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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
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Journal DOI :
The Korean Society of Mechanical Engineers
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Volume & Issues
Volume 21, Issue 12 - Dec 1997
Volume 21, Issue 11 - Nov 1997
Volume 21, Issue 10 - Oct 1997
Volume 21, Issue 9 - Sep 1997
Volume 21, Issue 8 - Aug 1997
Volume 21, Issue 7 - Jul 1997
Volume 21, Issue 6 - Jun 1997
Volume 21, Issue 5 - May 1997
Volume 21, Issue 4 - Apr 1997
Volume 21, Issue 3 - Mar 1997
Volume 21, Issue 2 - Feb 1997
Volume 21, Issue 1 - Jan 1997
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Natural convection cooling of discrete heaters with same heat generation in a vertical open top cavity
Yu, Gap-Jong ; Chu, Hong-Rok ; Kim, Byeong-Ha ; Choe, Byeong-Cheol ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 1~14
DOI : 10.22634/KSME-B.19188.8.131.52
Natural convection cooling of discrete heaters located in a two-dimensional vertical open top cavity is investigated experimentally. The five discrete heaters with same heat generation are located on the wall of the cavity. The heaters are arranged in two configurations; flush-mounted on a vertical wall and protruding from the wall about 4.5 mm. The materials used for the vertical walls are copper and epoxy-resin, and air is used as the cooling fluid. The temperature and flow fields in the cavity were visualized by means of Mach-Zehnder interferometer and smoke-method. Also, local temperature measurements are made along the vertical wall. Results are obtained for cavity aspect ratios of 4.6, 7.5 and 9.5 and modified Rayleigh numbers ranging from 10
. Results indicate that the cooling efficiency for the copper wall is superior to that of the epoxy-resin. For the epoxy-resin wall, the protrusion of the heaters plays a role in decreasing the heat transfer performance. The location of maximum temperature is significantly influenced by the wall materials and heater configurations. Correlations relating the Nusselt number to the modified Rayleigh number are proposed.
The optimal array of various heat-generating heaters located on one wall of a vertical open top cavity
Yu, Gap-Jong ; Chu, Hong-Rok ; Choe, Byeong-Cheol ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 15~23
DOI : 10.22634/KSME-B.19184.108.40.206
An experimental investigation of two-dimensional steady natural convection cooling in a vertical open top cavity with conducting side walls of finite thickness is presented. The various heat-generating discrete heaters are located on one vertical wall of the cavity. When each heater dissipates different amount of power, the purpose of the work is to obtain the optimal array condition of the heaters. The four cases of non-uniform heating conditions are considered. The temperature fields in the cavity were visualized by the interferometer and local temperatures of the vertical wall were measured by thermocouples. The heaters were arranged in two configurations: flush-mounted on a vertical wall or protruding from the wall about 4.5 mm. The vertical wall was constructed out of copper or epoxy-resin sheet. Experiments have been conducted for air with constant Prandtl number(Pr=0.7), the aspect ratio of 4.6, 7.5, 9.5, power input in the range of 0.9 W ~ 4.2 W. For the enhancement of the cooling effectiveness, the upper and lower of vertical wall would give the better position for the heaters of higher heat flux.
Phase change process of the initially subcooled material in a vertical cylinder
Baek, Yeong-Ryeol ; Lee, Jae-Heon ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 24~35
DOI : 10.22634/KSME-B.19220.127.116.11
Melting process inside in a vertical cylinder has been investigated numerically to observe heat transfer characteristics in the latent heat storage vessel applied to the thermal storage system. The time-dependent boundary fitted coordinate system was introduced to overcome the difficulty caused by the moving boundary. The present results are in good agreement with the available previous data when the initial subcooling effect of the solid phase is not considered. It is found that the melting is promoted by the natural convection, but is delayed by the initial subcooling effect of the solid phase.
A basic study on ignitor for lean burn
Lee, Sang-Jun ; Na, Seong-O ; Lee, Jong-Tae ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 36~48
DOI : 10.22634/KSME-B.1918.104.22.168
In order to establish the ignition system for lean burn, the influence of the number of spark plug, spark times and spark intervals on discharge pattern of spark energy on ignitability and combustion characteristics were evaluated. It showed that, ignitability remarkably increased with the case of multiple spark ignition system than with the case of single spark and the lean limit extended fuel/air equivalence ratio by 0.1, the increase of magnitude and lasting time of capacity component and inductance component was multi spark discharge in a row.
Calculation of a 2-D channel flow with a dimple
Choe, Seo-Won ; Baek, Yeong-Ho ; Kim, Du-Yeon ; Gang, Ho-Cheol ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 49~56
DOI : 10.22634/KSME-B.1922.214.171.124
Heat-transfer enhancement is seeked through modifications of fin surface. Real life plate-fin heat exchangers have complex three-dimensional geometries. Fins can have arrays of dimples and are attached to rows of penetrating tubes. To isolate the effect of surface modification, we model the real flow by a two-dimensional channel flow with a dimple on one side. The flow is analysed by solving the incompressible Navier-Stokes equation by a finite volume method on a generalized boundary-fitted coordinate. Results show a trapped vortex inside the dimple for all cases computed. Local maximum of Nusselt number occurs near the downstream end of the dimple, due to such a vortex. Location of the vortex does not change with respect to the wall temperature change, but moved downstream when Reynolds number increases. This, together with the results that in all cases vortex core is somewhat downstream of the dimple center, suggests that the mean flow above continuously feeds the kinetic energy to the recirculating flow. Heat transfer enhancement and pressure losses are studied through analysing the relevant dimensionless parameters like, Nusselt number and friction factor. In all cases computed, dimpled channel flow experiences less pressure loss than two-dimensional Poiseuille flow.
An analysis on the solidification process of alloy casting with a contact resistance
Kim, U-Seung ; Lee, Gwan-Su ; Kim, Gwang-Seon ; Im, Ik-Tae ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 57~67
DOI : 10.22634/KSME-B.19126.96.36.199
The solidification process of Al 4.5%Cu alloy is numerically studied in the presence of contact resistance between mold and cast. Natural convection is considered in the liquid and mushy regions. The porosity approach is applied to the mushy zone modeling and linear variation of the solid fraction on the temperature is assumed. Results show that the mushy region is wider in the case with a contact resistance compared to the perfect contact condition. The temperature of the cast with a temporal variation in the contact heat transfer coefficient changes very rapidly in the early stage of the casting process compared to that with constant contact heat transfer coefficient.
A numerical study on the transient operation of high temperature heat pipe with a switching heat source
Park, Jong-Heung ; Lee, Jae-Heon ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 68~78
DOI : 10.22634/KSME-B.19188.8.131.52
A numerical study on the transient vapor flow and heat transfer is performed to investigate the ideal switching operation of heat source in a high temperature heat pipe. The cylindrical 2-dimensional compressible laminar vapor flow is assumed for the vapor space and the conjugate heat transfer for the heat pipe wall, wick and vapor space is calculated. The different boundary conditions such as constant heat flux, convective or radiative boundary at the outer wall are used respectively to compare the influence of boundary conditions on the transient operation. The transient temperature profile and the internal flow of the entire pipe for the switching operation are described as a result. The results show that the transient time is not significantly affected by the boundary conditions at the outer wall in present study. During the transition, two independent flows are observed temporarily on the right side and left side of the heat pipe. It is also found that the trend of temperature variation in the vapor region is different from the variation in the wick and wall region.
A study of unsteady heat and mass transfer in the modified chemical vapor deposition process
Park, Gyeong-Sun ; Choe, Man-Su ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 79~88
DOI : 10.22634/KSME-B.19184.108.40.206
An analysis of unsteady heat and mass transfer in the Modified Chemical Vapor Deposition has been carried out including the effects of chemical reaction and variable properties. It was found that commonly used quasi-steady state assumption could be used to predict overall efficiency of deposition, however, the assumption would not provide detailed deposition profile. The present unsteady calculations of wall temperature profile and deposition profile have been compared with the existing experimental data and were in good agreement. The effects of variable torch speed were studied. Linearly varying torch speed case until time=120s resulted in much shorter tapered entry than the constant torch speed case.
Theoretical study on compression wave propagating in a sudden reduction duct
Kim, Hui-Dong ; Kim, Tae-Ho ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 89~98
DOI : 10.22634/KSME-B.19220.127.116.11
Compression waves propagating in a high speed railway tunnel impose large pressure fluctuations on the train body or tunnel structures. The pressure fluctuations can cause ear discomfort for the passengers and increase the aerodynamic resistance of trains. As a fundamental research to resolve the pressure wave phenomenon in the tunnel, a steady theory of Chester-Chisnell- Whitham was applied to a simple shock tube with a sudden cross-sectional area reduction to model trains inside the tunnel. The results of the present theoretical analysis were compared with the experiments of the shock tube. The results show that the reflected compression wave from the model becomes stronger as the strength of incident compression wave and the blockage ratio increase. However, the compression wave passing through the model is not strongly dependent on the blockage ratio. The theoretical results are in good agreement with the experiments.
An experimental study on flow distribution and mixing in impinging jets
Lee, Chung-Hun ; Jeong, Yeong-Ho ; Jeong, Seok-Ho ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 99~112
DOI : 10.22634/KSME-B.1918.104.22.168
Mixing process of impinging jets of liquid oxidizer and liquid fuel is simulated by using water and sodium carbonate (Na
) solution. The shapes of liquid sheets are visualized and flowrate distributions are measured by collecting droplets using measuring cells. Mixing charateristics are studied by using acid-base titration. Stable liquid sheets are formed and two liquid jets are well mixed for symmetric impinging jets. Similarity in flowrate distribution for various measuring heights is observed. For asymmetric impinging jets, liquid sheets become unstable as the difference in the velocities of jets increases. In some extreme cases, liquid sheets are not formed and the jets are separated. Dimensionless variables are adopted demonstrating similarly in flowrate distribution. Mixing characteristics vary significantly with experiment conditions.
A large scale model test to investigate the pressure drop and heat transer characteristics in the air side of two-row heat exchanger
Gang, Hui-Chan ; Kim, Mu-Hwan ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 113~124
DOI : 10.22634/KSME-B.1922.214.171.124
This work is performed to investigate the pressure drop and heat transfer characteristics in the air side of finned-tube heat exchanger for air conditioner. Experimental apparatus and method are described to simulate the heat exchanger performance by using the three times enlarged model. The pressure drop and heat transfer coefficient were measured and compared for the heat exchangers with a plane fin and a commercial strip fin. The measured data for the strip fin agree well with those of prototype within a few percentages. For the plane fin, the measured data had similar trend to Gray & Webb's correlation at high air velocity, however a new correlation is needed to give more accurate prediction at low air velocity. It is found that most heat was transferred around the front row of the two-row heat exchanger, and the ratio of thermal load at the front tube row was increased for decreasing air velocity.
Numerical study on extinction of premixed flames using local flame properties
Jeong, Dae-Heon ; Jeong, Seok-Ho ; Cho, P. ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 125~131
DOI : 10.22634/KSME-B.19126.96.36.199
The extinction of premixed flames under the influence of stretch is studied numerically. A wide range of fuel (hydrogen, ethylene, acetylene, methane, propane and methanol) and air mixtures are established in an opposed jet and their flame properties such as flame speed, flame thickness, thermal diffusivity, and stretch rate at extinction are computed. Computations are made using several chemical kinetic mechanism (Smooke, Kee et al. and Peters). The major result is that, in contrast to the various previous claims of extinction Karlovitz number varying over three orders of magnitude, it is found to be constant around two for all of the mixtures tested. That is, premixed flames are extinguished when the physical flow time decreases (due to increased stretch rate) to the point where it approximately equals the chemical reaction time. Here the relevant chemical reaction time is not the one computed using the one-dimensional flame properties as originally suggested in the formulation of Karlovitz number, but rather it is the one obtained using the stretched flame properties which fully reflect the effect of straining on the flame structure.
Spray characteristics of twin-fluid atomization using external-mixing sonic nozzles
Park, Byeong-Gyu ; Lee, Jun-Sik ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 132~139
DOI : 10.22634/KSME-B.19188.8.131.52
Spray characteristics of external mixing sonic twin-fluid atomization nozzles are investigated experimentally. Particle sizes are measured by the Fraunhofer diffraction method using the Malvern particle analyzer, and their radial distributions are obtained using the tomographical transformation technique. The spatial distribution of SMD shows that the drop size increases in the radial direction at a fixed liquid flow rate, and the distribution is getting uniform rapidly as the atomizing gas pressure increases. The SMD decreases as the liquid flow rate increases at a fixed GLR. It is found that the atomization efficiency of the flush type sonic nozzle is superior to that of protrusion type. The effect of laser beam diameter of the particle analyzer on the spatial SMD distribution is minor at present experimental conditions.
Correlation of the Wall Skin-Friction and Streamwise Velocity Fluctuations in a Turbulent Boundary Layer(I) -Analysis of Long-Time Averaged Space-Time Correlation-
Yang, Jun-Mo ; Yu, Jeong-Yeol ; Choe, Hae-Cheon ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 140~152
DOI : 10.22634/KSME-B.19184.108.40.206
A simultaneous measurement of the wall skin friction and near-wall streamwise velocity fluctuations is performed using hot film and hot wire anemometers to investigate the relation between them. Near-wall turbulence statistics measured with a hot-wire probe are in good agreement with previous results. Turbulence properties of the wall skin friction fluctuations measured with a hot film also show fairly good agreements with those measured by others except that rms level is lower in the present study. Long-time averaged space- time correlations show that the wall skin friction is highly correlated with a turbulence structure which is tilted from the wall in the streamwise direction. Tilting angles are obtained from the phase shifts between the wall skin-friction and streamwise velocity fluctuations. The convection velocity of the near-wall streamwise velocity obtained from the space-time correlation is in good agreement with that from the direct numerical simulation database.
An experimental study on instability and control of co-flow diffusion flames
Lee, Hyeon-Ho ; Hwang, Jun-Yeong ; Jeong, Seok-Ho ; Lee, Won-Nam ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 153~164
DOI : 10.22634/KSME-B.19220.127.116.11
Flame oscillation phenomena in a co-flow diffusion flame was experimentally studied with periodic fuel supply using a solenoid valve. The degree of excitation was controlled by changing the volume flux of fuel passing through the valve. Flame oscillation frequencies were measured utilizing a photodiode, a spectrum analyzer, video and high speed movies. Laser planar visualization was employed to study the correlation between the flame oscillation and the toroidal vortices. Observed are three regimes of flame oscillation, where the oscillation frequencies are for the multiples of excitation, the excitation itself and the flame natural oscillation. Both periods of natural oscillation and of excitation induced oscillation exist over one cycle of the excitation in the frequency multiplied regime. It is considered as an effect of balancing the influence of buoyancy driven vortex with that of excitation induced vortex near the excitation rate of 0.2. Flame shapes are become monotonous as increasing the excitation frequency to the range of over two fold of the natural oscillation. The flame oscillation can be modulated to the frequency of either multiples of excitation or excitation itself under certain conditions. This implies that the flame oscillation could be modulated to avoid the resonance frequency of the combustor, and shows the possibility of active control of the flame oscillation.
Experimental study to enhance cooling effects on total-coverage combustor wall
Jo, Hyeong-Hui ; Goldstein, R. J. ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 165~173
DOI : 10.22634/KSME-B.1918.104.22.168
The present study investigates heat/mass transfer for flow through perforated plates for application to combustor wall and turbine blade film cooling. The experiments are conducted for hole length to diameter ratios of 0.68 to 1.5, for hole pitch-to-diameter ratios of 1.5 and 3.0, for gap distance between two parallel perforated plates of 1 to 3 hole diameters, and for Reynolds numbers of 60 to 13, 700. Local heat/mass transfer coefficients near and inside the cooling holes are obtained using a naphthalene sublimation technique. Detailed knowledge of the local transfer coefficients is essential to analyze thermal stress in turbine components. The results indicate that the heat/mass transfer coefficients inside the hole surface vary significantly due to flow separation and reattachment. The transfer coefficient near the reattachment point is about four and half times that for a fully developed circular tube flow. The heat/mass transfer coefficient on the leeward surface has the same order as that on the windward surface because of a strong recirculation flow between neighboring jets from the array of holes. For flow through two perforated plate layers, the transfer coefficients on the target surface (windward surface of the second wall) affected by the gap spacing are approximately three to four times higher than that with a single layer.
Passive control of strength of shock wave
Choe, Yeong-Sang ; Gwon, Sun-Beom ; Jo, Cheol-Yeong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 174~184
DOI : 10.22634/KSME-B.1922.214.171.124
A shock wave, being an irreversible process, gives rise to entropy increase. A great deal of effort has been made to control shock wave and boundary layer interaction related to energy losses as well as problems of vibration and noise. In the present study, tests are performed on a roof mounted half circular arc in an indraft type supersonic wind tunnel to evaluate the effects of porosity, length and depth of cavity in passive control of shock wave on the attenuation of shock strength by reviewing the measured static pressures at the porous wall and cavity. Also the flow field is visualized by a Schlieren system. The results show that in the present study the porosity of 8% produced the largest reduction of pressure fluctuations and that for the same porosity, the strength of shock wave decreases with the increasings of the depth and length of cavity.
Effect of baffle parameters on heat transfer in shell-and-tube heat exchangers
Lee, Sang-Cheon ; Jo, Yeong-U ; Nam, Sang-Cheol ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 1, 1997, Pages 185~194
DOI : 10.22634/KSME-B.19126.96.36.199
An experimental study has been performed on the effect of baffle parameters on shell -side heat transfer in a conventional shell-and-tube heat exchanger. The baffle spacing distance and the number of baffle were varied to investigate the behavior of unequal baffle spacing correction factor which is appeared in the Bell Delaware method for prediction of the shell-side heat transfer coefficient. It was obvious that heat duties obtained from the experiment significantly deviated from those calculated by the conventional Bell-Delaware method. A new correlation of the unequal baffle spacing correction factor was developed. It was shown that the new correlation improves the accuracy of the Bell-Delaware method considerably. This result may induce the use of the Bell-Delaware method in developing a computer software for design of shell-and-tube heat exchangers.