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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Transactions of the Korean Society of Mechanical Engineers B
Journal Basic Information
Journal DOI :
The Korean Society of Mechanical Engineers
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Volume & Issues
Volume 25, Issue 12 - Dec 2001
Volume 25, Issue 11 - Nov 2001
Volume 25, Issue 10 - Oct 2001
Volume 25, Issue 9 - Sep 2001
Volume 25, Issue 8 - Aug 2001
Volume 25, Issue 7 - Jul 2001
Volume 25, Issue 6 - Jun 2001
Volume 25, Issue 5 - May 2001
Volume 25, Issue 4 - Apr 2001
Volume 25, Issue 3 - Mar 2001
Volume 25, Issue 2 - Feb 2001
Volume 25, Issue 1 - Jan 2001
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Characteristics of Turbulent Impinging and Wall Jet Flow for a Circular Nozzle with Various Exit Wall Thickness
Yang, Geun-Yeong ; Yun, Sang-Heon ; Son, Dong-Gi ; Choe, Man-Su ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 6, 2001, Pages 751~757
DOI : 10.22634/KSME-B.2001.25.6.751
An experimental study of impinging jet-flow structure has been carried out for a fully developed single circular jet impingement cooling on a flat plate, and the effect of the wall thickness at nozzle exit edge is investigated. Impinging jet flow structures have been measured by Laser-Doppler Velocimeter to interpret the heat transfer results presented previously by Yoon et al.(sup)(10) The peaks of heat transfer rate are observed near the nozzle edge owing to the radial acceleration of jet flow when the nozzle locates close to the impingement plate. The growth of the velocity fluctuations in the wall jet flow is induced by the vortices which originate in the jet shear layer, and consequently the radial distribution of local Nusselt numbers has a secondary peak at the certain radial position. As a wall of circular pipe nozzle becomes thicker for small nozzle-to-target distance, the entrainment can be inhibited, consequently, the acceleration of wall jet flow is reduced and the heat transfer rate decreases.
Experimental Study on the Slit Cover Hood for Reducing the Micro Pressure Waves in High-Speed Train-Tunnel Interfaces
Kim, Dong-Hyeon ; Min, Dong-Ho ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 6, 2001, Pages 758~765
DOI : 10.22634/KSME-B.2001.25.6.758
Purpose of the present is to investigate the food configuration at a tunnel entrance for reducing the micro pressure wave that is generated according to train speed. Two configurations were examined for tunnel of 0.5 km length. The experimental results show that a slit cover hood installed at the entrance of the tunnel reduces the maximum micro pressure wave by 41.2%, and a configuration with a slit cover hood installed at the entrance and a 45
slanted portal at the exit of the tunnel suppresses it by 47.7%.
Cooling Performance of a Notebook PC Mounted with Heat Spreader
No, Hong-Gu ; Im, Gyeong-Bin ; Park, Man-Heung ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 6, 2001, Pages 766~775
DOI : 10.22634/KSME-B.2001.25.6.766
Parametric study to investigate the cooling performance of a notebook PC mounted with heat spreader has been numerically performed. Two cases of air-blowing and air-exhaust at inlet were tested. The cooling effect on parameters such as, inlet velocities in the cases of air-blowing and air-exhaust, materials of heat spreader, and CPU powers were simulated for two cases. Cooling performance in the case of air-blowing was better than the case of air-exhaust.
Experimental Study of Boundary Layer Transition on an Airfoil Induced by Periodically Passing Wake (I) -A Time-Averaged Characteristic-
Park, Tae-Chun ; Jeon, U-Pyeong ; Gang, Sin-Hyeong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 6, 2001, Pages 776~785
DOI : 10.22634/KSME-B.2001.25.6.776
Hot-wire measurements are performed in boundary layers developing on a NACA0012 airfoil over which wakes pass periodically. The Reynolds number based on chord length of the airfoil is 2
10(sup)5 and the wakes are generated by circular cylinders rotating clockwise and counterclockwise around the airfoil. This paper and its companion Part II describe the phenomena of wake-induced transition of the boundary layers on the airfoil using measured data; phase-and time-averaged streamwise mean velocities, turbulent fluctuations, integral parameters and wall skin frictions. This paper describes the background and facility together with results of time-averaged quantities. Due to the passing wake with mean velocity defects and high turbulence intensities, the laminar boundary layer is periodically disturbed at the upstream station and becomes steady-state transitional boundary layer at the downstream station. The velocity defect in the passing wake changes the local pressure at the leading of the airfoil, significantly affects the time-mean pressure distribution on the airfoil and eventually, has influence on the transition process of the boundary layer.
Experimental Study of Boundary Layer Transition on an Airfoil Induced by Periodically Passing Wake (II) -A Phase-Averaged Characteristic-
Park, Tae-Chun ; Jeon, U-Pyeong ; Gang, Sin-Hyeong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 6, 2001, Pages 786~798
DOI : 10.22634/KSME-B.2001.25.6.786
This paper describes the phenomena of wake-induced transition of the boundary layers on a NACA0012 airfoil using measured phase-averaged data. Especially, the phase-averaged wall shear stresses are reasonably evaluated using the principle of Computational Preston Tube Method. Due to the passing wake, the turbulent patch is generated in the laminar boundary layer on the airfoil and the boundary layer becomes temporarily transitional. The patches propagate downstream with less speed than free-stream velocity and merge with each other at further down stream station, and the boundary layer becomes more transitional. The generation of turbulent patch at the leading edge of the airfoil mainly depends on velocity defects and turbulent intensity profiles of passing wakes. However, the growth and merging of turbulent patches depend on local streamwise pressure gradients as well as characteristics of turbulent patches. In this transition process, the present experimental data show very similar features to the previous numerical and experimental studies. It is confirmed that the two phase-averaged mean velocity dips appear in the outer region of transitional boundary layer for each passing cycle. Relatively high values of the phase-averaged turbulent fluctuations in the outer region indicate the possibility that breakdown occurs in the outer layer not near the wall.
Application of Miniature Heat Pipe for Notebook PC Cooling
Mun, Seok-Hwan ; Hwang, Geon ; Choe, Tae-Gu ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 6, 2001, Pages 799~803
DOI : 10.22634/KSME-B.2001.25.6.799
Miniature heat pipe(MHP) with woven-wired wick was used to cool the CPU of a notebook PC. The pipe with circular cross-section was pressed and bent for packaging the MHP into a notebook PC with very limited compact packaging space. A cross-sectional area of the pipe is reduced about 30% as the MHP with 4mm diameter is pressed to 2mm thickness. In the present study a performance test has been performed in order to review varying of operating performance according to pressed thickness variation and heat dissipation capacity of MHP cooling module that is packaged on a notebook PC. New wick type was considered for overcoming low heat transfer limit when MHP is pressed to thin-plate. The limiting thickness or pressing is shown to be within the range of 2mm∼2.5mm through the performance test with varying the pressing thickness. When the wall thickness of 0.4mm is reduced to 0.25mm for minimizing conductive thermal resistance through the wall of heat pipe, heat transfer limit and thermal resistance of MHP were improved about 10%. In the meantime, it is shown that the thermal resistance and heat transfer limit for the MHP with central wick type are higher than those of MHP with existing wick types. The results of performance test for MHP cooling modules with woven-wired wick to cool a notebook PC shows the stability as cooling system since T(sub)j(Temperature of Processor Junction) satisfy a demand condition of 0∼100
under 11.5W of CPU heat.
Transition of Natural Convective Flows in a Horizontal Cylindrical Annulus: Pr=0.2
Yu, Ju-Sik ; Ha, Dae-Hong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 6, 2001, Pages 804~810
DOI : 10.22634/KSME-B.2001.25.6.804
Transition of flows in natural convection in a horizontal cylindrical annulus is investigated for the fluid with Pr=0.2. The unsteady streamfunction-vorticity equation is solved with finite difference method. As Rayleigh number is increased, the steady crescent-shaped eddy flow bifurcates to a time-periodic flow with like-rotating eddies. After the first Hopf bifurcation, however, a reverse transition from oscillatory to a steady flow occurs by the flow pattern variation. Hysteresis phenomenon occurs between the solution branches of up-scan and down-scan stages, and dual solutions with one steady and one oscillatory flow are found. Overall Nusselt of the flows at the flows at the down-scan stage is greater than that at the up-scan stage.
A Study on an Atomization Model of a High-Pressurized Liquid Jet with a Stability Theory
Kim, Hong-Seok ; Seong, Nak-Won ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 6, 2001, Pages 811~818
DOI : 10.22634/KSME-B.2001.25.6.811
The wave characteristics for a non-reacting high-speed liquid jet were investigated using a linear stability theory. In this study, 2-D incompressible viscid momentum equation for a liquid jet was considered, and the effects of injection parameters, such as Weber number, Reynolds number, and density ratio, on the wave characteristics were investigated. With the wavelength obtained from the stability analysis, the atomization model was suggested. The droplet sizes after breakup were determined by the wavelengths of fast growing waves, and the mass of the shed droplets was determined by the breakup time derived by ORouke et al. It was found that in comparison with measurements of diesel fuel spray, the results of calculation had a similar trend of the decrease of overall SMD with the increase of Reynolds number.
A Study on the Three Dimensional Statistical Turbulent Flow Characteristics Around a Small-Sized Axial Fan for Refrigerator
Kim, Jang-Gwon ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 6, 2001, Pages 819~828
DOI : 10.22634/KSME-B.2001.25.6.819
The operating point of a small-sized axial fan is strongly dependent upon the system resistance. Therefore, the turbulent flow characteristics around a small-sized axial fan may change significantly according to the operating point. This study represents three-dimensional turbulent flow characteristics around a small-sized axial fan measured at the ideal design point
=0.25, which is equivalent to the maximum total efficiency point, by using three dimensional fiber-optic type LDA system. This LDA system is composed of a 5 W Argon-ion laser, two optics in back-scatter mode, three BSAs, a PC, and a three-dimensional automatic traversing system. A kind of paraffin fluid is used to supply particles by means of fog generator. Mean velocity profiles downstream of a small-sized axial fan along the radial distance show that the streamwise and the tangential components exist in a predominant manner, while the radial component has a small scale distribution and shows the inflection which its flow direction is inward or outward. Moreover, the turbulent intensity profiles show that the radial component exists the most greatly among turbulent energies.
A Finite Element Formulation for the Inverse Estimation of an Isothermal Boundary in Two-Dimensional Slab
Kim, Seon-Gyeong ; Heo, Hun ; Lee, U-Il ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 6, 2001, Pages 829~836
DOI : 10.22634/KSME-B.2001.25.6.829
A dependable boundary reconstruction technique is proposed. The finite element method is used for the analysis of the direct heat conduction problem to realize the deformable grid system. An appropriate strategy for grid update is suggested. A complete sensitivity analysis is performed to obtain the derivatives required for restoration of the optimal boundary. With the result of the sensitivity analysis, the unknown boundary is sought using the sequential quadratic programming. The method is applied to reconstruction of boundaries with sinusoidal, step, and cavity form. The overall performance of the proposed method is examined by comparison between the estimated the exact boundaries.
A Fundamental Study of Supersonic Coaxial Jets for Gas Cutting
Lee, Gwon-Hui ; Gu, Byeong-Su ; Kim, Hui-Dong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 6, 2001, Pages 837~844
DOI : 10.22634/KSME-B.2001.25.6.837
Jet cutting technology currently makes use of a generic supersonic gas jet to improve the cutting speed and performance. In order to get a better understanding of the flow characteristics involved in the supersonic jet cutting technology, the axisymmetric Navier-Stokes equations have been solved using a fully implicit finite volume method. Computations have been conducted to investigate some major characteristics of supersonic coaxial turbulent jets. An assistant gas jet has been imposed on the primary gas jet to simulate realistic jet cutting circumstance. The pressure and the temperature ratios of the primary and assistant gas jets are altered to investigate the major characteristics of the coaxial jets. The total pressure and Mach number distributions, shock wave systems, and the jet core length which characterize the coaxial jet flows are strongly affected by the pressure ratio, but not significantly dependent on the total temperature ratio. The assistant gas jet greatly affects the basic flow characteristics of the shock system and the core length of under and over-expanded jets.
Evaporation Cooling of Single Droplet on a Heated Solid Surface
Yu, Gap-Jong ; Bang, Chang-Hun ; Kim, Jeong-Su ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 6, 2001, Pages 845~852
DOI : 10.22634/KSME-B.2001.25.6.845
The characteristics of evaporation cooling of single droplet on a heated surface were studied experimentally. The two kinds of heater modules were tested to measure cooling characteristics of metal surface (high conductivity) and Teflon surface (low-energy surface, low conductivity). The results showed that time averaged heat flux during droplet evaporation increased exponentially with initial surface temperatures of brass, copper and steel. The heat flux and evaporation time did not varied with metal conductivities. However, the temperature drop after the deposition of droplet was larger on Teflon than on the metals. Thus, the correlation of interface temperature between liquid droplet and metal surface was proposed as a function of the initial surface temperature of heating materials, which could be applied to both metal and non-metal ones.
Extension of Topological Improvement Procedures for Triangular Meshes
Maeng, Ju-Seong ; Han, Seok-Yeong ; Choe, Hyeong-Il ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 6, 2001, Pages 853~859
DOI : 10.22634/KSME-B.2001.25.6.853
This paper describes the extended topological clean up procedures to improve the quality of unstructured triangular meshes. As a postprocessing step, topological improvement procedures are applied both for elements that are interior to the mesh and for elements connected to the boundary and then Laplacian-like smoothing is used by default. Previous clean up algorithms are limited to eliminate the nodes of degree 3,4,8,9,10 and pairs of nodes of degree 5. In this study, new clean up algorithms which minimize the triple connection structures combined with degree 5 and 7 (ie ; 5-7-5, 7-7-5, 7-5-7 etc) are added. The suggested algorithms are applied to two example meshes to demonstrate the effectiveness of the approach in improving element quality in a finite element mesh.
Experimental Study on R-22 Condensation Heat Transfer Characteristic in Plate and Shell Heat Exchanger
Seo, Mu-Gyo ; Park, Jae-Hong ; Kim, Yeong-Su ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 6, 2001, Pages 860~867
DOI : 10.22634/KSME-B.2001.25.6.860
In this study, condensation heat transfer experiments were conducted with plate and shell heat exchangers(P&SHE) using R-22. An experimental refrigerant loop has been established to measure the condensation heat transfer coefficient of R-22 in a vertical P&SHE. Two vertical counter flow channels were formed in the P&SHE by three plates of geometry with a corrugated trapezoid shape of a chevron angle of 45°. Downflow of the condensing R-22 in one channel releases heat to the cold upflow of water in the other channel. The effect of the refrigerant mass flux, average heat flux, system pressure and vapor quality of R-22 on the measured data were explored in detail. The results indicate that at a higher vapor quality the condensation heat transfer coefficients are significantly higher. A rise in the refrigerant mass flux causes an increase in the h(sub)r. Also, a rise in the average heat flux causes an increase in the h(sub)r. Finally, at a higher system pressure the h(sub)r is found to be slightly lower. Correlation is also provided for the measured heat transfer coefficients in terms of the Nusselt number.
Average Droplet Size Distribution of a GDI Spray by Simultaneous Fluorescence/Scattering Image Technique
Gwak, Su-Min ; Ryu, Gyeong-Hun ; Choe, Dong-Seok ; Kim, Deok-Jul ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 6, 2001, Pages 868~875
DOI : 10.22634/KSME-B.2001.25.6.868
The objective of this study is to investigate the average droplet size distributions of a GDI spray by simultaneous fluorescence/scattering image technique. GDI engine is recently very popular because of high engine efficiency and low emissions. However, the injectors must have good spray characteristics because the fuel is directly injected into the cylinder. The fuel mixtures used in this study were 2% of fluorobenzene, 9% of DEMA(diethyl-methyl-amine) and 89% of hexane by volume. The system for obtaining 2-D fluorescence/scattering images of fuel spray was constituted of a laser sheet, a doubling prism, optical filters, and an ICCD camera. Using the ratio of the fluorescence to the scattering intensities, SMD distributions were obtained. SMD measured by the technique was compared with that obtained by PDA. It was found that average droplet size was bigger at spray center in the early stage of injection and at the outer periphery of the spray in the late stage of injection.