• Journal of Advanced Marine Engineering and Technology
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• 제35권2호
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• pp.182-188
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• 2011

본 논문은 R744-R404A용 캐스케이드 냉동시스템의 기초 설계자료를 제공하기 위해서 성능특성에 대해 분석하였다. 작동변수로는 R404A용 고온사이클과 R744용 저온사이클의 과냉각도와 과열도, 압축효율, 응축과 증발온도이다. 이에 대한 주요결과를 요약하면 다음과 같다. 고온사이클에만 과열도를 주는 것이 가장 높은 COP를 가지는 반면에 저온 고온사이클 모두에 대해 과냉도를 주는 것이 가장 높은 COP를 가진다. 과열도, 과냉각도, 압축효율, 증발온도, 응축온도 등의 인자들이 R744와 R404A용 캐스케이드 냉동사이클의 COP에 영향을 미치는 것을 확인할 수 있었고, 이들 각각의 인자들은 캐스케이드 냉동사이클의 성능을 최대로 하는 캐스케이드 증발온도가 존재함을 알 수 있었다.

• 설비공학논문집
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• 제18권11호
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• pp.874-880
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• 2006

The power density and heat dissipation rate per unit area of the telecommunication equipment have been increased with the technology development in the footprint of telecommunication hardware. A proper heat dissipation method from the PCB module is very important to allow reliable operation of its electronic component. In this study, a hybrid air-conditioner for the telecommunication equipment room was designed to save energy and obtain system reliability. For high outdoor temperatures, the hybrid system operates in the vapor compression cycle, while, for low outdoor temperatures, the hybrid system works in the secondary fluid cooling cycle with no operation of the compressor. The performance of the hybrid air-conditioner was measured by varying outdoor and indoor temperatures. The hybrid air-conditioner yielded 50% energy saving compared with the conventional refrigeration system when the mode switch temperature was $8.3^{\circ}C$.

• 한국태양에너지학회 논문집
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• 제32권3호
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• pp.170-177
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• 2012

To apply the nanofluids into the general vapor compression cycle, basically have to know the thermal properties including thermal conductivity and dynamic viscosity. And needs to show the dispersion characteristics for various nanofluids and concentrations. So, firstly this study showed experimentally the thermal properties for various concentration (0.1%~0.7%, as mass balance) and temperature($20^{\circ}C{\sim}40^{\circ}C$) on $Al_2O_3$, $TiO_2$, and CuO nanofluids using base fluid as POE oil that has used in the scroll compressor for various refrigeration system. From the results, the dynamic viscosity of nanofluids was considerably changed from the base POE oil. And, the dispersion characteristics of various nanofluids using the simple methods like as analyzing the RGB value or measuring the sinking height of nanofluids were showed experimentally. Through the results, the dispersion characteristics of $Al_2O_3$ nanofluid was better than those of $TiO_2$, and CuO nanofluids not considering the real refrigeration cycle rurming conditions.

• 설비공학논문집
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• 제21권9호
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• pp.519-526
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• 2009

Environmental control system is adopted to control the thermal load from the avionic equipment in the reconnaissance pod which is mounted under a fighter aircraft, undergoing large and rapid environmental changes with the variations of flight altitude and velocity. In this study, an environmental control system was designed and built by adopting vapor compression cycle using R-124. The cooling performance characteristics of the system were measured varying operating parameters: thermal load in the pod, air mass flow rate through evaporator, condenser inlet air temperature, and air mass flow rate through condenser. The effects of the experimental parameters on the system performance were analyzed based on the experimental results. The problems on the designed system were also analyzed and the solutions were suggested to improve system efficiency and to obtain stable operation.

• Journal of Advanced Marine Engineering and Technology
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• 제35권2호
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• pp.189-195
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• 2011

본 논문은 R744-R404A용 캐스케이드 냉동시스템의 기초 설계자료를 제공하기 위해서 COP 예측 상관식을 제안하고 그 결과를 타 상관식과 비교하였다. 작동변수로는 R404A용 고온사이클과 R744용 저온사이클의 과냉각도와 과열도, 압축기효율, 응축과 증발온도이다. 이에 대한 주요결과를 요약하면 다음과 같다. 다중회귀 분석을 통해 R744-R404A용 캐스케이드 냉동시스템의 성능 예측식을 제안하였고, 그 결과를 타 연구자들의 상관식과 비교하였다. 그 결과 본 연구에서 제안한 성능 예측식은 타 연구자들의 상관식과 일치하지 않았다. 따라서 향후 R744-R404A용 캐스케이드 냉동시스템에 대한 추가 실험 데이터와 본 연구에서 제안한 COP 예측 상관식을 비교하여 그 신뢰성을 확보할 필요가 있다.

• 설비공학논문집
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• 제18권12호
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• pp.964-970
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• 2006

Vapor compression refrigerators have much critical variables such as the controls of temperature and pressure switches, control durations and operating hours of electronic valves. This study compares and analyzes the data which is obtained from system controlling of the evaporation temperatures which are generally used in automatic pump down operating systems. Through this study, the automatic evaporation control operation system will be more ideal for the system to keep the proper temperature distribution depending on the purpose of evaporation side. The automatic pump down control operation is more appropriate for the system to aim at the effective use of evaporation side without using the temperature difference. And this test will be proved that the changes at the low pressure side didn't have significant impacts on the high pressure side.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.821-826
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• 2009

Due to environmental concerns $CO_2$ has been reintroduced as a potential candidate to replace HFCs in refrigeration systems. Oils are always required in a vapor-compression cycle, and thus actual working fluid in the system is $CO_2$-oil mixtures even though the oil concentrations are low at the heat exchangers and the expansion device. The cooling heat transfer coefficients for $CO_2$-oil mixtures under supercritical condition are required to designing of the gas cooler in the $CO_2$ refrigeration system properly. In the present study, the gas cooling heat transfer coefficients for $CO_2$-PEC9 was estimated by using the Gnileinski correlation, and the Kim and Ghajar model through the previous prediction models for the thermo-physical properties of $CO_2$-oil mixture. The Gnileinski correlation was used when the oil wt.% in the mixture is less than 1.0, and for the higher oil concentration the Kim and Ghajar model was applied. The estimated results agree with the experimental results conducted by the Dang et al.

• 설비공학논문집
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• 제20권11호
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• pp.733-738
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• 2008

Due to environmental concerns $CO_2$ has been reintroduced as a potential candidate to replace HFCs in refrigeration systems. Oils are always required in a vapor-compression cycle, and thus it is necessary to precisely estimate the thermodynamic mixture properties of $CO_2$-lubricant oil. In the present study, the density and the viscosity of the mixture was calculated by the Redlich and Kwong type EoS and the modified Peng and Robinson type viscosity EoS, respectively. The viscosity model was based on the similarity between P-v-T and T-$\mu$-P relationships. The predicted results were compared with the experimental data of Pens ado et al. whose test conditions were 100$\sim$650 bar of pressure and 303 K$\sim$353 K of temperature with the $CO_2$-POEs mixtures under 92.2 wt.% and 83.3 wt.% of $CO_2$ concentration. The mean deviations of the mixture density were 7.93% and 8.32% for 92.2 wt.% and 83.3 wt.% of $CO_2$ concentration, respectively. Concerning the viscosity, the mean deviations were 4% and 10% for 92.2 wt.% and 83.3 wt.% of $CO_2$ concentration under the Pensado et al.'s test conditions.

• 한국수소및신에너지학회논문집
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• 제28권4호
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• pp.401-406
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• 2017

When Liquified Natural Gas (LNG) is vaporized into NG for industrial and household usage, tremendous cold energy was transferred from LNG to seawater during phase-changing process. This heat exchanger loop is not only a waste of huge cold energy, but will cause thermal pollution to the coastal fishery area also when cold water was re-injected into the sea. In this study, an innovation design has been performed to reclaim the cold energy for -35 to $62^{\circ}C$ refrigerated warehouse. Conventionally, this was done by installing mechanical refrigeration systems, necessitating tremendous electrical power to drive temperature. A closed loop LNG heat exchangers in series was designed to replace the mechanical or vapor-compression refrigeration cycle by process simulator. The process simulation software of PRO II with provision has been used to simulate this process for various conditions, what to effect on cold energy and used energy for re-liquefaction and evaporation process. In addition, through analysis the effect of the change of LNG supply pressure on sensible and latent heat, optimum operational conditions was suggested for LNG cold energy warehouse.

• 한국산학기술학회논문지
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• 제12권3호
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• pp.1473-1478
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• 2011

본 연구에서는 전처리 공정을 거친 천연가스로부터 에탄 이상의 성분을 회수하기 위한 탈메탄탑에 대한 전산모사와 공정 최적화를 수행하였다. 전처리된 천연가스는 탈메탄탑 상부의 차가운 기상류와의 열교환 및 프로판 냉동 사이클이 포함된 예냉공정을 거친 후에 기상과 액상이 분리된다. 기상은 터보 팽창기를 거치면서 생산되는 동력을 residue gas의 압력을 높이기 위한 압축기에 전달한 후에 부분적으로 응축되어 탈메탄탑 상부로 주입된다. 액상류는 줄-톰슨 팽창 밸브를 거친 후 더욱 냉각되어 탈메탄탑의 중간부로 주입된다. 원료 대비 에탄의 회수율은 75% 이상으로 정하였으며, 탈메탄탑의 탑저에서 에탄에 대한 메탄의 몰비는 0.015로 정하였다. 한편 프로판 냉동 사이클의 heat duty를 최소화시키기 위해서 원료를 분리하여 side reboiler와 열교환시킴으로써 냉열의 일부 회수할 수 있었다.