• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2012년도 춘계학술발표대회 논문집
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• pp.534-542
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• 2012

Vertical closed-loop ground source heat pump systems(GSHP) have been installed widely in Korea since it can extract moderate temperature level of geothermal heat in a small area. As a ground heat exchanger, a vertical closed-loop type with brine circulation is mostly preferred since it is simple and less harmful to ground environment. However, it requires a secondary heat exchange loop between the refrigerant in a heat pump and the brine. By adding a geothermal heat exchanger in the secondary heat exchange loop, circulation pumps should be attached and the temperature difference between refrigerant and ground is increased, which are important parts of performance degradation. In this paper, annual and seasonal performances of direct expansion(DX) geothermal heat pump were estimated mathematically as an alternative of classical indirect geothermal heat pump based on the annual performance evaluation. As a result, DX geothermal heat pump showed 43% higher annual performance than the classical U-tube geothermal heat pump.

• 한국태양에너지학회 논문집
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• 제32권3호
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• pp.114-122
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• 2012

Vertical closed-loop ground source heat pump systems(GSHP) have been installed widely in Korea since it can extract moderate temperature level of geothermal heat in a small area. As a ground heat exchanger, a vertical closed -loop type with brine circulation is mostly preferred since it is simple and less harmful to ground environment. However, it requires a secondary heat exchange loop between the refrigerant in a heat pump and the brine. By adding a geothermal heat exchanger in the secondary heat exchange loop, circulation pumps should be attached and the temperature difference between refrigerant and ground is increased, which are important parts of performance degradation. In this paper, annual and seasonal performances of direct expansion(DX) geothermal heat pump were estimated mathematically as an alternative of classical indirect geothermal heat pump based on the annual performance evaluation. As results, DX geothermal heat pump showed 43% higher annual performance than the classical U-tube geothermal heat pump.

• 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.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.534-539
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• 2007

The objectives of the present work is to investigate the influence of the solution cooled absorber(SCA), refrigerant drain heat exchanger(RSX), exhaust gas/solution heat exchanger(ESX) and high efficiency solution heat exchanger on COP for a double-effect series-flow absorption chiller. A simulation program has been prepared for the cycle analysis of absorption chillers. As a result, Solution heat exchangers(LSX, HSX) are a most effective element for the COP than the others. In spite of the poor contribution to COP, SCA make a rule to reduce the crystallization phenomena of LiBr solution at solution heat exchanger. And the optimum solution split ratio are varied with the relative size of RSX and LSX.

• 설비공학논문집
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• 제20권10호
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• pp.662-668
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• 2008

The objectives of the present work are to investigate the influence of the solution cooled absorber(SCA), refrigerant drain heat exchanger(RSX), exhaust gas/solution heat exchanger(ESX) and high efficiency solution heat exchanger on COP for a double-effect series-flow absorption chiller. A simulation program has been prepared for the cycle analysis of absorption chillers. As a result, solution heat exchangers(LSX, HSX) are the most effective element for the COP than the others. In spite of the poor contribution to COP, SCA plays an important role to reduce the crystallization phenomena of LiBr solution at solution heat exchanger. And the optimum solution split ratio varies with the relative size of RSX and LSX.

• Journal of Advanced Marine Engineering and Technology
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• 제27권1호
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• pp.108-116
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• 2003

In this paper, the experimental results of condensation heat transfer were reported for the plate and shell heat exchangers(P&SHE) using R-l34a. An experimental refrigerant loop has been established to measure the condensation heat transfer coefficient of R-l34a in a vertical P&SHE. Two vertical counter flow channels were formed in the P&SHE by three plates of geometry with a corrugated trapezoid shape of a chevron angle of 45$^{\circ}$. Downflow of the condensing R-l34a in one channel releases heat to the cold up flow of water in the other channel. The effect of the refrigerant mass flux, average heat flux, system pressure and vapor quality of R-l34a on the measured data were explored in detail. The results indicate that at a higher vapor quality the condensation heat transfer coefficients are significantly higher. Condensation heat transfer coefficients were increased when the refrigerant mass flux was increased. A rise in the average heat flux causes an slight increase in the hr. Finally, at a higher system pressure the hr is found to be lower. Correlation is also provided for the measured heat transfer coefficients in terms of the Nusselt number.

• 한국자동차공학회논문집
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• 제17권1호
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• pp.146-153
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• 2009

The performance characteristics of heat exchangers which consist of a gas cooler, an evaporator and an internal heat exchanger have been investigated at various operating conditions of $CO_2$ air conditioning system by experiments. The heat exchangers were designed for use in the vehicle $CO_2$ air conditioning system, when considering the characteristics of heat transfer and high pressure as $CO_2$ refrigerant. This paper studied the performance of heat exchangers at various compressor speeds and expansion valve openings, and quantified the heat transfer rates and pressure drops. Heat transfer rates at the gas cooler and the evaporator were 6.9 kW and 5.2 kW, respectively, when the compressor speed was 4000 rpm and refrigerant vapor quality at the evaporator outlet was 0.98. Therefore, this paper carried out that the heat exchangers were analyzed to achieve superior performance for the vehicle transcritical $CO_2$ cycle.

• Journal of Advanced Marine Engineering and Technology
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• 제20권3호
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• pp.91-100
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• 1996

Experimental results for forced convection condensation of non-azeotropic refrigerant mixtures inside a horizontal smooth tube are presented. The mixtures of R-22+R-134a and pure refrigerants R-22 and R-134a are used as the test fluids and a double pipe heat exchanger of 7.5mm ID and 4800mm long inside tube is used. The range of parameters are 100-300kg/h of mass flow rate, 0-1.0 of quality, and 0, 33, 50, 67, and 100 weight percent of R-22 mass fraction in the mixtures. The heat flux, vapor pressure, vapor temperature and tube wall temperature were measured. Using the data, the local and average heat transfer coefficients for the condensation have been obtained. In the same given experimental conditions, the liquid heat transfer coefficients for NARMs were considerally lower than that of the pure refrigerant of R-22 and R-134a. Local heat transfer characteristics for NARMs were different from pure refrigerant R-22 and R-134a. In some regions, local heat transfer coefficients for NARMs were increased in the following order ; Bottom$\rightarrow$Top$\rightarrow$Side. The condensation heat transfer coefficients for NARMs increased with mass velocity, heat flux, and quality, but were considerably lower than that of pure refigerant R-22 and R-134a.

• Journal of Advanced Marine Engineering and Technology
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• 제35권1호
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• pp.40-45
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• 2011

본 연구의 목적은 팽창장치 후에 설치된 액기분리기와 예냉 열교환기를 갖는 냉동시스템의 특성을 파악하고자 하는 것이다. 냉장고의 전형적 냉매인 냉매 R134a의 팽창공정 후 액기분리기에서 분리된 찬 증기를 이용하여 예냉 열교환기에서 팽창장치에 주입되는 냉매를 과냉시킨다. 분석결과 냉동능력은 8.9% 상승하였으며, COP는 1.4% 증가하였다. 이러한 성능 향상의 이유는 냉매 모리엘선도의 포화액선과 포화기체선의 기울기가 다르기 때문이다.

• 설비공학논문집
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• 제7권3호
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• pp.488-500
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• 1995

An air-cooled ammonia/water GAX(Generator-Absorber heat eXchange) absorption cooling cycle is proposed and its performance is numerically evaluated. It is shown that the performance of the system is greatly dependent on the quality of the refrigerant leaving the evaporator. For any refrigerant concentration in the investigated range(99.1~99.9% ammonia), the cycle COP(coefficient of performance) reaches the highest value, when some amount(about 7%) of refrigerant evaporates in the refrigerant heat exchanger. Among temperature differences in various heat exchangers, the temperature difference between GAX-absorber and the GAX-generator shows the greatest effect on the system performance, whereas pressure losses cause no significant decrease in COP. The system COP increases almost linearly with increasing evaporator temperature, decreasing absorber temperature or decreasing condenser temperature. If both absorber and condenser temperature increase simultaneously, the decrease in the COP becomes larger.