• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.1 s.173
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• pp.103-109
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• 2000

A method to measure the crack length in rubbery materials is described. Through dimensional analysis and experiments, an equation is derived to give the crack length as a function of the change of strain energy density in a region remote from the crack. The function is provided in a form of separated terms of loading and material, the validity of which is experimentally proved using separation parameters.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.7 s.250
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• pp.622-629
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• 2006

The shape optimization of blade sweep in a transonic axial compressor rotor of NASA Rotor 37 has been performed using response surface method and the three-dimensional Wavier-Stokes analysis. Two shape variables of the rotor blade, which are used to define the rotor sweep, are introduced to increase the adiabatic efficiency of the compressor. Throughout the optimization, optimal shape having a backward sweep is obtained. Adiabatic efficiency, which is the objective function of the present optimization, is successfully increased. Separation line due to the interference between a shock and surface boundary layer on the blade suction surface is moved downstream for the optimized blade compared to the reference one. The increase in adiabatic efficiency for the optimized blade is caused by suppression of the separation due to a shock on the blade suction surface.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.11
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• pp.856-862
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• 2008

This paper presents the characterization of a continuous magnetophoretic microseparator for separating white and red blood cells from peripheral whole blood cells based on their native magnetic properties. The magnetophoretic microseparator separated the blood cells using a high gradient magnetic separation (HGMS) method without the use of additives such as magnetic beads or probing materials. Experimental results show that the paramagnetic capture mode microseparator can continuously separate out 93.5% of red blood cells and 97.4% of white blood cells from diluted whole blood, and the diamagnetic capture mode microseparator can continuously separate out 89.7% of red blood cells and 72.7 % of white blood cells by using applying an external magnetic flux of 0.2 T using a permanent magnet.

• Proceedings of the Membrane Society of Korea Conference
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• 2003.07a
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• pp.25-28
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• 2003

Low cost composite metallic membranes for the hydrogen separation and production have been prepared by using thin Pd-Ag foils reinforced by metallic (stainless steel and nickel) structures. Especially, “supported membranes” have been obtained by a diffusion welding procedure in which Pd-Ag thin foils have been joined with perforated metals (nickel) and expanded metals (stainless steel): in these membranes the thin palladium foil assures both the high hydrogen permeability and the perm-selectivity while the metallic support provides the mechanical strength. A second studied method of producing "laminated membranes" consists of coating non-noble metal sheets with very thin palladium layers by diffusion welding and cold-rolling. Palladium thin coatings over these metals reduce the activation energy of the hydrogen adsorption process and make them permeable to the hydrogen. In this case, the dense non-noble metal has been used as a support structure of the thin Pd-Ag layers coated over its surfaces: a proper thickness of the metal assures the mechanical strength, the absence of defects (cracks, micro-holes) and the complete hydrogen selectivity of the membrane. membrane.

• International Journal of Industrial Entomology and Biomaterials
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• v.5 no.2
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• pp.163-170
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• 2002

In this paper, silk fibroin (SF)/polyurethane (PU) blend films were fabricated to develop a new biomaterial for biomedical applications. These blend films were prepared using formic acid as a cosolvent, and structural characteristics and properties of blend films were investigated. FTIR results suggested that there was no specific interaction between SF and PU, implying molecular immiscibility in SF/PU blend films. Furthermore, it was revealed by XRD method that the crystalline region of blend components was not perturbed by counterpart polymers. The degree of phase separation of SF/PU blend films was diminished by increasing PU content in blend. Especially, the blend with 70% content of PU showed no evidence of macro-phase separation in SEM observation. However, SF/PU blend (70/30) was revealed to be phase-separated in a lower dimension confirmed by DMTA measurement. TGA result showed that thermal decomposition temperature of blend film was slightly decreased compared to those of SF and PU polymer itself, Though mechanical properties of SF/PU blend films were not good enough due to the solvent, blood compatibility of PU can be enhanced markedly by mixing with SF for SF/PU blend film.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.933-945
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• 1994

A shock-wave in a supersonic flow can be theoretically determined by a given pressure ratio at upstream and downstream flowfields, and then the obtained shock-wave is stable in its position. Under the practical situation in which the shock-wave interacts with the boundary layer along a solid wall, it cannot, however, be stable even for the given pressure ratio being independent of time and oscillates around a time-mean position. In the present study, oscillations of a weak normal shock-wave in a supersonic diffuser were measured by a Line Image Sensor(LIS), and they were compared with the data of the wall pressure fluctuations at the foot of the shock-wave interacting with the wall boundary layer. LIS was incorporated into a conventional schlieren optical system and its signal, instantaneous displacement of the interacting shock-wave, was analyzed by a statistical method. The results show that the displacement of an oscillating shock-wave increase with the upstream Mach number and the dominant frequency components of the oscillating shock-wave are below 200 Hz. Measurements indicated that shock-wave oscillations may not entirely be caused by the boundary layer separation. The statistical properties of oscillations appeared, however, to be significantly affected by shock-induced separation of turbulent boundary layer.

• Bulletin of the Korean Chemical Society
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• v.23 no.11
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• pp.1541-1544
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• 2002

The concentration of B in steels is important due to its influence on mechanical properties of steel such as hardenability, hot workability, and creep resistance. An analytical method has been developed to determine B in steel samples by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). National Institute of Standard and Technology Standard Reference Material (NIST SRM) 348a was analyzed to validate the analytical method. The steel sample was digested in a centrifuge bottle with addition of aqua regia and $^{10}B$ spike isotope. Sample pH was then adjusted to higher than 10 to precipitate most matrix elements such as Fe, Cr, and Ni. After centrifugation, the supernatant solution was passed through a cation exchange column to enhance the matrix separation efficiency. B recovery efficiency was about 37%, while matrix removal efficiency was higher than 99.9% for major matrix elements. The isotope dilution method was used for quantification and the determined B concentration was in good agreement with the certified value.

• Journal of the Korean institute of surface engineering
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• v.50 no.3
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• pp.212-218
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• 2017

$Mg_xNi_yZn_{1-x-y}Fe_2O_4$ ferrite powders were prepared by self-propagating high temperature synthesis followed by classifying with an ultrasonic wet-magnetic separation unit to get high pure nano-sized particles. The $Mg_xNi_yZn_{1-x-y}Fe_2O_4$ ferrites were well formed by using several powders like iron, nickel oxide, zinc oxide and magnesium oxide at 0.1 MPa of oxygen pressure. The ultrasonic wet-magnetic separation of pre-mechanical milled ferrite powders resulted in producing the powders with average size of 800 nm. The addition of a surfactant during the wet-magnetic separation process improved productivity more than twice. The coercive force, maximum magnetization and residual magnetization of the $Mg_xNi_yZn_{1-x-y}Fe_2O_4$ nano-powders with 800 nm size were 3651 A/m, $53.92Am^2/kg$ and $4.0Am^2/kg$, respectively.

• Membrane Journal
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• v.33 no.1
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• pp.1-12
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• 2023

In this review, surface modification methods of hydrophobic poly(tetrafluoroethylene) (PTFE) membrane are introduced and their improved hydrophilicity results are discussed. Fluoropolymer based membranes, represented by PTFE membranes have been used in various membrane separation processes, including membrane distillation, oil separation and gas separation. However, despite excellent physical properties such as chemical resistance, heat resistance and high mechanical strength, the strong hydrophobicity of PTFE membrane surface has become a challenging factor in expanding its membrane separation application. To improve the separation performance of PTFE membranes, wet chemical, hydrophilic coating, plasma, irradiation and atomic layer deposition are applied, modifying the surface property of PTFE membranes while maintaining their inherent properties.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.4
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• pp.353-360
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• 2011

The prediction of binary droplet collisions is important in the formation of falling drops and the evolution of sprays. The droplet velocity, impact parameter, and drop-size ratio influence the interaction between the droplets. The effect of these parameters results in complicated collision phenomena. Droplet collisions can be classified into four types of interactions: bouncing, coalescence, reflexive separation, and stretching separation. In the present study, the interfacial flow problem of the droplet collision was numerically simulated by using the level set method. 2D axisymmetric simulations on the head-on collisions and 3D simulation on the off-center collisions were performed. The numerical results of droplet behavior after the collision agreed well with the experimental and analytical results. The mixing of the mass of the initial droplets after the collision was also predicted by using different species index of colliding droplets.