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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 22, Issue 7 - Jul 1998
Volume 22, Issue 6 - Jun 1998
Volume 22, Issue 5 - May 1998
Volume 22, Issue 4 - Mar 1998
Volume 22, Issue 3 - Mar 1998
Volume 22, Issue 2 - Feb 1998
Volume 22, Issue 1 - Jan 1998
Volume 22, Issue 10 - 00 1998
Selecting the target year
Transient heat transfer in thin films
Bae, Cheol-Ho ; Jeong, Mo ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 1, 1998, Pages 1~11
DOI : 10.22634/KSME-B.19188.8.131.52
For the analysis of phonon heat transfer within short time and spatial scales, conventional macroscopic heat conduction equations with jump boundary conditions are tried and the results are compared to those of equation of phonon radiative transport(EPRT), which is one of microscopic transport equation. In transient state the macroscopic temperatures show far different behavior from EPRT. In steady state the hyperbolic temperatures with temperature jump at the wall from time relaxation model agrees well with EPRT temperatures. Since EPRT is also an approximate form of microscopic transport equation and there are no experimental results to verify the proposed model in this study, we can not conclude whether the approaching method from this study is valid or not. To the authors' knowledge, there are no experimental results available which can be used to test the validity of these models. Such an experiment, while difficult to conduct, would be invaluable.
An experimental study on the secondary flow and losses in turbine cascades
Jeong, Yang-Beom ; Sin, Yeong-Ho ; Kim, Sang-Hyeon ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 1, 1998, Pages 12~24
DOI : 10.22634/KSME-B.19184.108.40.206
The paper presents the mechanism of secondary flows and the associated total pressure losses occurring in turbine cascades with turning angle of about 127 and 77 degree. Velocity and pressure measurements are taken in seven traverse planes through the cascade passage using a prism type five hole probe. Oil-film flow visualization is also conducted on blade and endwall surfaces. The characteristics of the limiting streamlines show that the three dimensional separation is an important flow feature of endwall and blade surfaces. The larger turning results in much stronger contribution of the secondary flows to the loss developing mechanism. A large part of the endwall loss region at downstream pressure side is found to be very thin when compared to that of the cascade inlet and suction side endwall. Evolution of overall loss starts quite early within the cascade and the rate of the loss growth is much larger in the blade of large turning angle than in the blade of small turning angle.
Flow visualization Study on the Turbulent Mixing of Two Fluid Streams(I)
Kim, Gyeong-Cheon ; Sin, Dae-Sik ; Lee, Bu-Hwan ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 1, 1998, Pages 25~33
DOI : 10.22634/KSME-B.19220.127.116.11
An experimental study has been carried out to obtain optimal conditions for turbulent mixing of two fluid streams at various angle branches by a flow visualization method. The main purpose of this study is the utilization of flow visualization method as a fast and efficient way to find the optimal mixing conditions when several flow control parameters are superimposed. It is verified that the optimal conditions estimated by flow visualization method have good agreement with the concentration field measurements. The results demonstrate that the diameter ratio is mainly attributed to the mixing phenomena than the branch pipe angle and the Reynolds number. The most striking fact is that there exists the best diameter ratio, d/D.ident. O.17, which requires the minimum momentum ratio in the range of the present experiment. The velocity ratio for the optimal mixing condition has a value within 2 to 16 according to the different flow parameters.
Large eddy simulation of turbulent flows in a grooved channel
Yang, Gyeong-Su ; Kim, Do-Hyeong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 1, 1998, Pages 34~49
DOI : 10.22634/KSME-B.1918.104.22.168
In this study, turbulent flows in a grooved channel are numerically investigated by Large Eddy Simulation (LES). Especially, a parametric study is carried out to study effects of length and depth of a groove on large-scale flow structures. For one test case, comparison of LES results with those of DNS reveals a good agreement even though the number of grid points of LES is only 6.5% of that of DNS. This confirms that LES is a suitable tool for a parametric study of turbulent flows. The subsequent parametric study using LES shows that the large-scale turbulent structures are significantly affected by the geometry of the groove. Especially, when the length of the groove is short such that the recirculation region occupies the entire groove, the turbulent flow in the groove becomes very weak in both mean and fluctuation quantities.
Formation of a paraffin slurry and its convective heat transfer in a circular pipe
Choe, Eun-Su ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 1, 1998, Pages 50~60
DOI : 10.22634/KSME-B.1922.214.171.124
As a method to develop an enhanced heat transfer fluid, the fine particles of a phase-change material were mixed with a conventional heat transfer fluid. Paraffin, which can be obtained easily in domestic market, was used for the phase-change material and water was used as a carrier fluid. Fine liquid particles of paraffin were formed in water as an emulsion by using an emulsifier, and they were cooled rapidly to become solid particle, resulting in paraffin slurry. The average diameter of produced solid particles was inversely proportional to the amount of the added emulsifier, which was theoretically proved. The produced paraffin slurry was tested thermally in heat transfer test section having a constant-heat-flux boundary condition. The test section was made of a circular stainless-steel pipe, which was directly heated by the power supply having a maximum of 50 Volts-500 Amperes. DSC(Differential scanning calorimeter) tests showed that two kinds of phase change were involved in the melting of paraffin, and it was explained in two different ways. A five- region-melting model was developed by extending the conventional three-region-melting model, and was used to obtain the local bulk mean temperatures of paraffin slurry in the heating test section. The local heat transfer coefficient showed a maximum where the bulk mean temperature of the paraffin slurry reached at the melting temperature of paraffin.
Particle deposition on a rotating disk in application to vapor deposition process (VAD)
Song, Chang-Geol ; Hwang, Jeong-Ho ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 1, 1998, Pages 61~69
DOI : 10.22634/KSME-B.19126.96.36.199
Vapor Axial Deposition (VAD), one of optical fiber preform fabrication processes, is performed by deposition of submicron-size silica particles that are synthesized by combustion of raw chemical materials. In this study, flow field is assumed to be a forced uniform flow perpendicularly impinging on a rotating disk. Similarity solutions obtained in our previous study are utilized to solve the particle transport equation. The particles are approximated to be in a polydisperse state that satisfies a lognormal size distribution. A moment model is used in order to predict distributions of particle number density and size simultaneously. Deposition of the particles on the disk is examined considering convection, Brownian diffusion, thermophoresis, and coagulation with variations of the forced flow velocity and the disk rotating velocity. The deposition rate and the efficiency directly increase as the flow velocity increases, resulting from that the increase of the forced flow velocity causes thinner thermal and diffusion boundary layer thicknesses and thus causes the increase of thermophoretic drift and Brownian diffusion of the particles toward the disk. However, the increase of the disk rotating speed does not result in the direct increase of the deposition rate and the deposition efficiency. Slower flow velocity causes extension of the time scale for coagulation and thus yields larger mean particle size and its geometric standard deviation at the deposition surface. In the case of coagulation starting farther from the deposition surface, coagulation effects increases, resulting in the increase of the particle size and the decrease of the deposition rate at the surface.
Performance prediction of mixed-flow pumps
O, Hyeong-U ; Yun, Ui-Su ; Jeong, Myeong-Gyun ; Ha, Jin-Su ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 1, 1998, Pages 70~78
DOI : 10.22634/KSME-B.19188.8.131.52
The present study has tested semi-empirical loss models for a reliable performance prediction of mixed-flow pumps with four different specific speeds. In order to improve the predictive capabilities, this paper recommends a new internal loss model and a modified parasitic loss model. The prediction method presented here is also compared with that based on two-dimensional cascade theory. Predicted performance curves by the proposed set of loss models agree fairly well with experimental data for a variety of mixed-flow pumps in the normal operating range, but further studies considering 'droop-like' head performance characteristic due to flow reversal in mixed-flow impellers at low flow range near shut-off head are needed.
Air-side flow and heat transfer for a two-row lanced finned tube heat exchanger
Bae, Jin-Hyo ; Lee, Jae-Heon ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 1, 1998, Pages 79~92
DOI : 10.22634/KSME-B.19184.108.40.206
A numerical study has been performed to obtain the air-side flow and heat transfer characteristics for a two-row lanced finned tube heat exchanger with 7 mm tube outer diameter. The increases of dimensionless local heat flux at the leading edge of slit and bottom surface of the fin were noticed. The temperature of air at downstream of the 2nd row of the lanced fin becomes more uniform than that of the plain fin because the mixing of energy increases by the slit and the side-slit. As the inlet velocity increases, the contribution of the 1st row to heat transfer decreases and that of 2nd row increases.
Prediction of Turbulent Flow Over L-Shaped Riblet Surfaces with
Myeong, Hyeon-Guk ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 1, 1998, Pages 93~103
DOI : 10.22634/KSME-B.19220.127.116.11
The paper reports the outcome of a numerical study of flow over idealized L-shaped ribleted surfaces with two-equation turbulence models. In the present study, the Launder and Sharma's k-.epsilon. turbulence model (LS model) is basically N employed, but with a little modification of the additional .epsilon.-source term without affecting its level under 2-dimensional straining in which the term has been calibrated. Compared to the original LS model, the present model has predicted greatly improved drag reduction behavior for this geometry. As a drag reduction mechanism, it is found that the skin-friction in the riblet valleys might be sufficient to overcome the skin-friction increase near the riblet tip. The present predicted results are in good agreement with the recent DN S ones by Choi et al. (1993): differences in the mean velocity prof ile and turbulence quantities are found to be limited to the riblet cavity region. It is also found that turbulent kinetic energy and Reynolds shear stress above the riblets are also reduced in drag-reducing configurations.
Development of an implicit filling algorithm
Im, Ik-Tae ; Kim, U-Seung ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 1, 1998, Pages 104~112
DOI : 10.22634/KSME-B.1918.104.22.168
The mold filling process has been a central issue in the development of numerical methods to solve the casting processes. A mold filling which is inherently transient free surface fluid flow, is important because the quality of casting highly depends on such phenomenon, Most of the existing numerical schemes to solve mold filling process have severe limitations in time step restrictions or Courant criteria since explicit time integration is used. Therefore, a large computation time is required to analyze casting processes. In this study, the well known SOLA-VOF method has been modified implicitly to simulate the mold filling process. Solutions to example filling problems show that the proposed method is more efficient in computation time than the original SOLA -VOF method.
A study on the performance of a split system inverter air-conditioner at different operation conditions
Kim, Man-Hoe ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 1, 1998, Pages 113~121
DOI : 10.22634/KSME-B.1922.214.171.124
The performance evaluation of a residential split system inverter air-conditioner has been conducted analytically and experimentally at different system operating conditions. A simulation program for modelling an air-conditioning system which consists of a compressor, a condenser, a capillary tube, an evaporator and related attachments was developed on the basis of the Oak Ridge heat pump design model, MARK III. The accuracy of the simulation results for the compressor frequencies of 32, 68 and 79 Hz for the residential split system inverter air-conditioner has been estimated by comparing calculation results to the experimental data and parametric study has been performed to investigate the effect of design parameters and operation conditions on the system performance.
The thermal and flow analysis in the channel of plate heat exchanger with dimples
Lee, Gwan-Su ; Jeong, Je-Won ; Baek, Chang-In ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 1, 1998, Pages 122~130
DOI : 10.22634/KSME-B.19126.96.36.199
The present work analyzes the pressure drop and heat transfer characteristics of the plate heat exchanger with staggered dimples. The flow is assumed to be constant property, three dimensional and laminar. A thermal boundary condition is uniform wall temperature and it is assumed that the flow is periodically fully developed. Elliptic grid generation is used for proper modelling of the internal tube geometry with dimples. Computations have been carried out for a variety of geometric parameters, Reynolds number, and Prandtl number. The friction factor ratio and the ratio of a module average Nusselt number are presented for the cases considered in this study. It is found that the distance between dimples has a substantial effect on the pressure drop and heat transfer.
Proposition of a new yaw function for the use of hot wire
Kim, Jeong-Hun ; Yu, Jeong-Yeol ; Jo, Seong-Gwan ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 1, 1998, Pages 131~138
DOI : 10.22634/KSME-B.19188.8.131.52
Conventional yaw functions are compared with actual response of a hot wire to various yaw angles, and a new function is proposed, which can be applied at large yaw angles and low velocities. To compare the accuracy of the new yaw function with those of the conventional ones, measurements are made for the jet flow at the nozzle exit and at .chi./D=15 with an X hot-wire probe. In the potential core, the flow angles reduced by the present function, ideal angle method and full velocity-angle method are shown to be more accurate than those reduced by the cosine function and Hinze's formula. No matter which yaw functions are used, the profiles of mean velocity and turbulence intensity show little discrepancy at .chi./D=15. However, there is a significant difference between the probability density functions obtained by the present function, ideal angle method and full velocity-angle method and those obtained by the cosine function and Hinze's formula.