• 대한기계학회논문집
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• 제19권8호
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• pp.2012-2021
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• 1995

An experimental study was performed for the analysis of dynamic characteristics of refrigeration system by controlling the evaporator superheat. Experimental data have been taken utilizing two different devices, thermostatic expansion valve(T.E.V.) and electronic expansion valve(E.E.V.), for the control of the evaporator superheat. The ranges of parameters, such as superheat, mass flow rate of refrigerant and inlet temperature of evaporator were 5-30.deg. C 90-170 kg/h and 10-25.deg. C, respectively. The data taken from the T.E.v.and E.E.v.were discussed with the control of the superheat, pressure drop, refrigerating capacity, compression work, evaporating temperature, condensing temperature and COP affecting performance characteristics of refrigeration system. In case of the refrigerant flow control with T.E..V., the superheat and pressure drop of the evaporator varied periodically, but the control with E.E.V., the parameters were very stable. In E.E.v.control, refrigerating capacity, compression work and evaporating temperature were decreased with increasing superheat, and the highest COP was obtained in the range of superheat from 5.deg. C to 15.deg. C.

• 동력기계공학회지
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• 제18권1호
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• pp.57-62
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• 2014

This paper present the performance characteristics of R404A two-stage compression refrigeration system. The operating parameters considered in this study include evaporating and condensing temperature, subcooling and superheating degree, compressor efficiency. The main results were summarized as follows: The COP of two-stage compression refrigeration system using R404A has an effect on the variation of evaporation temperature, condensation temperature, subcooling degree and compressor efficiency, but not an effect on the superheating degree. R404A two-stage compression refrigeration system is unstable because COP of this system is significantly changed when evaporating temperature and compressor efficiency decreased. In particular, when compressor efficiency decreased, COP is significantly decreased. This is inefficient for long-term use.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.621-626
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• 2006

Regenerative evaporative cooling is known as an environment-friendly and energy efficient cooling method. A regenerative evaporative cooler (REC) consisting of dry and wet channels is able to cool down the air stream below the inlet wet-bulb temperature. In the regenerative evaporative cooler, the cooling effect is achieved by redirecting a portion of the air flown out of the dry channel into the wet channel and spraying water onto the redirected air. In this study, a horizontal regenerative cooler is considered. In the horizontal regenerative cooler, the flow direction of evaporating water has a right angle to the flow direction of supply air. This difference was investigated with visualization technique and simplified 2-module performance test was done in a thermo-environment chamber. Optimum design configuration is changed due to the wet channel which are easily fully covered with evaporating water and block the air flow inside the channel. Applying the optimized fin configuration design with the highly wetting surface treatment, a regenerative evaporative cooler was fabricated and tested to Identify the cooling performance improvement and operation characteristics. From the experimental results at the intake condition of $32^{\circ}C$ and 50% RH, the supply temperature was measured to be around $23.4^{\circ}C$. The cooling effectiveness based on the inlet dewpoint temperature was evaluated 73% which is almost close to the design expectation.

• 대한설비공학회지:설비저널
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• 제17권4호
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• pp.456-465
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• 1988

The performance of the cold latent heat storage is investigated by experiment and by a simplified analytic approach. The heat storage tank has eight horizontal circular tubes and one path of refrigerant evaporating tube. The phase change material in the heat storage tank is water which is frozen by evaporating refrigerant of refrigeration system and melts by the warm air in the heat storage tank. In the experiment, the performance has been studied by the various conditions including the initial water temperature on solidification and flow rate and temperature of air. The rate of recovered heat has been simulated by a simplified model and the results shows a good agreement. In solidification process, initial water temperature causes time delay corresponding to the sensible heat and it is found that the shape of evaporator is important. In melting process, the recovered heat rate from the heat storage tank is proportional to $Re^{0.8}(T_{bi}-T_f)$ of air where $T_{bi}$ and $T_f$ indicate temperatures of inlet air and phase change, respectively. And the deminishing rate of the recovered heat is higher for the higher heat rate.

• Journal of Advanced Marine Engineering and Technology
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• 제37권6호
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• pp.575-581
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• 2013

본 논문은 R744-R404A 캐스케이드 냉동시스템의 최적 냉매 충전을 위해 과냉도, 과열도, 내부열교환기 효율 등에 대한 영향을 분석한 것이다. 연구에 사용된 캐스케이드 냉동시스템의 고온 사이클에는 R404A, 저온 사이클에는 R744를 적용하였다. 그 주요 결과는 다음과 같다 : 고온 사이클의 과냉도, 과열도, 내부열교환기 효율과 저온 사이클의 증발온도와 압축효율은 크게 할수록 질량유량비가 작게 나타났다. 그리고 캐스케이드 온도차와 고온 사이클의 증발온도, 응축온도와 저온 사이클의 과냉도, 과열도, 내부열교환기 효율은 작을수록 질량유량비가 작게 나타났음을 확인하였다.

• 한국태양에너지학회 논문집
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• 제31권3호
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• pp.73-79
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• 2011

ORC(organic Rankine cycle) has potential of reducing consumption of fossil fuels and has many favorable characteristics to exploit low-temperature heat sources. This work analyzes performance of ORC with superheating using low-temperature energy sources in the form of sensible energy. Maximum mass flow rate of a working fluid relative to that of a source fluid is considerd to extract maximum power from the sources. Working fluids of R134a, $iC_4H_{10}$ and $C_6C_6$, and source temperatures of $120^{\circ}C$, $200^{\circ}C$ and $300^{\circ}C$ are considered in this work. Results show that for a fixed source temperature thermal efficiency increases with evaporating temperaure, however net work per unit mass of source fluid has a maximum with respect to the evaporating temperature in the range of low source temperature. Results also show that the maximum power extraction is possible with R134a for the source temperature of $120^{\circ}C$, with $iC_4H_{10}$ for $200^{\circ}C$, and with $C_6C_6$ for $300^{\circ}C$.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2001년도 춘계학술대회 논문집
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• pp.106-111
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• 2001

The performance characteristics of heat pump system using the new refrigerant subcooling system were investigated. The new heat pump system has the ice storage tank to accumulate the latent heat of the refrigerant during the night-time. The heat is released to subcool the saturated refrigerant liquid at the outlet of a condenser in the daytime. The experimental apparatus is a well-instrumented heat pump which consisted of a refrigerant loop and a coolant loop. The test sections(condenser and evaporator) were made of tube-in-tube heat exchanger with the horizontal copper tube of 12.7[mm] outer diameter and 9.5[mm] inner diameter. The evaporating temperatures ranged from $-5[^{\circ}C]$ to $0[^{\circ}C]$ and the subcooling degrees of the refrigerant varied from $15[^{\circ}C]$ to $25[^{\circ}C]$. The test of the ice storage was carried out at evaporating temperature of $-10[^{\circ}C]$ and the ice storage mode is an ice-on-coil type. The main results were summarized as follows ; The refrigerant mass flow rate and compressor shaft power of the heat pump system were independent of the subcooling degrees. The cooling capacity o the heat pump system increases as the evaporating temperature and subcooling degree increases. The cooling capacity of the heat pump system is about 25 to 30% higher than that of normal heat pump system. The COP of the heat pump system which subcooled the refrigerant liquid at the outlet of the condenser is about 28% higher than that of the normal heat pump system.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2012년도 전기공동학술대회 논문집
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• pp.239-239
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• 2012

• Journal of Advanced Marine Engineering and Technology
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• 제25권3호
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• pp.573-580
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• 2001

When investigating optimum design of the evaporator in the refrigeration and heat pump systems, there is still lack of data for the dynamic characteristics of the evaporator, This is due to the fact that the static characteristics in the evaporator are absolutely difficult to measure and are burdened with uncertainties. In this study, the simulation works for static characteristics in the evaporator of small air conditioner are carried out to obtain the data of dynamic characteristics. In the simulation, the test evaporator is divided by two-phase evaporating region and single-phase heating region. The major parameters are refrigerant flow rate, heat transfer coefficient of air, air velocity and air temperature. The results show that the calculation method for tube length is an easy-to-use to model analysis of static characteristics and to determine state of refrigerant in the evaporator. The effects of the four parameters on the length of evaporating completed point and heat flow rate to the evaporator are clarified.

• 한국산업융합학회 논문집
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• 제14권3호
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• pp.113-119
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• 2011

This study analyzed facts affecting the performance of refrigeration systems after throttling actions, by changing the amount of refrigerant according to adjusting the opening of manual expansion valve to 80%, or 20% with vapor compressional refrigeration training equipment. At opening of 20%, the inlet and outlet temperature of compressor, subcooling and superheat, condenser heat, refrigeration effect, flash gas heat, coefficient of performance were higher, while at 80%, condensing pressure, evaporating pressure, compression work were higher, Thus, we could see changes in the amount of refrigerant affect the performance of the refrigeration system.