Jongwook Choi

Temperature Analysis for Optimizing the Configuration of the Linear Cell

The market demand of display devices is drastically increasing in the information technology age. The research on OLED (Organic Light Emitting Diodes) display with the luminescence in itself is being more paid attention than LCD (Liquid Crystal display) with the light source from the back. The vapor deposition process is most essential in manufacturing OLED display. The temperature distribution of the linear cell in this process is closely related to securing the uniformity of organic materials on the substrate. This work analyzed the temperature distribution depending on the intervals between the crucible and the heating band as well as on the amount of the heat flux from the heating band. Moreover, the roles of the water jacket and the configuration of the cover within the linear cell were examined through the temperature analysis for six configurations of the linear cell. Under the above temperature analysis, the variations in the intervals and the amount of the heat flux were considered to have an effect on building the uniform temperature distribution within the crucible. It is predicted that the water jacket and the adequate configuration of the cover will prevent the blowout and clogging phenomena, respectively. The results can be used as the fundamental data for designing the optimal linear cell.

Effects of an Air Spoiler on the Wake of a Road Vehicle by PIV Measurements

A particle image velocimetry (PIV) technique has been used to analyze the flow characteristics behind a road vehicle with/without an air spoiler attached on its trunk and also to estimate its effect on the wake. A vehicle model scaled in the ratio of 1/43 is set up in the mid-section of a closed-loop water tunnel. The Reynolds number based on the vehicle length is 105. To investigate the three-dimensional structure of the recirculation zone and vortices, measurements are carried out on the planes both parallel and perpendicular to the free stream, respectively. The results show significantly different vorticity distributions in the recirculation region according to the existence of the air spoiler. The focus and the saddle point, appearing in the wake, are disposed differently along the spanwise direction. Regarding the streamwise vortices, the air spoiler produces large wing tip vortices. They have opposite rotational directions to C-pillar vortices which are commonly observed in the case that an air spoiler is absent. The wing tip vortices generate the down force and as a result, they might make the vehicle more stable in driving.

Computation of a Two-dimensional Nozzle Flow with the Variation of Pressure and Length Ratios

The Navier-Stokes equations are numerically solved for a two-dimensional small nozzle with the area ratio of 1.8 between the throat and the exit. The shock structures are verified inside the nozzle and near the exit varying with the pressure ratio and the length of the diverging part, respectively. Especially the irregular patterns in the pressure distribution near the throat are analyzed based on the geometric characteristics. It is found that there are similar phenomena in the shock wave structure between the pressure ratio and the length changes. Also there exists a normal shock just between two different oblique shocks crossing each other in special cases.ࠀȀ耀Ѐ

Temperature Analysis for the Linear Cell in the Vapor Deposition Process

The OLED (Organic Light Emitting Diodes) display recently used for the information indicating device has many advantages over the LCD (Liquid Crystal Display), and its demand will be increased highly. The linear cell should be designed carefully considering the uniformity of thin film on the substrate. Its design needs to compute the temperature field analytically because the uniformity for the thin film thickness depends on the temperature distribution of the source (organic material). In the present study, the design of the linear cell will be modified or improved on the basis of the temperature profiles obtained for the simplified linear cell. The temperature distributions are numerically calculated through the STAR-CD program, and the grids are generated by means of the ICEM CFD program. As the results of the simplified linear cell, the temperature deviation was shown in the parabolic form among the both ends and the center of the source. In order to reduce the temperature deviation, the configuration of the rectangular ends of the crucible was modified to the circular type. In consequence, the uniform temperature is maintained in the range of about 90 percent length of the source. It is expected that the present methods and results on the temperature analysis can be very useful to manufacture the vapor deposition device.

Temperature Analysis for the Point-Cell Source in the Vapor Deposition Process

The information indicating device plays an important part in the information times. Recently, the classical CRT (Cathod Ray Tube) display is getting transferred to the LCD (Liquid Crystal Display) one which is a kind of the FPDs (Flat Panel Displays). The OLED (Organic Light Emitting Diodes) display of the FPDs has many advantages for the low power consumption, the luminescence in itself, the light weight, the thin thickness, the wide view angle, the fast response and so on as compared with the LCD one. The OLED has lately attracted considerable attention as the next generation device for the information indicators. And also it has already been applied for the outside panel of a mobile phone, and its demand will be gradually increased in the various fields. It is manufactured by the vapor deposition method in the vacuum state, and the uniformity of thin film on the substrate depends on the temperature distribution in the point-cell source. This paper describes the basic concepts that are obtained to design the point-cell source using the computational temperature analysis. The grids are generated using the module of AUTOHEXA in the ICEM CFD program and the temperature distributions are numerically obtained using the STAR-CD program. The temperature profiles are calculated for four cases, i.e., the charge rate for the source in the crucible, the ratio of diameter to height of the crucible, the ratio of interval to height of the heating bands, and the geometry modification for the basic crucible. As a result, the blowout phenomenon can be shown when the charge rate for the source increases. The temperature variation in the radial direction is decreased as the ratio of diameter to height is decreased and it is suggested that the thin film thickness can be uniformed. In case of using one heating band, the blowout can be shown as the higher temperature distribution in the center part of the source, and the clogging can appear in the top end of the crucible in the lower temperature. The phenomena of both the blowout and the clogging in the modified crucible with the nozzle-diffuser can be prevented because the temperature in the upper part of the crucible is higher than that of other parts and the temperature variation in the radial direction becomes small.

Topological Flow Characteristics in a Butterfly Valve Used for a Spark Ignition Engine

The flow fields in a butterfly valve, consisting of a circular cylinder and a circular plate with a circular shaft, are numerically investigated with changing the valve angle, i.e., 15°, 45°, 75° and 90°(full-open). The corresponding Reynolds numbers are chosen as 104, 4 × 104, 7 × 104, and 105. The pressure drops between the entrance and the exit of the valve are 0.904, 0.575, 0.382 and 0.199, respectively at the above four valve positions. The moment coefficients calculated for the valve shaft are mostly due to the unbalanced pressure distribution on the both sides of the valve plate and -0.365, -0.082, -0.033 and 0, respectively, for each valve angle. The pressure distribution on the valve cylinder and the topological streamline patterns qualitatively show the flow field exceedingly agitated by the valve plate and its shaft.

On the effect of the body force on the symmetry breaking in miscible two‐fluid channel flow

The two‐dimensional flow field is numerically investigated using a compact finite difference and a pseudo‐spectral method when two fluids with different physical properties are mixing under gravity as well as flow rate. The gravity and the viscous mobility affect the fingering instability, i.e. the mixing range shrinks much at the large viscous mobility or the strong gravity. When the gravitation acts parallel to the main stream, the flow decelerates or accelerates according to its direction. The fingertip velocity is exactly expressed by a pure cosine function and especially invariant when the gravity acts along the −y direction at the high Peclet number. The maximum and fingertip velocities at the very low Peclet number are nearly symmetric with respect to the −y direction perpendicular to the main flow direction x. When the gravity acts along the −y direction, the flow field shows the asymmetry, and a pair of vortices is generated at both the very high Peclet number and less viscous mobility number. As the viscous mobility becomes large, the vortex scale enlarges at the small Peclet number, while the vortices are slightly destroyed at the relatively high Peclet number. As the gravitational angle changes clockwise from downstream to upstream, a pair of vortices evolves through a process of asymmetry.

Effect of cross flow on aerodynamics of a commercial airplane

Summary This paper analyzes computationallythe flow field for the full geometry model of a commercial passenger airplane, Boeing747-400. The geometric dimension of an airplane was acquired by means of the reverse engineering technique adopting the photo scanning measurement. The steady three-dimensionalviscous compressible flow field was calculated when the airplane cruises under side flow. The basic computationalconditionswereconsideredasthesametothoseofBoeing747-400’s cruisingstate,i.e., theatmosphericconditionat 13km abovethesealevel and Mach numberof 0.85. Theboundaryconditionsare thesame thatthefreestream withside flow approaches to the aircraft. And the pressure conditions are set on the all remaining boundaries. The high Reynolds turbulence model is used, and the flow characteristics around the aircraft are discussed. Aerodynamic forces according to the Mach number and the angle of attack were analyzed; in addition effects of side flow on force and moment coefficients were described. When the rage of Mach number of crossflow is between 0 and 0.3, lift and drag coefficients were remarkably decreased and increased, respectively starting from cross flow Mach number 0.118; theformer decreases nearly 50% and thelatterincreases nearly 56% as comparison with the cruising condition.

Geometry Realization of an Airplane and Numerical Flow Visualization

The geometry of a commercial passenger airplane is realized based on a Boeing 747-400 model through the photographic scanning and reverse engineering. The each element consisting of the plane such as fuselage, wing, vertical fin, stabilizer and engines, is individually generated and then the whole body is assembled by the photomodeler. The maximum error in the realized airplane is about 1.4% comparing with the real one. The three-dimensional inviscid steady compressible governing equations are solved in the unstructured tetrahedron grid system, and in a finite volume method using STAR-CD when the airplane flies at the cruise condition. The pressure distribution on the surface and the wing-tip vortices are visualized, and in addition to the aerodynamics coefficients, lift and drag are estimated.

Aerodynamic Characteristics of Delta Wing According to Leading Edge Geometries

Flow visualization and aerodynamic characteristics of delta wings with two different leading edge geometries are investigated by PIV system and wind tunnel balance when the Reynolds number is about based on the freestream velocity and the root chord length. Delta wing models have 65-deg swept angle, and the leading edge shapes are divided into round- and sharp- type. The experimental results indicated that the leading-edge vortex strength and aerodynamic coefficient in the round leading edge are stronger and more, respectively than those in the sharp one. Therefore the flow interactions between vortices and the boundary layer are more desirable or more rapidly swirled in the round-type leading edge.