• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.2
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• pp.288-297
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• 2000

This paper describes the results of an experimental investigation of the flow characteristics and the heat transfer rate on a surface by interaction of a pair of vortices. The test facility consists of a boundary-layer wind tunnel with a vortex introduced into the flow by half-delta wings(vortex generators) protruding from the surface. In order to control the strength of the two longitudinal vortices, the angles of attack of the vortex generators are varied from 20 degree to 45 degree, but spacings between the vortex generators are fixed to 4 cm. The 3-dimensional mean velocity downstream of the vortex generators is measured by a five-hole pressure probe, and the hue-capturing method using the thermochromatic liquid crystals has been used to provide the local distribution of the heat transfer coefficient. By using the method mentioned above, the following conclusions are obtained from the present experiment. The boundary layer is thinned in the regions where the secondary flow is directed toward the wall and thickened where it is directed away from the wall. The peak augmentation of the local heat transfer coefficient occurs in the downwash region near the point of minimum boundary-layer thickness. Streamwise distributions of averaged Stanton number on the measurement planes show very similar trends for all the cases(${\beta}=20^{circ},\;30^{\circ}\;and\;45^{\circ}$).

• The Journal of Korean Physical Therapy
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• v.22 no.6
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• pp.77-83
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• 2010

Purpose: The aim of this study was to do numerical analysis of the wavelength dependence in low level laser therapy (LLLT) using a finite element method (FEM). Methods: Numerical analysis of heat transfer based on a Pennes' bioheat equation was performed to assess the wavelength dependence of effects of LLLT in a single layer and in multilayered tissue that consists of skin, fat and muscle. The three different wavelengths selected, 660 nm, 830 nm and 980 nm, were ones that are frequently used in clinic settings for the therapy of musculoskeletal disorders. Laser parameters were set to the power density of 35.7 W/$cm^2$, a spot diameter of 0.06 cm, and a laser exposure time of 50 seconds for all wavelengths. Results: Temperature changes in tissue based on a heat transfer equation using a finite element method were simulated and were dominantly dependent upon the absorption coefficient of each tissue layer. In the analysis of a single tissue layer, heat generation by fixed laser exposure at each wavelength had a similar pattern for increasing temperature in both skin and fat (980 nm > 660 nm > 830 nm), but in the muscle layer 660nm generated the most heat (660 nm ${\gg}$ 980 nm > 830 nm). The heat generation in multilayered tissue versus penetration depth was shown that the temperature of 660 nm wavelength was higher than those of 830 nm and 980 nm Conclusion: Numerical analysis of heat transfer versus penetration depth using a finite element method showed that the greatest amount of heat generation is seen in multilayered tissue at = 660 nm. Numerical analysis of heat transfer may help lend insight into thermal events occurring inside tissue layers during low level laser therapy.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.719-725
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• 1997

This paper presents results of experimental studies on the heat transfer and solidification of the molten metal pool with overlying coolant with boiling. The metal pool is heated from the bottom surface and coolant is injected onto the molten metal pool. As a result, the crust, which is a solidified layer, may form at the top of the molten metal pool. Heat transfer is accomplished by a conjugate mechanism, which consists of the natural convection of the molten metal pool, the conduction in the crust layer and the convective boiling heat transfer in the coolant. This work examines the crust formation and the heat transfer rate on the molten metal pool with boiling coolant. The simulant molten pool material is tin (Sn) with the melting temperature of 232$^{\circ}C$. Demineralized water is used as the working coolant. The crust layer thickness was ostensibly varied by the heated bottom surface temperature of the test section, but not much affected by the coolant injection rate. The correlation beかeon the Nusselt number and the Rayleigh number in the molten metal Pool region of this study is compared against the crust formation experiment without coolant boiling and the literature correlations. The present experimental results are higher than those from the experiment without coolant boiling, but show general agreement with the Eckert correlation, with some deviations in the high and low ends of the Rayleigh number. This discrepancy is currently attributed to concurrent rapid boiling of the coolant on top of the metal layer.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.223-224
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• 2002

The mechanisms of formation of transfer film under the condition of wear of Steel AISI1020 by natural rubber were investigated. The transfer film was observed and the formation mechanisms were clarified. The formation process of transfer film on the worn surface of the steel could be divided into two stages. Firstly, the adhesive layer emerged on the worn surface of the steel by adhesion of natural rubber. in which the macromolecular chains of natural rubber joined to the surface of the steel by Van der Waals' force. And then, the iron atom and metal oxide reacted with the macromolecular of natural rubber in the adhesive layer and produced Fe-polymer compound. As a result, the transfer film was formed on the worn surface of the steel. The transfer film was joined to the worn surface of the steel by the chemical bonds and electrostatic force.

• Journal of Broadcast Engineering
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• v.26 no.6
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• pp.809-812
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• 2021

Air bubbles which may be generated during the PCB coating process can be a major cause of malfunction. so it is necessary to detect the bubbles in advance. In previous studies, candidates for bubbles were extracted using the brightness characteristics of bubbles, and the candidates were verified using CNN(Convolutional Neural Networks). In this paper, we propose a bubble detection method using a transfer learning-based CNN model. The VGGNet is adopted and sigmoid is used as a classification layer, and the last convolutional layer and classification layer are trained together when transfer learning is applied. The performance of the proposed method is F1-score 0.9044, which shows an improvement of about 0.17 compared to the previous study.

• Journal of the Korean Applied Science and Technology
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• v.32 no.2
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• pp.232-239
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• 2015

In this paper, we study the dry transfer technology utilizing PDMS (Polydimethylsiloxane) stamp of a large single-layer graphene grown on Cu-foil as catalytic metal by using Chemical Vapor Deposition (CVD). By changing the surface property of the target substrate through $UV/O_3$ treatment, we can transfer the graphene on the target substrate while minimizing mechanical damages of graphene layer. Multi-layer (1~4 layers) graphene was stacked on $SiO_2/Si$ wafer successfully by repeating thetransfer method/process and then optical transmittance and sheet resistance of graphene layers have been measured as a quality assessment.

• Membrane and Water Treatment
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• v.3 no.3
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• pp.151-168
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• 2012

Gas sparging is one of the techniques used to control the concentration polarization during ultrafiltration. In this work, the effects of gas sparging in stratified flow regime were investigated during gel layer controlling cross flow ultrafiltration in a rectangular channel. Synthetic solution of pectin was used as the gel forming solute. The liquid and gas flow rates were selected such that a stratified flow regime was prevalent in the channel. A mass transfer model was developed for this system to quantify the effects of gas flow rates on mass transfer coefficient (Sherwood number). The results were compared with the case of no gas sparging. Gas sparging led to an increase of mass transfer coefficient by about 23% in this case. The limitation of the developed model was also evaluated and it was observed that beyond a gas flow rate of 20 l/h, the model was unable to explain the experimental observation, i.e., the decrease in permeate flux with flow rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.8
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• pp.1131-1139
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• 2001

Experimental results are presented, which describe the effect of blowing ratio on film cooling from two rows of holes with opposite orientation angles. The inclination angle is fixed at 35°, and the orientation angles are set to be 45°for the downstream row, and -45°for the upstream row. The studied blowing ratios are 0.5, 1.0 and 2.0. The boundary layer temperature distributions are measured using thermocouple at two downstream locations. Detailed adiabatic film cooling effectiveness and heat transfer coefficient distributions are measured with TLC(Thermochromic Liquid Crystal). The adiabatic film cooling effectiveness and heat transfer coefficient distributions are discussed in connection with the injectant behaviors inferred from the boundary layer temperature distributions. Film cooling performance, represented by heat flux is evaluated from the adiabatic film cooling effectiveness and heat transfer coefficient data. The results show that the investigated geometry provides improved film cooling performance at the high blowing ratios of 1.0 and 2.0.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.11
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• pp.1192-1198
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• 2004

Hole transporting polymer(poly［N-(p-diphenylamine)phenylmethacrylamide］, PDPMA) was doped with nile red dye at various concentrations to study the influence of doping on the energy transfer during light emitting processes. Organic LEDs composed of ITO/blend(PDPMA -nile red)/ Alq$_3$/Al as well as thin films of blend(PDPMA -nile red)/ Alq$_3$ were manufactured for investigating photoluminescence, electroluminescence, and current-voltage characteristics. Atomic Force Microscopy was also used to observe surface morphology of the blend films. It was found that such doping. significantly influences the efficiency of the energy transfer from the Alq$_3$ layer to blended layer and the optical/electrical properties could be optimized by choosing the right concentration of the dye molecule. The results also showed a interesting correlation with the morphological aspect, i.e. the optimum luminescence at the concentration with the least surface roughness. When the concentration of nile red was 0.8 wt%, the maximum energy transfer could be achieved.

• Journal of the Korean earth science society
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• v.23 no.1
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• pp.59-71
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• 2002

Theoretical models of radiative transfer are developed to simulate the 85 GHz brightness temperature (T85) observed by the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) radiometer as a function of rain rate. These simulations are performed separately over regions of the convective and stratiform rain. TRMM Precipitation Radar (PR) observations are utilized to construct vertical profiles of hydrometeors in the regions. For a given rain rate, the extinction in 85 GHz due to hydrometeors above the freezing level is found to be relatively weak in the convective regions compared to that in the stratiform. The hydrometeor profile above the freezing level responsible for the weak extinction in convective regions is inferred from theoretical considerations to contain two layers: 1) a mixed (or mixed-phase) layer of 2 km thickness with mixed-phase particles, liquid drops and graupel above the freezing level, and 2) a layer of graupel extending from the top of the mixed layer to the cloud top. Strong extinction in the stratiform regions is inferred to result from slowly-falling, low-density ice aggregates (snow) above the freezing level. These theoretical results are consistent with the T85 measured by TMI, and with the rain rate deduced from PR for the convective and stratiform rain regions. On the basis of this study, the accuracy of the rain rate sensed by TMI is inferred to depend critically on the specification of the convective or stratiform nature of the rain.