에 대한 최적 설계를 위해서 히트펌프의 성능 특성을 실험적으로 조사하였다. 본 연구에서 고려된 작동변수로는 과냉각도, 증발온도, 응축온도 등이다. 그 실험결과를 요약하면 다음과 같다. 지열 이용 코일 침적형 히트펌프 시스템의 증발온도와 과냉각도가 증가할수록, 응축온도는 감소할수록 성능계수는 증가함을 알 수 있다. 즉, 지열 이용 코일 침적형 히트펌프 시스템의 증발온도, 응축온도, 과냉각도는 냉방과 난방의 성능계수에 영향을 미치는 것을 알 수 있다. 따라서 본 연구에서 제안하는 히트펌프 시스템이 최고의 성능을 나타내기 위한 최적의 운전조건을 결정할 필요가 있다.

• 대한기계학회논문집B
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• 제40권3호
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• pp.191-200
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• 2016

환기는 자연환기와 강제환기로 분류되며, 최근에는 하절기에 작업장의 환경개선을 위해 냉각된 공기를 공급하는 환기를 적용하는 경우가 많아지고 있다. 하지만 대규모의 작업장에 냉각된 공기를 공급하기 위해서는 많은 에너지가 필요하며, 이를 보완하기 위해 물의 증발열을 이용하여 공기를 냉각시킨 후 공급하는 환기장치의 도입사례가 증가하고 있으며, 본 실험연구는 부산의 모 신발공장에 실제 적용된 기화방열식 환기장치의 성능을 평가한 사례연구로서 하절기에 외부의 대기온도에 대해 어느 정도의 냉각능력을 구현할 수 있는지 측정하였다. 실험결과로부터 하절기에 약 $6{\sim}7^{\circ}C$ 정도의 냉각효과를 구현하지만 급기의 상대습도가 매우 높아짐을 정량적으로 측정할 수 있었다. 실험결과에 의하면 기화방열식 전체환기 설비가 타방식과 비교하여 작동방식이 단순하며, 에너지 소비가 적은 경제적인 냉각설비이며, 급기의 습도 제어기능만 부가되면 매우 효율적인 환기 - 냉각기능을 동시에 수행할 수 있는 설비임을 확인하였다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.304-308
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• 2008

The optimal design of two stage evaporation & absorption system which is related to the large temperature difference system was investigated numerically in the absorption refrigeration system. The concentrations at inlet & oulet of absorber are 62.9% and 56.9%, but in two stage absorption system the values are 62.2% and 56.2%. Therefore strong solution & weak solution became diluted than the standard value. The amount of weak solution circulation can be reduced in absorption refrigeration system, and the sensible heat load is more reduced to enhance the COP of system. As UAR is increased, COP becomes larger, and this means the role of top section is more important than bottom section in two stage evaporation & absorption system. But the increase of COP becomes slower at 0.7 of UAR ratio. The performance of Type2 is higher than Type1 in COP with the flow direction of cooling waters. This phenomena is due to the active absorption of vapor -absorption & lower temp. cooling water is more effective. The pressure at bottom section becomes higher & that at top section becomes lower and therefore the circulation rate can be diminished more.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.203-211
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• 2008

The optimal design of two stage evaporation & absorption system which is related to the large temperature difference system was investigated numerically in the absorption refrigeration system. The concentrations at inlet & oulet of absorber are 62.9% and 56.9%, but in two stage absorption system the values are 62.2% and 56.2%. Therefore strong solution & weak solution became diluted than the standard value. The amount of weak solution circulation can be reduced in absorption refrigeration system, and the sensible heat load is more reduced to enhance the COP of system. As UAR is increased, COP becomes larger, and this means the role of top section is more important than bottom section in two stage evaporation & absorption system. But the increase of COP becomes slower at 0.7 of UAR ratio. The performance of Type2 is higher than Type1 in COP with the flow direction of cooling waters. This phenomena is due to the active absorption of vapor -absorption & lower temp. cooling water is more effective. The pressure at bottom section becomes higher & that at top section becomes lower and therefore the circulation rate can be diminished more.