• 한국추진공학회지
• /
• 제14권1호
• /
• pp.20-28
• /
• 2010

스크램제트 연소기 내 파일런 분사기의 연료-공기 혼합특성을 살펴보았으며, 공력가열로부터 파일런을 보호하기 위한 막냉각의 효과를 조사하였다. 수치연구를 위하여 3차원 Navier-Stokes 방정식과 $k-{\omega}$ SST 난류 모델을 이용하였다. 연료인 수소와 공기를 냉각 유체로 고려하였다. 파일런 분사기를 이용하는 경우 침투거리가 증대되고, 혼합률도 주목할 만큼 증대되었으나, 공력가열에 의한 파일런의 전방 표면 과열을 확인하였다. 파일런 전방에 파일런 표면에 평행한 냉각 제트를 분사하는 막냉각을 이용하면 파일런 표면의 과열을 막을 수 있음을 확인하였다.

• 청정기술
• /
• 제11권1호
• /
• pp.29-39
• /
• 2005

잔류성 유기오염 물질 (POPs) 중의 하나인polychlorinated biphenyls (PCBs)는 강한 독성 및 난분해성으로 암, 내분기계장애(환경호르몬) 등을 유발할 수 있는데, 대부분의 PCBs는 변압기, 콘덴서 같은 전기 설비의 절연유를 오염시키고 있다. 국내외의 PCBs 관련 오염 현황및 관련 대책을 살펴보고, PCBs를 무해화 분해 처리하기 위한 기술로서 소각, 화학적 탈염소, 광화학, 생물학적 처리를 중심으로 국내외 기술 현황 비교 평가 및 특허 출원 동향을 분석하였다. 이를 바탕으로 향후 국내 PCBs 기술 개발및 대응 방향과 전망을 기술하였다.

• 열처리공학회지
• /
• 제5권4호
• /
• pp.224-232
• /
• 1992

Coolingability of coolants is important factor in cooling processor heat treatment of steel. Using standard apparatus and method defined in the Korean Industrial Standard three different shapes of probe were designed, ie, cylinderical, spherical and square on shape with same volume of standard probe. Distilled water and sodium aquious solutions with different concentration of NaOH, NaCl and $Na_2CO_3$ were examined. Estimation of coolingability of each quenchants for the probes of cylinderical, spherical or square shape, the cooling rate is greater square, cylinder and sphere in order. Coolingability of sodium aquious solution of NaCl, $Na_2CO_3$ and NaOH is found generally greater then that of distilled water. Effectiveness of ingredients is in the order of $Na_2CO_3$, NaOH and NaCl. In both solutions coolingability increases in 20%, 5%, and 10%in order. Analytical results obtained from Finite Element Method were compared with experimental ones and found as practically satisfactional.

• 천문학회보
• /
• 제42권1호
• /
• pp.33.2-33.2
• /
• 2017

Symbiotic stars and quasars show strong far UV resonance doublets including O VI 1032 and 1038, which are known to be major coolants of astrophysical plasma with high temperature T > $10^5K$. We investigate the transfer of $H{\alpha}$ and $Ly{\beta}$ in an emission nebula of temperature T ~ $10^5$, where n=2 population is significant. Line photons of $H{\alpha}$ and $Ly{\beta}$ are transferred in the medium through spatial and frequency diffusion altering their identity according to the branching ratios. We adopt a Monte Carlo technique to describe the transfer of $H{\alpha}$ and $Ly{\beta}$ in an emission nebula with a uniform density and a simple geometrical figure. We find that the temperature of the emission nebula is the major controlling parameter to produce a nonnegligible flux of $Ly{\beta}$. In particular, when T exceeds $10^5K$ the number flux ratio may reach ~ 25% with line center optical depth of a few. We discuss the formation of broad $H{\alpha}$ wings from Raman scattering of $Ly{\beta}$ emergent from a hot emission nebula.

• 소성∙가공
• /
• 제17권4호
• /
• pp.249-256
• /
• 2008

Combined phase transformation and heat transfer was considered on the simulation of hot press forming process, using material properties modeler, $JMatPro^{(R)}$ and a finite element package, $DEFORM^{TM}$-HT. In order to obtain high temperature mechanical properties and flow curves for different phases, a material properties modeler, $JMatPro^{(R)}$ was used, avoiding expensive and extensive high temperature materials tests. The results successfully show that the strength of hot press forming parts may exhibit different strength in the same parts, depending on the contact of blank with tooling. It was also shown effectively that the strength of the parts can be controlled by designing appropriate cooling paths and coolants. This was shown in terms of different heat convection coefficient in the calculation. Overall, current combination of software was shown to be an effective tool for the tool and process design of hot forming process, although the material modeler needs to be additionally verified by an appropriate set of high temperature materials test.

• 한국압력기기공학회 논문집
• /
• 제7권4호
• /
• pp.44-50
• /
• 2011

Turbulent mixing of hot and cold coolants is one of the possible causes of high cycle thermal fatigue in piping systems of nuclear power plants. A typical situation for such mixing appears in turbulent flow through a T-junction. Since the high cycle thermal fatigue caused by thermal striping was not considered in the piping fatigue design in several nuclear power plants, it is very important to evaluate the effect of thermal striping on the integrity of mixing tees. In the present work, before conducting detailed evaluation, three thermal striping evaluation methodology suggested by EPRI, JSME and NESC are analyzed. Then, a by-pass pipe connected to the shutdown cooling system heat exchanger is investigated by using these evaluation methodology. Consequently, the resulting thermal stresses and the fatigue life of the mixing tee are reviewed and compared to each other. Futhermore, the limitation of each methodology are also presented in this paper.

• Nuclear Engineering and Technology
• /
• 제50권1호
• /
• pp.182-189
• /
• 2018

A neutron generation system was developed to induce fissile fission in a lead slowing down spectrometer (LSDS) system. The source neutron is one of the key factors for LSDS system work. The LSDS was developed to quantify the isotopic contents of fissile materials in spent nuclear fuel and recycled fuel. The source neutron is produced at a multilayered target by the (e,${\gamma}$)(${\gamma}$,n) reaction and slowed down at the lead medium. Activation analysis of the target materials is necessary to estimate the lifetime, durability, and safety of the target system. The CINDER90 code was used for the activation analysis, and it can involve three-dimensional geometry, position dependent neutron flux, and multigroup cross-section libraries. Several sensitivity calculations for a metal target with different geometries, materials, and coolants were done to achieve a high neutron generation rate and a low activation characteristic. Based on the results of the activation analysis, tantalum was chosen as a target material due to its better activation characteristics, and helium gas was suggested as a coolant. In addition, activation in a lead medium was performed. After a distance of 55 cm from the lead surface to the neutron incidence, the neutron intensity dramatically decreased; this result indicates very low activation.

• 한국분무공학회지
• /
• 제19권2호
• /
• pp.88-93
• /
• 2014

Nanofluids is that metallic or nonmetallic nanometer-sized particles are dispersed in liquid and they can be used in various fields to increase the heat transfer rate. This study conducted experiments to evaluate whether the cooling efficiency of nanofluids is better than that of water in spray cooling. A heated surface was designed and fabricated to make the temperature distribution be linear, which was confirmed by three thermocouple measurements under the heated surface. Spray cooling experiments were conducted using water, 0.2% wt. (weight), and 0.5% wt. $Al_2O_3$ nanofluids at the pressure of 0.2 MPa and 0.3 MPa. Based on the results, it is shown that the cooling efficiency of nanofluids is higher than that of water especially in the region of single phase heat transfer. As a result, we can expect that nanofluids can be used as efficient coolants in the cooling of electronic packages where the temperature of the heated surface is not high enough for boiling incipience.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2005년도 춘계학술대회 논문집
• /
• pp.138-143
• /
• 2005

Finite Element analysis is widely applied to elevated temperature forging processes and shows a lot of information of plastic deformation such as strain, stress, defects, damages and temperature distributions. In highly elevated temperature deformation processes, temperature of material and tool have significant influence on tool life, deformation conditions and productivities. To predict temperature related properties accurately, adequate coefficients of not only contact heat transfer between material and dies but also convection heat transfer due to coolants are required. In most F.E analysis, too higher value of contact heat transfer coefficient is usually applied to get acceptable temperature distribution of tool. For contact heat transfer coefficients between die and workpiece, accurate values were evaluated with different pressure and lubricants conditions. But convection heat transfer coefficients have not been investigated for forging lubricants. In this research, convection heat transfer coefficients for cooling by emulsion lubricants are suggested by experiment and Inverse method. To verify acquired convection and contact heat transfer coefficients, tool temperature was measured for the comparison between measured tool temperature and analysis results. To increase analysis accuracy, repeated analysis scheme was applied till temperature of the tool got to be in the steady-state conditions. Verification of heat transfer coefficients both contact and convection heat transfer coefficients was proven with good accordance between measurement and analysis.

• Nuclear Engineering and Technology
• /
• 제41권9호
• /
• pp.1157-1170
• /
• 2009

A variety of Generation III/III+ reactor designs featuring enhanced safety and improved economics are being proposed by nuclear power industries around the world to solve the future energy supply shortfall. Nanofluid coolants showing an improved thermal performance are being considered as a new key technology to secure nuclear safety and economics. However, it should be noted that there is a lack of comprehensible design works to apply nanofluids to Generation III+ reactor designs. In this work, the review of accident scenarios that consider expected nanofluid mechanisms is carried out to seek detailed application spots. The Axiomatic Design (AD) theory is then applied to systemize the design of nanofluid-engineered nuclear safety systems such as Emergency Core Cooling System (ECCS) and External Reactor Vessel Cooling System (ERVCS). The various couplings between Gen-III/III+ nuclear safety features and nanofluids are investigated and they try to be reduced from the perspective of the AD in terms of prevention/mitigation of severe accidents. This study contributes to the establishment of a standard communication protocol in the design of nanofluid-engineered nuclear safety systems.