• 한국가스학회지
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• 제18권4호
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• pp.13-20
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• 2014

상업용 천연가스 배급 시스템에서 천연가스의 공급압력은 압력조절밸브를 사용하여 제어하며 이때 막대한 압력에너지가 낭비된다. 이러한 폐압에너지는 터보 팽창기와 같은 터보기계를 사용하여 회수할 수 있으나 팽창과정에서 발생하는 Joule-Thompson 효과에 따라서 큰 온도강하가 발생한다. 터보 팽창기 전단 또는 후단에 보일러를 설치하여 영하의 온도를 방지할 수 있으며 또한 보일러를 대체하여 연료전지나 가스엔진의 폐열을 이용하여 천연가스를 예열할 수도 있으나 하이브리드 시스템의 구동을 위해 운영규모에 따라 일정량을 소모해야 한다. 이 연구에서는 천연가스가 가지고 있는 압력에너지를 활용하여 천연가스의 소모 없이 터보 팽창기와 연결된 히트펌프를 구동하여 천연가스를 예열하는 시스템을 제안하고 증발온도, 응축온도 및 작동유체의 변화에 따른 시스템의 열역학적 특성을 분석하였다. R717 냉매가 예상 작동범위 내에서 가장 높은 COP와 가장 낮은 압축일을 나타내 제안된 하이브리드 시스템에 적합함을 확인하였다. 보일러시스템과의 경제성 분석을 통해 천연가스를 LNG 형태로 수입하고 있는 국내의 경우 히트펌프 하이브리드 시스템이 경쟁력 있음을 확인하였다.

• 대한기계학회논문집B
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• 제28권3호
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• pp.289-295
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• 2004

The heat transfer coefficient and pressure drop during gas cooling process of carbon dioxide in a horizontal tube were investigated. The experiments were conducted without oil in the refrigerant loop. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flowmeter, an evaporator, and a gas cooler(test section). The main components of the water loop consist of a variable-speed pump, an isothermal tank, and a flowmeter. The gas cooler is a counterflow heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. The test section consists of smooth, horizontal stainless steel tube of the outer diameter of 9.53mm and of the inner diameter of 7.75mm. The length of the test section is 6m. The refrigerant mass fluxes were 200∼300kg/(m2$.$s) and the inlet pressure of the gas cooler varied from 7.5㎫ to 8.5㎫. The main results were summarized as follows : Pressure drop of CO2 increases with increasing gas cooler pressure. The friction factors of CO2 in a horizontal tube show a relatively good agreement with the correlation by Blasius. The heat transfer coefficient of CO2 in transcritical region increases with decreasing gas cooler pressure and decreasing mass flux of CO2. Most of correlations proposed in a transcritical region showed significant deviations with experimental data except for those predicted by Gnielinski.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.200.1-200.1
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• 2011

Underground air is a special energy source in Jeju and distributes lava cave, pyroclastic, open joint, and crushing zone. A possible area to utilize underground air is 85% of Jeju except to the nearby area of Sambang Mt. and 25m high coastal area from sea level. In Jeju, underground air is used for heating agricultural facilities such as greenhouse cultivated mangos, Hallbong and mandarin orange, pigsty, mushroom cultivation house, etc. and fertilizing natural $CO_2$ gas by suppling directly into agricultural facilities. But this heating method causes several problem because the underground air has over 90% relative humidity and is inadequate in heating for crops. Mangos are the most widely grown tropical fruit trees and have been cultivated since 1993 in Jeju. In Jeju, the cultivating area is about 20ha and amount of harvest is 275ton/year in 2010. In this study, the heat pump system using underground air as heat source was installed in mangos greenhouse which area is $495m^2$. The capacity of heat pump system and heat storage tank was 10RT, 5ton respectively and heating effect and heating performance of the system were analysed.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.279-282
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• 2006

Upon a turbopump's running, cavitation may occur at the inlet of the LOx pump by pressure drop and heat transfer along the LOx feeding line. Since the cavitation can cause serious damage to the pump or to stop running, the absence of the cavitation at the inlet of a turbopump should be confirmed before the using the turbopump. In the present study, the calculation of the volume fraction of LOx gas phase at the inlet of the pump are performed with different temperatures of LOx in the tank, pressure drops and heat transfers along the feeding line. This calculation method can be applied to define the limits of thermal and hydraulic characteristics during the design of a LOx feeding system.

• 설비공학논문집
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• 제17권2호
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• pp.101-109
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• 2005

The purpose of this study is to investigate the performance of outdoor heat exchanger for heat pump using carbon dioxide. Two types of fin and tube heat exchangers (2 rows for type A and 3 rows for B) are tested. Both heat exchangers have counter-cross flow and 1-circuit arrangement. Test results such as heat transfer rate, pressure drop characteristics and temperature distribution in the heat exchanger are shown with respect to mass flow rate of refrigerant and frontal air velocity For cooling mode, the minimum temperature difference between air and refrigerant of type B is smaller than that of type A by $1^{circ}C$, but the pressure loss of air side is much higher for type B by $29\%$. It is found that a large temperature gradient of carbon dioxide during gas cooling Process Promotes thermal conduction through tube wall and fins which results in degradation of heat transfer performance. For heating mode operation, type B heat exchanger shows higher heat transfer performance compared to type A. However, because pressure loss of refrigerant side of type B is much greater than that of type A, the refrigerant outlet pressure of type B becomes lower than that of type A.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 후기학술대회논문집
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• pp.246-247
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• 2005

The paper presents the heat transfer characteristics during cooling process of carbon dioxide($CO_2$) in a helically coiled tube. The main components of the apparatus consist of a receiver, a variable speed pump, a mass flowmeter, a pre-heater, a gas cooler(test section) and an isothermal tank. The test section with the inner diameter 4.55 [mm] is a tube in tube type heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. The main results were summarized as follows : The heat transfer coefficient increases with respect to the decrease of the gas cooler pressure in a supercritical region and the increase of the refrigerant mass flux. The pressure drop decreases in increases of the gas cooler pressure and increases with respect to increases the refrigerant mass flux.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.378-383
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• 2005

This experimental study presents the results of the cooling performance test of a $CO_2$ heat pump system for fuel cell vehicles. The experimental facility provides the cool ing and heating environment for cabin and heat releasing component. The test loop is designed to target the cooling capacity of 5kW and its coefficient of performance (COP) of 2.2. The cooling performance of the heat pump system is strongly dependent on the refrigerant charge and the degree of superheat. We carried out basic experiments to obtain optimum refrigerant charge and the degree of superheat level at the internal heat exchanger outlet. The heat pump system for fuel cell vehicles is different from that of engine-driven vehicles, where the former has an electricity-driven compressor and the latter has the belt-driven (engine-driven) compressor. In the fuel cell vehicle, the compressor speed is an independent operating parameter and it is controlled to meet the cooling/heating loads. Experiments were carried out at cooling mode with respect to the compressor speed and the incoming outdoor air speed. The results obtained in this study can provide the fundamental cool ing performance data using the $CO_2$ heat pump system for fuel cell vehicles.

• Journal of Advanced Marine Engineering and Technology
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• 제31권6호
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• pp.699-706
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• 2007

The cooling heat transfer coefficient and pressure drop of $CO_2$(R-744) in helical coil copper tubes were investigated experimentally The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter. a pre-heater and a inclined helical coil type gas cooler (test section). The test section consists of a smooth copper tube of 2.45 and 4.55mm inner diameter The refrigerant mass fluxes were varied from 200 to $600 [kg/m^2s]$ and the inlet pressures of 9as cooler were 7.5 to 10.0 [MPa]. The heat transfer coefficients of $CO_2$ in helical coil tubes increase with the increase of mass flux and gas cooling pressure of $CO_2$. The pressure drop of $CO_2$ in the gas cooler shows a relatively food agreement with those Predicted by Ito's correlation developed for single-phase in helical coil tubes. Though a few correlation available with the data. the local heat transfer coefficient of $CO_2$ agrees well with those presented by Pitla et al. among the predictions. However at the region near pseudo-critical temperature. the experiment data indicate higher values than the Pitla et al. correlation.

• 설비공학논문집
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• 제17권6호
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• pp.596-604
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• 2005

This paper presents the work on evaluating the LCC (Life-Cycle Cost) of a heat pump system as unutilized energy system. The river water as an unutilized energy source was used for the heat source of heat pump system. LCC analysis is a concrete method for evaluating the economical efficiency of energy facilities of building. The present case study shows an example of adequate use of the LCC analysis on a heat pump system and conventional gas boiler and refrigerator for building heat supply. A life cycle of 20 years was used to calculated net present value of energy cost. Over a 20 year life cycle, the energy cost could be reduced by 612 million won if a heat pump system were used instead of a conventional boiler and an absorption refrigerator.

• 한국수소및신에너지학회논문집
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• 제4권1호
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• pp.21-30
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• 1993

The operational characteristics of a metal hydride heat pump system are strongly dependent on the amound of hydrogen gas transferred by hydriding and dehydriding reactions between the reactors under dynamic conditions. A new metal hydride heat pump combined with hydrogen compressor was constructed and the dependency of its operating conditions on such as cycle time, amount of hydrogen to be transferred between two reacting metal hydride reactors, operating temperature, and heat transmission characteristics of the reactors was investigated to find the optimum operating efficiency. These conditions were also evaluated in connection with the cooling output and hydrogen compressor connected to the system in order to enhance the total efficiency.