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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
Selecting the target year
A Study on the Liquid Encapsulant Czochralski(LEC) Crystal Growth with Magnetic Fields
Kim, Mu-Geun ; Seo, Jeong-Se ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1667~1675
DOI : 10.22634/KSME-B.2001.25.12.1667
Numerical simulations are carried out for the liquid encapsulant Czochralski(LEC) by imposing a magnetic field. The use of a magnetic field to the crystal growth is to suppress melt convection and to improve the homogeneity of the crystal. In the present numerical investigation, we focus on the range of 0-0.3Tesla strength for the axial and cusped magnetic field and the effect of the magnetic field on the melt-crystal interface, flow field and temperature distribution which are the major factors to determine the quality of the single crystal are of particular interest. For both axial and cusped magnetic field, increase of the magnetic field strength causes a more convex interface to the crystal. In general, the flow is weakened by the application of magnetic field so that the shape of the melt-crystal interface and the transport phenomena are affected by the change of the flow and temperature field.
Experimental Study on In-Tube Condensation Heat Transfer Characteristics of Helically Coiled Spiral Tubes
Park, Jong-Un ; Gwon, Yeong-Cheol ; Han, Gyu-Il ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1676~1683
DOI : 10.22634/KSME-B.2001.25.12.1676
An experimental study on condensation heat transfer characteristics of helically coiled spiral tubes was performed. The refrigerant is R-113. A refrigerant loop was established to measure the condensation heat transfer coefficients. Experiments were carried out uniform heat flux of 15 kw/m
, refrigerant quality of 0.1∼0.9, curvature ratio of 0.016, 0.025 and 0.045. The curvature of a coil was defined as the ratio of the inside diameter of the tube to the diameter of the bending circle. To compare the condensation heat transfer coefficients of coiled spiral tubes, the previous results on coiled plain tubes and straight plain tubes were used. The results shows that the condensation heat transfer coefficients of coiled spiral tubes largely increase, as increasing Re and quality, compared to those of coiled plain tubes and straight plain tubes. As increasing degree of subcooling, however, the condensation heat transfer coefficients on coiled spiral tubes decrease. It is found that the heat transfer enhancement is more better than coiled plain tubes and straight plain tubes, as increasing curvature ratio.
A Study on the Mechanism of Clusters Formation of ER Fluid Through Visualization
Lee, Eun-Jun ; Park, Myeong-Gwan ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1684~1691
DOI : 10.22634/KSME-B.2001.25.12.1684
Electrorheological fluids(ERFs) show a rapid and reversible increase in apparent viscosity by applied electric field. It is called the electrorheological effect (ER effect). The reason for ER effect is the induction of an electric dipole in each particle, leading to the formation of clusters in the direction of the field, which resist fluid flow. Generally, the behavior of ER fluids has been modeled on those of Bingham fluids. But there are some differences between Bingham fluids and ER fluids. The visualization of ER fliuds are presented and ER effects by the forming, growing and breaking of clusters are discussed. In the low shear rate area, the pressure drop is measured by a pressure sensor and the formation of ER particles is visualized by video camera. The reason for the nonlinear behavior of ER fluids at low shear rate is explained through results of visualization. As result, the behavior of ER fluids is nonlinear at low shear rate with overshoot area because it is different to from the clusters according to the strength of electric field. The gap of electrodes becomes narrow because of the cluster layer occurrence near to electrodes in any conditions.
A Study of the Combustion Characteristics Using a 2-valve Sl Optically Acessible Engine with SCV
Jeong, Gu-Seop ; Jeon, Chung-Hwan ; Jang, Yeong-Jun ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1692~1701
DOI : 10.22634/KSME-B.2001.25.12.1692
This study describes the combustion characteristics under various condition of air excess ratio and ignition timing in a 2-valve SI optically accessible engine with swirl control valve(SCV). It adapted three different types of SCV(open ratio 72.5%, 78%, 59%) to strengthen a swirl flow. Pressure data were acquired using pressure sensor to investigate the effect of swirl flow on combustion, and from these pressure data, IMEP(indicated mean effective pressure) and MFB(mass fraction burnt) were calculated to explain burn rate and flame speed. From acquired flame images, we inspected the flame propagation direction, flame area, and flame centroid. Flame propagation direction showed different tendency between with/without SCV, and flame area with SCV was faster and larger than that of conventional engine. Finally, the representative flame images at each crank angle were acquired by PDF method to verify flame growth process. It is found that strengthened swirl flow is more beneficial for faster and stable combustion.
Study of the Flow Characteristics of Supersonic Coaxial Jets
Lee, Gwon-Hui ; Gu, Byeong-Su ; Kim, Hui-Dong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1702~1710
DOI : 10.22634/KSME-B.2001.25.12.1702
Supersonic coaxial jets are investigated numerically by using the axisymmetric, Wavier-Stokes equations which are solved using a fully implicit finite volume method. Three different kinds of coaxial nozzles are employed to understand the flow physics involved in the supersonic coaxial jets. Two convergent-divergent supersonic nozzles are designed to have the same Mach number 2.0, and used to compare the coaxial jet flows with those discharging from one constant-area nozzle. The impingement angle of the annular jets are varied. The primary pressure ratio is changed in the range from 2.0 to 10.0 and the assistant jet ratio from 1.0 to 3.0. The results obtained show that the fluctuations of the total pressure and Mach number along the jet axis are much higher in the constant-area nozzle than those in the convergent-divergent nozzles, and the constant-area nozzle lead to higher total pressure losses, compared with the convergent-divergent nozzles. The assistant jets from the annular nozzle affect the coaxial jet flows within the distance less than about ten times the nozzle throat diameter, but beyond it the coaxial jet is conical with self-similar velocity profiles. Increasing both the primary jet pressure ratio and the assistant jet pressure ratio produces a longer coaxial jet core.
A Study on the Operational Characteristics of a U-shape Heat Pipe
Gang, Hwan-Guk ; Kim, Cheol-Ju ; Lee, Yong-Su ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1711~1720
DOI : 10.22634/KSME-B.2001.25.12.1711
In this study, the heat transfer characteristics of a U-shape heat pipes were investigated. Heat is supplied to the U heat pipe through its middle zone(evaporator), and is released to the environment through its both arms(condensers). Both heat transfer coefficients and heat transport limitations were measured and compared with correlations previously developed for straight type heat pipes. Special concerns were focused to the cases, when each of condensers were submitted to a different cooling conditions, relatively. As a result. the heat transfer limitation of a U-shape heat pipe was found out to be 10∼15% less than the value for a straight heat pipe with an equivalent size.
Predictions of Fouling Phenomena in the Axial Compressor of Gas Turbine Using an Analytic Method
Song, Tae-Won ; Kim, Dong-Seop ; Kim, Jae-Hwan ; Son, Jeong-Rak ; No, Seung-Tak ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1721~1729
DOI : 10.22634/KSME-B.2001.25.12.1721
The performance of gas turbines is decreased as their operating hours increase. Fouling in the axial compressor is one of main reasons for the performance degradation of gas turbine. Airborne particles entering with air at the inlet into compressor adhere to the blade surface and result in the change of the blade shape, which is closely and sensitively related to the compressor performance. It is difficult to exactly analyze the mechanism of the compressor fouling because the growing process of the fouling is very slow and the dimension of the fouled depth on the blade surface is very small compared with blade dimensions. In this study, an improved analytic method to predict the motion of particles in compressor cascades and their deposition onto blade is proposed. Simulations using proposed method and their comparison with field data demonstrate the feasibility of the model. It if found that some important parameters such as chord length, solidity and number of stages, which represent the characteristics of compressor geometry, are closely related to the fouling phenomena. And, the particle sloe and patterns of their distributions are also Important factors to predict the fouling phenomena in the axial compressor of the gas turbine.
Field Performance Test and Prediction of Power Consumption of a Centrifugal Chiller
Jang, Yeong-Su ; Sin, Yeong-Gi ; Kim, Yeong-Il ; Baek, Yeong-Jin ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1730~1738
DOI : 10.22634/KSME-B.2001.25.12.1730
This paper presents an overview of testing and analyzing field performance of a centrifugal chiller which has a rated capacity of 200 RT(703 kW). Field data of a chiller installed in the cleanroom research building of KIST has been collected far performance analysis. The operating data included start-up, shut-down, and quasi-static state where cooling capacity and compressor power consumption varied cyclically. It was found that the steady-state thermodynamic model could be applied to relate the cooling capacity and COP under quasi-static conditions. The results led to finding the required cooling load pattern and a possible energy saving method. This study provides a method of evaluating performance of a large capacity centrifugal chiller in which field test is necessary.
Experimental Study on the Improvement of Release Application Characteristics of Pneumatic Brakes for Freight Train
Nam, Seong-Won ; Mun, Gyeong-Ho ; Lee, Dong-Hyeong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1739~1747
DOI : 10.22634/KSME-B.2001.25.12.1739
Experimental study has been conducted to clarify the pneumatic characteristics of brake system for freight train and enhance the performance of diaphragm valve. Empty-load and diaphragm valves are installed in pneumatic brake system for freight trains of KNR (Korean National Railroad). Experiments are conducted by using freight train and diesel locomotive in operation. From the experimental results. new quick release valve shortens release time after brake application. In case of normal brake application, the release time is shortened to 34% of the original diaphragm valve. Reducing the release time of pneumatic brake system will be helpful to assure brake-release application and save maintenance efforts like wheel grinding.
An Experimental Study of Shell and Tube Heat Exchanger Performance with Baffle Spacing
Lee, Yuk-Hyeong ; Kim, Sun-Yeong ; Park, Myeong-Gwan ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1748~1755
DOI : 10.22634/KSME-B.2001.25.12.1748
The shell and tube heat exchangers were introduced to apply to a big capacity condenser and a high pressure feed water heater for power plant in the beginning of 1990s. Design and manufacturing technology fur shell and tube heat exchangers have been developed until now. But it is very difficult to calculate the expected performance characteristics of the shell and tube heat exchanger, because there are many design parameters to be considered according to internal structure and the shell side heat transfer mechanism complicately related to the design parameters. Design parameters to be considered in the design stage of shell and tube heat exchanger are shell and tube side fluids, flow rate, inlet and outlet temperature, physical properties, type of heat exchanger, outer diameter, thickness, length of tube, tube arrangement, tube pitch, permissive pressure loss on both sides, type of baffle plate, baffle cutting ratio. The propose of study is an analysis TEMA(Tubular Exchanger Manufacturers Association) E shell and tube heat exchanger performance with changing a number of baffles(3, 5, 7, 9, 11) and tubes(16, 20) and determined optimal baffle spacing.
A Numerical Analysis of cleat and Mass Transfer on the Dehumidifier of Liquid Desiccant Cooling System
Go, Gwang-Ho ; O, Myeong-Do ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1756~1765
DOI : 10.22634/KSME-B.2001.25.12.1756
The heat and mass transfer process between the falling liquid desiccant(TEG) film and the air in counter flow at the dehumidifier of desiccant cooling system were investigated. The governing equations with appropriate boundary and interfacial conditions describing the physical problems were solved by numerical analysis. As a result, the effects of the design parameters and the outside air conditions on the rates of dehumidification and sensible cooling were discussed. The results of the dehumidification and sensible cooling rates were compared with those of the cross flow at the same conditions.
Analysis of Heat and Mass Transfer in an Evaporative Cooler with Fully Wetted Channel
Song, Chan-Ho ; Lee, Dae-Yeong ; No, Seung-Tak ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1766~1775
DOI : 10.22634/KSME-B.2001.25.12.1766
A theoretical analysis on the heat and mass transfer in an evaporative cooler is presented in this work. The evaporative cooler is modeled as a channel filled with porous media the interstitial surface of which is covered by thin water film. Assuming that the Lewis number is unity and the water vapor saturation curve is linear, exact solutions to the energy and vapor concentration equations are obtained. Based on the exact solutions, the characteristics of the heat and mass transfer in the evaporative cooler are investigated. The comparison of the cooling performance between the evaporative cooler and the usual sensible heat exchanger is also carried out. Obviously, the evaporative heat exchanger shows better cooling performance than the sensible heat exchanger. This is due to the latent heat of water vaporization, which results in apparent increases both in the interstitial heat transfer coefficient and the specific heat of the air stream in the evaporative cooler.
A Study on the Heat Recovery from Boiler Exhaust Gas with Multi-stage Water-fluidized-bed Heat Exchanger
Kim, Dae-Gi ; Park, Sang-Il ; Kim, Han-Deok ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1776~1783
DOI : 10.22634/KSME-B.2001.25.12.1776
Heat recovery from boiler exhaust gas with multi-stage water-fluidized-bed heat exchanger is analyzed in this study. The recovered energy here is not only sensible heat but also latent heat contained in the exhaust gas. In this system direct contact heat transfer occurs while exhaust gas passes through water bed and the thermal energy recovered this way is again delivered to the water circulating through heat exchanging pipes within the bed. Thus the thermal energy of exhaust gas can be recovered as a clean hot water. A computer program developed in this study can predict the heat transfer performance of the system. The results of experiments performed in this study agree well with the calculated ones. The heat and mass transfer coefficients can be fecund through these experiments. The performance increases as the number of stage increases. However at large number of stages the increasing rate becomes very low.
Heat and Flow Analysis of a Parallel Flow Heat Exchanger Using Porous Modeling
Jeong, Gil-Wan ; Lee, Gwan-Su ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1784~1792
DOI : 10.22634/KSME-B.2001.25.12.1784
Numerical analysis on a parallel flow heat exchanger(PFHE) is performed using 2 dimensional turbulent porous modeling. This modeling can consider three-dimensional configuration of passage (flat tube with micro-channels), and the stability and accuracy of numerical results are improved. The geometrical parameters(e.g., the position of separators, inlet/outlet, and porosity of passages of a PFHE) are varied in order to examine the flow and thermal characteristics and flow distribution of the single phase multiple passages system. The flow non-uniformities along the paths of the PFHE are observed to evaluate the thermal performance of the heat exchanger. The location of inlet affects the heat transfer, and the location of outlet affects the pressure drop. The porosity with the optimum thermal performance is around 0.53.
A Study for Development and Application of a Low NOx 2-staged Swirl Atomizer
Song, Si-Hong ; Kim, Hyeok-Pil ; An, Sang-Taek ; Lee, Ik-Hyeong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1793~1801
DOI : 10.22634/KSME-B.2001.25.12.1793
A study of low NOx atomizer was carried out to reduce nitrogen oxides(NOx) in a liquid fuel burner flame. The basic concept of NOx reduction in this atomizer is the fuel 2-staging combustion which is generated by a single atomizer forming two different stoichiometric flames. Two orifices swirl atomizer was selected and modified to realize this concept, and it was tested to obtain the design process of low NOx atomizer. These experiments were achieved to find out the relationship between the injection pressures and the flow rate, spray angle and drop size of swirl atomizer as well as to confirm the NOx reduction concept in real plant(power boiler). In comparison between experimental and theoretical results, the correct discharge coefficient and spray angle were obtained. In real burning test, NOx reduction rate was reached to above 27% of the case using conventional swirl atomizer.
Numerical Study on the Particle Movement of a Particle-Laden Impinging Jet
Lee, Jae-Beom ; Seo, Yeong-Seop ; Lee, Jeong-Hui ; Choe, Yeong-Gi ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1802~1812
DOI : 10.22634/KSME-B.2001.25.12.1802
The purpose of this study is to analyze numerically the movement of particles included in turbulent fluid flow characteristics of metallic surfaces. To describe fluid flew, the incompressible Navier-Stokes equation discretized by the finite volume method were solved on the non-orthogonal coordinates with non-staggered variable arrangement, and the k-
turbulence model was adapted. After fluid flow was calculated, particle movement was predicted from the Lagrangian approaches. Non-essential complexities were avoided by assuming that the particles had spherical shapes and the Stoke's drag formula only consisted of external farces acting upon them. In order to validate the numerical calculations, the results were compared with the experimental data reported in literature and agreed well with them. The drag force coefficient equation showed better agreement with the experimental data in the prediction of particle movement than the correction factor equation. Impact velocity and impact angle increased as inlet turbulence intensity decreased, relative jet height was lower. or the Reynolds number was larger.
Characteristics of Spray from Pressure-Swirl Nozzle with Different Liquid Properties and Nozzle Geometries
Choe, Yun-Cheol ; Jeong, Ji-Won ; Kim, Deok-Jul ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1813~1820
DOI : 10.22634/KSME-B.2001.25.12.1813
The purpose of this study was to investigate the significant characteristics in atomization process of industrial etching spray fur the design or Precise pressure-swirl nozzles. The experiment was carried out with different viscosities and densities of the liquid. The macro characteristics of liquid spray, such as the spray angle and breakup process were captured by PMAS and the micro characteristics of liquid spray. such as droplet size and velocity measurements were obtained by PDA. The droplet axial and radial velocity and SMD were measured along axial and radial direction. The RMS of two velocities was measured along radial direction. It was found that the fluid with higher kinematic viscosity resulted in the larger SMD and the lower mean droplet velocity. And we could divide breakup processes into three regions that is atomization, non-dilution and dilution one in spray of pressure-swirl nozzle. The radial as well as axial velocity of droplet played an important role in the atomization process of higher kinematic viscosity fluid.
Effect of Cylinder Aspect Ratio on Wake Structure Behind a Finite Circular Cylinder Located in an Atmospheric Boundary Layer
Park, Cheol-U ; Lee, Sang-Jun ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1821~1830
DOI : 10.22634/KSME-B.2001.25.12.1821
The flow around free end of a finite circular cylinder (FC) embedded in an atmospheric boundary layer has been investigated experimentally. The experiments were carried out in a closed-return type subsonic wind tunnel with varying aspect ratio of the finite cylinder mounted vertically on a flat plate. The wakes behind a 2-D cylinder and a finite cylinder located in a uniform flow were measured for comparison. Reynolds number based on the cylinder diameter was about Re=20,000. A hot-wire anemometer was employed to measure the wake velocity and the mean pressure distributions on the cylinder surface were also measured. The flow past the FC free end shows a complicated three-dimensional wake structure and flow phenomenon is quite different from that of 2-D cylinder. The three-dimensional flow structure was attributed to the downwashing counter rotating vortices separated from the FC free end. As the FC aspect ratio decreases, the vortex shedding frequency decreases and the vortex formation length increases compared to that of 2-D cylinder. Due to the descending counter-rotating twin-vortex, near the FC free end, regular vortex shedding from the cylinder is suppressed and the vortex formation region is hardly distinguished. Around the center of the wake, the mean velocity for the FC located in atmospheric boundary layer has large velocity deficit compared to that of uniform flow.
Forced Convective Boiling of Pure Refrigerants in a Bundle of Enhanced Tubes
Kim, Nae-Hyeon ; Jeong, Ho-Jong ; Jo, Jin-Pyo ; Choe, Guk-Gwang ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1831~1843
DOI : 10.22634/KSME-B.2001.25.12.1831
In this study, convective boiling tests were conducted for enhanced tube bundles. The surface geometry consists of pores and connecting gaps. Tubes with three different pore sizes (d
= 0.20, 0.23 and 0.27 mm) were tested using R-123 and R-l34a for the following range: 8 kg/m
s G 26 kg/m
s, 10 kW/m
q0 40 kW/m
0.9. The convective boiling heat transfer coefficients were strongly dependent on heat flux with negligible dependency on mass flux or quality. For the present enhanced geometry (pores and gaps), the convective effect was apparent. The gaps of the present tubes may have served routes for the passage of two-phase mixtures, and enhanced the boiling heat transfer. The convective effect was more pronounced at a higher saturation temperature. More bubbles will be generated at a higher saturation temperature, which will lead to enhanced convective contribution. The pore size where the maximum heat transfer coefficient was obtained was larger for R-l34a (d
= 0.27 mm) compared with that for R-123 (d
= 0.23 mm). This trend was consistent with the previous pool boiling results. For the enhanced tube bundles, the convective effect was more pronounced for R-134a than for R-123. This trend was reversed for the smooth tube bundle. Possible reasoning is provided based on the bubble behavior on the tube wall. Both the modified Chen and the asymptotic model predicted the present data reasonably well. The RMSEs were 14.3% for the modified Chen model and 12.7% for the asymptotic model.model.
Flow Characteristics in a Microchannel Fabricated on a Silicon Wafer
Kim, Hyeong-U ; Won, Chan-Sik ; Jeong, Si-Yeong ; Heo, Nam-Geon ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1844~1852
DOI : 10.22634/KSME-B.2001.25.12.1844
Recent developments in microfluidic devices based on microelectromechanical systems (MEMS) technique find many practical applications, which include electronic chip cooling devices, power MEMS devices, micro sensors, and bio-medical devices among others. For the design of such micro devices, flows characteristics inside a microchannel have to be clarified which exhibit somewhat different characteristics compared to conventional flows in a macrochannel. In the present study microchannels of various hydraulic diameters are fabricated on a silicon wafer to study the pressure drop characteristics. The effect of abrupt contraction and expansion is also studied. It is found from the results that the friction factor in a straight microchannel is about 15% higher than that in a conventional macrochannel, and the loss coefficients in abrupt expansion and contraction are about 10% higher than that obtained through conventional flow analysis.
The Numerical Study on the Heat Transfer Characteristics of Heat Exchanger for Condensing Gas Boiler
Kim, Seok-Cheol ; Geum, Seong-Min ; Lee, Chang-Eon ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1853~1860
DOI : 10.22634/KSME-B.2001.25.12.1853
Characteristics of fluid flow and heat transfer in a tube with disk and annular baffle for heat exchanger of condensing boiler was numerically studied. The STAR-CD code was used to solve the governing equations and the temperature and flow fields were investigated. The interval between tube and annular baffle, height and diameter of baffle were selected as important design parameters, and the effects of these parameters on heat transfer and fluid flow were studied. As a result, in the case of with interval, the pressure was decreased, but heat transfer was increased. Heat transfer was slowly increased as the size of disk and annular baffle were increased and the distance between baffles were decreased. The pressure drop was rapidly changed fur diameter and size of disk and annular baffle. In addition, it was desirable that optimal conditions to design heat exchanger were about B
On Vortical Structures in Near-Wake Region of a Cubic Obstacle Mounted on a Channel Wall
Hwang, Jong-Yeon ; Yang, Gyeong-Su ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1861~1868
DOI : 10.22634/KSME-B.2001.25.12.1861
Vortical structures in the near-wake region of a cubic obstacle are studied using numerical simulation. We consider flow between two parallel plates with a cube mounted on one of the plates. In the turbulent near-wake region of the flow, coherent structures such as hairpin vortices are found. Quasi-periodic behavior of the hairpin vortices is noticed; its dimensionless frequency at Re=1,000 is about 0.82 which is consistent with the result of Elavarasan of et al.'s experiment [Fluid Dyn. Research, 2000, 27] although their geometry is somewhat different from on. In the case of Re=3,500, the dimensionless frequency of the hairpin vortex is about 1.60. It is observed that the translating speed of the head of the hairpin vortex is lower than the streamwise mean velocity at that location. In the vicinity of the lower plate downstream of the cube, various length scales are identified thus less coherent. However, it is noticed that the vortical structures become gradually elongated downstream of the new reattachment.
Effect of Pulsations on Flow and Heat Transfer Characteristics of an Impinging Jet
Lee, Eun-Hyeon ; Lee, Seong-Hyeok ; Lee, Jun-Sik ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1869~1878
DOI : 10.22634/KSME-B.2001.25.12.1869
Experiments are carried out to investigate the effect of pulsations on the flow and heat transfer characteristics of an axisymmetric impinging jet on a flat plate heated by using a gold coated aim. Vertex motion in the impinging jet is visualized using a fog generator, and a thermochromatic liquid crystal (TLC) technique is used to measure the time averaged local temperature distributions on the impingement plate. In addition, the quantitative data for mean velocity and turbulence intensity are obtained employing hot-wire anemometer. Parameters such as pulsating frequency (f = 0, 10 and 20 Hz) and the nozzle-to-palate spacing (H/D = 2, 10) are considered at the jet Reynolds number of 20,000. Consequently, the significant changes of flow structure and local Nusselt number distribution due to pulsations are observed. In the case of H/D = 2, the enhanced heat transfer coefficient exceeding 30 % is observed at the stagnation point. At the high H/D, heat transfer rate increases with pulsation frequency.
The Effect of a Bubble in B nard Convection at Low Rayleigh Number
Eom, Yong-Gyun ; Gwon, Gi-Han ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1879~1886
DOI : 10.22634/KSME-B.2001.25.12.1879
n a enclosed square cavity occurred B nard convection, the flow phenomena in the surrounding of the bubble attached at the upper cooled solid wall were studied by using a thermo-sensitive liquid-crystal tracer and image processing techniques. This method offers the advantage of measuring the entire flow field in a selected plane within the fluid at a given instant of time in contrast to point by point method like T/C. Quantitative data of the temperature were obtained by applying a colour-image-processing to the visualized image. As the flowing in a bubble, In a bubble size appears the flow phenomena which the direction of flow is reversed in the entire temperature and flow field. The observed phenomena are described with regard to the thermocapillary convection.
Steam Explosion Experiments using ZrO
Song, Jin-Ho ; Kim, Hui-Dong ; Hong, Seong-Wan ; Park, Ik-Gyu ; Sin, Yong-Seung ; Min, Byeong-Tae ; Kim, Jong-Hwan ; Jang, Yeong-Jo ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1887~1897
DOI : 10.22634/KSME-B.2001.25.12.1887
Korea Atomic Energy Research Institute (KAERI) launched an intermediate scale steam explosion experiment named "Test for Real Corium Interaction with water (TROI)" using reactor material to investigate whether the molten reactor material would lead to energetic steam explosion when interacted wish cold water at low pressure. The melt-water interaction experiment is performed in a pressure vessel with the multi-dimensional fuel and water pool geometry. The novel concept of cold crucible technology, where powder of the reactor material in a water-cooled cafe is heated by high frequency induction, is firstly implemented for the generation of molten fuel. In this paper, the lest facility and cold crucible technology are introduced and the results or the first series of tests were discussed. The 5 kg of molten ZrO
jet was poured into the 67cm deep water pool at 30 ∼ 95
. Either spontaneous steam explosions or quenching was observed. The morphology of debris and pressure wave profiles clearly indicate the differences between the two cases.
Evaluation of Flow Measurement Uncertainty of Sonic Nozzle
Choe, Hae-Man ; Park, Gyeong-Am ; Choe, Yong-Mun ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1898~1904
DOI : 10.22634/KSME-B.2001.25.12.1898
Measurement uncertainty should be evaluated according to ISO/IEC 17025. In Flow measurement area, uncertainty evaluation scheme was applied to the reference flow meter, sonic nozzle. Uncertainty was calculated by evaluating various uncertainty factors affected in flow measurement. The expanded uncertainty(U) of the sonic nozzle was 2.1
(confidence level of 95 %). This evaluation example will be useful in flow measurement uncertainty determination of other flow meters.
A Study on the Pressure Resonance with Combustion Chamber Geometry for a Spark Ignition Engine
Park, Gyeong-Seok ; Jang, Seok-Hyeong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 25, issue 12, 2001, Pages 1905~1910
DOI : 10.22634/KSME-B.2001.25.12.1905
Pressure resonance frequency that is caused in the combustion chamber can be interpreted by acoustic analysis. Until now the pressure resonance has been assumed and calculated to a disc type combustion chamber that neglected the combustion chamber height because the knock occurs near the TDC(top dead center). In this research FEM(finite element method) has been used to calculate the pressure resonance frequency inside the experimental engine combustion. The error of the resonance frequency obtained by FEM has decreased about 50% compared to the calculation of Draper's equation. Due to the asymmetry in the shape of the combustion chamber that was neglected in Draper's equation we could find out that a new resonance frequency could be generated. To match the experimental results, the speed of sound that satisfies Draper's equation is selected 13% higher than the value for pent-roof type combustion chamber.