• 한국전산유체공학회지
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• 제11권1호
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• pp.29-35
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• 2006

A code is developed to analyze a spherically symmetric underwater explosion. The arbitrary Lagrangian-Eulerian(ALE) Godunov scheme for two-phase flow is used to calculate numerical fluxes through moving control surfaces. For detonation gas of TNT and liquid water, the Jones-Wilkins-Lee(JWL) equation of states and the isentropic Tait relation are used respectively. It is suggested to use the Godunov variable to estimate the velocity of a material interface. The code is validated through comparisons with other results on the gas-water shock tube problem. It is shown that the code can handle generation of discontinuity and recovering of continuity in the normal velocity near the material interface during shock waves interact with the material interface. The developed code is applied to analyze a spherically symmetric underwater explosion. Repeated transmissions of shock waves are clearly captured. The calculated period and maximum radius of detonation gas bubble show good agreements with experimental and other numerical results.

• 동력기계공학회지
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• 제8권1호
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• pp.36-40
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• 2004

Two-phase loop systems using the latent heat capacity of their working fluids can meet the increasing power requirements and are well suited to thermal management systems of future large applications, due to its abilities to handle large heat loads and to provide them at uniform temperatures regardless of the changes in the heat loads. Therefore some experiments on the effect of the gas and liquid superficial velocities, $j_G,\;j_L$ on flow pattern transition, void fraction and frictional pressure loss were performed on a co-current air-water flow in an adiabatic horizontal tube. The flow patterns were depended on the superficial velocity of each phase. It snowed that the increasing $j_L$, resulted in a significant increase in the frictional pressure loss for all flow patterns, at a constant $j_G$. The experimental results were also evaluated with some of existing models and correlations.

• 대한설비공학회지:설비저널
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• 제17권4호
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• pp.342-349
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• 1988

The characteristics of flow pattern transitions in a horizontal cocurrent gas-liquid flow have been investigated by means of a statistical analysis of instantaneous pressure drop curves at an orifice. The dimensionless intensity of pressure drop fluctuation shows a sudden change during the course of flow transitions, indicating that it may be a good measure to identify the flow regime transitions. The probability density function of the curves feature a unique pattern depending upon the flow regimes and the statistical properties of the PDF also have particular ranges for each flow regime. In conclusion, the statistical analysis of instantaneous pressure drops may be a powerful tool for predicting the flow regime transitions.

• 설비공학논문집
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• 제18권10호
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• pp.800-810
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• 2006

The R-134a flow distribution is experimentally studied for a heat exchanger composed of round headers and 10 flat tubes. The effects of tube protrusion depth as well as mass flux, and quality are investigated, and the results are compared with the previous air-water results. The flow at the header inlet is stratified. For the downward flow configuration, the liquid distribution improves as the protrusion depth or the mass flux increases, or the quality decreases. For the upward configuration, the liquid distribution improves as the mass flux or quality decreases. The protrusion depth has minimal effect. For the downward configuration. the effect of quality on liquid distribution is significantly affected by the flow regime at the header inlet. For the stratified inlet flow, the liquid is forced to rear part of the header as the quality decreases. However, for the annular inlet flow, the liquid was forced to the frontal part of the header as the quality decreased. For the upward flow, the effect of the mass flux or quality on liquid distribution of the stratified inlet flow is opposite to that of the annular inlet flow. The high gas velocity of the annular flow may be responsible for the trend. Generally, the liquid distribution of the stratified inlet flow is better than that of the annular inlet flow. Possible explanation is provided from the flow visualization results.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2006년도 전기학술대회논문집
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• pp.269-270
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• 2006

A finite difference lattice Boltzmann model which allows us to simulate gas-liquid two-phase flows with large density difference, for instance, 800 times for air and water is considered. Two-particle model is used and the density difference is introduced by changing the acceleration according to the fluid density. Numerical measurement of surface tension agrees well with theoretical predictions. Simulations of two-phase phenomenon for phase-transition is carried out, showing applicability of the model for two-phase flows. The two-dimensional cavitating flow around a board set up in the fluid way is also simulated. As a result, it was confirmed that the FDLB method with two-particle model was effective in numerical simulation of cavitating flow and the bubble periodically grew up at the low pressure area behind the board, in which the fluid condition was influenced by the cavitation number.

• Journal of Mechanical Science and Technology
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• 제15권7호
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• pp.941-950
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• 2001

A study of counter-current two-phase flow in narrow rectangular channels has been performed. Two-phase flow regimes were experimentally investigated in a 760mm long and 100mm wide test section with 2.0 and 5.0mm gap widths. The resulting flow regime maps were compared with the existing transition criteria. The experimental data and the transition criteria of the models showed relatively good agreement. However, the discrepancies between the experimental data and the model predictions of the flow regime transition become pronounced as the gap width increased. As the gap width increased the transition gas superficial velocities increased. The critical void fraction for the bubbly-to-slug transition was observed to be about 0.25. The two-phase distribution parameter for the slug flow was larger for the narrower channel. The uncertainties in the distribution parameter could lead to a disagreement in slug-to-churn transition between the experimental findings and the transition criteria. For the transition from churn to annular flow the effect of liquid superficial velocity was found to be insignificant.

• Geomechanics and Engineering
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• 제13권1호
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• pp.1-23
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• 2017

A coupled liquid-gas-solid three-phase model, linking two numerical codes (TOUGH2/EOS3 and $FLAC^{3D}$), was firstly established and validated by simulating an in-situ air flow test in Essen. Then the coupled model was employed to investigate responses of multiphase flow and soil skeleton deformation to compressed air or freshwater injection using the same simulation conditions in an aquifer of Tianjin, China. The simulation results show that with injecting pressurized fluids, the vertical effective stress in some area decreases owing to the pore pressure increasing, an expansion of soil skeleton appears, and land uplift occurs due to support actions from lower deformed soils. After fluids injection stops, soil deformation decreases overall due to injecting fluids dissipating. With the same applied pressure, changes in multiphase flow and geo-mechanical deformation caused by compressed air injection are relatively greater than those by freshwater injection. Furthermore, the expansion of soil skeleton induced by compressed air injection transfers upward and laterally continuously with time, while during and after freshwater injection, this expansion reaches rapidly a quasi-steady state. These differences induced by two fluids injection are mainly because air could spread upward and laterally easily for its lower density and phase state transition appears for compressed air injection.

• Ocean Systems Engineering
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• 제1권1호
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• pp.31-57
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• 2011

Impact pressure due to sloshing is of great concern for the ship owners, designers and builders of the LNG carriers regarding the safety of LNG containment system and hull structure. Sloshing of LNG in partially filled tank has been an active area of research with numerous experimental and numerical investigations over the past decade. In order to accurately predict the sloshing impact load, a new numerical method was developed for accurate resolution of violent sloshing flow inside a three-dimensional LNG tank including wave breaking, jet formation, gas entrapping and liquid-gas interaction. The sloshing flow inside a membrane-type LNG tank is simulated numerically using the Finite-Analytic Navier-Stokes (FANS) method. The governing equations for two-phase air and water flows are formulated in curvilinear coordinate system and discretized using the finite-analytic method on a non-staggered grid. Simulations were performed for LNG tank in transverse and longitudinal motions including horizontal, vertical, and rotational motions. The predicted impact pressures were compared with the corresponding experimental data. The validation results clearly illustrate the capability of the present two-phase FANS method for accurate prediction of impact pressure in sloshing LNG tank including violent free surface motion, three-dimensional instability and air trapping effects.

• International Journal of Air-Conditioning and Refrigeration
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• 제13권1호
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• pp.44-50
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• 2005

In the present study, the characteristics of upward bubble flow were experimentally investigated in a liquid bath. An electro-conductivity probe was used to measure local volume fraction and bubble frequency. Since the gas was concentrated at the near the nozzle, the flow parameters were high near the nozzle. In general their axial and radial values tended to decrease with increasing distance. For visualization of flow characteristics, a Particle Image Velocimetry (PIV) and a thermo-vision camera were used in the present study. The experimental results showed that heat transfer from bubble surface to water was largely completed within z = 10 mm from the nozzle, and then the temperature of bubble surface reached that of water rapidly. Due to the centrifugal force, the flow was more developed near the wall than at bubble-water plume. Vortex flow in the bottom region was relatively weaker than that in the upper region.

• 한국가시화정보학회지
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• 제15권1호
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• pp.41-46
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• 2017

Control of mixing and transport processes are the key areas that can be benefited by understanding the hydrodynamics in gas-liquid two-phase flows. In particular, the enhanced bubble-induced liquid-phase mixing is known to be a function of void fraction distribution, gas phase velocity and so on. To further our insight on the characteristics of the liquid-phase mixing induced by the bubbles, in the present study, we experimentally investigate the mixing performance of a rectangular bubble column while changing the void fraction from 0.006 to 0.075%. A shadowgraphy technique is used to measure the gas-phase properties such as void fraction and size/velocity of bubbles. On the other hand, we use dye visualization with low diffusive buoyant dye to directly measure the level of mixing. Finally, we confirm that the time taken for full mixing scales with the inverse of volume void fraction.