• Nuclear Engineering and Technology
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• v.40 no.2
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• pp.117-126
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• 2008

In this paper, a new reactor core design is proposed on the basis of a mixed core concept consisting of a thermal zone and a fast zone. The geometric structure of the fuel assembly of the thermal zone is similar to that of a conventional thermal supercritical water-cooled reactor(SCWR) core with two fuel pin rows between the moderator channels. In spite of the counter-current flow mode, the co-current flow mode is used to simplify the design of the reactor core and the fuel assembly. The water temperature at the exit of the thermal zone is much lower than the water temperature at the outlet of the pressure vessel. This lower temperature reduces the maximum cladding temperature of the thermal zone. Furthermore, due to the high velocity of the fast zone, a wider lattice can be used in the fuel assembly and the nonuniformity of the local heat transfer can be minimized. This mixed core, which combines the merits of some existing thermal SCWR cores and fast SCWR cores, is proposed for further detailed analysis.

• Korean Journal of Optics and Photonics
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• v.4 no.3
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• pp.266-275
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• 1993

We made $P_2O_5-SiO_2$ films on silicon for integrated optics application by low pressure chemical vapor deposition using TEOS (tetraethylorthosilicate) and TMPite (trimethylphosphite) and studied the deposition characteristics. The activation energy of the reaction was changed from 54.6 kcal/mole to 39.2 kcal/mole by incorporating the TMPite into the reaction of TEOS. The deposition rate and the P concentration of films increased in proportion to the flow of TMPite. As the deposition temperature increased, the deposition rate of the films increased but the P concentration decreased. The fabricated films showed the increase of refractive index of 0.0019 per 1 wt% of P concentration. The nonuniformity of films was ${\pm}$7% in thickness and ${\pm}$0.5wt% in P concentration and we showed this'nonuniformity is due to the nonuniform transport of TMPite. The films of more than 10wt% P concentration developed phosphoric acid on its surface when exposed to air for long time.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.6
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• pp.870-879
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• 2000

An experimental investigation is conducted to improve a slot film cooling system which can be used for the cooling of gas turbine combustor liner. The tangential slots are constructed of discrete holes with different injection types which are the parallel, vertical, and combined to the slot lip. The investigation is focused on the coolant supply systems of normal-, parallel-, and counter-flow paths to the mainstream direction. A naphthalene sublimation technique has been employed to measure the local heat/mass transfer coefficients in a slot with various injection types and coolant feeding directions. The velocity distributions at the exit of slot lip for the parallel and vertical injection types are fairly uniform with mild periodical patterns with respect to the hole positions. However, the combined injection type increases the nonuniformity of flow distribution with the period equaling twice that of hole-to-hole pitch due to splitting and merging of the ejected flows. The secondary flow at the lip exit has uniform velocity distributions for the parallel and vertical injection types, which are similar to the results of a two-dimensional slot injection. In the results of local heat/mass transfer coefficient, the best cooling performance inside the slot is obtained with the vertical injection type among the three different injection types due to the effect of jet impingement. The lateral distributions of Sh with the parallel- and counter-flow paths are more uniform than the normal flow path. The averaged Sh with the injection holes are $2{\sim}5$ times higher than that of a smooth two-dimensional slot path.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.10
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• pp.885-891
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• 2010

Thermal management is important for enhancing the performance and durability of polymer electrolyte membrane fuel cells (PEMFCs) and is taken into account in the design of PEMFCs. In general, cooling pates with circulating liquid coolant (water) are inserted between several unit cells to exhaust the reaction heat from PEMFCs. In this study, computational fluid dynamics (CFD) simulations were performed to characterize the uniform cooling performance of parallel multipass serpentine flow fields (MPSFFs) that were used as coolant flow channels in PEMFCs. The cooling performances of conventional serpentine and parallel flow fields were also evaluated for the purpose of comparison. The CFD results showed that the use of parallel MPSFFs can help reduce the temperature nonuniformity, and thus, can favorably enhance the performance and durability of PEMFCs.

• 유체기계공업학회:학술대회논문집
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• 2000.12a
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• pp.211-218
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• 2000

Off-design experimental performance was investigated for a small centrifugal compressor, whose impeller diameter is about 125mm, used in an industrial gas turbine. Test rig was designed and manufactured with a radial inflow turbine and a combustor to supply driving power to the compressor. Static pressure was measured on the casing of the impeller, vaneless diffuser, vaned diffuser and volute. Total pressure was obtained using specially fabricated rakes at the vaned diffuser throat and exit. Circumferential nonuniformity was found, near surge, in the Impeller, vaned diffuser and volute region. Spanwise nonuniform flow from the impeller affected the total pressure defects in the vaned diffuser region. Static pressure distortion in the circumferential direction in the volute was found near surge, where the minimum occurred near 140 degree position.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.6
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• pp.1518-1528
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• 1995

The deformation and departure processes of a bubble attached to the wall are studied experimentally and numerically to understand the phenomena of the nucleate boiling heat transfer enhancement under DC electric field. An air-bubble is injected in a dielectric liquid with different electric fields generated by changing three types of electrode system (Type 1,2 and 3) in the bubble generator. Experimental variables are the electric field strength and the distance and the shape of the electrodes under DC electric field. From experimental results, it is observed that the bubble under Dc electric field is elongated in the same direction as the electric field and the contact angle increases. For the parallel plate electrode which generates a uniform electric field, bubble departure volume doesn't seem to decrease within our experimental range. However, when a needle is raised a few millimeters from the lower electrode to make a nonuniform electric field around the needle, bubble departure volume decreases continuously with the increase of an applied voltage. The reduction effect of bubble departure volume is the most effective under a strong nonuniform electric field generated with Type 3. As the nonuniformity of the electric field due to the shape of a electrode increases, the terminal velocity and the acceleration of a bubble increase largely. For the comparison with visualization results, the deformation of a bubble attached to the electrode is carried out by a numerical method. Numerical results show good agreement qualitatively with experimental results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.2
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• pp.225-232
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• 2012

A chemical reactor network (CRN) was developed for a lean premixed gas turbine combustor to predict the emission of pollutants such as NOx and CO. In this study, the predictions of NOx and CO emissions from lean premixed methane-air combustion in the gas turbine were carried out using CHEMKIN and a GRI 3.0 methane-air combustion mechanism, which includes the four NO formation mechanisms for various load conditions. The calculated results were compared with experimental data obtained from a modified test combustor to validate the model. The contributions of the four NO pathways were investigated for various load conditions. The effects of nonuniformity of the mass flux and of the equivalence ratio of the injector on the NOx formation were investigated, and a method of reducing the pollutant formation was suggested for the development of a sub-10 ppm gas turbine combustor.

• 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.

• Korean Journal of Agricultural and Forest Meteorology
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• v.11 no.4
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• pp.151-161
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• 2009

Configuration of soil hydraulic property is an essential component to understand the hydrological processes at the hillslope scale. In this study, we investigated temporal variations in pore development and soil hydraulic properties during the period from March to October in 2008. Characteristics for macropore flow and hydraulic conductivity were measured at two hillslopes: one is the hillslope located at the Buprunsa in Sulmachun watershed, and the other is the hillslope located in Gwangneung Research Forest. Vertical fluxes through macropore were measured using a tension infiltrometer at the depth of surface. The saturated hydraulic conductivities in March, June, July and September were relatively high compared to those in May and October. Temporal variations in several soil hydraulic features could be explained by the differences in vegetation activity and soil moisture content determined by antecedent precipitation. Particularly, the features of macropores had a substantial impact on hydraulic conductivity in the forest hillslope. The temporal nonuniformity of the soil hydraulic properties observed in this study manifests the dynamic features of hydrological processes in the hillslope scale and the experimental results will be useful to understand the internal hydrological processes in the mountainous hillslope.