• Journal of Sensor Science and Technology
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• v.27 no.6
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• pp.386-391
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• 2018

To analyze the film cooling in a liquid rocket engine, it is necessary to understand the characteristics of the wall-impingement liquid film. We designed an optimal two-dimensional device for measuring the thickness of the liquid film thickness. This device quantitatively measures the liquid-film thickness distribution. In previous liquid-film thickness measuring devices, the liquid film was formed over the entire area of the sensor. However, its formation depended on injection conditions. To compensate for this, optimal resistors are selected. Additionally, saturation variations with partial saturation are analyzed. Furthermore, calibration using the enhanced plate method is conducted with improvements in spatial resolution. The device designed here can be used to analyze the properties of an impingement liquid film with a slit injector. This study can be used for film-cooling analysis in liquid rocket engines.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.9
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• pp.688-698
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• 2009

Using the multi-dimensional, multi-phase, nonisothermal Polymer Electrolyte Fuel Cell (PEFC) model presented in Part I, the effects of land/channel flow-field on temperature and liquid saturation distributions inside PEFCs are investigated in Part II. The focus is placed on exploring the coupled water transport and heat transfer phenomena within the nonisothermal and two-phase zone existing in the diffusion media (DM) of PEFCs. Numerical simulations are performed varying the land and channel widths and simulation results reveal that the water profile and temperature rise inside PEFCs are considerably altered by changing the land and channel widths, which indicates that oxygen supply and heat removal from the channel to the land regions and liquid water removal from the land toward the gas channels are key factors in determining the water and temperature distributions inside PEFCs. In addition, the adverse liquid saturation gradient along the thru-plane direction is predicted near the land regions by the numerical model, which is due to the vapor-phase diffusion driven by the temperature gradient in the nonisothermal two-phase DM where water evaporates at the hotter catalyst layer, diffuses as a vapor form and then condenses on the cooler land region. Therefore, the vapor phase diffusion exacerbates DM flooding near the land region, while it alleviates DM flooding near the gas channel.

• 한국전산유체공학회:학술대회논문집
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• 1997.10a
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• pp.120-125
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• 1997

In the present work the influence of various physical parameters on the two-phase flow behavior in a self-heated porous medium has been studied using a numerical model, that is, the effects of heat generation rate, of porosity, of particle size, and of system pressure on the dryout process. To analyze the effect of these parameters, the variation of both liquid volumetric fraction (i.e., liquid saturation) and liquid axial velocity is evaluated at the steady state or at the onset of a first boiled-out region. The analysis of computational results indicate that a qualitative tendency exists between the parameters such as heat generation rate, porosity, effective particle diameter and the temporal development of the liquid volumetric fraction field up to dryout. In addition to these parameters, a variation of fluid properties such as phase density, phase viscosity due to a change of system pressure can be used for gaining insight into the nature of two-phase flow behavior up to dryout.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.5
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• pp.22-28
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• 2003

Flash boiling mechanism in the injector interferes with fine fuel metering in a liquid phase LPG injection engine. This study presents a mathematical model to precisely predict an injection quantity. A calibration procedure of injection quantity, which is very prompt and precise in measuring, is developed using a gas analyzer. According to this procedure, injection quantity can be obtained under various fuel compositions, temperatures and injection pressures. The release pressure of liquid phase LPG is estimated based on these experimental data. Although the release pressure is much lower than the saturation pressure, it is linearly proportional to the saturation pressure.

• Progress in Superconductivity and Cryogenics
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• v.3 no.2
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• pp.77-83
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• 2001

The thermal characteristics of solid nitrogen are investigated by experiment and analysis for the purpose of evaluating its feasibility as a cooling medium for HTS (high T$_{c}$ superconductor) magnets. A cryostat to refrigerate a liquid-nitrogen container well below its freezing temperature with a 2-stage GM cryocooler is designed and constructed. The spatial distribution of temperature is measure as a function of time during the freezing and melting processes. from which the thermal diffusivity of solid nitrogen can be approximately calculated. the freezing process is formulated and solved by the integral method with an assumption of phase equilibrium at the solid-liquid interface and experimental observation. It may be concluded that the thermal diffusion in solid phase is much slower than in liquid and the degree of super-saturation is quite severe in the solidification of nitrogen.n.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.686-691
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• 2010

Flash boiling takes place when the thermodynamic state of the liquid deviates from its saturation limit over which the liquid temperature exceeds by a certain degree of superheat. The liquid jet introduced into the lower pressure zone than the liquid saturation pressure experiences a sequence of the atomization and disintegrated into numerous faster and smaller droplets. In the present study spray characteristics for a flash swirl spray were experimentally investigated. Injectant temperature is raised by a high frequency dielectric heating method and local spray characteristics are instantly measured by Global Sizing Velocimetry (GSV, TSI Inc.). Dependence of dimensionless superheat degree and injection pressure on total and local SMDs and mean droplet size is quantitatively examined. The flash swirl spray has the relation in the injection pressure and nozzle diameter in order to determine the spray quality, including the dimensionless superheat degree. Small droplets occur in the void core and local droplet size distributions largely depend on the dimensionless superheat degree and the injection pressure.

• Korean Journal of Hazardous Materials
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• v.6 no.2
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• pp.95-104
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• 2018

Gas-liquid bubble column reactors are extensively used in industrial processes. A detailed knowledge of bubble size distribution is needed for determining the mass transfer in gas-liquid film. Experimental data on bubble size distribution and liquid-side mass transfer coefficient($k_L$) were used to calculate the estimated time to saturation in bubble column reactor. Also, the gas flux was evaluated to the liquid-side mass transfer coefficient($k_L$) and solubility data for hydrogen sulfide($H_2S$) and chlorine($Cl_2$) absorption into water. Simulation results show that $H_2S$ absorption time to 50 % of saturation concentrations are 611 sec and 1,329 sec when bubble diameters are 0.5 mm and 4.5 mm, while absorbing 1 % $H_2S$ gas. In case of $Cl_2$, absorption time range 657 to 1,400 sec when bubble size range 0.5 mm to 4.5 mm, while absorbing 1 % $Cl_2$ gas. Calculated simulation results can be used in the design of emergency relief bubble reactors.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.17-19
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• 2009

The voltage and frequency dependence of voltage holding ratio (VHR) in a homogeneously-aligned liquid-crystal (LC) cell is studied in this paper. The discharge curves with different scan frequencies are obtained and the saturation phenomenon of VHR is observed under specific amplitudes of driving voltage. Our results suggest a reasonable concept to improve the VHR in LC displays without increasing the frame rate.

• Korean Journal of Optics and Photonics
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• v.17 no.1
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• pp.23-30
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• 2006

Effects of liquid-crystal droplets size on electro-optical properties of the polymer dispersed liquid crystals are investigated experimentally The liquid crystal droplets size was varied by controlling the Laser power for phase separation and LC/oligomer composition ratio. Electro-optical switching voltage is dependent on the LC/oligomer composition ratio and liquid crystal droplet size. The experimental results showed droplet size will be small and saturation voltage is increased but rise time will be short at high power illumination laser light for phase separation.

• Journal of Powder Materials
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• v.24 no.2
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• pp.122-127
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• 2017

Fe-6.5 wt.% Si alloys are widely known to have excellent soft magnetic properties such as high magnetic flux density, low coercivity, and low core loss at high frequency. In this work, disc-shaped preforms are prepared by spark plasma sintering at 1223 K after inert gas atomization of Fe-6.5 wt.% Si powders. Fe-6.5 wt.% Si sheets are rolled by a powder hot-rolling process without cracking, and their microstructure and soft magnetic properties are investigated. The microstructure and magnetic properties (saturation magnetization and core loss) of the hot-rolled Fe-6.5 wt.% Si sheets are examined by scanning electron microscopy, electron backscatter diffraction, vibration sample magnetometry, and AC B-H analysis. The Fe-6.5 wt.% Si sheet rolled at a total reduction ratio of 80% exhibits good soft magnetic properties such as a saturation magnetization of 1.74 T and core loss ($W_{5/1000}$) of 30.7 W/kg. This result is caused by an increase in the electrical resistivity resulting from an increased particle boundary density and the oxide layers between the primary particle boundaries.