• 설비공학논문집
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• 제11권2호
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• pp.205-214
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• 1999

The objective of this paper is to investigate the thermal properties of TMA clathrate compound applicable to cold storage system for building air-conditioning. Especially, the test tube experiments are performed by comparing and analyzing the temperature of phase change, specific heat and subcooling characteristic according to the variation of density, temperature of heat source and charging quantity in TMA clathrate compound. The results are summarized as follows:1) $-15^{\circ}C$ is not proper as the temperature of heat source because the temperature of subcooling is above $8.3^{\circ}C$ 2) temperature of phase change is dropped as the temperature of heat source is lower, 3) the effect of subcooling suppression with about 8$^{\circ}C$ is confirmed when the temperature of heat source is $-10^{\circ}C$ in case of 26, 27, and 30wt%, while the temperature of subcooling is about $0^{\circ}C$ when the temperature of heat source is $-15^{\circ}C$ in case of 25, 26 and 30wt%. Thus, the effect of subcooling suppression is greater as the temperature of heat source is lower. Additionally, the concentrative study is needed on mass concentration causing the phase change without subcooling phenomenon when the temperature of heat source is $-15^{\circ}C$. Thus, it is concluded that TMA clathrate compound has enough thermal properties as the cold storage medium for building air-conditioning.

• 한국지구과학회지
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• 제26권6호
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• pp.560-572
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• 2005

이 연구에서는 1979년부터 1999년까지 21년 동안에 한반도 겨울철 한파와 관련된 대기 순환 및 열원$(Q_1)$의 분포 특성을 조사하였다. 한파 발생 빈도는 1년간 약 1개로 나타났으며, 1989년을 중심으로 전반기에 전체의 $60\%$가 발생하였다. 한파 발생 동안 하층의 대기 순환 패턴은 평년에 비해 서고동저형의 기압 패턴이 더 뚜렷하며, 상층에서도 한반도에 기압골의 영향이 더 강하게 나타난다. 한파가 발생하는 동안에 한반도 부근의 기온 하강 패턴은 바이칼호 부근의 기온 패턴과 반대로 나타나며, 기온의 연직 구조에서도 400 hPa을 기준으로 하층과 상층의 기온 편차는 반대로 나타난다. 열원에 대한 분석은 한파 발생 시 한랭 이류에 의한 냉각은 하강 운동에 의한 단열 승온에 의해 균형을 이룬다는 것을 보여주는데, 이것은 한랭 핵의 이동이 열흡수원의 이동 경로와 연관되어 있음을 나타낸다. 따라서 한파의 유지 기작을 이해하고 한파를 예측하기 위해서는 열원 그리고 열흡수원의 이동 기작이 밝혀져야 할 것이다.

• 설비공학논문집
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• 제12권8호
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• pp.725-734
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• 2000

The objective of this paper is to investigate the thermal properties of TMA clathrate applicable to cold storage system for building air-conditioning. Especially, the test tube experiments are peformed by comparing and analyzing the temperature of phase change, specific heat and subcooling characteristic according to the variation of concentrations and temperature of heat source in TMA clathrate. The results are summarized as follows; 1) temperature of phase change is dropped as the temperature of heat source is lower, 2) the effect of subcooling suppression with about $9.3^{\circ}C$ is confirmed when the temperature of heat source is $-10^{\circ}C$ in case of 30wt%, while the temperature of subcooling is about $0^{\circ}C$ when the temperature of heat source is $-15^{\circ}C$ in case of 25, 29wt% and 30wt% . Thus, the effect of subcooling suppression is greater as the temperature of heat source is lower. Additionally, the concentrative study is needed on mass concentration causing the phase change without subcooling phenomenon when the temperature of heat source is $-15^{\circ}C$ Thus, it is concluded that TMA clathrate has proper properties as the cold storage medium for building air-conditioning.

• 대한기계학회논문집
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• 제16권11호
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• pp.2189-2195
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• 1992

본 연구에서는 대향류 열교환기에 대하여 출력과 효율 등을 계산하는 예를 보 이고, 동시에 최대의 출력을 얻기 위한 조건들을 수치적으로 구하였다. 또한 열교환 기의 장치비용과 열원의 생성비용을 적절히 취급하여 경제적 최적조건에 대해서도 살 펴보고자 한다. 여기서 저온유체의 가용 에너지 획득량으로서 출력은 열전달로 인한 부분만을 생각하기로 한다.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제21권4호
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• pp.245-275
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• 2017

The present investigation deals, Dufour and heat source effects on radiative MHD slip flow of a viscous fluid in a parallel porous plate channel in presence of chemical reaction. The non-linear coupled partial differential equations are solved by using two term perturbation technique subject to physically appropriate boundary conditions. The numerical values of the fluid velocity, temperature and concentration are displayed graphically whereas those of shear stress, rate of heat transfer and rate of mass transfer at the plate are presented in tabular form for various values of pertinent flow parameters. By increasing the slip parameter at the cold wall the velocity increases whereas the effect is totally reversed in the case of shear stress at the cold wall. It is observed that the effect of Dufour and heat source parameters decreases the velocity and temperature profiles.

• 한국수소및신에너지학회논문집
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• 제24권6호
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• pp.510-517
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• 2013

The ammonia-water based power generation cycle utilizing liquefied natural gas (LNG) as its heat sink has attracted much attention, since the ammonia-water cycle has many thermodynamic advantages in conversion of low-grade heat source in the form of sensible energy and LNG has a great cold energy. In this paper, we carry out thermodynamic performance analysis of a combined power generation cycle which is consisted of an ammonia-water regenerative Rankine cycle and LNG power generation cycle. LNG is able to condense the ammonia-water mixture at a very low condensing temperature in a heat exchanger, which leads to an increased power output. Based on the thermodynamic models, the effects of the key parameters such as source temperature, ammonia concentration and turbine inlet pressure on the characteristics of system are throughly investigated. The results show that the thermodynamic performance of the ammonia-water power generation cycle can be improved by the LNG cold energy and there exist an optimum ammonia concentration to reach the maximum system net work production.

• 설비공학논문집
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• 제14권8호
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• pp.634-640
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• 2002

The purpose of this study is to investigate the propriety of TMA clathrate as a cold storage medium. Particularly, this is to examine the extent of subcooling improvement when the additives is added to the TMA clathrate, because water used for cold storage ma terial has low phase change temperature and subcooling. This study has been analyzed and compared pure water with TMA 30 wt% clathrate how phase change temperature, subcooling and specific heat in the various concentrations are changed. This results prove low phase change temperature and subcooling control effect when the ethanol is added to the TMA 30 wt% clathrate than the TMA 30 wt% clathrate. In addition, it results low specific heat when there is added to the TMA 30 wt% clathrate over 0.5 wt% ethanol in the cold heat source temperature under $-7^{\circ}C$. The other side, it results high specific heat when the ethanol is added in it at the cold heat source temperature under $-5^{\circ}C$. Therefore, it is found that the additive must be controlled by available solution limit and study for new additive must be lasted to know its effect.

• 한국지구과학회지
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• 제27권3호
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• pp.302-312
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• 2006

이 연구에서는 1979년부터 2004년까지 25년 동안에 극 진동의 강도가 한반도 겨울 한파에 미치는 영향을 대기순환과 열원을 분석하여 조사하였다. 북극 진동이 강할 때 한파의 발생 횟수는 약할 때 보다 약 14.3% 더 발생하는 것으로 나타났다. 월 발생 횟수에서도 양의 AO에서 1.05회/월, 음의 AO에서 1.33회/월로 나타나서 북극 진동이 강할 때가 약할 때 보다 약 26.6% 더 많았다. 이것은 북극 진동이 강한 특정 달에 한파가 자주 발생한다는 것을 의미한다. 또한 북극 진동이 강할 때가 약할 때보다 $0.6^{\circ}C$ 더 낮은 기온을 보였다. 북극 진동의 강약에 따른 열원의 차이를 고찰한 결과, 북극 진동이 강해졌을 때 한반도 주변의 기온은 이류항에 의한 냉각이 강화되어 더 낮아지지만, 열원항에 의한 상쇄 효과에 의해 기온 하강을 억제하는 것으로 나타났다. 그 결과 대기 순환의 유의한 차이에도 불구하고 음의 AO와양의 AO 사이에 기온 차이는 평균적으로 $0.6^{\circ}C$로 작게 나타난다.

• Journal of Biosystems Engineering
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• 제25권5호
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• pp.385-390
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• 2000

The heat pump is one of heating and cooling systems driven by electricity using natural energy as a heat source. The heat pump system was mainly adopted to a cooling system or a refrigeration system. In regions with a large amount of electricity, it is used as a heating system or a heating and cooling system of houses, buildings and agricultural facilities. During cold weather, air source heat pumps do not work well because of some technical problems, such as frosting on evaporator coil when outside air temperature is below -5$^{\circ}C$. In this research, the heat regenerative technology was employed to eliminate the frosting on evaporator coil and improve the COP of the heat pump system. This fiber belt heat regeneration system(FBHRS) has very simple structure consisting of a geared motor and a porous fiber belt passing through alternatively between cold and warm air duct. The laboratory test showed that the heat pump system with a FBHRS yielded an impressive COP higher than 3.5 at the outside air temperature of -7$^{\circ}C$ in heating mode.

• KIEAE Journal
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• 제16권3호
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• pp.25-34
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• 2016

Purpose: The temperature in Seoul has risen 3 times more than the average global temperature increase for the past 100 years. Today, summer starts 15 days earlier than the early 20th century and is 32 days longer. This tendency causes rapid increase of cooling energy demand. Following this effect, seawater heat resources are to be used as an countermeasure for global warming. Incheon Port near the Western Sea has the lowest water temperature in the winter in South Korea in which it is suitable to use seawater cold heat resources. Method: The cold heat resource is gained from seawater when the water temperature is the lowest in the winter time and saved in a seasonal thermal storage. This can be used as cold heat resource in the summer time. A heat exchanger is essential to gain seawater cold energy. Due to this necessity, sea water heat resource heat exchangers are modeled by heat transfer equations and the fluid characteristics are analyzed. Also, a CFD (computational fluid dynamics) program is used to conduct simulation on the fluid characteristics of heat exchangers. The analyzed data of deducted from this process are comprehensively analyzed and discussed. Result: Regarding the performance of the heat exchanger, the heat exchanger was operated following the prediction within the range of heat transfer rate of minimum 3.3KW to maximum 33.6KW per device. In the temperature change analysis of the heat exchanger, fluid analysis by heat transfer equations almost corresponded to the temperature change by CFD simulation. Therefore, it is considered that the results of this study can be used as design data of heat exchangers.