• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2002.04a
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• pp.65-69
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• 2002

Unsteady vaporization of a droplet quiescent in a high pressure environment are studied with emphasis placed oil the modeling of equilibrium at vapor-liquid interface. Complete set of conservation equations for liquid and gas phases is numerically time integrated. Vapor-liquid interfacial thermodynamics are solved by f]ash equilibrium calculation method. The model was proper]y validated with experiment and the improvement in the solution accuracy was made. Vaporization of n-pentane fuel droplet in nitrogen background gas is examined. Effects of ambient gas solubility, property variation, transient diffusion, and multicomponent transport on the droplet vaporization are investigated systematically. High-pressure effects on the droplet vaporization is examined and discussed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.417-418
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• 2009

Aiming at time-dependent performance prediction of Liquid Rocket Engine(LRE) system, Program for Dynamic Characteristic Prediction of LRE is overviewed, and a modeling and dynamic analysis of rocket engine system with reference to developed transient simulator for LRE is outlined.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.414-416
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• 2009

In order to build a transient simulation program for a high thrust liquid rocket engine(LRE), a static performance simulation program for components were made. The components were the thrust chamber (combustion chamber and supersonic nozzle), centrifugal pump (impeller and volute casing), impulse turbine, and flow control devices (control valve and orifice). Simplified mathematical models based on classical thermodynamic and inviscid theories were used to remove complexity and enhance the utility of the program. We examined the results of each program qualitatively for validate each component modeling.

• Journal of ILASS-Korea
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• v.3 no.3
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• pp.49-59
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• 1998

The vaporization characteristics and spray combustion processes in the high-pressure environment are numerically investigated. This study employ the high-pressure vaporization model together with the state-of-art spray submodels. The present high-pressure vaporization model can account for transient liquid heating, circulation effect inside the droplet forced convection, Stefan flow effect, real gas effect and ambient gas solubility in the liquid droplets. Computations are carried out for the evaporating sprays, the evaporating and burning sprays, and the spray combustion processes of the turbocharged diesel engine. Numerical results indicate that the high-pressure effects are quite crucial for simulating the spray combustion processes including vaporization, spray dynamics, combustion, and pollutant formation.

• Journal of ILASS-Korea
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• v.13 no.2
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• pp.91-98
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• 2008

In the present study, in order to understand the overall spray combustion characteristics of DME fuel as well as to identify the distinctive differences of DME combustion processes against the conventional hydrocarbon liquid fuels, the sequence of the comparative analysis have been systematically made for DME and n-heptane liquid fuels. To realistically represent the physical processes involved in the spray combustion, this studyemploys the hybrid breakup model, the stochastic droplet tracking model, collision model, high-pressure evaporation model, and transient flamelet model with detailed chemistry. Based on numerical results, the detailed discussions are made in terms of the autoignition, spray combustion processes, flame structure, and turbulence-chemistry interaction in the n-heptane and DME fueled spray combustion processes.

• Nuclear Engineering and Technology
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• v.50 no.1
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• pp.80-87
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• 2018

Consideration is given to the possibility to use changes in buoyancy as a negative reactivity feedback mechanism during temperature transients in heavy liquid metal fast reactors. It is shown that by the proper use of heavy pellets in the fuel elements, fuel rods could be endowed with a passive self-ejection mechanism and then with a negative feedback. A first estimate of the feasibility of the mechanism is calculated by using a simplified geometry and model. If in addition, a neutron poison pellet is introduced at the bottom of the fuel, then when the fuel element is displaced upward by buoyancy force, the reactivity will be reduced not only by disassembly of the core but also by introducing the neutron poison from the bottom. The use of induced buoyancy opens up the possibility of introducing greater amounts of actinides into the core, as well as providing a palliative solution to the problem of positive coolant temperature reactivity coefficients that could be featured by the heavy liquid metal fast reactors.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1491-1498
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• 2003

Droplet evaporation can be used to transfer large amounts of energy since heat is transferred across a thin liquid film. Spreading the drop over a larger area can enhance this heat transfer. One method of accomplishing this is to dissolve gas into the liquid. When the drop strikes the surface, a gas bubble nucleates and can grow and merge within the liquid, resulting in an increase in the droplet diameter. In this study, time and space resolved heat transfer characteristics for a single droplet striking a heated surface were experimentally investigated. The local wall heat flux and temperature measurements were provided by a novel experimental technique in which 96 individually controlled heaters were used to map the heat transfer coefficient contour on the surface. A high-speed digital video camera was used to simultaneously record images of the drop from below. The measurements to date indicate that significantly smaller droplet evaporation times can be achieved. The splat diameter was observed to increase with time just after the initial transient dies out due to the growth of the bubble, in contrast to a monotonically decreasing splat diameter for the case of no bubbles. Bursting of the bubble corresponded to a sudden decrease in droplet heat transfer.

• 제어로봇시스템학회:학술대회논문집
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• 1990.10b
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• pp.1184-1189
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• 1990

In order to investigate liquid fuel filming over the intake manifold wall, an electrode-type probe has been developed by lines of authors and this probe was employed in a single cylinder two and four-stroke cycle engine and in a four cylinder four-stroke engine operated by neat methanol fuel. The performance of the probe was dependent upon several parameters including the liquid fuel layer thickness, temperature, additive in the fuel, and electric power source (i.e., AC and voltage level) and was independent of other variables such as direction of liquid flow with respect to the probe arrangement. Several new findings from this study may be in order. The flow velocity of the fuel layer in the intake manifold of engine was about (if the air velocity in the steady state operation, the layer thickness of liquid fuel varied in both the circumferential and longitydinal directions. In the transient operation of the engine, the temporal variation of fuel thickness was determined, which clearly suggests that there was difference between fuel/air ratio in the intake manifold and that in the cylinder. The variation was greatly affected by the engine speed, fuel/air ratio and throttle opening. And the variation was also very significant from cylinder to cylinder and it was particularly strong different engine speeds and throttle opening.

• Progress in Superconductivity and Cryogenics
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• v.8 no.1
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• pp.65-70
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• 2006

Transient heat transfer caused by an impulsive heating in subcooled liquid nitrogen is investigated experimentally. This study is part of out ongoing efforts directed to a stable cryogenic cooling system lot superconducting fault current limiters (SFCL). A thin heater attached by epoxy on one surface of a GFRP plate is immersed in liquid-nitrogen bath at temperatures between 77 K and 55 K. A strong heat flux up to $150W/cm^2$ is generated lot 100 ms, and the temperature of the heater sulfate is measured as a function of time. The behavior of bubbles on the heating surface can be explained by comparing the measured temperature history for vertical and two horizontal (up and down) orientations. It is concluded that the subcooling of liquid nitrogen below 70 K is very effective in suppressing bubbles, resulting in better thermal protection and faster recovery from an impulsive heat.

• Applied Chemistry for Engineering
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• v.9 no.2
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• pp.268-272
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• 1998

Water leak phenomena in the liquid sodium which is a coolant of liquid metal reactor, were investigated by carrying out sodium-water reaction experiment. It was confirmed that sodium and water react each other by the analysis of material composition of aspecimen at the end of experiment. When steam of $100kg/cm^2$ was passed through the leak path of the specimen for 4 hours, reaction products from sodium-water reaction were observed on the leak site. However, re-opening phenomena were not observed at this condition. It was interpretted that the reaction product precipitated on leak path and thermal transient caused self-plugging and re-openning phenomena, respectively.