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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 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
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Effects of the secondary flow on the turbulent heat transfer of a flat plate wake
Kim, Hyeong-Su ; Lee, Jun-Sik ; Gang, Sin-Hyeong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 4, 1998, Pages 417~427
DOI : 10.22634/KSME-B.1922.214.171.1247
The effect of secondary flow on the heat transfer of a turbulent wake generated by a flat plate was experimentally investigated. The secondary flow was induced in a curved duct in which the flat plate wake generator was installed. All three components of turbulent heat flux were measured in the plane containing the mean radius of curvature of the curved duct. The results showed that mean temperature profiles deviate from the similarity of the straight wake because of the cold fluid transported from the free-stream. The half-width of the mean temperature profile increased rapidly by upwash motion of the secondary flow. The changes to turbulence structure caused by the secondary flow show more pronounced effect on heat transport than on momentum transport. This is because the response to the variation of flow conditions is delayed in temperature field. Negative production of the turbulent heat flux is observed in the inner wake region. From the conditional averaging, it has been found that the negative production of the turbulent heat flux is generated due to a mixing process between the hot and low momentum eddies occupied in the inner wake region and the cold and high momentum eddies in the potential region.
Heat transfer characteristics by an oscillating flow in a tube with a regenerator
Lee, Geon-Tae ; Gang, Byeong-Ha ; Lee, Jae-Heon ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 4, 1998, Pages 428~439
DOI : 10.22634/KSME-B.19126.96.36.1998
Fluid flow and heat transfer have been numerically investigated for an oscillating flow in a tube with a regenerator. The regenerator is placed between hot and cold spaces which are heated and cooled at uniform temperature. An oscillating flow is generated by the piston motion at both ends of a tube. The time dependent, two-dimensional Navier-Stokes equations and energy equation are solved by using the finite-volume and moving grid method. The regenerator is adopted as Brinkmann-Forchheimer extended Darcy model. Numerical results are obtained for the flow and temperature fields, and described the effects of the oscillating frequency and amplitude ratio by the piston motion as well as the aspect ratio. The numerical results obtained indicate that the heat transfer between the tube wall and oscillating flow is increased as the oscillating frequency, amplitude ratio and the aspect ratio are increased.
Visualization of double-diffusive convection during solidification processes of a binary mixture
Jeong, U-Ho ; Jeong, Jae-Dong ; Yu, Ho-Seon ; Lee, Jun-Sik ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 4, 1998, Pages 440~451
DOI : 10.22634/KSME-B.19188.8.131.520
An experimental study has been conducted to investigate solidification of NH
0 mixtures inside a vertical rectangular enclosure. Solidification process is visualized by the shadowgraph method. Emphasis is placed on the effect of solidification parameters such as the aspect ratio, cooling wall temperature and initial composition. The aspect ratio shows a dominant effect on the number and developing time of the double diffusive layers which reveals the relative strength of solutal convection to thermal convection. Similar flow pattern is observed when the concentration difference between interdendritic liquid and the pure liquid which drives solutal convection is the same regardless of the different cooling wall temperature and initial concentration.
Instability of High-Speed Impinging Jets(II)
Gwon, Yeong-Pil ; Im, Jeong-Bin ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 4, 1998, Pages 450~467
DOI : 10.22634/KSME-B.19184.108.40.2060
The characteristics of the unstable impinging circular jet is investigated based on the frequency characteristics and the sound field of the impinging-tones. Two symmetric modes S1 and S2, associated with low frequency and high frequency respectively, and one helical mode H have been observed. At low speed the S2 mode is dominant and switched by the S1 mode as the speed increases. When the jet speed is high the S1 mode is very active over the impinging distance from half the nozzle diameter to its ten times, while the S2 mode occurs at shorter distance corresponding to stage 2 and 3. The helical mode H seems unstable, likely to be influenced much by the experimental environment, and occurs at relatively high speed with almost the same frequency characteristics as the S2 mode. By estimating the convection speed of the unstable jet, it is found that the ratio of the convection speed to the jet speed decreases with both Strouhal number and Reynolds number and the speed of S2 mode is faster than the Si mode. When the present experimental results are compared with the previous investigations performed for the hole tone and the impinging tone with a small plate, the S1 mode is found to be associated with the ring vortex of large diameter with low speed, but the S2 mode with the vortex of small diameter with high speed. In addition, the frequency is found to be influenced by the nozzle configuration but the characteristics is almost the same. From the impinging distance and frequency range, it can be deduced that S1 mode is related with the jet column mode and S2 mode with the shear mode.
Instability of High-Speed Impinging Jets(I)
Gwon, Yeong-Pil ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 4, 1998, Pages 452~458
DOI : 10.22634/KSME-B.19220.127.116.112
The objective of this study is to obtain the unstable characteristics of the high-speed two-dimensional jet impinging normally onto a flat plate. The study is based on the feedback model and the experiment of the frequency characteristics of the impinging tones. Using the experimental data for the tonal frequencies of the impinging tones the convection speed of the unstable jet is obtained along with all the other features. Three kinds of unstable modes are clarified: asymmetric
and symmetric S. The condition for the excitation of each mode is found in terms of Strouhal number and Reynolds number. The convection speed is estimated and discussed in comparison with existing theoretical models. It is found that the convection speed increases with frequency when the mode is asymmetric, but decreases when it is symmetric. In addition, the characteristics of the high-speed impinging jet are compared with the low-speed impinging jet.
Measurements of sooting in single droplet combustion under the normal-gravity condition
Lee, Gyeong-Uk ; Lee, Chang-Eon ; O, Su-Cheol ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 4, 1998, Pages 468~480
DOI : 10.22634/KSME-B.1918.104.22.1688
The temporal and spatial distributions of soot volume fractions were measured for single toluene droplet flames as a function of pressure under the normal-gravity condition. In order to characterize the transient nature of the flame and sooting regions, a full-field light extinction and subsequent tomographic inversion technique was used. The reduction in sooting as a function of pressure was assessed by comparison of the maximum soot volume fractions at several vertical positions along the axis above the droplet. The maximum soot volume fraction was reduced by 70% when the pressure was reduced by 60% from 1 atm to 0.4 atm. The reduction in sooting is attributed to variation of the geometric configuration of flame which reduces the system Grashof number as well as only the change in the adiabatic flame temperature as the pressure decreases. The gravimetrically-measured total soot yield was also compared to the optically-measured soot volume fraction to obtain a correlation between the two measurements. As a result, the total soot yield was linearly proportional to the optically-measured maximum soot volume fraction and linearly reduced as the pressure decreased. Accordingly, the non-intrusive full-field light extinction-measurements were able to be calibrated not only to measure soot volume fraction, but to simultaneously evaluate the total soot yield emitted from the toluene droplet flame (which is useful in the practical application).
A study on the usability of used vegetable oil as a diesel substitute in diesel engine
O, Yeong-Taek ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 4, 1998, Pages 481~488
DOI : 10.22634/KSME-B.1922.214.171.1241
In recently, lots of researcher have been attached to develope various alternative fuels and to use renewable fuels for solution of the exhaust emission problems. In this study, the usability of used vegetable oil as alternative fuel for diesel engines has been investigated. This paper was compared with the exhaust emissions and performance in diesel engine with used vegetable oil and conventional diesel fuel. Since the vegetable oil includes oxygen of about 10%, it influenced the combustion process strongly. So, the smoke emissions of used vegetable oil were exhausted to be lower than those of diesel fuel. Also, the used vegetable oil was much the same cycle to cycle variation with diesel fuel except
d.theta.)max/, but the cycle to cycle variation of used vegetable oil was reduced significantly by preheating of the fuel and swirling of the intake air. It was concluded that used vegetable oil could be utilized effectively as renewable fuel for diesel engine.e.
Effects of Non-Absorbable Gases on the Absorption Process of Aqueous LiBr Solution Film in a Vertical Tube (I)
Kim, Byeong-Ju ; Lee, Chan-U ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 4, 1998, Pages 489~498
DOI : 10.22634/KSME-B.19126.96.36.1999
Among the heat/mass exchange units composing an absorption system, the absorber, where the refrigerant vapor is absorbed into the liquid solution is the one least understood. In the present study, the effects of non-absorbable gas on the absorption process of aqueous lithium bromide solution falling film inside a vertical tube were experimentally investigated. In the range of film Reynolds number of 30 ~ 195, heat and mass transfer characteristics were investigated as a function of non-absorbable gas volumetric concentration, 0.2 ~ 20%. An increase of non-absorbable gas volumetric concentration degraded the mass transfer rate dramatically in the absorption process. The reduction of mass transfer rate was significant for the addition of small amount of non-absorbable gas to the pure vapor. At film Reynolds number of 130, an increase of non-absorbable gas concentration from 0.2 to 6.0% resulted in the decrease of mass transfer rate by 36% and 20% of non-absorbable gas by 59%. However the decrease of film Nusselt number with the increase of volumetric concentration of non absorbable gas was relatively smaller than the decrease of Sherwood number. Critical film Reynolds number was identified to exist for the maximum heat and mass transfer regardless of the volumetric concentration of non-absorbable gases.
Effects of Non-Absorbable Gases on the Absorption Process of Aqueous LiBr Solution Film in a Vertical Tube (II)
Kim, Byeong-Ju ; Lee, Chan-U ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 4, 1998, Pages 499~509
DOI : 10.22634/KSME-B.19188.8.131.529
In the absorption process of water vapor in a liquid film, the composition of the gas phase, in which a non-absorbable gas is combined with the absorbate influences the transport characteristics remarkably. In the present study, the absorption processes of water vapor into aqueous solution of lithium bromide in the presence of non-absorbable gases were investigated analytically. The continuity, momentum, energy and diffusion equations for the solution film and gas phase were formulated in integral forms and solved numerically. It was found that the mass transfer resistance in gas phase increased with the concentration of non-absorbable gas. However the primary resistance to mass transfer was in the liquid phase. As the concentration of non-absorbable gas in the absorbate increased, the liquid-vapor interfacial temperature and concentration of absorbate in solution decreased, which resulted in the reduction of absorption rate. The reduction of mass transfer rate was found to be significant for the addition of a small amount of non-absorbable gas to the pure vapor, especially at the outlet of an absorber where non-absorbable gases accumulated. At higher non-absorbable gas concentration, the decrease of absorption flux was almost linear to the volumetric concentration of non-absorbable gas.
Convective heat transfer on the rotor fan and endring of the TEFC induction motor with telemetry system
Yun, Myeong-Geun ; Ha, Gyeong-Pyo ; Go, Sang-Geun ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 4, 1998, Pages 510~519
DOI : 10.22634/KSME-B.19184.108.40.2060
Recently, computer modelling is increasingly used as a design tool, which requires more detailed data for heat transfer coefficients in various regions of the induction motor. But there are little information about those of rotor fan and endring because of difficulty in measuring signals in rotating bodies. In the present studies, the temperature signals were precisely measured with self-developed telemetry system, which had multi-channels and high rotational speed. After some losses were compensated, the heat transfer coefficients of the rotor endring and fan surfaces were measured. Minimum heat transfer region was existed with endcap plate distance and maximum heat transfer was found at some rotor fan width. It was also studied that how the guide plate and endcap inside rib effected on the rotor heat transfer. The higher heat transfer were obtained with decreasing guide plate distance, increasing the number and height of endcap inside rib. The correlation equations of the results were obtained and compared with others. Above results of the heat transfer coefficients can be used as basic data for cooling design of the various kind of motors.
Numerical prediction of hydrogen storaging performance of finned metal hybride beds
Kim, Myeong-Chan ; Lee, Sang-Yong ; Gu, Jae-Hak ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 4, 1998, Pages 520~529
DOI : 10.22634/KSME-B.19220.127.116.110
Heat and mass transfer behaviors of metal hydride beds were predicted by solving a set of volume-averaged equations numerically both for the gas (hydrogen) and the solid(metal hydride) phases. Time variations of temperature and hydrogen concentration ratio distributions were obtained for internally cooled, cylindrical-shaped beds with metal(aluminum) fins imbedded in them. Also, time variations of the space-averaged hydrogen concentration ratio were obtained. Temperature and velocity of the coolant, hydrogen pressure at the gas inlet, and the fin spacing were taken as the parameters. The hydrogen absorption rate increases with the higher velocity and the lower temperature of the coolant, and with the decrease of the fin spacing. Increasing of the hydrogen pressure at the gas inlet also promotes the rate of absorption though the increasing rate gradually slows down. The amount of the hydrogen storage per unit volume of the bed decreases with the tighter fin spacing despite of the higher absorption rate ; therefore, there should be an optimum fin spacing for a given volume of the system and the amount of the hydrogen storage, in which the absorption rate is the highest.
Augmented heat transfer in a rectangular duct with angled ribs
U, Seong-Je ; Kim, Wan-Sik ; Jo, Hyeong-Hui ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 4, 1998, Pages 530~541
DOI : 10.22634/KSME-B.1918.104.22.1680
Heat transfer augmentation in a rib-roughened duct is affected by the rib configurations, such as rib height, angle of attack, shape, rib to rib pitch, and aspect ratio of a duct. These have been the main subjects in studying the average heat transfer and the friction loss of the fully developed flow. Investigating distributions of local heat transfer coefficients and flow patterns in a duct with the rib turbulators is necessary to find the characteristics of heat transfer augmentation and to decide the optimal configurations of ribs. In the present study the numerical analyses and the mass transfer experiments are performed to understand the flow through a rib roughened duct and the heat transfer characteristics with various angles of attack of ribs. A pair of counter-rotating secondary flow in a duct has a main effect on the lateral distributions of local mass transfer coefficients. Downwash of the rotating secondary flow, reattachment of main flow between ribs and the vortices near ribs and wall enhanced the mass transfer locally up to 8 times of that in case of the duct without ribs.
Analysis of a gas-particle direct-contact heat exchanger with two-phase radiation effect
Park, Jae-Hyeon ; Baek, Seung-Uk ; Gwan, Se-Jin ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 4, 1998, Pages 542~550
DOI : 10.22634/KSME-B.1922.214.171.1242
A direct contact heat exchanger using particle-suspended gas as a heat transfer medium is analyzed with an extended emphasis on the radiation, i. e., considering the radiation by both gas and particles. While the Runge-Kutta method is used for a numerical analysis of the momentum and energy equations, the finite volume method is utilized to solve the radiative transfer equation. Present study shows a notable effect by the gas radiation in addition to the particle radiation, especially when changing the chamber length as well as the gas and particle mass flow rate. When the gas and particle mass flow rate is raised, the gas temperature in the particle heater still increases as the gas absorption coefficient increases, which is different from the results for the small scale heat exchanger.
Heat transfer characteristics around a circular combustion chamber of kerosene fan heater
Kim, Jang-Gwon ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 4, 1998, Pages 551~561
DOI : 10.22634/KSME-B.19126.96.36.1991
This paper was studied to understand the characteristics of heat transfer coefficients and surface temperature distributions around a circular combustion chamber within the heat-intercept duct of kerosene fan heater. The experiment was carried out in the heat-intercept duct of kerosene fan heater attached to the blow-down-type subsonic wind tunnel with a test section of 240 mm * 240 mm * 1200 mm. The purpose of this paper was to obtain the basic data related with normal combustion for new design from conventional kerosene fan heater, and to investigate the effect of surface temperature, local and mean heat transfer coefficients versus flow-rate of convection axial fan according to the variations of heat release conditions from kerosene fan heater during normal combustion. Consequently it was found that (i) the revolution of convection axial fan during combustion had a smaller value than that of non-combustion because of the thermal resistance due to the high temperature in the heat-intercept duct, (ii) the pressure ratio P
had a comparatively constant value of 0.844 according to the revolution increase of turbo fan and the heating performance of kerosene fan heater had a range of 1,494 ~ 3,852 kcal/hr, (iii) the local heat transfer coefficient around a circular combustion chamber had a comparatively larger scale in the range of 315 deg. < .theta. < 45 deg. than that in the range of 90 deg. < .theta. < 270 deg. as a result of heat transfer difference between front and back of a circular combustion chamber, and (iv) the mean heat transfer coefficient around a circular combustion chamber increased linearly like a H
=95.196Q+104.019 in condition of high heat release according to the increase of flow-rate of axial fan.n.