• 한국산학기술학회논문지
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• 제11권12호
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• pp.4721-4726
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• 2010

본 논문은 압축기 인버터 주파수 제어에 따른 CO2용 수냉식 열펌프의 성능 특성에 대해서 실험적으로 조사하였다. 실험장치는 압축기, 가스냉각기, 팽창밸브, 증발기, 내부 열교환기, 수액기로 구성된다. 실험장치에 사용된 모든 열교환기는 동관으로 제작된 이중관식 대향류형이다. 가스냉각기와 증발기는 2.4 m인 소시험부 6개와 4개로 각각 구성된다. 실험결과를 요약하면, 우선 증발기와 가스냉각기의 입구온도와 냉매유량이 일정한 조건하에서 압축기 인버터 주파수가 증가할수록 압축비와 토출압력이 증가한다. 또한 인버터 주파수가 증가할수록 난방능력과 압축일량은 증가하는 반면 성능계수는 감소한다. 그리고 증발기 입구 2차유체의 온도가 $15^{\circ}C$에서 $25^{\circ}C$로 증가함에 따라 압축비와 압축일량은 감소하지만 질량유량, 난방능력, 성능계수는 증가한다. 위의 이러한 경향은 종래의 프레온계 냉매 시스템의 성능 변화와 유사하다.

• 대한기계학회논문집B
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• 제31권6호
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• pp.531-538
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• 2007

In this study, an air conditioning system using carbon dioxide as a refrigerant was developed for automotive cabin cooling. Experiments have been carried out to examine the steady state and dynamic characteristics of this system. The system consists of a compressor, a gas cooler, an evaporator, an expansion device, an internal heat exchanger and an accumulator. The compressor is a variable displacement type, driven by the electric motor, and the gas cooler and the evaporator are aluminum extruded heat exchangers of micro channel type. The $CO_2-refrigerant$ charge, the compressor speed, the air inlet temperature of the gas cooler, the air inlet temperature and the air flow rate of the evaporator and the cooling load are varied and the performance of the system is experimentally investigated. As the compressor speed increased, cooling capacity increased, but the coefficient of performance was deteriorated. As the cabin air temperature or the air flow rate to the cabin was set high, both the cooling capacity and the COP increased. In the cool down experiment with 1.0 or 2.0 kW of heat load, the dynamic characteristics of the air-conditioning system were investigated. For a given capacity of compressor, cool down speed was monitored, and the temperature change was acceptable fur low heat load condition.

• 한국자동차공학회논문집
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• 제16권3호
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• pp.159-165
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• 2008

This paper deals with the optimum high pressure control algorithm for a transcritical $CO_2$ mobile air-conditioning system with belt-driven compressor to achieve the maximum COP. The experiments were performed to find out the maximum COP conditions with various operating conditions. The experimental results showed that the COP was increased and then decreased with increase of the refrigerant high pressure for the system. Therefore the value of high pressure which has maximum COP could be selected. Furthermore, the strong (linear) relation between the optimum high pressure and the gas cooler outlet temperature was revealed, which suggests the use of a simple controller with only one parameter for the transcritical $CO_2$ cycle.

• 설비공학논문집
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• 제14권7호
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• pp.531-542
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• 2002

Transcritical$CO_2$ systems are under consideration for use as residential/mobile air conditioners. In these systems, an internal heat exchanger is usually adopted to improve both capacity and/or COP of the $CO_2$ system in lower operating pressure range of gas cooler. A program has been developed to analyse the performance of internal heat exchangers using the section-by-section method. The internal heat exchanger of coaxial configuration is first analyzed and fairly good agreements with the data are obtained, And then the internal heat exchanger of multiple circular coil configuration has been investigated. The results obtained from the parametric study provide the guidelines for the initial design and manufacturing concepts of the internal heat exchanger in transcritical $CO_2$ system. Further studies are necessary to develop the heat transfer correlations of carbon dioxide in the tubes to obtain more accurate results.

• 설비공학논문집
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• 제25권1호
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• pp.20-27
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• 2013

Numerical modeling of $CO_2$ water heater was conducted prior to optimal design of medium and large sized $CO_2$ water heater, and the experimental test with small sized $CO_2$ water heater having heat capacity of 4 kW was completed to verify the present numerical model. The present model estimated the experimental data of COP(coefficient of performance), heating capacity, and the hot water outlet temperature within the range of 3% to 8% of mean deviation. As increase of EEV(electric expansion valve) opening area, decreasing of heating capacity and the hot water outlet temperature, and increasing of COP were found in both experimental and numerical investigation.

• 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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• 제16권1호
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• pp.84-90
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• 2004

In order to evaluate the performance of carbon dioxide cycle, a simulation model was developed to predict the steady state performance of $CO_2$ transcritical cycle. The expansion process is treated as an isenthalpic throttling process or isentropic expansion process. The mathematical model is based entirely on the basic energy conservation law and thermodynamic and transport properties of $CO_2$. A Parametric study has been conducted in order to investigate the effect of isentropic efficiency of expansion turbine and various operating conditions on the cycle performance. An optimal heat rejection pressure existed for the given evaporating temperature and outlet temperature of gas cooler.

• Journal of Advanced Marine Engineering and Technology
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• 제33권6호
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• pp.827-834
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• 2009

The cooling heat transfer coefficient of $CO_2$ in a brazing type small diameter tube was investigated experimentally. The main components of the refrigerant loop are a receiver, a $CO_2$ compressor, a mass flow meter, an evaporator and a brazing type small diameter tube as a test section. The mass flux of $CO_2$ is $400{\sim}1600$ [kg/$m^2s$], the mass flowrate of coolant were varied from 0.15 to 0.3 [kg/s], and the cooling pressure of gas cooler were from 8 to 10 [MPa]. The cooling heat transfer coefficients of the brazing type small diameter copper tube is about $4{\sim}11.7%$ higher than that of the conventional type small diameter copper tube. In comparison with test results and existing correlations, correlations failed to predict the cooling heat transfer coefficient of $CO_2$ in a brazing type small diameter copper tube. therefore, it is necessary to develope reliable and accurate predictions determining the cooling heat transfer coefficient of $CO_2$ in a brazing type small diameter copper tube.

• 설비공학논문집
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• 제25권4호
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• pp.173-179
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• 2013

Middle-sized $CO_2$ water heater having compressor power of 7.45 kW was designed, and its performances were experimentally tested. Besides, optimum design of the $CO_2$ water heater was conducted by cycle simulation. When ambient temperature of $7^{\circ}C$ and hot water outlet temperature of $80^{\circ}C$ the $CO_2$ water heater showed the COP of 3.2. As hot water temperature increased the COP is getting decreased due to significant increase of compressor power consumption compared to increasing rate of heating capacity. When ambient temperature increased from $-3^{\circ}C$ to $12^{\circ}C$ the COP increased by 30%. The optimum components design of a gas cooler, an internal heat exchanger, and an evaporator were conducted, and the experimental correlation between amount of EEV opening and ambient temperature, and hot water temperature was suggested.

• 설비공학논문집
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• 제30권3호
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• pp.107-115
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• 2018

A design combining the use of a compressor and expander was introduced in order to improve the cycle performance of a $CO_2$ automotive air conditioning system. Both the compressor and expander used were of rotary vane type and were designed to share a common shaft in a housing. Numerical simulation was carried out to evaluate the merit of the combined unit. In a typical automotive air conditioning operating conditions, the COP of the system was improved by 8.7% by the application of the combined unit. The compressor input was reduced by 5.2% through use of the expander output. In addition, about 3.06% increase in the cooling capacity was obtained through isentropic expansion in the expander. Our study noted that, as the pressure difference between the gas cooler and the evaporator becomes larger, the COP of the system improved increases unless the mass flow rate in the expander exceeds that in the compressor.