• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.93-101
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• 2003

The extinction of unsteady diffusion flame was experimentally studied in an opposing jet counterflow burner using diluted methane. The stabilized flame was perturbed by linearly varying velocity change that was generated by pistons installed on both sides of the air and fuel stream. As the results, the extinction of unsteady flame is dependent not only on the history of unsteadiness, but also on the initial condition. We found that there are several unsteady effects on the flame extinction. First, the extinction strain rates of unsteady cases are extended well beyond steady state extinction limits. Second, as the slope of the strain rate change increases, the unsteady extinction strain rate becomes larger. Third, the extension of unsteady extinction strain rate becomes smaller as the initial strain rate increases. We also found that the extension of the extinction limit mainly results from the unsteady response of the reaction zone because there is no retardation effect of a mixing layer for our experimental condition.

• Journal of the Korean Vacuum Society
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• v.4 no.S2
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• pp.148-155
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• 1995

(1) The metastable crystalline(MX) phases formed by ion mixing are classified into 5 types, i.e. the super-saturated solid solutions and the enlarged HCP-I phases reported earlier, and the newly observed FCC-I phases in hcp-based alloys, The FCC-ll and HCP-ll phases in bcc-based alloys. The growth kinetics of the MX phases is discussed. (2) The interfacial free energy in the multilayered films was found to play an important role in ion beam mixing(IM) induced amorphization. By adding sufficient interfaces, amorphous alloys were obtained even in the systems with rather positive heat of formation. (3) Gibbs free energy diagrams of some representative systems were constructed, by calculating the free energy curves of all the competing phases. Steady-state thermal annealing was conducted and the results confirmed the relevance of the constructed diagrams, which were inturn employed to interpret the MX phase formation as well as the glass forming ability upon IM in the binary metal systems.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.12 no.3
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• pp.167-173
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• 1979

It is preented the removable moving screen media-activated sludge (REMSMAS) process by using the biological fixed-film systems. The substrate removal kinetic difference between the aeration-only completed mixing activated sludge (CMAS) process and REMSMAS process were observed. The substrate removal kinetics were developed based on the attached and suspended microbial growths. The units of the aeration-only CMAS process were continously operated with the normal detention time of 4.5, 6, 9.5 and 12 flours studies after steady-state condition and the operating of the REMSMAS units conducted with the normal detention time of 6 and 12 hours studies in nonsteady-state condition. The feed solution was diluted 18 times to the raw starch wastewater in of order to maintain the proper COD (950mg/l) and BOD (450mg/l) concentration. Design parameters related to the suspended microbial growths were caculated by the equations used in the aeration-only CMAS model and these parameters used to evalute the kinetic constants in the REMSMAS process. The kinetic constant values of $Y_2,\;K_d,(\mu_{max})_s\;and\;K_s$ from Monod equations were respectively 0.78, 0.027/hr, 1.1/hr and 95mg/l in the aeration-only CMAS process. The value of the aera capacity (F) appeared to be $9.1\;mg/cm^2-day$ and the mean value of the saturation constant $(K_g)$ appeared to be 53.5 mg/l in the REMSMAs process. Also, the substrate removal .ate of the REMSMAS process was higher than that of the normal activated sludge process when this system was operated in steady-state condition. However, the rate was reduced as the critical operating day was approached.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.3038-3043
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• 2008

Tumble or swirl flow is used adequately to promote mixing of air and fuel in the cylinder and to enlarge turbulent intensity in the late time of compression stroke. However, since in-cylinder flow is a kind of transient state with rapid flow variation, that is, non-steady state flow, swirl or tumble flow has not been analyzed sufficiently and not been recognized whether they are available for combustion theoretically yet. In the investigation of intake turbulent characteristics using PIV method, different flow characteristics were showed according to SCV figures. SCV installed engine had higher vorticity, turbulent strength by fluctuation and turbulent kinetic energy than a baseline engine, especially around the wall and lower part of the cylinder. Consequently, as swirl flow was added to existing tumble flow, it was found that fluctuation component increased and flow energy was conserved effectively through the experiment.

• Journal of the Korean Society for Marine Environment & Energy
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• v.11 no.2
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• pp.92-97
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• 2008

Salt wedge into the river from the sea or fresh water flume (fresh wedge) in the ocean from the sea has density current characteristics. However, when temperature and salinity simultaneously determine the density of wedges, one of salinity and temperature can distributed in the reversed profiles against gravity, even though the density profile is stable. In this case, the double diffusive process is critical in determining mixing rate. The present work studies relative contribution of shear driven mechanical mixing component and double diffusive layering process, when warm salty denser water is introduced into the cold fresh lighter water column. Laboratory experiment releases warm salty denser water into cold fresh lighter water controlling discharge amount to achieve the steady state of density current. When longitudinal density rate becomes 15, the released amount ratio of salt and heat changes sharply and in the releasing point, vigorous mixing occurs with increase of discharged amount due to double diffusion. Double diffusion distabilizes gravitational stability and enhances the mixing rate up to $6{\times}10$ times at the lower density ratio comparing to the higher density ratio.

• 한국해양학회지
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• v.30 no.4
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• pp.288-301
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• 1995

Rates of the sedimentation and particle mixing have been estimated by applying uranium-series disequilibrium techniques to three sediment cores collected from the korea Deep Ocean Study (KODOS) site between the clarion and Clipperton Fracture Zones (CCFZ) of the Equatorial Pacific. Sedimentation rates based on the profiles of excess /SUP 230/Th activity and /SUP 230/ Th/SUB xs//SUP 232/ Th activity ratios at the southeastern part of the study area were estimated to be in the order of a few millimeters per thousand year, while at the northwestern part a factor of ten lower. Excess activities of /SUP 230/Th and /SUP 230/Th ratios showed intervals of constant values in the upper part of the sediment cores, probably generated by biological particle mixing. A "two-box" advection-diffusion steady state mixing model was employed in order to estimate particle mixing rates in the upper and the lower layers, based on the distribution profiles of excess /SUP 210/Pb activities. Particle mixing coefficients were estimated to be in the order of 10$^1$ cm$^2$/y in the upper layer and 10/SUP -1/-10/SUP 0/ cm$^2$/y in the lower layer.

• Journal of Environmental Science International
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• v.6 no.3
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• pp.267-276
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• 1997

It has been studded that combustion and the production of air pollution of anthracite - bituminous coal blend In a fluidized bed coal combustor, The objects of thIns study were to investigate mixing characteristics of the particles as well as the combustibility of the low grade domestic anthracite coal and Imported h19h calorific bltununous coal in the fluidized bed coal combustor. They were used as coal samples ; the domestic low grade anthracite coal with heating value of 2,010kca1/kg and the Imported high grade bituminous coal with beating value of 6,520kca1/kg. Also, the effects of air flow rate and anthracite fraction on the reaching time of steady state condition have been studied. The experimental results are presented as follows. The time of reaching to steady state was affected by the temperature variation. The steady state time was about 120 minute at 300sc1h which was the fastest. It has been found that $O^2$ and $CO^2$ concentration were reached steady state at about 100 minute. It has been found that $O^2$ concentration decreased and $CO^2$ concentration increased as the height of fluidlzed bed Increased. It was found that splash zone was mainly located from 25cm to 35cm above distributor. Also, as anthracite traction Increased, the mass of elutrlatlon particles Increased, and $CO^2$ concentration decreased. As gk flow rate Increased,$O^2$ concentration decreased and $CO^2$ concentration increased. Regardless of anthracite fraction and flow rate, the uncombustible weight percentage according to average diameter of elutriation particles were approldmately high In the case of One Particles. As anthracite traction and k now rate Increased, elutriation ratio Increased. As anthracite fraction was increased, exit combustible content over feeding combustible content was Increased. Regardless of anthracite fraction, size distribution of Ued material from discharge was almost constant. Over bed temperature 85$0^{\circ}C$ and excess air 20% , the difference of combution efficiencies were little. It is estimate that the combustion condition In anthracite-bituminous coal blend combustion is suitable at the velocity 0.3m/s, bed temperature 85$0^{\circ}C$, the excess air 20%.

• Nuclear Engineering and Technology
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• v.48 no.4
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• pp.941-951
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• 2016

The aim of this work is to simulate the thermohydraulic consequences of a main steam line break and to compare the obtained results with Rossendorf Coolant Mixing Model (ROCOM) 1.1 experimental results. The objective is to utilize data from steady-state mixing experiments and computational fluid dynamics (CFD) calculations to determine the flow distribution and the effect of thermal mixing phenomena in the primary loops for the improvement of normal operation conditions and structural integrity assessment of pressurized water reactors. The numerical model of ROCOM was developed using the FLUENT code. The positions of the inlet and outlet boundary conditions and the distribution of detailed velocity/turbulence parameters were determined by preliminary calculations. The temperature fields of transient calculation were averaged in time and compared with time-averaged experimental data. The perforated barrel under the core inlet homogenizes the flow, and therefore, a uniform temperature distribution is formed in the pressure vessel bottom. The calculated and measured values of lowest temperature were equal. The inlet temperature is an essential parameter for safety assessment. The calculation predicts precisely the experimental results at the core inlet central region. CFD results showed a good agreement (both qualitatively and quantitatively) with experimental results.

• The KSFM Journal of Fluid Machinery
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• v.7 no.2 s.23
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• pp.27-34
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• 2004

The performance of a centrifugal compressor composed of an impeller, tandem diffuser rows and axial guide vanes has been predicted numerically and compared with available experimental results on its design rotational speed. The pitchwise-averaged mixing plane method was employed for the boundaries between rotor and stator to obtain steady state solutions. The overall characteristics showed difference according to the relative positions of tandem diffuser rows while the characteristics of impeller showed almost identical result. The numerical results agree with the measured data in respect of their tendency. It turned out that $0\%$ of relative positions is the worst case in terms of static pressure recovery and efficiency. According to the experimental results, some pressure fluctuations and malfunction of the compressor were observed for $75\%$ case. However, this numerical calculation using mixing plane method did not capture any of those phenomena. Thus, unsteady flow calculation should be performed to investigate the stability of the compressor caused by different diffuser configuration.

• Journal of the Korean Society for Marine Environment & Energy
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• v.10 no.1
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• pp.53-58
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• 2007

In an estuary, mixing and transport of contaminant sometimes occurs in the salt finger favorable condition (Hwang ang Rehmann, 2004). Linearized theory is applied to predict flow dynamics in salt finger favorable condition. The simulated results match well with previous laboratory experiments. When the density ratio is larger than 2, the heat and salt system shows $0.55{\sim}0.57$ as Turner (1967) found, and the salt and sugar system produces 0.87 of Griffiths (1980). As the ratio of molecular diffusivities of two scalars increases, the flux ratio increases. The flux and eddy diffusivity ratios decrease with increase of density ratio, and it takes longer time for flux ratio to be steady state at the higher density ratios.