• Journal of Biosystems Engineering
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• 제26권5호
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• pp.449-460
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• 2001

This study was carried out to develop a simulation model with EES(Engineering equation solver) for analyzing the performance of a grain cooler. In order to validate the developed simulation model, several main factors which have affected on the performance of the gain cooler were investigated through experiments. A simulation model was developed in the standard vapor compression cycle, and then this model was modified considering irreversibe factors so that the developed alternate model could predict the actual cycle of a grain cooler. The compressor efficiency in vapor compression cycle considering irreversibility much affected on the coefficient of performance(COP). The COP in the standard vapor compression cycle model was greatly as high as about 6.50, but the COP in an alternative model considering irreversibility was as low as about 3.27. As a result of comparison between the actual cycle and the vapor compression cycle considering irreversibility, the difference of pressure at compressor outlet(inlet) was a little by about 48kPa (8.8kPa), the temperatures of refrigerant at main parts of the grain cooler were similar. and the temperature of chilled air was about 8$\^{C}$ in both. The model considering irreversibility could predict performance of the grain cooler. The theoretical period required to chill grain of 1,383kg from the initial temperature 24$\^{C}$ to below 11$\^{C}$ was about 55 hours 30 minutes, and the actual period required in a grain bin was about 58 hours. The difference between the predicted and an actual period was about 2 hours 30 minutes. The cooling performance predicted by the developed model could well estimate the cooling period required to chill the grain.

• 설비공학논문집
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• 제13권1호
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• pp.48-58
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• 2001

For the past few decades the vapor compression cycle with a solution circuit (VCCSC) has been known to provide high efficiency and variable capacity. In this study performance of a VCCSC cycle is examined through computer simulation. In the simulation heat exchangers were modelled by specifying UA or effectiveness values while the compressor performance was specified by an isentropic efficiency. Aqua/ammonia solution was chosen as the working fluid which can be used in the high temperature range. The results show that there exists an optimum operation condition which is dependent upon the temperatures of the external heat transfer fluids(HTFs). Besides the HTF\`s temperature, the maximum system pressure and the size of the solution heat exchanger are shown to have an influence on the optimum operation condition. Finally, as compared to a simple vapor compression heat pump with HFC134a, the COP of the VCCSC is shown to be 2∼22% higher.

• 한국수소및신에너지학회논문집
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• 제23권5호
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• pp.521-529
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• 2012

Since the energy demand for refrigeration and air-conditioning has greatly increased all over the world, thermally activated refrigeration cycle has attracted much attention. This study carries out a performance analysis of a vapor compression cycle (VCC) driven by organic Rankine cycle (ORC) utilizing low-temperature heat source in the form of sensible heat. The ORC is assumed to produce minimum net work which is required to drive the VCC without generating an excess electricity. Effects of important system parameters such as turbine inlet pressure, condensing temperature, and evaporating temperature on the system variables such as mass flow ratio, net work production, and coefficient of performance (COP) are thoroughly investigated. The effect of choice of working fluid on COP is also considered. Results show that net work production and COP increase with increasing turbine inlet pressure or decreasing condensing temperature. Out of the five kinds of organic fluids considered $C_4H_{10}$ gives a relatively high COP in the range of low turbine inlet pressure.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.459-464
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• 2009

This study has been conducted on how to determine the multi-evaporator vapor compression cycle system is charged correctly by using sensor readings which are used to control system. In this paper, the characteristics of the multi-evaporator were presented and sensor values were classified using fuzzy clustering. finally classification logic and it's performance were discussed by applying commercial VRF system.

• 설비공학논문집
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• 제27권7호
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• pp.362-368
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• 2015

This paper presents a numerical study on the performance of a vapor compression cycle equipped with an ejector as an expansion device to improve the COP by reducing the expansion loss and compressor work. The simulation is carried out using a model based on the conservation of mass, energy and momentum in the ejector. From the results of the simulation, the vapor compression cycle equipped with an ejector showed a maximum COP improvement of 14.0% when using R134a refrigerant and 16.8% when using R1234yf. In addition, the performance of the system with an ejector represents the increased performance as the temperature difference between condensing and evaporating increased.

• 한국산학기술학회논문지
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• 제10권1호
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• pp.32-38
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• 2009

R744용 초임계 증기압축식 냉동시스템의 작동변수에 대한 기초설계자료를 제공하고자 냉동능력, 압축일량, 성적계수에 대한 사이클 성능분석을 실시하였다. 본 연구에서 고려된 작동변수는 R744 증기압축식 사이클의 과열도, 가스냉각기 출구온도, 증발온도이다. R744의 냉동능력은 과열도가 증가할수록 증가하는 반면, 증발온도와 가스냉각기 출구온도가 증가할수록 감소한다. 압축일량은 R744의 과열도와 냉각압력과 함께 증가하나 증발온도는 증가할수록 감소한다. 그리고 성적계수는 가스냉각기의 출구온도와 증발온도가 증가할수록 증가하는 반면, 과열도는 감소한다. 그러므로, R744용 초임계 증기압축식 냉동시스템의 냉동능력, 압축일량, 성적계수는 과열도, 가스냉각기 출구온도, 증발온도에 영향을 받는 것을 알 수 있었다. 따라서, R744용 초임계 증기압축식 냉동시스템을 설계할 경우에는 이러한 영향을 면밀하게 파악하여야 한다.

• 설비공학논문집
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• 제15권6호
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• pp.461-470
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• 2003

The purpose of this study is to investigate the performance of a transcritical cycle for hot water heating using $CO_2$ as a working fluid. Some of the main parameters that affect the practical performance of the $CO_2$ system are discussed; the performance on the variation of refrigerant charge, changes in flow conditions of secondary fluids, and that with or without internal heat exchanger, The experimental results show that the optimum charge is approximately the same for various mass flow rates of the secondary fluid at gas cooler. The experimental results on the effect of secondary fluids are in general agreement with the experimental results of transcritical cycle in the open literature and show similar trend for conventional subcritical vapor compression cycles. The heat exchanger effectiveness increases with an increase of the heat exchange area of the internal heat exchanger regardless of the mass flow rate at the gas cooler.

• 대한기계학회논문집B
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• 제37권12호
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• pp.1137-1145
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• 2013

본 연구에서는 열 구동 냉동사이클로서 유기 랭킨사이클 (ORC)과 증기 압축 냉동사이클(VCC)의 복합 사이클에 대한 엑서지 해석을 수행하였다. 시스템의 열원으로는 다양한 재생 에너지 열원이나 산업체에서의 폐열 등 현열 형태의 저온 열원을 고려하였으며 작동유체로서 R143a, R22, R134a, 프로판, 이소부탄, 부탄, R245fa 및 R123 등 여덟가지 작동유체들을 고려하였다. 터빈 입구 압력의 변화나 작동유체의 종류에 따라 시스템의 COP 나 엑서지 효율은 물론 시스템의 각 요소에서의 엑서지 파괴 (아너지)에 미치는 다양한 영향에 대해 분석하고 논의하였다. 해석 결과는 주어진 열원 온도에 대해 시스템에서 가장 엑서지 파괴가 큰 구성 요소는 터빈 입구 압력과 작동유체에 따라 민감하게 변화하는 사실을 보여준다.

• 한국가스학회:학술대회논문집
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• 한국가스학회 1998년도 추계학술발표회 논문집
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• pp.255-260
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• 1998

This study describes the results of Coefficient Of Performance(COP) analysis by cycle simulation for two types of absorption-compression hybride cycle using the water/Lithium Bromide solution pair, These types are basic hybride systems introducing a mechanical compression process into the refrigerant vapor phase of the single effect absorption cycle. In absorption-compression hybrid cycles, coefficient of performance is improved compared with absorption cycle. Hybride cycle Type ll is considered as a key technology to support energy utilization system, given its capability of utilizing waste heat to drive system with a high level of efficiency.

• 한국가스학회지
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• 제3권1호
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• pp.14-20
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• 1999

[ $H_2O/LiBr$ ]계 흡수식 사이클에 압축기를 조합한 흡수압축사이클을 도입하여 증기를 단열압축시켜 그 증기의 응축열을 재생열로 이용하는 사이클에 대해서 시뮬레이션을 통하여 횹수압축사이클의 특성을 밝힌 연구이다. 기존의 흡수사이클에 압축기를 도입함에 따라 고효율 사이클을 실현할 수 있음을 제시하였으며, 흡수$\cdot$압축사이클의 구체적인 가능성을 제시하였다. 재생기에서 발생한 냉매증기를 단열압축시킨 TYPE 2는 단열압축 증기의 응축열만으로는 재생이 어려우므로 외부로부터 별도의 열량을 투입해야 하며 투입하는 외부열량에 폐열이나 2차 에너지를 이용할 수 있다면 높은 COP를 얻을 수 있어 실현가능성이 높다.