• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.38 no.4
• /
• pp.329-335
• /
• 2014

This study aimed to understand the internal flow characteristics of a liquid droplet subject to periodic forced vibration. In order to predict the resonance frequency of a droplet, a high-speed camera and macro lens were used to capture internal flow characteristics of a droplet placed on a vibrating hydrophobic surface. Results showed that the droplet assumed a variety of shapes depending on the resonance mode of free droplet, particularly in modes 2, 4, 6, and 8. In addition, the induced internal vortex flow inside the droplet was also observed in each mode. Typically, the induced flow moved upwards along the axis of symmetry and downwards along the surface of the droplet, that is, from the apex to the contact line in modes 2 and 4, after which it broke into a smaller vortex. On the other hand, the large-scale vortex always remained steady in modes 6 and 8. The speed of the flow in mode 4 was always greater than that in mode 2, but those in modes 6 and 8 were similar.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.10 no.5
• /
• pp.545-565
• /
• 2018

A numerical code is developed based on potential flow theory to investigate nonlinear sloshing in rectangular Liquefied Natural Gas (LNG) tanks under forced excitation. Using this code, internal free-surface elevation and sloshing loads on liquid tanks can be obtained both in time domain and frequency domain. In the mathematical model, acceleration potential is solved in the calculation of pressure on tanks and the artificial damping model is adopted to account for energy dissipation during sloshing. The Boundary Element Method (BEM) is used to solve boundary value problems of both velocity potential and acceleration potential. Numerical calculation results are compared with published results to determine the efficiency and accuracy of the numerical code. Sloshing properties in partially filled rectangular and membrane tank under translational and rotational excitations are investigated. It is found that sloshing under horizontal and rotational excitations share similar properties. The first resonant mode and excitation frequency are the dominant response frequencies. Resonant sloshing will be excited when vertical excitation lies in the instability region. For liquid tank under rotational excitation, sloshing responses including amplitude and phase are sensitive to the location of the center of rotation. Moreover, experimental tests were conducted to analyze viscous effects on sloshing and to validate the feasibility of artificial damping models. The results show that the artificial damping model with modifying wall boundary conditions has better applicability in simulating sloshing under different fill levels and excitations.

• Fire Science and Engineering
• /
• v.30 no.6
• /
• pp.111-117
• /
• 2016

The present study examined the free surface flow of a liquid sheet near a sprinkler head using a Computational Fluid Dynamics (CFD) model and considered the feasibility of the empirical model for predicting the initial spray characteristics of the sprinkler head through a comparison of the CFD results. The CFD calculation for a simplified sprinkler geometry considering the nozzle and deflector were performed using the commercially available CFD package, CFX 14.0 with the standard $k-{\varepsilon}$ turbulence model and theVolume of Fluid (VOF) method. The predicted velocity of the empirical model at the edge of deflector were in good agreement with that of the CFD model for the flat plate region but there was a certain discrepancy between the two models for the complex geometry region. The mean droplet diameter predicted by the empirical model differed significantly from the measured value of the real sprinkler head. On the other hand, the empirical model can be used to understand the mechanism of droplet formation near the sprinkler head and predict the initial spray characteristics for cases without experimental data.

• Proceedings of the KSME Conference
• /
• 2001.06a
• /
• pp.243-249
• /
• 2001

In this study, the progressive inelastic deformation, so called, thermal ratchet phenomenon which can occur in high temperature liquid metal reactor was simulated with thermal ratchet structural test facility and 316L stainless steel test cylinder. The inelastic deformation of the reactor baffle cylinder can occur due to the moving temperature distribution along the axial direction as the hot free surface moves up and down under the cyclic heat-up and cool-down of reactor operations. The ratchet deformations were measured with the laser displacement sensor and LVDTs after cooling the structural specimen which experiences thermal load up to $550^{\circ}$ and the temperature differences of about $500^{\circ}C$. During structural thermal ratchet test, the temperature distribution of the test cylinder along the axial direction was measured from 28 channels of thermocouples and the temperatures were used for the ratchet analysis. The thermal ratchet deformation analysis was performed with the NONSTA code whose constitutive model is nonlinear combined kinematic and isotropic hardening model and the test results were compared with those of the analysis. Thermal ratchet test was carried out with respect to 9 cycles of thermal loading and the maximum residual displacements were measured to be 1.8mm. It was shown that thermal ratchet load can cause a progressive deformation to the reactor structure. The analysis results with the combined hardening model were in reasonable agreement with those of the tests.

• Journal of the Korean Chemical Society
• /
• v.57 no.4
• /
• pp.432-438
• /
• 2013

We report a contact angle goniometer that can be easily assembled and used in high school and general chemistry experiments. It consists of an LED flash, a sample stand, and a camera fixed on an optical bread board, and the sample area is covered to block light from outside with a box with holes on both sides. ImageJ, free image analyzing software and a JAVA plugin (Drop_analysis) were used to determine the contact angle of liquid drop resting on solid surface. The contact angles of various liquids were successfully measured on various surfaces. The solid surface energies have also been determined using the Owen-Wendt method from the contact angles of $H_2O$ and $CH_2I_2$. The results reasonably agree with the previously reported values, showing the surface characteristics and modification as well as the dispersive and polar contributions. These contact angle goniometer and method for determination of the contact angle and surface energy can be applied to observation of various surface properties including wettability, hydrophilicity, and water repelling. Students can learn how the surface properties are related to the intermolecular interactions and gain experience about the equilibrium between the related forces, optics, and mathematical derivations.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.27 no.2
• /
• pp.21-30
• /
• 1990

Theoretical and experimental techniques to analyze the two-dimensional liquid motion in a tank are discussed. A Lagrangian FEM with a velocity correction procedure is introduced to describe incompressible free surface fluid flow. A mesh rezoning technique is used to prevent strong distortion of finite elements in the Lagrangian description. Model test technique for sloshing tank is developed using a hydraulic type bench tester. The influence of the variation in the exciting frequency and amplitude are observed for various fill depths. The results of theoretical calculations are compared with those of experiments.

• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• v.4 no.1
• /
• pp.121-131
• /
• 2000

Melt flow, heat and mass transfer of oxygen have been analyzed numerically in the process of Czochralski single crystal growth of silicon under the influence of misaligned cusp magnetic fields. Since the silicon melt in a crucible for crystal growth is of high temperature and of highly electrical-conducting, experimentation method has difficulty in analyzing the behavior of the melt flow. A set of simultaneous nonlinear equations including Navier-Stokes and Maxwell equations has been used for the modelling of the melt flow which can be regarded as a liquid metal. Together with the melt flow which forms the Marangoni convection, a flow circulation is observed near the comer close both to the crucible wall and the free surface. The melt flow tends to follow the magnetic lines instead of traversing the lines. These flow characteristics helps the flow circulation exist. Mass transfer characteristics influenced by the melt flow has been analyzed and the oxygen absorption rate to the crystal has been calculated and turned out to be rather uniform than in the case of an aligned magnetic field.

• Electrical & Electronic Materials
• /
• v.8 no.3
• /
• pp.340-351
• /
• 1995

Electrical, physical and optical properties of Aluminum(Al), Copper(Cu) thin films were investigated in order to establish the optimum sputtering parameters in Liquid Crystal Display (LCD) panel applications. DC-magnetron sputtered film on coming 7059 samples were fabricated with variations of deposition power densities, deposition pressures and substrate temperatures. Low resistivity films(AI;2.80 .mu..ohm.-cm, Cu:1.84 .mu..ohm-cm),which lower than the reported values, were obtained under sputtering parameters of power density(250W), substrate temperature(450-530.deg. C) and 5*10$\^$-3/ Torr deposition pressure. Expected columnar growth and stable grain growth of both films was observed through the Scanning Electron Microscope(SEM) micrographs. Dependency of the applicable defect-free film density upon depositon power and temperature was also characterized. Not too noticable variations in X-ray diffraction patterns were remarked under the alterations of sputtering parameters. High optical reflectivities of Al, Cu films, approximately 70-90 %, showed high degree of surface flatness.

• Journal of the Korean Society for Heat Treatment
• /
• v.9 no.1
• /
• pp.19-26
• /
• 1996

Melt-quenching of steels leads to various metallographic effects such as refinement of grain size, extension of the solid solubility of carbon and alloying elements, and is expected to improve the mechanical properties of conventional steels. Furthermore, this technique is a useful method for producing sheet directly from liquid state. And it will lend itself to development as a continuous cast process which offers significant savings in energy and product costs. The purpose of this study is to present the microstructures of melt-quenched austenitic stainless steels. As the results of this study, the morphology of melt-quenched microstructure show that the roll contact area is columnar structure, and the free surface area is dendrite structure. As the line speed increases, the ratio of $d_{colunnar}/d_{total}$ increases from 0.12 to 0.60, but the ribbon thickness decreases from $150{\mu}m$ to $30{\mu}m$.

• Journal of Korea Foundry Society
• /
• v.13 no.5
• /
• pp.462-475
• /
• 1993

A numerical analysis on the microstructural evolutions of microcellular and cellular ${\alpha}-aluminum$ phase in the gas-atomized Al-8wt. pct droplets was represented. The 2-dimensional non-Newtonian heat transfer and the dendritic growth theory in the undercooled melt were combined under the assumptions of a point nucleation on droplet surface and the macroscopically smooth solid-liquid interface enveloping the cell tips. It reproduced the main characteristic features of the reported microstructures quite well. It predicted a considerable volume fraction of segregation-free region in a droplet smaller than $l0{\mu}m$ if an initial undercooling larger than 100K is given. The volume fractions of the microcellular region($g_A$) and the sum of the microcellular and cellular region($g_a$) were predicted as functions of the heat transfer coefficient, h and initial undercooling, ${\triangle}T$. It was shown that $g_A$ and $g_a$, in the typical gas-atomization processes with $h=0.1-1.0W/cm^2K$, are dominated by ${\triangle}T$ and h, respectively, but for h larger than $4.0W/cm^2K$, a fully microcellular structure can be obtained irrespective of the initial undercooling.