• 설비공학논문집
• /
• 제17권4호
• /
• pp.285-296
• /
• 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.

• 한국가스학회지
• /
• 제7권4호
• /
• pp.36-43
• /
• 2003

본 논문에서는 LNG 냉열 에너지를 활용한 지역 냉방 시스템 가능성에 대해 고찰하고자 한다. 액상의 LNG는 기상의 가스로 변환하는 과정에서 많은 냉열 에너지를 발생한다. 최근에 빙축열을 이용한 건물의 냉방 시스템 구축과 심층수를 이용한 지역 냉방 시스템이 도심지의 기존 사무실 건물이나 대규모 건물의 냉방장치로 도입되고 있는 상황이다. LNG의 냉열 에너지는 기존의 냉매에 의존한 개별 냉방 시스템을 대체하는 새로운 냉열 에너지 공정으로 쾌적한 공간을 제공하는 천연의 대규모 냉각매체로 재사용될 수 있다. 버려지는 냉열 에너지는 낮은 코스트로 운영될 수 있는 중요한 청정 에너지원이기 때문에 냉방 시스템으로 개발되면, 기존의 에어콘 시스템에 견주어 볼 때 공기중에 유해한 오염원의 발생과 환경적으로 유해한 냉매 방출을 대폭적으로 줄일 수 있는 우수한 냉방 시스템이 될 것이다. 따라서, 본 연구에서는 냉열 에너지를 활용한 지역 냉방 시스템에 대한 환경 친화적 기본적 설계 개념, 여러 가지 냉방 시스템 성능에 대한 유익한 기반적 정보를 제공하고자 한다.

• Journal of Welding and Joining
• /
• 제20권4호
• /
• pp.459-466
• /
• 2002

• 한국수소및신에너지학회논문집
• /
• 제30권3호
• /
• pp.282-288
• /
• 2019

When liquefied natural gas (LNG) is vaporized to form natural gas for industrial and household consumption, a tremendous amount of cold energy is transferred from LNG to seawater as a part of the phase-change process. This heat exchange loop is not only a waste of cold energy, but causes thermal pollution to coastal fishery areas by dumping the cold energy into the sea. This project describes an innovative new design for reclaiming cold energy for use by cold storage warehouses (operating in the 35 to $62^{\circ}C$ range). Conventionally, warehouse cooling is done by mechanical refrigeration systems that consume large amounts of electricity for the maintenance of low temperatures. Here, a closed loop LNG heat exchange system was designed (by simulator) to replace mechanical or vapor-compression refrigeration systems. The software PRO II with PROVISION V9.4 was used to simulate LNG cold energy, gas re-liquefaction, and the vaporized process under various conditions. The effects on sensible and latent heats from changes to the array type of heat exchangers have been investigated, as well as an examination of the optimum.

• 한국가스학회지
• /
• 제24권4호
• /
• pp.56-61
• /
• 2020

수소의 액화에는 예냉 에너지, 상변화 에너지, 수소 변환열 제거 등 다량의 에너지가 요구되어진다. 본 논문의 목적은 예냉공정에 필요한 에너지로 LNG냉열로 액체질소를 제조하여 사용하는 LNG냉열 간접 이용 방식과, Cold box의 단열에 냉공기를 이용하는 새로운 에너지절약 공정을 제안하여 수소액화 수율을 향상시키고자 하였다. 분석 결과를 보면, LNG냉열 간접이용 방식은 에너지 절약과 함께 액체수소 플랜트의 안전성을 제공하는 장점을 갖는다. 새로운 Cold box 단열 방식은 외벽 철판 3mm/우레탄폼 20cm/공기 5cm/우레탄폼 20cm/설비의 구조일 때 현재 펄라이트 단열에 비교하여 열유입량이 약 35%~50%가 감소하게 된다. 또한 냉공기 보다 온도가 높은 설비는 냉각의 효과를 얻게 된다. 수소액화 플랜트의 공정에 본 결과를 적용한다면 액체 수율이 50% 내외로 크게 향상되는 효과를 제공하게 된다.

• 천문학회보
• /
• 제44권1호
• /
• pp.34.1-34.1
• /
• 2019

To study the formation and evolution of stellar bars and gaseous nuclear rings in barred galaxies in realistic environments, we run fully self-consistent three-dimensional simulations of isolated disk galaxies. We consider two groups of models with cold or warm disks that differ in the radial velocity dispersion. We also vary the gas fraction of the disks. We found that a bar forms earlier and more strongly as the gas fraction increases in the cold disks, while the gas delays the bar formation in the warm disks. The bar formation enhances a central mass concentration which in turn weakens the bar strength temporarily, after which the bar regrows to become stronger in a model with a smaller gas fraction in both cold and warm disks. Although all bars rotate fast in the beginning, they rapidly turn to slow rotators. Gas infalling to the central region forms a dense star-forming nuclear ring. The ring size is very small when it first forms and grows over time. The ring star formation is episodic and bursty due to star formation feedback, and has a good correlation with the mass inflow rate to the ring. Some expanding shells produced by star formation feedback are sheared out in the bar regions and collide with dust lanes to appear as filamentary interbar spurs.

• 천문학회보
• /
• 제44권2호
• /
• pp.75.4-75.4
• /
• 2019

We present a quantitative analysis of the relationship between the gas dynamics and star formation history of DDO 210 which is an irregular dwarf galaxy in the local Universe. We perform profile analysis of an high-resolution neutral hydrogen (HI) data cube of the galaxy taken with the large Very Large Array (VLA) survey, LITTLE THINGS using newly developed algorithm based on a Bayesian Markov Chain Monte Carlo (MCMC) technique. The complex HI structure and kinematics of the galaxy are decomposed into multiple kinematic components in a quantitative way like 1) bulk motions which are most likely to follow the underlying circular rotation of the disk, 2) non-circular motions deviating from the bulk motions, and 3) kinematically cold and warm components with narrower and wider velocity dispersion. The decomposed kinematic components are then spatially correlated with the distribution of stellar populations obtained from the color-magnitude diagram (CMD) fitting method. The cold and warm gas components show negative and positive correlations between their velocity dispersions and the surface star formation rates of the populations with ages of < 40 Myr and 100~400 Myr, respectively. The cold gas is most likely to be associated with the young stellar populations. Then the stellar feedback of the young populations could influence the warm gas. The age difference between the populations which show the correlations indicates the time delay of the stellar feedback.

• Journal of Welding and Joining
• /
• 제13권4호
• /
• pp.113-121
• /
• 1995

This study deals with the quality and the optimum range of laser cutting process. Cold rolled steel sheets for automobile application were cut by a high power CO$_{2}$ laser system with beam quality of TEM$_{\infty}$ mode. Both process parameters such as travel speed and assist gas pressure, and quality factors were considered to optimize the laser cutting. It was revealed that the thinner the sheet thickness, the less effect of oxidation energy for contributing the cutting process. High speed photographs demonstrated that molten spot on the cut surface moved in a random and vigorous manner according to its viscosity and the flowing direction of assist gas, which resulted in so called striation. Laser cutting produced a very smooth surface of average roughness(Ra) about less than 1.5.mu.m at the optimum range. It was also shown that the characteristics of dross formation was influenced by the flowing durection of assist gas and the fluidity of molten metal drop..

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 추계학술대회논문집B
• /
• pp.335-340
• /
• 2000

Most vehicle's exhaust emissions come from the cold transient period of the FTP-75 test. In this study, UEGI technology was developed to help close-coupled catalytic converter (CCC) reach light-off temperature within a few seconds after cold-start. In the UEGI system, unburned exhaust mixture is ignited by four glow plugs installed upstream of the catalyst. Experimental results showed that the temperature of CCC rises faster with the UEGI technology, and the CCC reaches light-off temperature earlier. Under the conditions tested, the light-off time of the baseline case was 62 seconds and that of the UEGI case was 33 seconds.

• 한국자동차공학회논문집
• /
• 제9권2호
• /
• pp.43-49
• /
• 2001

In order to satisfy the ULEV emissions regulation, fast light-off of a catalyst is essential for reduction of HC and CO emissions during the cold start. Cranking Exhaust Gas Ignition(CEGI) method developed in this study showed that the catalyst reaches the light-off temperature in a few seconds. The CEGI stops the ignition signal for a few seconds during the cranking period, so the unburned fuel-air mixture bypasses the combustion chamber and flows through the exhaust manifold. When the unburned mixture reaches two glow plugs installed upstream of the catalyst, it burns and releases the thermal energy to heat up the catalyst, In the FTP-75 vehicle tests, the CEGI showed that the exhaust emissions reduced by 47.7% for THC and by 88.6% for CO in the cold-transient phase of the test.