• 한국태양에너지학회 논문집
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• 제28권2호
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• pp.1-9
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• 2008

This paper describes water circulation characteristics of a water/steam receiver at various heat fluxes. The water/steam receiver for a solar tower power system is a natural circulation type. Experimental conditions of water and steam were set at a pressure of 5 bar and temperature of $151.8^{\circ}C$. The experimental device for the water/steam receiver consisted of a steam drum, upper/lower header, riser tubes, and downcomer tube. The experiments were conducted by varying heat fluxes in terms of mass flow rate in each riser tube. However, the total mass flow rate on the riser tubes was fixed at 217.4 g/s. For the uniform heat flux, while the water temperature of the steam drum and upper header were kept at steady state, the temperature of the lower header was fluctuated. For the non-uniform heat flux, while the temperature of the steam drum was kept steady state, the temperature difference increased in the right and left side of the upper header, and the temperature of the lower header was fluctuated.

• 한국방재학회 논문집
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• 제10권5호
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• pp.75-82
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• 2010

본 연구에서는 화재강도에 따른 산림연료의 연소특성을 고찰하기 위하여 산불에 가장 취약한 소나무 생엽을 대상으로 복사열을 변수(25 kW/$m^2$, 50 kW/$m^2$, 75 kW/$m^2$)로 하여 연소특성 실험을 수행하였다. 콘칼로리미터 장비를 이용하여 착화특성, 발열 특성, 발연량 및 CO, $CO_2$ 방출특성, 중량감소특성 등을 분석하였다. 60.66% 수분을 함유한 소나무 생엽은 25 kW/$m^2$, 50 kW/$m^2$, 75 kW/$m^2$ 복사열에서 착화가 일어나지 않았으며, 복사열 크기가 클수록 발열량과 열방출율은 2배 빠른 시간에 급격하게 최대값에 도달하고 최대값은 2배 정도 높은 것으로 나타났다. 발연량은 복사열 크기가 작을수록 불완전 연소로 인한 연기방출량은 많은 것으로 나타났다. CO 및 $CO_2$ 방출량은 복사열이 증가할수록 최대값이 급격히 높고, 빠른 시간에 최대값에 도달하는 것으로 나타나 복사열이 증가할수록 탄소산화물은 많은 것으로 나타나 산불발생 시 대형산불의 경우 많은 양의 CO와 $CO_2$를 방출할 것으로 사료된다.

• Journal of Advanced Marine Engineering and Technology
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• 제22권3호
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• pp.285-293
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• 1998

This paper presents an experimental study on condensing heat transfer characteristics of R-22 alternative refrigerants, R-290 and R-410a on water sources heat pump. The apparatus mainly consisted of vapor pump condenser used to the test section evaporator manual expansion valve and measuring device. Test section constructed a smoothed tube of 10.07 mm ID and 12.7mm OD with a total length 6,300 mm was horizontal double pipe counterflow condenser. The refrigerants R-22, R-290 and R-410a were cooled by a coolant circulated in a surrounding annulus. Experimental range of mass velocities was changed from about 100 to 300 kg/($m^2$.s) and inlet quality 1.0 The credibility of experimental apparatus was 6 percent between heating capacity and cooling capacity added to compressor shaft power. The condensing heat transfer coefficients were increased with increasing mass velocity. However in case of R-290 they were more increasing than those of R-410a and R-22 Comparing the heat transfer coefficient between the experimental data and other's data the Cavallini-Zecchin's data was revealed to more similar prediction of author's experimental results on the average heat transfer coefficients.

• 천문학회지
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• 제29권spc1호
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• pp.263-264
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• 1996

We have solved the radiative transfer problem using a Sobolev approximation with an escape probability method in case of the supersonic expansion of a stellar envelope to an ambient medium. The radiation from the expanding envelope turns out to produce a P-Cygni type profile. In order to investigate the morphology of the theoretical P-Cygni type profile, we have treated $V{\infty},\;V_{sto},\;{\beta}$ (parameter for the velocity field), M and $\epsilon$ (parameter for collisional effect) as model parametrs. We have found that the velocity field and the mass loss rate affect the shapes of the P-Cygni type profiles most effectively. The secondarily important factors are $V{\infty},\;V_{sto}$. The collisional effect tends to make the total flux increase but not so .much in magnitude. We have infered some physical parameters of 68 Cyg, HD24912, and $\xi$ persei such as V$\infty$, M from the model calculation, which shows a good agreement with the observational results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.526-531
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• 2003

A cone cylinder is used to obtain variable operation conditions of a sonic ejector-diffuser system. The cone cylinder is movable to change the ejector area ratio, thus obtaining variable mass flow rates. The present study investigates the effects of ejector throat area ratio and operating pressure ratio on the entrainment of secondary stream. The numerical simulations are based on a fully implicit finite volume scheme of the compressible, Reynolds-Averaged, Navier-Stokes equations. The ejector throat area is varied between 3.94 and 8.05, and the operating pressure ratio is changed from 3.0 to 9.0. The results show that the entrainment ratio and mass flux ratio become more dependent on the ejector throat area ratio, when the pressure operating ratio is low. The total pressure losses produced in the present ejector system increase with the operating pressure ratio and the ejector area ratio, but for a given operating pressure ratio, the losses are not significantly dependent on the ejector area ratio when it is larger than about 5.0.

• 한국대기환경학회지
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• 제22권1호
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• pp.99-106
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• 2006

Aircraft measurements have been executed for the purpose of monitoring the long range transported air pollution and estimation of air pollutant in/out-flux over the Yellow sea. Total 74 missions of measurements have been done since 1997, mainly in spring and fall. The main study domain was over $124^{\circ}$E $/sim$ $124^{\circ}$E, $35^{\circ}$N $/sim$ $37^{\circ}$N below 3,000m. In long-term trends, mixing ratios of $SO_{2}$N were around 2 ppbv expect in summer ( < 1 ppbv). NOx exhibited 24 ppbv and have no clear annual trends over the Yellow Sea. The concentrations of 03 were 51, 58, 41 ppbv in spring, summer and fall-winter, respectively. Backward trajectory was performed for three days to investigate the source regions of the air mass. Six regions were divided around Korea peninsular centering at $36^{\circ}$N, $126^{\circ}$E. I, II, III, IV and V regions represents in sequence northeast China and Siberia, Sandong peninsula and Balhae gulf, Sanghi and southern China, the south Pacific included Jeju island and the East sea included Japan. L region correspond to the airmass from Korea peninsula. Influx of $SO_{2}$N was approximately five times higher than outflux in yearly flux variation and showed a decreasing long-term trend since 1998. NOx outflux was average 0.095 ton/km/hr and three times higher than $SO_{2}$ outflux. In/out flux of 03 showed even distribution in yearly basis except 2002 (influx 5.45 ton/km/hr). The transported amounts from I, II, III regions were much higher than those from other region. In seasonal flux variation, influx levels of gas phases were the lowest in summer and the levels gradually increased from fall toward spring. As a result, transport of pollutants begins from fall and prevails in winter and spring.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2005년도 총회 및 춘계학술발표회
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• pp.304-307
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• 2005

A numerical modelling method using a backward-in-time advection dispersion equation is introduced in assessing the vulnerability of groundwater to contaminants as an alternative to classical vulnerability mapping methods. The flux and resident concentration measurements are normalized by the total contaminants mass released to the system to provide the travel time probability density function and the location probability function. With the results one can predict the expected travel time of a contaminant from up stream location to a well and also the relative concentration of the contaminant at a well. More specific groundwater vulnerability can be mapped by these predicted measurements.

• 천문학회지
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• 제29권2호
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• pp.93-105
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• 1996

We have solved the radiative transfer problem using a Sobolev approximation with an escape probability method in case of the supersonic expansion of a stellar envelope to an ambient medium. The radiation from the expanding envelope turns out to produce a P-Cygni type profile. In order to investigate the morphology of the theoretical P-Cygni type profile, we have treated $V_\infty,\;V_{sto},\;\beta$ (parameters for the velocity field), it and E(parameter for collisional effect) as model parameters. We have investigated that the velocity field and the mass loss rate affect the shapes of the P-Cygni type profiles most effectively. The secondarily important factors are $V_\infty,\;V_{sto}$. The collisional effect tends to make the total flux increased but not so much in magnitude. We have infered some physical parameters of 68 Cyg, HD24912, and $\xi$ persei such as $V_\infty,\;M$ from the model calculation, which shows a good agreenment with the observational results.

• 한국군사과학기술학회지
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• 제3권2호
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• pp.23-34
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• 2000

Three dimensional, compressible, mass weighted averaging of Favre, Navier-Stokes system with k-$\varepsilon$ turbulence, is numerically discretized to compute three dimensional multiple jet interaction flow fields for a hybrid projectile containing three rocket motors in the ogive section. Numerical flow field computations have been made for angled nose jets and rockets at supersonic speed using multiblock structured grid. The jet conditions include very high jet to free stream pressure ratio and high temperature. It is shown that the strength of nozzle stagnation pressure affects the flow field near the side nozzle and the high stagnation pressure increases total amount of drag by a few percent. However, minor drag loss due to the pressure drag might be fully overcomed by an additional axial thrust. The results of present study can be applied for the design of future hybrid projectile.

• Nuclear Engineering and Technology
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• 제38권3호
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• pp.301-310
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• 2006

Destructive methods were used for the burnup determination of U-Zr alloy nuclear fuel irradiated in the High-flux Advanced Neutron Application Reactor (HANARO) at KAERI. The dissolution rate of unirradiated U-Zr alloy fuel in $HNO_3$/HF mixtures was investigated for the experimental conditions of a different temperature, and initial concentrations of HF and $HNO_3$. The irradiated U-Zr alloy fuel specimen was dissolved in a mixed acid condition of 3 M HNO3 and 1 M HF at $90^{\circ}C$ for 8 hours under reflux. The total burnup was determined from measurement of the Nd isotope burnup monitors. The method includes U, Pu, $^{148}Nd,\;^P{145}Nd+^{146}Nd,\;^{144}Nd+^{143}Nd$ and total Nd isotopes determination by the isotope dilution mass spectrometric method (IDMS) using triple spikes $(^{233}U,\;^{242}Pu\;and\;^{150}Nd)$. The effective fission yield was calculated from the weighted fission yields averaged over the irradiation period. The results are compared with that obtained by the destructive -spectrometric measurement of the $^{137}Cs$ monitor.