• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.4
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• pp.424-431
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• 2003

The evaporation cooling phenomenon of a droplet containing a surfactant on a heated surface has been studied experimentally. The two kinds of heater modules made of brass and Teflon$^{TM}$ were tested to investigate the cooling characteristics of droplet. Solutions of water containing Sodium Lauryl Sulfate(0 ppm, 100 ppm, 1000 ppm) were tested in the experiments. The results showed that the contact angle decrease as the concentration of surfactant increases. The tendency did not very with different heated solid materials. As initial temperature of the heated surface becomes high, time averaged heat flux increases and evaporation time decreases with the denser concentration of surfactant. Therefore, water with denser concentration of surfactant could be effective to cool flammable materials. However, the effect of surfactant becomes low as the material temperature is higher than the boiling temperature of water.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.472-473
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• 2008

Flow boiling in parallel microchannels has received attention as an effective heat sink mechanism for power-densities encountered in microelectronic equipment. the bubble dynamics coupled with boiling heat transfer in microchannels is still not well understood due to the technological difficulties in obtaining detailed measurements of microscale two-phase flows. In this study, complete numerical simulation is performed to further clarify the dynamics of flow boiling in microchannels. The level set method for tracking the liquid-vapor interface is modified to include the effects of phase change and contact angle. The method is further extended to treat the no-slip and contact angle conditions on the immersed solid. Also, the reverse flow observed during flow boiling in parallel microchannels has been investigated. Based on the numerical results, the effects of channel shape and inlet area restriction on the bubble growth, reverse flow and heat transfer are quantified.

• Journal of Power System Engineering
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• v.1 no.1
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• pp.35-41
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• 1997

Annular jet pump can be used for the transportation of solid materials and fish. The effect of mixing chamber on the characteristics of annular jet pump is sought in this paper. Experiments were done for several reducing angles of mixing chamber, and for several throat area. Water was used for both the primary fluid and secondary fluid. A vortex was observed for the straight mixing chamber, but it was not observed for the mixing chamber whose reducing angle is $18^{\circ}$ or higher. The efficiency curves for the annular jet pump are presented in this paper, showing the annular jet pump which has 240 reducing angle and $0.611{\sim}0.73$ value of At/As. is most effective among the tested several annular jet pumps.

• Journal of Korean Neurosurgical Society
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• v.64 no.6
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• pp.922-932
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• 2021

Objective : It is challenging to make solid fusion by posterior screw fixation and laminectomy with posterolateral fusion (PLF) in thoracic and thoracolumbar (TL) diseases. In this study, we report our experience and follow-up results with a new surgical technique entitled posterior thoracic cage interbody fusion (PTCIF) for thoracic and TL spine in comparison with conventional PLF. Methods : After institutional review board approval, a total of 57 patients who underwent PTCIF (n=30) and conventional PLF (n=27) for decompression and fusion in thoracic and TL spine between 2004 and 2019 were analyzed. Clinical outcomes and radiological parameters, including bone fusion, regional Cobb angle, and proximal junctional Cobb angle, were evaluated. Results : In PTCIF and conventional PLF, the mean age was 61.2 and 58.2 years (p=0.46), and the numbers of levels fused were 2.8 and 3.1 (p=0.46), respectively. Every patient showed functional improvement except one case of PTCIF. Postoperative hematoma as a perioperative complication occurred in one and three cases, respectively. The mean difference in the regional Cobb angle immediately after surgery compared with that of the last follow-up was 1.4° in PTCIF and 7.6° in conventional PLF (p=0.003), respectively. The mean durations of postoperative follow-up were 35.6 months in PTCIF and 37.3 months in conventional PLF (p=0.86). Conclusion : PTCIF is an effective fusion method in decompression and fixation surgery with good clinical outcomes for various spinal diseases in the thoracic and TL spine. It provides more stable bone fusion than conventional PLF by anterior column support.

• Journal of Aerospace System Engineering
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• v.14 no.4
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• pp.1-9
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• 2020

The characteristics of an aerospike pintle nozzle system with excellent altitude compensation were analyzed using cold air testing. It was confirmed that reducing the stroke of the aerospike nozzle is effective in increasing the thrust. However, the results of additional numerical analysis indicated that the discharge coefficient factor was significantly lower at the maximum stroke. The Vena contracta due to the cowl reduction angle decreased the effective nozzle throat area at the maximum stroke and hindered expansion. Complementing the cowl design may thus increase the efficiency of a solid-propellant rocket engine that uses the aerospike pintle nozzle system.

• Journal of electromagnetic engineering and science
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• v.19 no.1
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• pp.31-36
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• 2019

In this study, an effective method for designing an electromagnetic multilayer radome is introduced. This method is achieved by using ant colony optimization for a continuous domain in the transmission coefficient maximization with stability for a wide angle of incidence in both perpendicular and parallel polarizations in specific X- and Ku-bands. To obtain the optimized parameter for a C-sandwich radome, particle swarm optimization algorithm is operated to give a clear comparison on the effectiveness of ant colony optimization for a continuous domain. The qualification of an optimized multilayer radome is also compared with an effective solid radome type in transmitted power stability and presented in this research.

• Journal of the Korea Organic Resources Recycling Association
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• v.28 no.4
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• pp.69-75
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• 2020

This study was conducted to improve the solid-liquid separation efficiency of clarifiers. To do so, the study did a bio-flocculation experiment simply by controlling the stirring speed (rpm) and baffle angle of a clarifier on a lab scale, but without using a coagulant. For the purpose of the experiment, the feed wall of a clarifier was so improved that a baffle could be installed on the clarifier. Then, it was ensured to change its stirring speed (to 0.0rpm, 0.6rpm, and 1.2rpm), with the angle fixed at 10°. As a result, it was found that concentration efficiency increased by 2.0%, and effluent removal efficiency (SS concentration) by 7.8%, at a stirring speed of 0.6ppm. This indicates the bio-coagulation efficiency of sludge increased with changing stirring speeds. Then, the baffle angle of the sedimentation unit was changed to analyze how the changed baffle angle would affect the sedimentation of sludge. As a result, it was found that the compression of sludge interface was very effective at a baffle angle of 20°. It is hoped that these experimental findings will be useful in improving the sedimentation efficiency of circular clarifiers.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.34 no.3
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• pp.1-8
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• 2002

The object of this study was to determine the surface energy of hydrophobically modified micro-crystalline cellulose (MCC) with AKD and evaluate the effect of surface energy of the solid particles dispersed in aqueous medium on flotation efficiency. Especially to eliminate the complication derives from the diverse parameters of solid particles including particle size, type, etc. MCC's modified with AKD have been used. The surface energy Parameters were calculated from advancing contact angles of apolar and polar liquids on MCC pellets using the Lifshitz-van der Waals acid-base (LW:AB) approach. Total surface energy of hydrophobic MCC ranged from 46.19 mN/m to 48.60 mN/m. The contribution of the acid-base components to the total surface energy ranged form 13% to 17% for hydrophobic MCC's. The effect of surface characteristics on the flotation efficiency was evaluated. It was shown that there exist critical values of surface energies to increase flotation efficiency. Total surface energy and polar component of solid particles should be lower than 47 mN/m and 7 mN/m, respectively, for effective removal in the flotation process.

• Transactions of Materials Processing
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• v.19 no.7
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• pp.411-415
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• 2010

A sandwich panel which is comprised of truss cores faced with solid face sheets is lightweight and multi-functional. So it is widely used to not only structural material but also heat transfer media in transportation field such as airplane, train and vessel. There are various core topologies such as pyramidal and tetrahedral truss, square honeycombs and kagome truss. The study focused on analytical approach to optimize compression and shear quality of the unit cell of PCM with pyramidal configuration. With various unit cell models which have the same core weight per unit area but different truss member angle, analytical solution for effective stress ($\bar{\sigma},\bar{\tau}$), peak stress ($\bar{\sigma}_{peak},\bar{\tau}_{peak}$) by yielding and buckling, relative density ($\bar{\rho}_c$) and effective stiffness ($\bar{E},\bar{G}$) have been computed and compared each other. With this approach, the most optimal core configuration was predicted. The result has become the efficient guidelines for the design of PCM core structure.

• Journal of Korea Foundry Society
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• v.12 no.3
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• pp.220-229
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• 1992

The degree of purification and the macrostructure of high purity aluminium were studied through the alternate stirring method in order to improve the nonuniformity of solute concentration in the unidirectional stirring method. The $2^3$ factorial design was done to examine the effects of experimental factors more qualitatively. In the relatively low stirring speed of 1500 rpm with alternate stirring mode, the uniform solute profile and refined grain structure were obtained due to strong washing effect and turbulent fluid flow. It was induced by the transition of the momentum boundary layer by alternation of the stirrer. It was concluded from this study that the alternate stirring mode was more effective to obtain the uniformity of solute even in the stirring speed of 1500 rpm. But the degree of purification decreased below the critical alternating period. When 2N(99.8wt.%) aluminium was used as the starting material the morphology of solid-liquid showed the cellular shape and the columnar grains were inclined to the direction of rotation. This inclined grain growth resulted from the difference of relative velocities of solid and liquid. The inclined angle was increased as the stirring speed increased and solidification proceeded. In the case of 4N aluminium, there was no inclined grain growth and it was confirmed from the macrostructure and SEM work that the morphology of solid-liquid interface was planar. From the factorial design, it was found that the alternate stirring mode showed poorer purification effect than that of unidirectional stirring mode at low speed(500 rpm). In addition, the factor that had the most significant effect on the degree of purification was the stirring speed.