• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.239-243
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• 2008

In many literatures the researchers pointed out that the using metal foam will significantly enhance the performance of heat exchanger. This paper focuses on theory study of metal foam, including calculation method of properties of foam (permeability ��K, inertial coefficient f, fiber diameter $d_f$, and effective conductivity $k_e$), model of pressure drop and model of heat transfer. Theory analysis on the performance of heat exchanger will be presented here. Finally the optimal material will be obtained from theory calculation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.4
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• pp.285-296
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• 2005

In order to reduce the compression power and to use the overall energy contained in LNG effectively, a combined cycle is devised and simulated. The combined cycle is composed of two cycles; one is an open cycle of liquid/solid carbon dioxide production cycle utilizing LNG cold energy in $CO_2$ condenser and the other is a closed cycle gas turbine which supplies power to the $CO_2$ cycle, utilizes LNG cold energy for lowering the compressor inlet temperature, and uses the heating value of LNG at the burner. The power consumed for the $CO_2$ cycle is investigated in terms of a production ratio of solid $CO_2$. The present study shows that much reduction in both $CO_2$ compression power (only $35\%$ of power used in conventional dry ice production cycle) and $CO_2$ condenser pressure could be achieved by utilizing LNG cold energy and that high cycle efficiency ($55.3\%$ at maximum power condition) in the gas turbine could be accomplished with the adoption of compressor inlet cooling and regenerator. Exergy analysis shows that irreversibility in the combined cycle increases linearly as a production ratio of solid $CO_2$ increases and most of the irreversibility occurs in the condenser and the heat exchanger for compressor inlet cooling. Hence, incoming LNG cold energy to the above components should be used more effectively.

• Nuclear Engineering and Technology
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• v.52 no.9
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• pp.2138-2150
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• 2020

We report the status of the cold neutron triple-axis spectrometer (Cold TAS) and thermal neutron triple-axis spectrometer (Thermal TAS) installed at HANARO. Cold TAS, whose specifications are standard across the world, is in the final phase of commissioning. Proper instrument operation was confirmed through a feasibility study of phonon measurements and data analyses with resolution convolution. In contrast, Thermal TAS is in the initial phase of commissioning, and improvement of the monochromator drum is now in progress from the viewpoint of radiation shielding. In addition, we report recent activities in the development of neutron basic elements, that is, film-coated Si-wafer collimators, which are promising for use in triple-axis spectroscopy, particularly in Cold TAS.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.3
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• pp.247-258
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• 1994

In this study, experimental investigations to find cold energy storage performance have been made for two different temperatures at condenser. Temperatures at inlet and outlet of condenser were measured to calculate global heat transfer coefficient of direct contact method in our cold energy storage system. Also storage performance by direct contact method was compared with that of Ice-On-Coil type ice storage which was calculated by analytic solution. Results show that, in the case of $-8.0^{\circ}C$ at condenser inlet, heat transfer coefficient of direct contact method is 3.25 times higher than that of conventional method and COP of system is improved by using R141b as refrigerant which produces gas hydrate and has higher phase change temperature than $0.0^{\circ}C$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.5
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• pp.692-699
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• 1999

The vortex tube is a sample device for separating a compressed gaseous fluid stream into two flows of high and low temperature without any chemical reactions. The phenomena of energy separation through the vortex tube were investigated experimentally, to see the effects of the number of nozzle holes on the energy separation. The experiment was carried out with the number of nozzle holes from 1 to 10 by varying inlet pressure and cold mass fraction. The experimental results were indicated that the effective number of nozzle holes for the best cooling performance was found as 4. Also, to find effective use in a given operation conditions, the temperature difference of cold air and the cooling capacity of vortex tube was compared. The result is that cooling capacity was more important than temperature difference of cold air.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.2
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• pp.79-84
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• 2013

In this study, a cold aisle containment system was proposed among various strategies to reduce the energy waste by recirculation air from the hot aisle. To verify the effectiveness of the cold aisle containment system, a test bed which is similar to an actually existing server room was set up in the Internet Data Center(IDC) building. Comparative experiments, conventional open type cooling system and cold aisle containment system were carried out under actual conditions. The result revealed that the range of inlet temperature of the server system was $20{\sim}25^{\circ}C$ in an existing cooling system and the range of inlet temperature dropped below $20^{\circ}C$ by the cold aisle containment system. After all, cold aisle containment system was proved to be the solution for energy saving cooling system.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.11
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• pp.2189-2195
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• 1992

The performance of heat exchanger as an energy conversion device can be described by the available energy output and efficiency. The efficiency is defined as the ratio of the available energy output and the exergy of the heat source flow. In present study, a counterflow heat exchanger is analyzed and the conditions to obtain maximum output is numerically determined. As a result, the avilable energy obtained by the cold flow can be determined as functions of the heat capacity flow, the cold flow inlet temperature and the heat transfer capacity of heat exchanger. At the maximum output condition the heat capacity flow of the cold fluid is larger than that of the heat source, and the heat capacity flow ratio is equal to the ratio of the cold flow inlet temperature and the atmospheric temperature. And the avilable energy output increases as the heat transfer capacity of the heat exchanger become larger, but in the economic point of view there is also an optimum heat transfer capacity for a given heat source flow.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.6
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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.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2001.05a
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• pp.71-74
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• 2001

• The Journal of Korean Medical History
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• v.27 no.2
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• pp.99-120
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• 2014

Purpose : There are two types of sleep disturbance: inability to sleep (不眠) and somnolence (多眠). This study is to examine treatments of the two types of sleep disturbance in the Books of Cold Damage and how those theories were established and formed. Methods : 1. Verses including the words related to inability to sleep and somnolence were extracted from "Treatise on Cold Damage Diseases" (傷寒論). 2. Among the Books on Cold Damages that are classified according to the symptoms, 17 books with contents related to inability to sleep and somnolence were selected to collect and classify data in three perspectives: mechanism of disease (病機), method of treatment (治法) and disease pattern (病證). 3. Data collected through the above methods were compared and diagramed. Results & Conclusions : 1. On Cold Damage, inability to sleep is mostly rooted when human body lacks yin energy while having excessive yang energy (陽盛陰虛) due to fire and heat (火熱). The reason could be misuse of perspiration inducing method (汗法) or purgation (下法) on the doctors' part. 2. On Cold Damage, somnolence is rooted when pathogen (邪氣) is spread to yin meridians (陰經) and the human body lacks yang while having excessive yin energy (陰盛陽虛) or when heat (熱邪) is invaded into interior parts (裏部). 3. Many scholars of Cold Damage in later periods had copied the "Treatise on Cold Damage Diseases" for treatments of sleep disturbance but many others have applied the verses from "Treatise on Cold Damage Diseases" or added new treatments. Do jeol-am (陶節庵) and Wang Geung-dang (王肯堂) particularly had deep understanding on "Treatise on Cold Damage Diseases" and utilized the content freely or suggested new remedies because they had thorough knowledge on relating formula as well.