• Macromolecular Research
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• v.17 no.8
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• pp.575-579
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• 2009

Copolymerization of L-lactide and s-caprolactone initiated by tin (II) octoate (Sn(Oct)$_2$) was carried out in supercritical chlorodifluoromethane (R22) with varying reaction conditions (time and temperature) and amounts of monomer and catalyst, under a pressure of 250 bar. The optimum conditions were a reaction time of 10 h and a temperature of 130 $^{\circ}C$, which is similar to the temperature used in bulk copolymerization system. The conversion increased from 56% to 76% by increasing the reaction time from 1 to 10 h. The molecular weight also increased to 75,900 g.mol$^{-1}$ over the same period, while the increased monomer concentration resulted in a high molecular weight of 86,400 g.mol$^{-1}$ and a monomer conversion of 84%. Raising the reaction temperature from 90 to 130 $^{\circ}C$ increased the monomer conversion as well as the poly-L-lactide-co-${\varepsilon}$-caprolactone (PLCL) molecular weight. The variation on the stannous octoate catalyst suggested that less catalyst would decrease the caprolactone content of the polymer.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1359-1365
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• 2014

In this study, 1-way fluid structure interaction analysis(FSI) for the shutter, component of side jet thruster was performed to evaluate the safety. Driving torque to open nozzle, thermal and high pressure load of hot gas was applied to shutter. Thus, the shutter must be designed to endure this load during combustion. We carried out computational fluid dynamics analysis to obtain the pressure, temperature, and heat transfer coefficient of hot gas of side jet thruster. We then used the data as the load condition for a thermal structural analysis using a mapping method. The locations with the maximum stress and temperature distributions were found. We compared the maximum stress with the tensile stress of shutter material according to temperature to evaluate the safety. We also analyzed the radial deformation of the shutter to set the proper interface gap with the side jet thruster parts.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.1
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• pp.96-100
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• 2011

The hydrostatic bearings have a relatively small run-out comparing to its shape error by fluid film effect in hydrostatic state as like pneumatic bearing and have a high stiffness, load capacity and damping characteristics. As there is no maintenance and semipermanent in these bearing type, it has been usually adopted as main spindle bearing for grinding machine. In this thesis, to develop hydrostatic bearing for high speed spindle, the cooler setting temperature, bearing clearance and nozzle pressure of belt-driven hydrostatic bearing are investigated. The bearing temperature is decreased, as the cooler setting temperature is lower, nozzle pressure is higher and bearing clearance is wider. The front temperature of bearing is nearly $8^{\circ}C$ higher than the rear one up to 13,000 rpm of spindle revolution. The thermal deflection of X-axis is ${\pm}16\;{\mu}m$ in range of 12,000 rpm-13,000 rpm. Therefore, it is conformed that the built-in motor hydrostatic bearing can be used to high speed spindle.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.183-190
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• 2002

In order to reduce NOx emissions in the 20kw class microturbines under development, the low NOx characteristics, as being an application to the lean premixed combustion technology, have been investigated. The study has been conducted at the conditions of high temperature and pressure. Air from a compressor with the temperature of 500K to 650K and the pressure of 0.3bar gauge to 0.7bar gauge, was supplied to the combustor through an air preheat-treatment. Sampling exhaust gases were measured at the immediate exit of the combustor. for the effect of temperature on NO and CO emissions. though NOx was increased, CO was decreased with increasing inlet air temperature. With increasing inlet air pressure, NOx and CO were increased also. NOx was decreased, but CO was increased with increasing inlet air mass flow rate. The test has been performed on the equivalent ratios of 0.10 to 0.25 in a lean region. NOx was increased with increasing equivalent ratios, but CO was decreased as an influence of flame temperature. In the very lean region of the equivalent ratio below 0.12, CO was increased suddenly, due to instability. As the results of this study, NOx and CO are found to be reduced to the similar level at the same time when operated at optimal conditions.

• Journal of ILASS-Korea
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• v.7 no.3
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• pp.12-17
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• 2002

In this paper, spray and combustion characteristics of a liquid-fueled ramjet engine were experimentally investigated. The spray penetrations were measured to clarify the spray characteristics of a liguid jet injected transversely into the subsonic vitiated airstream, which is maintained a high velocity and temperature. The spray penetrations are increased with decreasing airstream velocity, increasing airstream temperature, and increasing air-fuel momentum ratio. To compensate our results of penetrations, the new experimental equation were modified from Inamura's equation. In the case of insufficient penetration, the combustion phenomenon in ram-combustor were unstable. Therefore, the temperature distribution was slanted to the low wall of the ram-combustor. These trends gradually disappeared as the length and air temperature of the combustor became longer. Combustion efficiency increased when the length of the combustor was long and the air temperature was high. Especially, stable flame region is enlarged when the length of the combustor was long and the air temperature was high. Type Abstract here. Type Abstract here.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.1
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• pp.44-47
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• 1988

The present experiments of transient temperature variation and temperature fluctuation were conducted by bead type thermistors in pool boiling without a heat surface. The experimentally obtained conclusion were as follows. (1) The high transient temperature Variatian of 11.64.deg. C for a duration of 0.08 sec and a temperature freguency having a duration of 5.6*10$^{-2}$ sec in a flashing were measured. (2) The highest variation of transient temperature was shown at saturated temperature of 80.deg. C and superheat of 7.9.deg. C. (3) Temperature frequency was found to increase with superheat below 60.deg. C of saturated temperature, but above 60.deg. C it was relative to lower superheat and was found to decrease with higher superheat..

• The Journal of the Acoustical Society of Korea
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• v.43 no.1
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• pp.112-121
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• 2024

The pipping system is widely used in many industries as equipment for transporting fluids over long distances. In high-pressure pipe, as the speed of the fluid increases, a loud noise is generated. Therefore, various studies have been conducted to reduce pipe noise. In this paper, a pipe noise analysis was developed to predict and quantitatively assess the flow-induced vibration and acoustic-induced vibration due to valve flow in high-temperature and high-pressure. To do this, a high-fidelity fluid analysis technique was developed for predicting internal flow in the pipe with valve. In additional, the contribution of compressible/incompressible pressure by frequency band was evaluated using the wavenumber-frequency analysis. To predict a low/middle frequency pipe noise, the vibroacoustic analysis method was developed based on Finite Element Method (FEM). And the pipe noise prediction method for the middle/high frequency was developed based on Statistical Energy Analysis (SEA).

• Economic and Environmental Geology
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• v.28 no.2
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• pp.139-145
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• 1995

Tungsten skarn mineralization of the Sangdong mine is localized in the interbedded limestone layers of the Myobong Slate Formation and in the limestone of the Pungchon Limestone Formation of Cambrian age. Fluid inclusion, gas composition and Nd-Sr isotope for granites and skarns have been investigated. Gas compositions show $CO_2$ rich in the Sangdong granite and CH, rich in the Nonggeori and Eopyeong granites. The initial $^{87}Sr/^{86}Sr$ and $^{143}Nd/^{144}Nd$ ratios of the Sangdong granites have 0.714~0.716(${\varepsilon}_{Sr}$=138~162) and 0.51173~0.51178(${\varepsilon}_{Nd}$=-14.4~15.5), respectively. And their two stage model ages range from 1687 to 1764 Ma. The granite characterized by high strontium initial ratios and negative eNd value could have originated from the old continental crust source. Low homogenization temperature of the Sangdong granite having $203{\sim}296^{\circ}C$ with 1.9~9.2 NaCl equiv. wt% indicates the post-magmatic hydrothermal alteration temperature. Skarn ore fluid responsible for tungsten mineralization has been evolved from CH, rich fluid of early pyroxene garnet skarn to $CO_2$ rich later quartz-mica skarn.

• Journal of Mechanical Science and Technology
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• v.16 no.5
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• pp.683-695
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• 2002

The objective of the present study is to analyze the fluid flow with moving boundary using a finite element method. The algorithm uses a fractional step approach that can be used to solve low-speed flow with large density changes due to intense temperature gradients. The explicit Lax-Wendroff scheme is applied to nonlinear convective terms in the momentum equations to prevent checkerboard pressure oscillations. The ALE (Arbitrary Lagrangian Eulerian) method is adopted for moving grids. The numerical algorithm in the present study is validated for two-dimensional unsteady flow in a driven cavity and a natural convection problem. To extend the present numerical method to engine simulations, a piston-driven intake flow with moving boundary is also simulated. The density, temperature and axial velocity profiles are calculated for the three-dimensional unsteady piston-driven intake flow with density changes due to high inlet fluid temperatures using the present algorithm. The calculated results are in good agreement with other numerical and experimental ones.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.12
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• pp.1475-1483
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• 2004

Loop thermosyphon(LTS) has many good characteristics such as low thermal resistance, no power consumption, noiseless operation and small size. To investigate the overall performance of LTS, we have performed various experiments varying three parameters: input power of the heater, working fluid(water, ethanol, FC3283) and filling ratio of the working fluid. At a combination of these parameters, temperature measurements are made at many locations of the LTS. The temperature difference between the evaporator and the condenser is used to obtain the thermal resistance. In addition, flow visualization using a high speed camera is carried out. The thermal resistance is not constant. It is lower at higher input power, which is one of the distinct merits of LTS. Flow instabilities are frequently observed when changing the working fluid, the input power and the filling ratio. The results show that the LTS can be readily put into practical use. Future practical application in electronic cooling is recommended.