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Transactions of the Korean Society of Mechanical Engineers B
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The Korean Society of Mechanical Engineers
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Volume 23, Issue 4 - 00 1999
Volume 23, Issue 12 - 00 1999
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3-D Turbulent Heat & Fluid Flow Analysis with Solidification Under Electro-Magnetic Field
Jo, Myeong Jong ; Kim, In Cheol ; Kim, Sang Jun ; Kim, Jong Geun ;
Transactions of the Korean Society of Mechanical Engineers B, volume 23, issue 12, 1999, Pages 1491~1491
DOI : 10.22634/KSME-B.19220.127.116.111
In this investigation, 3-D numerical model has been developed to predict turbulent molten steel flow field and solidification phenomena within the thin slab casting mould with electro-magnetic field. The developed numerical model was verified by comparing with experimental data. By using the developed numerical model, the characteristics of EMBR(Electro-Magnetic Brake Ruler)has been investigated in view points of solid shell growth and flow pattern change. From these investigation, it was found that electro-magnetic force changed the flow pattern and solid shell thickness significantly.
A Study on the Effects of Idle Stability in Spark Ignition Engines
Han, Seong Bin ; Jang, Yong Hun ; Jeong, Yeon Jong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 23, issue 12, 1999, Pages 1503~1503
DOI : 10.22634/KSME-B.1918.104.22.1683
The stability of engine operation is improved, but the stability of engine operation at idle is not improved as a whole in the electronic controlled fuel injection compared with the gasoline engine o f carburetor type. It was recognized that the stability of engine at idle is affected by the factors of fuel the effects of stability and the variations of air-fuel ratio of the electronic controlled fuel injection gasoline engine at idle according to fuel injection timing and air-fuel ratio as the basic parameters, and analysis the variations of air-fuel ratio.
An Experimental Study on Inertial Impactor Efficiency Curve For Cavity Angle Variation of Inertial Impaction Plate
Choe, Nak Jun ; Park, Seok Ju ; Kim, Sang Su ;
Transactions of the Korean Society of Mechanical Engineers B, volume 23, issue 12, 1999, Pages 1510~1510
DOI : 10.22634/KSME-B.1922.214.171.1240
Inertial impactors have been used widely to measure particle size distribution, analyze chemical composition, and obtain aerosol sampling. Conventional impactors have particle-surface interaction problems. These problems reduced separation efficiency. To enhance separation efficiency. it is desirable that surface is coated. But coated surface has significant problem in high temperature environment and bio aerosol sampling. The cavity impactor that is not a conventional design can be used in such situations. The efficiency of a conventional impactor and the cavity impactor was investigated for different Reynolds numbers in this paper. 50% cut-off aerodynamic particle diameter was smaller in the cavity impactor than in the conventional impactor because of flow direction change. Fine particle contamination and reentrainment were reduced in the cavity impactor.
Freeze Coating of a Cylindrical Object with a Binary Alloy
Nam, Jin Hyeon ; Hong, Hui Gi ; Kim, Chan Jung ;
Transactions of the Korean Society of Mechanical Engineers B, volume 23, issue 12, 1999, Pages 1519~1519
DOI : 10.22634/KSME-B.19126.96.36.1999
An analytic solution of the freeze coating of a cylindrical object with a binary alloy is obtained by modeling the object as a line heat sink. In the freeze coating with a binary alloy, there exist s an extended region where phase change occurs instead of a sharp phase interface in the freeze coating of a pure substance. In this region, which is called mushy region, the solid and the liquid phases coexist in a geometrically complicated manner. Therefore a mushy model, which can properly treat the mushy region, is adopted in the present analysis. And the effect of convection in the liquid region is also considered. The system of governing equations and boundary conditions, derived from conservation law, is analyzed through similarity transformation and numerical integration. The effect of various processing parameters on the growth rate of the freeze coating is presented.
Effect of AC Electric Field Frequency on Electrical Agglomeration of Aerosol Particles
Kim, Yeon Seung ; Hwang, Jeong Ho ;
Transactions of the Korean Society of Mechanical Engineers B, volume 23, issue 12, 1999, Pages 1527~1527
DOI : 10.22634/KSME-B.19188.8.131.527
Growing concern regarding, global atmospheric pollution has led to increasing interest in reducing the emission of fly ash particles. Electrostatic precipitator is a flue gas particle collector commonly used in coal-fired power plants. Since ESP has relatively low efficiency for the collection of submicron-sized particles, electrostatic agglomeration has been proposed to enhance the collection efficiency. In this work, we investigated the characteristics of electrostatic agglomeration of fine aerosol particles which experience DC corona charging and AC applied particle motion control. The particles (primary particles) were produced from NaCl resolved solution using an atomizer. By controlling the concentration of the NaCl solution, it was possible to produce different sized particles. The primary particles collided with each other and then became pearl-chain shape agglomerates. This study was initiated for enhancing agglomeration among unipolar charged particles by using the alternating electric field to increase the relative motion between the particles. Application of AC voltage promotes agglomeration in addition to that caused by Brownian motion. A particle oscillating amplitude increases as the particle size increases from submicron to micron. By controlling the concentration of the NaCl solution, it was possible to use the initially different sized particles. The particle size was sampled and observed with SEM photograph. The results showed that the number of agglomerated particles mainly depend on the DC field intensity and the AC field frequency.
Numerical Calculations on Condensation/Coagulation of PbO and Fly Ashes in a Vertical-type Small Size Incinerator
Hong, Eun Gi ; Hwang, Jeong Ho ; Yun, Ung Seop ;
Transactions of the Korean Society of Mechanical Engineers B, volume 23, issue 12, 1999, Pages 1535~1535
DOI : 10.22634/KSME-B.19184.108.40.2065
This study is about numerical calculations on condensation and coagulation of hazardous metallic species which are important physical phenomena in an incinerator. Lead oxide(PbO), one of major metallic species produced in the combustion process, is selected for the study. Governing equations are three moment forms of the General Dynamic Equation and a vapor balance equation made by adding the effect of condensation and coagulation to the well-known convective diffusion equation. These differential equations, expressed in dimensionless variables, are solved using the finite differenced method. Temperature and velocity fields considering the gravitational force, number concentration of metal vapors, and ash particle size distribution are selected as the factors influencing the result of total aerosol size distribution.
Analysis of the Coupled Turbulent Flow and Heat Transfer in a Wedge-Shaped Pool According to Feed Type of Molten Steel
Kim, Deok Su ; Kim, U Seung ;
Transactions of the Korean Society of Mechanical Engineers B, volume 23, issue 12, 1999, Pages 1544~1544
DOI : 10.22634/KSME-B.19220.127.116.114
The proper choice of nozzle in a twin-roll strip casting process is important to achieve the stabilization of the molten steel and free surface, and the uniform temperature distribution, in a wedge -shaped pool, which depend on the transport phenomena of the pool. In this study, the numerical investigation of turbulent flow and heat transfer was performed for two patterns of the feed of molten steel through the nozzle. In addition, the patterns of the removal of superheat for different gap thicknesses were analyzed using local Nusselt number along the roll surface. The turbulent characteristics of the flow were considered using a low-Reynolds-number κ-ε turbulence model of Launder and Sharma. The results show that the use of submerged nozzle may be beneficial to the stabilization of the free surface zone. The increased gap thickness yielded the increased local Nusselt number in the downstream section of the wedge-shaped pool where the cross-sectional area of flow is reduced.
Spray Behavior and Atomization Characteristics of High-pressure Gasoline Injector
Lee, Chang Sik ; Lee, Gi Hyeong ; Jeon, Mun Su ; Choe, Su Cheon ; Kim, Min Gyu ;
Transactions of the Korean Society of Mechanical Engineers B, volume 23, issue 12, 1999, Pages 1555~1555
DOI : 10.22634/KSME-B.1918.104.22.1685
In direct-injection gasoline engine. the spray of fuel injector plays important roles in improvement of engine performance and reduction of exhaust emissions. This paper presents the spray development processes, spray structure, and atomization characteristics of high-pressure gasoline injector. Global spray structure was visualized using shadowgraph technique. Also, the cross-correlation particle image velocimetry and PDPA system were utilized to obtain the flow and quantitative characteristics of gasoline spray of high-pressure fuel injector. In this investigation, the visualization and experiment of velocity distribution in the spray were performed at 3, 5, and 7MPa of injection pressure under different ambient pressure conditions. Based on the experimental results, the spray behavior of high-pressure gasoline injector such as the spray visualization, spray structure and counter rotating vortex, spray tip penetration, spray width, and velocity vector fields were investigated. In addition, the other spray characteristics were discussed.
The Effect of Nozzle Geometry on the Heat Transfer Characteristics of Impinging Jet
Yun, Sun Hyeon ; Kim, Dong Geon ;
Transactions of the Korean Society of Mechanical Engineers B, volume 23, issue 12, 1999, Pages 1562~1562
DOI : 10.22634/KSME-B.1922.214.171.1242
Experiments are conducted to show the effects of nozzle geometry on heat transfer of two-dimensional impinging jets. The channel and orifice type of nozzles are used. To control the nozzle exit turbulent intensity, a square rod is installed at the nozzle exit. The temperature distribution on the heated flat plate was measured with a thermochromic liquid crystal. All of the measurements are made over a range of nozzle-to-plate distance from 1 to 10 for Re=20,000. The maximum Nusselt number at the stagnation point for the channel and orifice nozzle is occurred at H2=9 and H2=7, respectively. It is observed that heat transfer rate for the channel nozzle shows higher than that of the orifice nozzle. When intial turbulent intensity was increased with the square rod installed at the nozzle exit, it is shown that the heat transfer rate are rapidly increased in 1≤H/B≤4.
PIV Measurements of Flow Downstream of Polyurethane Heart Valve Prosthesis for Artificial Heart : Steady Flow Experiment
Kim, Jung Gyeong ; Seong, Jae Yong ; Jang, Jun Geun ; Yu, Jeong Yeol ; Min, Byeong Gu ;
Transactions of the Korean Society of Mechanical Engineers B, volume 23, issue 12, 1999, Pages 1570~1570
DOI : 10.22634/KSME-B.19126.96.36.1990
Hemodynamic performance of a polyurethane heart valve prosthesis was evaluated in comparison with that of Bjork-Shiley Monostrut mechanical valve in steady flow representing the systolic peak flow phase. Pressure losses through the valves were obtained from the streamwise pressure distributions downstream of the valves. Unsteady and turbulent flow field distal to the heart valve prostheses were investigated using M (Particle Image Velocimetry) which can measure the full-field velocity instantaneously and noninvasively. BY examining the velocity and Reynolds shear stress fields downstream of the polyurethane heart valve, it is known that there is a large recirculation region near the valve and high shear stress regions exist at the interface between strong axial jet flows along the wall and vortical flows in the central area. The possibilities of vascular complications, such as the thrombus formation and red blood cell damage, could be predicted from the overall view of the velocity and stress fields.
An Experimental Study for Improving the Performance of a Thermoacoustic Refrigerator
Park, Jong Ho ; Song, Gyu Jo ; Gang, Hyeon Taek ; U, Sam Yong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 23, issue 12, 1999, Pages 1582~1582
DOI : 10.22634/KSME-B.19188.8.131.522
The thermoacoustic refrigerator has not only considerable possibility but also commercial usability, because it has high reliability, lower vibration, no moving part, and can easily be constructed. In this study, the resonance characteristics of the thermoacoustic refrigerator were investigated for better performance, varying the length of stacks to 40mm -100mm. In order to deter-mine the optimum position of stack in the resonance tube and the motor frequency, the λ/4 thermoacoustic engine and the similar apparatus of Hofler type refrigerator were constructed. The resonance tube is 540mm in length. In case of using air as a coolant at frequency of 180Hz, the cold-part temperature of the heat exchanger fell to -3℃ after 1 minutes, generating frost on the stack's cold part. The first, third, and fifth harmonics have frequency of 180Hz, 480Hz, and 780Hz respectively. The highest efficiency were obtained from the third harmonic with resonant tube of 380mm in length.
Prediction of Autoignition Site in Spark Ignition Engines
Lee, Yong Gyu ; Kim, Man Sik ; Min, Gyeong Deok ; Kim, Eung Seo ;
Transactions of the Korean Society of Mechanical Engineers B, volume 23, issue 12, 1999, Pages 1590~1590
DOI : 10.22634/KSME-B.19184.108.40.2060
A three-dimensional knock model is developed to predict the knock occurrence and autoignition site in spark ignition engines. Weller's 1-equation combustion model and a flame wall quenching model a re applied to simulate flame propagation. A Reduced kinetic model developed by Keck and Hu is used to simulate autoignition in the unburned gas region. Engine experiments are performed to calibrate the reduced kinetic model and to verify the knock model. A spark plug integrated pressure transducer and 11 ion probes are installed in the cylinder head to detect knock occurrences, flame arrival angles, and autoignition sites. Autoignition site can be determined from the knock onset angle determined by cylinder pressure and flame arrival time determined by ion probes. Before the reduced kinetic model is combined with the combustion model, it was calibrated with measured cylinder pressure in a spark ignition engine. The cylinder pressure and flame arrival angles of numerical results are compared with the experiments. The numerical results are in good agreement with the experiments. The knock model developed in this study can predict knock occurrence and autoignition sites with reasonable accuracy.
Evaporation Heat Transfer Characteristics of R-290 in a Micro Fin Tube
Park, Cheol Min ; Im, Yong Bin ; Lee, Uk Hyeon ; Kim, Jong Su ;
Transactions of the Korean Society of Mechanical Engineers B, volume 23, issue 12, 1999, Pages 1598~1598
DOI : 10.22634/KSME-B.19220.127.116.118
Hydrocarbons are very suitable alternative refrigerants, because of their low GWP and ODP. These alternative refrigerants have been expected to have different heat transfer characteristics from that of HCFC-22 when the phase is changed in the evaporator. Thus, in this study, evaporation heat transfer coefficient, pressure drop and flow regimes of pure R-290(Propane) inside a micro fin tube were experimentally investigated. The length of test section was 500 mm and average diameter of a micro fin copper tube was 8.62 min. Test conditions were as follows: saturation temperature 5℃ mass velocity 100, 150 kg/m2s heat flux 10, 20 kW/m2 inlet quality 0.08 - 1.0. The observed flow regimes agreed with that of Breber's flow map. However, annular flow pattern appeared at the low quality, which was different from the flow pattern in a smooth tube. Pressure drop of R-290 was three times higher than that of R-22 at the same mass velocity and heat flux. Among the local surface temperature difference in circumferential direction of a micro fin tube, temperature difference of upper part was smallest and lower one was largest. Evaporation heat transfer coefficient of R-290 was two times higher than that of R-22 at the same mass velocity and heat flux.
Numerical Simulation on Rising Bubble Behaviors in Water
Son, Gi Hyeon ; Lee, Sang Ryeol ;
Transactions of the Korean Society of Mechanical Engineers B, volume 23, issue 12, 1999, Pages 1606~1606
DOI : 10.22634/KSME-B.1918.104.22.1686
A bubble rising in water was simulated numerically to predict its shape and terminal velocity. The liquid-gas interface was captured using a level set function which is defined as the signed distance from the interface. Since the distance function and its spatial derivative are smooth and continuous. The level set method can be used to compute an interfacial curvature more accurately than such methods using a step function as VOF and CIP methods. The level set method was modified to achieve volume conservation during the whole calculation procedure of transient bubble motion up to steady state. The calculated shape and terminal velocity of the rising bubble showed good agreement with the experimental data reported in the literature within 10% error range. Also, the present method was proven to be applicable to bubble merging phenomenon.
Pumping Characteristics of a Helical Drag Pump in the Molecular Transition Region
Heo, Jung Sik ; U, Nam Seop ; Hwang, Yeong Gyu ; Kim, Yun Je ;
Transactions of the Korean Society of Mechanical Engineers B, volume 23, issue 12, 1999, Pages 1614~1614
DOI : 10.22634/KSME-B.1922.214.171.1244
Pumping performance of a helical drag pump which works in the pressure range from 0.02 to 5 Torr is studied numerically and experimentally. The flow occurring in the pumping channel is developed from the molecular transition to the slip flow as traveling downstream. Two different numerical techniques are used: the first method is a continuum approach in solving the Navier-Stokes equations with slip boundary conditions, and the second one is a stochastic particle approach through the use of the direct simulation Monte-Carlo method. In the experimental study, the inlet pressures are measured for various outlet pressures of the test pump. Two different types of helical rotor are designed and tested to investigate the effect of geometrical parameters on performance. The rotational speed of the pump is 24000rpm, and nitrogen is used as a test gas. The numerical results show a good agreement with the experimental data.