• Carbon letters
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• v.6 no.2
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• pp.101-105
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• 2005

Like bamboo-sprouts after rains, numerous sub${\mu}m$-sized pyrocarbon whiskers growth on the Mullite ($3Al_2O_3{\cdot}2H_2O$) substrate could be observed through a looking glass during methane pyrolysis at the temperature of $1050^{\circ}C$ in this study. If the surface of substrate would be scrubbed strongly with iron metals, then finely sticked iron particles were more effective catalytic for nm-sized whisker growth. Numerous fine flakes of pyrolytic carbon were hanging by invisible nm-whiskers as like as small spiders hanging by a spiderweb. This is the identification of nm-sized whisker growth. Therefore if the pyrolysis would be stopped at the initial stage of the whisker growth, the primary lengthening growth was nm-sized whisker. So could we vary arbitrarily sizes of whisker from nm- to ${\mu}m$-sizes. But ${\mu}m$- and nm-whiskers grown with the different growth mechanism; the former was straight and the latter has twigs, The lengthening growth of whisker was depended on the flow pattern pyrolysis species on the active sites of substrate and on the growth duration. We could obtained straight whisker length of 10~20 ${\mu}m$/min during the primary growth and laboratory spiral whisker of 30~40 ${\mu}m$-diameter/hr during the secondary growth.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.4
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• pp.151-157
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• 2014

An algebraic scroll expander has been fabricated and tested in a R134a Rankine cycle with heat source of 20 kW. For the operating conditions of 20~26 bar and $90{\sim}93^{\circ}C$ at the expander inlet and 8~9 bar at the outlet, the expander produced the shaft output power of about 0.6~0.7 kW in the operating speed range of 1500~2000 rpm. These correspond to the expander efficiency of 40~45%. The volumetric efficiency increased with increasing of the expander speed, reaching to 80% at 2000 rpm. Comparing to numerical simulation results, mechanical efficiency from the test data was found to be considerably low by as much as 30%, indicating that reduction in the frictional loss should be made to improve the scroll expander efficiency.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.5
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• pp.440-446
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• 2012

A twisted cylinder has been newly designed by rotating the elliptic cross section along the spanwise direction in order to reduce the drag and vorticies in wake region. The flow around the twisted cylinder at a subcritical Reynolds number (Re) of 3000 is investigated to analyze the effect of twisted spiral pattern on the drag reduction and vortex suppression using large eddy simulation (LES). The instantaneous wake structures of the twisted cylinder are compared with those of a circular and a wavy cylinder at the same Re. The shear layer of the twisted cylinder covering the recirculation region is more elongated than that of the circular and the wavy cylinder. Successively, vortex shedding of the twisted cylinder is considerably suppressed, compared with those of the circular and the wavy cylinder. Consequently, the mean drag coefficient and the fluctuating lift of the twisted cylinder are less than those of the circular and the wavy cylinder.

• Journal of the Architectural Institute of Korea Planning & Design
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• v.35 no.5
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• pp.73-83
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• 2019

The purpose of this study is to analyze the spatial transformational patterns according to the spectator and the exhibition environment and to examine the role of 'the middle space' organically linking the exhibition space with MoA which is a representative example of 'sequential exhibition space'. The concept of sequential exhibition space in MoA is applied not only to building but also to extended continental concepts including neighborhood. MoA's exhibition space consists of the library area and the exhibition area. In particular, the spaces of library area perform a complex function as a quasi-exhibition space, and the exhibition spaces have variable spatial transformation through an associated structure of the library area and the educational area. The types of exhibition space those constitute the sequential exhibition space of MoA appear as 'Room type', 'Free plan type', and 'Gallery type'. Each exhibition space maintains independence, but it is changed according to the situation of exhibition. The flow is based on the spiral induction around the central void space, but with selective circulation considering the visitors. Therefore, through the transformation of the exhibition area and the division of the flow, the whole museum space appears as the area differentiation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1177-1189
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• 1994

This paper aims to develop the numerical model for prediction of the channel migration by analyzing of sediment and flow characteristics with patterns of channel in alluvial rivers. Flow in rivers constitutes to be the meandering or the braided form and rarely straight channel through morphologically stable patterns with mutual actions between the flowing water and bed materials. In order to develop the model for simulation of the channel migration, the channels are divided into two types with positive or negative sign by the direction of curvature radius of the centerline channel ($r_c$). That is, the single bend-channel consists of only one curvature of positive or negative sign and the multi-bend channel consists of two more curvatures of positive or negative sign, respectively. The model analyzes the sediment and flow characteristics under the influence of superelevation, spiral motion, irregularity in bed topography and depth-averaged velocity of channels. For reliability of this model, the single bend-channel and the multi bend channel are compared with experiment data in other models and the measured field data in the Keum-River, respectively. As a result, the both com parisians turn out to be excellent.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.216-227
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• 2004

A new cavitating model by using bubble size distribution based on bubbles-mass has been proposed. Both liquid and vapor phases are treated with Eulerian framework as a mixture containing minute cavitating bubbles. In addition vapor phase consists of various sizes of vapor bubbles, which are distributed to classes based on their mass. The bubble number-density for each class was solved by considering the change of the bubble-mass due to phase change as well as generation of new bubbles due to heterogeneous nucleation. In this method, the bubble-mass is treated as an independent variable, and the other dependent variables are solved in spatial coordinates and bubble-mass coordinate. Firstly, we employed this method to calculate bubble nucleation and growth in stationary super-heated liquid nitrogen, and bubble collapse in stationary sub-cooled one. In the case of bubble growth in super-heated liquid, bubble number-density of the smallest class based on its mass is increased due to the nucleation. These new bubbles grow with time, and the bubbles shift to larger class. Therefore void fraction of each class is increased due to the growth in the whole class. On the other hand, in the case of bubble collapse in sub-cooled liquid, the existing bubbles are contracted, and then they shift to smaller class. It finally becomes extinct at the smallest one. Secondly, the present method is applied to a cavitating flow around NACA00l5 foil. Liquid nitrogen and liquid oxygen are employed as working fluids. Cavitation number, $\sigma$, is fixed at 0.15, inlet velocities are changed at 5, 10, 20 and 50m/s. Inlet temperatures are 90K in case of liquid nitrogen, and 90K and 1l0K in case of liquid oxygen. 110K of oxygen is corresponding to the 90K of nitrogen because of the same relative temperature to the critical one, $T_{r}$=$T/T_c^{+}$. Cavitating flow around the NACA0015 foils was properly analyzed by using bubble size distribution. Finally, the method is applied to a cavitating flow in an inducer of the LE-7A hydrogen turbo-pump. This inducer has 3 spiral foils. However, for simplicity, 2D calculation was carried out in an unrolled channel at 0.9R cross-section. The channel moves against the fluid at a peripheral velocity corresponding to the inducer revolutions. Total inlet pressure, $Pt_{in}$, is set at l00KPa, because cavitation is not generated at a design point, $Pt_{in}$=260KPa. The bubbles occur upstream of the foils and collapse between them. Cavitating flow in the inducer was successfully predicted by using the bubble size distribution.

• Fire Science and Engineering
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• v.33 no.3
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• pp.56-62
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• 2019

This study examined effects of the operating characteristics of a pump according to the rotational speed of a pump and the change in flow rate when a centrifugal pump operates under the following conditions: regulated flow rate, head, rotational speed, and specific speed of 0.7 m/min, 8 m, 1750 rpm, an 182 (m, ㎥/min, rpm), respectively. The pump in the experiment did not have a guide vane and was connected directly to the rim, so that the rotational speed of the volute pump in a spiral or volute casing increased by 100 rpm from 1350 to 1750 rpm. The result of the relationship between the H-Q, L-Q, and 𝜂-Q characteristics and the dimensionless performance characteristics, such as the head coefficient, power coefficient and efficiency were studied. The change in pump performance could be estimated depending on the increase in the number of revolutions. The maximum efficiency of the pump was 52% with 1450 rpm, 0.165 ㎥/min flux, and 4.73 m of lift. The efficiency reached 50% with a maximum of 1750 rpm, 0.183 ㎥/min of flux, and 6.72 m of lift. The efficiency curve on the performance characteristics of the lift versus flux curve became oval not a curve from a quadratic equation that passes through the starting point according to the similarity law of the pump. Finally, when the flux coefficient increased, the power coefficient increased and the lift coefficient decreased. When the flux coefficient was 0.08, the maximum efficiency was 52%. Therefore, the change in flux affects the driving characteristics.

• Journal of Korean society of Dental Hygiene
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• v.8 no.1
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• pp.119-131
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• 2008

This study was peformed in order to find out the relationship between the causing factors and the production of each gas 01 oral malodor, to contribute the oral malodor control at dental clinic as well as to establish the effective application of malodor control project for public oral health program 127 patients from 20 to 40 years old who had been visited for preventive dental cares were participated for the study. Such items as caries status, periodontal status, salivary flow, viscosity, pH. Snyder test, plaque deposit and tongue plaque were checked through the oral examination in order to find out the contributing factors Hydrogen sulfide, Methyl mercaptan, Di-methyl sulfide and Ammonia gas components were checked with Oral-Chroma and Attain, the oral malodor check units. Not only the corelation coefficiencies but also the multi-way variance analysis were calculated between each causing factor and each component of oral malodor gases to estimate the contributing factors of the oral malodor. 1. There was no relationship between the caries status and each component pf the oral malodor such as sulfur compound or Ammonia, both in laboratory test and VAS test (pF0.05). It revealed negative relationship between Hydrogen sulfide and FT(rM-0.1904. pE0.05) as well as the VAS and FT (rM-0.210. pE0.05). S0, it was estimated that the less oral malador was recognized when caries state changed to filled state in Hydrogen sulfide laboratory test or VAS test 2. High relationship was showed between salivary flow and Hydrogen sulfide (rM-0.183, pM0.039), Methyl mercaptan(rM-0.234, p-0.008). Dimethyl sulfide(rM-0.234, pM0.008) and Ammonia(-0.361. pM0.001) gas(pE0.05). 3. There was a high relationship between M-PHP(Modified-Patient Hygiene Performance Index) and tong plaque all kinds of sulfide(rM0.249. pM0.005). Ammonia gas component(rM0.232, pM0.009). 4. It was found that considerable relationship was appeared between the periodontal status and Ammonia gas (rM0.274, pM0.002), so, it should be needed to control Ammonia. Such dental Cares as the prevention or early treatment of periodontal disease and the accelerating the salivary flow as well as reducing the amounts and activities of filament or spiral typed oral micro-organism were recommended for adults, not only for dental care program at the dental clinics but also for public health programs, in order to promote the oral health and quality of file for individual and community peoples.

• Journal of Korea Water Resources Association
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• v.52 no.10
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• pp.743-752
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• 2019

The flow in the meandering channel is characterized by the spiral motion of secondary currents that typically cause the erosion along the outer bank. Hydraulic structures, such as spur dike and groyne, are commonly installed on the channel bottom near the outer bank to mitigate the strength of secondary currents. This study is to investigate the effects of submerged vanes installed in a $90^{\circ}$ meandering channel on the development of secondary currents through three-dimensional numerical modeling using the hybrid RANS/LES method for turbulence and the volume of fluid method, based on OpenFOAM open source toolbox, for capturing the free surface at the Froude number of 0.43. We employ the second-order-accurate finite volume methods in the space and time for the numerical modeling and compare numerical results with experimental measurements for evaluating the numerical predictions. Numerical results show that the present simulations well reproduce the experimental measurements, in terms of the time-averaged streamwise velocity and secondary velocity vector fields in the bend with submerged vanes. The computed flow fields reveal that the streamwise velocity near the bed along the outer bank at the end section of bend dramatically decrease by one third of mean velocity after the installation of vanes, which support that submerged vanes mitigate the strength of primary secondary flow and are helpful for the channel stability along the outer bank. The flow between the top of vanes and the free surface accelerates and the maximum velocity of free surface flow near the flow impingement along the outer bank increases about 20% due to the installation of submerged vanes. Numerical solutions show the formations of the horseshoe vortices at the front of vanes and the lee wakes behind the vanes, which are responsible for strong local scour around vanes. Additional study on the shapes and arrangement of vanes is required for mitigate the local scour.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.3
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• pp.361-366
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• 2012

This paper proposes a low power capacitor cross-coupled 5.2 GHz band low noise amplifier(LNA) using the current-reused topology with the TSMC 0.18 ${\mu}m$ CMOS process. The proposed 5.2 GHz band LNA uses a capacitor cross-coupled $g_m$-boosting method for reducing current flow of circuit and a current-reused topology to decrease total power dissipation. The parallel LC networks are used to reduce size of spiral inductors. The simulation results show high gain of 17.4 dB and noise figure(NF) of 2.7 dB for 5.2 GHz.