• 천문학회보
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• 제45권1호
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• pp.61.1-61.1
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• 2020

We examine the HI gas kinematics and distribution of galaxy pairs in group or cluster environment from high-resolution Australian Square Kilometre Array Pathfinder (ASKAP) WALLABY pilot observations. We use 22 well-resolved galaxies in the Hydra cluster of which 4 galaxies are visually identified as pairs and others are isolated ones. We perform profile decomposition of HI velocity profiles of the galaxies using a new tool, BAYGAUD which enables us to separate a line-of-sight velocity profile into an optimal number of Gaussian components based on Bayesian MCMC techniques. All the HI velocity profiles of the galaxies are decomposed into kinematically cold or warm gas components with their velocity dispersion, 4~8 km/s or > 8 km/s, respectively. We derive the mass fraction of the kinematically cold gas with respect to the total HI gas mass, f = log10(M_cold / M_HI), of the galaxies and correlate them with their dynamical mass. The cold gas reservoir of the paired galaxies in the Hydra cluster is found to be relatively higher than that of the isolated ones which show a negative correlation with the dynamical mass in general.

• 천문학회보
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• 제44권1호
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• pp.34.1-34.1
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• 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
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• 제38권2호
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• pp.40.1-40.1
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• 2013

We perform a set of N-body/SPH simulations of galaxy interactions between early- and late-type galaxies with the mass ratio of 2 to 1. We show that mass transfer during a fly by interaction (the closest approach distance ~50kpc) can cause the morphology transformation of an early-type galaxy to a late type. In our simulations, we vary the orbital parameters of the interactions and the cold gas fraction of the late-type galaxy to compare how the morphology transformation is affected by the amount of mass transfer and orbital angular momentum of cold gas accreted to the early type. We also include hot halo gas in the galaxy models and show the location of the tidal bridge can be influenced by the shock generated during the collision.

• 대한기계학회논문집
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• 제18권10호
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• pp.2675-2685
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• 1994

A study has been conducted to provide the experimental information for the velocity and temperature profiles of steam-air mixutre and to investigate their roles on the film condensation with wavy interface. Saturated gas mixture of steam-air was made to flow through the nearly horizontal$(4.1^{\circ})$ square duct of 0.1m width and 1.56m length at atmospheric pressure, and was condensated on the bottom cold plate. The air mass fraction in the gas mixture was changed from zero(W =0, pure steam) to one(W =1, pure air), and the bulk velocity was varied from 2 to 4 m/s. Water film was injected concurrently to investigate the effect of wavy interface on the condensation. The velocity and temperature profiles were measured by LDA system and thermocouples along the three parameters ; air mass fraction, mixture velocity and film flow rate. The profiles moved toward the interface with increasing steam mass fraction, mixture velocity and film flow rate. The Prandtl and Schmidt numbers were near one in the present experimental range, however there was no complete similarity between the velocity and temperature profiles of gas mixture. And the heat transfer characteristics and interfacial structure were coupled with each other.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.770-775
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• 2001

Numerical calculation has been performed to investigate the fluid flow, heat transfer and local mass fraction of chemical species in the MOCVD (metalorganic chemical vapor deposition) manufacturing process. The mixing of reactants (trimethylgallium with hydrogen gas and ammonia) was presented by the concentration of each reactants to predict the uniformity of film growth. Effects of inlet size, location, mass flow rate and susceptor/cold wall tilt angle on the concentration were reported. The newly developed reactor, that precursors were supplied at separated inlet to prevent from premixing, was investigated to obtain the quantitative verification. As a results, the optimum mass flow rate, wall tilt angle and inlet conditions were proposed.

• 한국수소및신에너지학회논문집
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• 제31권4호
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• pp.363-371
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• 2020

Recently, the technologies to utilize the cold energy of liquefied natural gas (LNG) have attracted significant attention. In this paper, thermodynamic performance analysis of combined cycles consisting of ammonia Rankine cycle (AWR) and organic Rankine cycle (ORC) with LNG Rankine cycle to recover low-grade heat source and the cold energy of LNG. The mathematical models are developed and the effects of the important system parameters such as turbine inlet pressure, ammonia mass fraction, working fluid on the system performance are systematically investigated. The results show that the thermal efficiency of AWR-LNG cycle is higher but the total power production of ORC-LNG cycle is higher.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2002년도 제25회 KOSCI SYMPOSIUM 논문집
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• pp.165-172
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• 2002

This paper discusses hydrodynamic characteristics of cold circulating fluidized bed(CFB) in different solid mass inventories. Operating parameters of solid mass inventory, primary air and J-valve fluidizing air were varied to find out the effect on the flow fludization pattern. Experimental measurements were made in a 3m tall CFB that has 0.05m riser diameter and black silica-carbonate of particle sizes from $100{\mu}m$ to $500{\mu}m$ were employed as the bed material. The operating conditions of superficial gas velocity and J-valve fluidizing velocity were in the ranges of 1.39~3.24 m/s and 0.139~0.232 m/s respectively. The axial solid fraction and solid circulation rate of CFB were observed and compared with modelling through IEA-CFBC Model and commercial CFD code.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2910-2915
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• 2008

This paper was investigated the behaviors of the engine and combustion phenomena for various LPG compositions in the semi-return type system, which is not recircurated to LPG tank through furl rail, applied LPi engine during a cold idle condition and including a cold start of the engine. Cyclic HC and NOx emissions were measured at exhaust port to examine their formation mechanical and reduction mechanical with fast response gas analyzers. Various ignition timing is experimented to study the characteristics of combustion phenomena, HC/NOx emissions during fast idle. Also, this study was investigated start delay time, cylinder pressure, HC/NOx emissions, Mass Fraction Burned, starting time to evaluate performance of transient cold startability. Compared to the return type system, the semi-return type system have advantages in point of production cost and equivalent performance of engine starting time and pressure settling time.

• 한국진공학회지
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• 제10권3호
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• pp.341-349
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• 2001

수평형 MOCVD (유기금속 화학기상법) 제조공정에서 유체유동, 열전달 및 화학종의 국소적 질량분율을 고찰하기 위한 수치계산을 수행하였다. 수송가스로 작용하는 수소가스와 TMG및 암모니아의 농도분포를 예측함으로서 혼합과정을 분석하고 필름성장의 균일성을 예측하였다. 농도분포에 미치는 입구크기, 위치, 질량유량 및 벽면의 경사각도의 영향이 검토되었다. 계산결과로서 무차원 대류 열전달 계수 Nu에 의해 반응물의 농도분포를 정성적으로 예측할 수 있었으며, 균일한 필름성장을 위한 최적 질량유량, 벽면 경사도 및 입구조건이 제시되었다.

• 대한기계학회논문집B
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• 제38권6호
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• pp.483-491
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• 2014

본 연구에서는 현열 형태의 저온 열원과 LNG의 냉열을 이용하는 복합 동력 생산시스템에 대한 열역학적 성능 해석을 수행하였다. 시스템의 작동유체로서 암모니아-물의 비공비 혼합물을 고려하였으며 재생기가 없는 기본 사이클과 있는 재생 사이클의 경우를 비교 해석하였다. 작동유체의 암모니아 농도나 응축 온도에 따라 시스템의 순생산일, 엑서지 파괴, 열효율이나 엑서지 효율 등에 미치는 다양한 영향에 대해 분석하고 논의하였다. 해석 결과는 시스템의 성능 특성이 작동유체의 암모니아 농도나 응축 온도에 따라 민감하게 변화하며, 열원유체 단위질량당 순생산일은 기본 사이클이 유리하나 열효율이나 엑서지 효율은 재생 사이클이 유리하다는 사실을 보여준다.