• 한국수소및신에너지학회논문집
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• 제20권6호
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• pp.526-533
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• 2009

In this paper, cycle performance analysis of $CO_2-C_3H_8$ (R744-R290) cascade refrigeration system with internal heat exchanger is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include subcooling and superheating degree and gas cooling pressure and evaporating temperature in the propane (R290) low temperature cycle and the carbon dioxide (R744) high temperature cycle. The main results were summarized as follows : The COP of cascade refrigeration system of $CO_2-C_3H_8$ (R744-R290) increases with the increasing subcooling degree, but decreases with the increasing superheating degree. The COP of cascade refrigeration system increases with the increasing evaporating temperature, but decreases with the increasing gas cooling pressure. Therefore, superheating and subcooling degree, compressor efficiency, evaporating temperature and gas cooling pressure of $CO_2-C_3H_8$ (R744-R290) cascade refrigeration system have an effect on the COP of this system.

• 한국태양에너지학회 논문집
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• 제26권2호
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• pp.19-25
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• 2006

Methane hydrate, non-polluting new energy resource, satisfies requirement and considered as a precious resource that can prevent the global warming. Fortunately, there are abundant resources of methane hydrate distribute in the earth widely. Therefore, developing the techniques that can utilize these gases effectively is highly desired. The work in this paper here is to develop a skill which can transport and store methane hydrate. As a first step, the equilibrium experiment was carried out by increasing temperatures in the cell at fixed pressures. The influence of gas consumption rates under variable degree of subcooling, stirring and water injection has been investigated formation to clarify kinetic characteristics of the hydrate. The results of present investigation showed that the enhancements of the hydrate formation in terms of the gas/water ratio are closely related to operational pressure, temperature, degrees of subcooling, and water injection.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.979-983
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• 2009

This study has been conducted the possibility of the subcooling type ice storage cooling system that the stored ice used to subcool the condensed refrigerant. The experimental study was done to fine the characteristics of the cooling capacity according to the variation of the subcooling degree and the analysis for the peak shift effect of the full storage, partial storage and subcooling type ice storage system compared to the normal air conditioning system was also done. The result of the analysis was shown that the peak shift effect of this subcooling type ice storage system could be 61%.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1512-1517
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• 2003

Augmentation of CHF by ultrasonic is experimentally studied under subcooling pool boiling condition. Experiment is carried out for downward-facing plate with and without the ultrasonic. The working fluid is distilled water. Experimental apparatus is composed of a bath, power supply, test section, ultrasonic generator, DAQ system. Experiment is performed with the subcooling temperature of $5^{\circ}C$, $20^{\circ}C$, $40^{\circ}C$ and the inclined angle of $0^{\circ}$, $10^{\circ}$, $20^{\circ}$, $45^{\circ}$, 90. From the experimental results, it is found that ultrasonic effect enhances CHF of the downward-facing plate. As increasing the degree of subcooling, the rate of CHF increase is enhanced. As increasing the inclined angle, the rate of CHF increase decreases. Also, we can see that the heat transfer mechanism of CHF augmentation is closely connected with the dynamic behavior of bubble generation and departure.

• 동력기계공학회지
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• 제21권3호
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• pp.45-50
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• 2017

This paper presents the Coefficient of performance(COP) and mass flow ratio of cascade refrigeration system with respect to refrigerants appling to high temperature cycle. The operating parameters considered in this study include degree of superheating and subcooling, compressor efficiency, evaporating temperature, condensing temperature and internal heat exchanger effectiveness in high temperature cycle. The result of this study is as follows : The COP of cascade system increases with increasing degree of superheating and subcooling, compressor efficiency and internal heat exchanger effectiveness except increasing condensing temperature. The mass flow ratio of low and high temperature cycle increases with increasing evaporating temperature and condensing temperature, but decreases with increasing internal heat exchanger effectiveness, degree of superheating and subcooling. Also, the mass flow ratio has no correlation with compressor efficiency at high temperature cycle.

• 설비공학논문집
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• 제5권1호
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• pp.10-17
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• 1993

This paper describes the boiling heat transfer phenomena to be divided into three regions, nonboiling, nucleate boiling and burn-out in the impinging subcooled water jet system. In the nonboiling region, Nusselt number is a function of Prandtl number, Reynolds number and ${\Delta}T_{sub}/T_{ast}$ In the nucleate boiling region, the heat flux increases with increment of the nozzle exit velocity. But the degree of liquid subcooling does not affect the shape of the nucleate boilng curve. The dimensionless correlations can be expressed in the form of $q{\ell}/K_f{\Delta}T_{ast}=C(Bo{\cdot}C_p{\cdot}{\Delta}T_{sat}/Vo^2)^m{\cdot}(Re/We)^n$. The burn-out heat flux increases linearly with increment of the nozzle exit velocity, but independs of degree of subcooling and the supplementary water height.

• 설비공학논문집
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• 제13권8호
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• pp.771-779
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• 2001

In this study, a simulation program has been developed to predict the performance of a parallel flow condenser of an air conditioning system for an automobile. The well-known correlations for he heat transfer rates and the pressure drops are included in this model. It is fond that the numerical model can predict the heat transfer rate and the pressure drop accurately. As the condensing pressure increases of fixed air inlet temperature, the heat transfer rate increases and the pressure drop decreases. The effect of he degree of subcooling on the performance of the condenser is greater than that of the degree of super-heating because the ratio of the area occupied by he tow-phase refrigerant the total area is significantly affected by he degree of subcooling rather than the degree of superheating.

• Nuclear Engineering and Technology
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• 제29권1호
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• pp.35-44
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• 1997

Critical too-Phase flow rates of subcooled water through Short Pipes (L 140039n) with small diameters (D$\leq$7.15 min) have been experimentally investigated for wide ranges of subcooling (0~199$^{\circ}C$) and pressure (0.5~2.0 MPa). To examine the effects of various parameters (i.e., the location of flashing inception, the degree of subcooling, the stagnation temperature and pressure, and the pipe size) on the critical two-phase flow rates of subcooled water through short pipes with small diameters, a total of 135 runs were made for various combinations of test parameters using four different L/D test sections. Experimental results that show effect of various parameters on subcooled critical two phase flow rates are presented in the form of graphs such as the dimensionless mass flux ( $G^{*}$) versus the dimensionless subcooling ( $T_{sub}$$^{*}$) curve. An empirical correlation expressed in terms of a dimensionless subcooling is also obtained for subcooled two-phase flow rates through present test sections. Comparisons between the mass fluxes calculated by present correlation and a total of 755 selected experimental data points of 9 different investigators show that the agreement is fairly good except for very low subcooling data obtained from small L/D (less than 10) orifices.s.s.s.

• 한국가스학회지
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• 제16권3호
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• pp.42-47
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• 2012

본 논문에서는 규제 프레온냉매 R22의 대체 자연냉매의 후보인 R290(프로판), R600(부탄), R717(암모니아), R1270(프로필렌)을 작동유체로 사용하는 2단압축 1단팽창 냉동시스템의 성능 특성을 비교하였다. $-20^{\circ}C{\sim}-50^{\circ}C$ 정도의 저온을 얻기 위해 사용되는 2단압축 1단팽창 냉동장치에서의 증발온도, 응축온도, 과열도 및 과냉각도의 변화에 따른 성능계수(COP) 변화를 규명하고자 하였다. 성능특성 규명 결과, 과냉각도 및 중간냉각기에서의 냉매유량 증가에 따라 시스템의 COP는 증가하였으나, 증발온도, 응축온도 및 과열도가 증가할수록 COP는 저하되는 결과를 나타내었다. 또한, 자연냉매를 사용하는 2단압축 1단팽창 냉동시스템의 COP는 규제 프레온냉매 R22를 사용하는 경우보다 높기 때문에 자연냉매를 사용하고자 하는 냉동시스템의 안전성이 확보되면 충분히 대체 냉매로서의 경쟁력이 있을 것으로 판단되었다.

• 한국산학기술학회논문지
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• 제10권10호
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• pp.2565-2571
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• 2009

본 논문은 시스템의 운전조건하에서 R717-R747용 이원냉동 사이클의 성능 분석에 대한 기초 설계자료를 제공하는 것이다. 본 논문에서 고려한 운전변수는 암모니아 고온사이클과 이산화탄소 저온사이클의 과냉각도, 과열도, 응축과 증발온도이다. 이원 냉동사이클의 성적계수는 과열도가 증가할수록 증가하는 반면, 과냉각도가 증가할수록 감소한다. 그리고, 이원 냉동사이클의 성적계수는 응축온도와 함께 증가하지만, 증발온도와는 반대로 감소한다. 따라서, 과열도, 과냉도, 응축과 증발온도는 본 시스템의 성적계수에 영향을 미치는 것을 알 수 있었고, 최대 성능계수와 최적의 증발온도에 대한 수학 방정식을 개발하기 위해 이러한 변수들을 포함시켜 다중 회귀분석을 통해 제안하였다.