• Journal of Ocean Engineering and Technology
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• 제25권4호
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• pp.36-41
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• 2011

In the present paper, a direct forcing/fictitious domain (DF/FD) level set method is proposed to simulate the FSI (fluid-solid interaction) in two-phase flow. The main idea is to combine the direct-forcing/fictitious domain (DF/FD) method with the level set method in the Cartesian coordinates. The DF/FD method is a non-Lagrange-multiplier version of a distributed Lagrange multiplier/fictitious domain (DLM/FD) method. This method does not sacrifice the accuracy and robustness by employing a discrete ${\delta}$ (Dirac delta) function to transfer quantities between the Eulerian nodes and Lagrangian points explicitly as the immersed boundary method. The advantages of this approach are the simple concept, easy implementation, and utilization of the original governing equation without modification. Simulations of various water-entry problems have been conducted to validate the capability and accuracy of the present method in solving the FSI in two-phase flow. Consequently, the present results are found to be in good agreement with those of previous studies.

• Advances in nano research
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• 제5권3호
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• pp.203-214
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• 2017

In this study we present the reaction mechanism of $Cu_2ZnSnSe_4$ (CZTSe) nanoparticles synthesized by microwave-assisted chemical synthesis. We performed reactions every 10 minutes in order to identify different phases during quaternary CZTSe formation. The powder samples were analyzed by x-ray diffraction (XRD), Raman spectroscopy, energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results showed that in the first minutes copper phases are predominant, then copper and tin secondary phases react to form ternary phase. The quaternary phase is formed at 50 minutes while ternary and secondary phases are consumed. At 60 minutes pure quaternary CZTSe phase is present. After 60 minutes the quaternary phase decomposes in the previous ternary and secondary phases, which indicates that 60 minutes is ideal reaction time. The EDS analysis of pure quaternary nanocrystals (CZTSe) showed stoichiometric relations similar to the reported research in the literature, which falls in the range of Cu/(Zn+Sn): 0.8-1.0, Zn/Sn: 1.0-1.20. In conclusion, the evolution pathway of CZTSe synthesized by this novel method is similar to other synthesis methods reported before. Nanoparticles synthesized in this study present desirable properties in order to use them in solar cell and photoelectrochemical cell applications.

• Journal of the Korean Society of Visualization
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• 제1권2호
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• pp.52-57
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• 2003

The present paper investigated the effect of ultrasonic vibrations on the melting process of a phase-change material (PCM). The melting process in the square cavity with a heated vertical wall has been studied in terms of acoustic streaming. In the present study, applying with ultrasonic vibrations to the liquid were found to induce acoustic streaming which was clearly observed using by a particle image velocimetry (PIV) and a thermal infrared camera. The experimental results revealed that acoustic streaming could accelerate the melting process as much as 2.5 times, compared to the rate of natural melting (i. e., the melting without acoustic streaming). In addition, temperature and Nusselt numbers over time provided conclusive evidence of the important role of the acoustic streaming on the melting phenomena of the PCM.

• Journal of the Korean Mathematical Society
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• 제51권1호
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• pp.163-187
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• 2014

We present a multi-stage Roe-type numerical scheme for a model of two-phase flows arisen from the modeling of deflagration-to-detonation transition in granular materials. The first stage in the construction of the scheme computes the volume fraction at every time step. The second stage deals with the nonconservative terms in the governing equations which produces states on both side of the contact wave at each node. In the third stage, a Roe matrix for the two-phase is used to apply on the states obtained from the second stage. This scheme is shown to capture stationary waves and preserves the positivity of the volume fractions. Finally, we present numerical tests which all indicate that the proposed scheme can give very good approximations to the exact solution.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 추계 학술대회논문집
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• pp.169-177
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• 2005

A high resolution scheme for solving gas-liquid two-phase flows with cavitation is described. This scheme uses the curvilinear coordinate grid and solves the density based momentum equations for mixture of gas-liquid medium with a preconditioning method to treat both compressible and incompressible flow characteristics. The present preconditioned method is based on the Runge-Kutta explicit finite-difference scheme, and is improved by using the diagonalization, the flux difference splitting and the MUSCL-TVD schemes to save computational effort and to increase stability and resolvability, especially at gas-liquid contact surfaces. A homogeneous equilibrium cavitation model is used to treat the gas-liquid two-phase medium in cavitating flow as a locally homogeneous pseudo-single-phase medium. Therefore, it is easy to solve cavitating flow, including wave propagation, large density changes and incompressible flow characteristic at low Mach number. Some numerical results obtained by the present scheme are shown.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2005년도 제31회 KOSCO SYMPOSIUM 논문집
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• pp.20-27
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• 2005

I consider the structure of steady wave system which is admitted by the continuum equations for materials that undergo phase transformations with exothermic chemical reaction. In particular, the dynamic phase front structures between liquid and gas phases, and solid and liquid phases are computationally investigated. Based on the one-dimensional continuum shock structure analysis, the present approach can estimate the nano-width of waves that are present in combustion. For illustration purpose, n-heptane is used in the evaporation and condensation analysis and HMX is used in the melting and freezing analysis of energetic materials of interest. On-going effort includes extension of this idea to include broad range of liquid and solid fuels, such as rocket propellants.

• ETRI Journal
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• 제25권4호
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• pp.238-246
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• 2003

This paper introduces the modeling and analysis of a discrete-time, two-phase queueing system for both exhaustive batch service and gated batch service. Packets arrive at the system according to a Bernoulli process and receive batch service in the first phase and individual services in the second phase. We derive the probability generating function (PGF) of the system size and show that it is decomposed into two PGFs, one of which is the PGF of the system size in the standard discrete-time Geo/G/1 queue without vacations. We also present the PGF of the sojourn time. Based on these PGFs, we present useful performance measures, such as the mean number of packets in the system and the mean sojourn time of a packet.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제18권6호
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• pp.518-525
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• 2006

The present experiments have been performed for obtaining the melting heat transfer characteristics of micro-encapsulated solid-liquid phase-change material and water mixture slurry flow in a circular tube heated with constant wall heat flux. The phase change material having a low melting point was selected for a domestic cooling system in the present study. The governing parameters were found to be latent heat material concentration, heat flux, and the slurry velocity. The experimental results revealed that the increase of tube wall temperature of latent microcapsule slurry was lower than that of water caused by the heat absorption of fusion.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 춘계 학술대회논문집
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• pp.219-222
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• 2005

A compressible two-fluid two-phase flow computation model using the stiffened-gas equation of state is formulated. Since the conservation equation system is of mixed type, it gives complex eigenvalues. The sonic speeds obtained from the individual single phase have been simply used in the literature for the fastest wave speeds necessary in the HLL scheme. This method has worked fine but proved to be quite diffusive according to our test. To improve the accuracy, we here propose to utilize the analytic eigenvalues evaluated from an approximate Jacobian matrix lot the fastest wave speeds. The interfacial transfer terms were dropped in constituting the Jacobian matrix for this purpose. The present scheme proved efficient, robust and accurate in comparison with other existing methods. We solved the cavitating flow problem using the present scheme. The result shows more detailed wave structure in the cavitating process caused by the strong expansion waves.

• Journal of the Korean Society for Heat Treatment
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• 제16권2호
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• pp.78-82
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• 2003

Nitrided compound layer and diffusion layer structure were observed by SEM. The compound layer and the constituent of nitrided surface of STS 304, STS 316, STS 410 and SACM 645 steel were analysed using EMPA and XRD respectively. The depth of nitriding layer that is obtained from similar nitriding condition decrease in the order of SACM 645 > STS 410 > STS 316 > STS 304. Result of phase transformation of the nitrided at $550^{\circ}C$ by XRD analysis were as follows; The austenitic stainless steel was mainly consist of $Cr_2N$ accompanying with $Fe_4N$ and $Fe_{2-3}N$ phase and martensitic stainless steel was mainly consist of present $Fe_{2-3}N+Cr_2N$ phase, but SACM 645 steel was $Fe_{2-3}N$ phase present only.