• 대한기계학회논문집
• /
• 제18권12호
• /
• pp.3386-3394
• /
• 1994

An experimental study has been performed on the flow over a rotating disk, where the diameter of the disk is 500 mm and the maximum vertical deviation of the upper surface is $50 \mu{m}$ for the whole range of the angular velocity up to 3400 rpm. The flow visualization experiment for the wall jet flow induced by impinging circular jet is carried out using schlieren system and measurements are made by 3-hole and 5-hole pitot tubes. Schlieren photographs show that as the rotating speed increases the wall jet flow becomes more stable and the size of the largest eddies becomes smaller. Measurements for impinging jet flow on the stationary disk verify the accuracy of the present experiment, and those for free rotating disk flow display the existence of transition region from laminar to turbulent flows. Measurements for impinging jet flow on the rotating disk exhibit the interaction between the wall jet and the viscous pumping effect, which explains the decay in size of turbulent eddies illustrated by the schlieren photographs.

• 한국분무공학회지
• /
• 제16권4호
• /
• pp.201-209
• /
• 2011

Optimum engine performance is obtained when the spray characteristics is well matched to the geometry of a combustion chamber. Among many parameters governing the combustion performance in internal combustion engine, fuel supply characteristics and atomization are important performance factors. Therefore, spray characteristics of high pressure multi-hole injector has been studied experimentally. An experimental test system has been made to operate high pressure injection system and to visualize spray behavior. Spray visualization has been performed to analyze spray formation, spray cone angle, bent angle and penetration length. Spray interaction with piston has been analyzed with various injector installation angle, injection pressure and ambient pressure. Test results show that penetration length is greatly influenced by the injection pressure. Penetration length is decreased as ambient pressure increased. Spray cone angle is increased as injection pressure and ambient pressure increased. However, bent angle is not influenced by the change of injection pressure and ambient pressure. Spray cone angle distribution map is plotted using the experimental data. Fuel movement around the spark-plug has been enforced as increasing injector installation angle.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
• /
• pp.122-128
• /
• 2000

Aerodynamic optimization of an automotive air-conditioning blower is a hard task because of the highly complex flow phenomena related to three-dimensional flow separations and the unsteady nature caused by the interaction between primary and secondary air flows throughout the fan. In this paper, an aerodynamic study on a forward-curved centrifugal fan has been carried out Firstly we obtained the fan performance curves versus flow rates showing its unstable nature in the surging operation range. Secondly aerodynamic characterizations were carried out by investigating the velocity and pressure fields in the casing flow passage using a 5-hole pilot probe, at different operating conditions. Surface flow pattern near the cut-off area exhibits similar flow behavior above the best efficiency operating point, although the pressure level increases substantially with the Increase of flow rate. Vorticity in the casing passage flow occurs in all (low rates, downstream from the r-Z plane $\theta$=120 deg., where the position of its core changes with the circumferential location. Although complex, the general flow behavior were common, giving insight in its main aerodynamic features.

• 한국자동차공학회논문집
• /
• 제20권5호
• /
• pp.44-52
• /
• 2012

Fuel cell electric vehicles have some noise problems due to its air processing unit which is required to feed the ambient air into the fuel cell stack. Discrete-frequency noises are radiated from a centrifugal blower due to rotor-stator interaction. Their fundamental frequency is the blade passing frequency, which is determined by the number of rotor blades and their rotating speed. To reduce such noises, multi-chamber perforated muffler has been designed. In this paper, in order to improve the transmission loss of a perforated muffler, the relationship between the impedance model of a perforated hole and its noise reduction performance is studied, and the applicability of a short-length perforated muffler to air processing unit of fuel cell system is described using acoustic simulation results and experimental data. The acoustic velocity vector across the neck of a perforated hole is very important design factor to optimize the transmission of an intake muffler. The suggested short-length perforated muffler is effective on discrete-frequency noises while keeping the volume of intake muffler minimized.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2002년도 추계학술대회 논문집 Vol.15
• /
• pp.375-378
• /
• 2002

There has recently been a great deal of interest in amorphous selenium for application of digital x-ray image sensor. The initial number of the electron-hole induced by interaction a-Se with x-ray photons and the collection efficiency to surface of generated charges are important parameters for x-ray sensitivity of the a-Se. Therefore, in this paper, we analyzed that thickness of a-Se film and electric field is affected on the initial number of electron-hole and the collection efficiency. The experimental value of x-ray induced charge about the various thickness and the electric field is compared with estimated absorbed energy through MCNP 4C code to analyze the mechanism x-ray induced signal of a-Se. The experimental results showed that the electric field depends on initial escape coefficient and the thickness depends on collection coefficient than escape efficient.

• 한국분무공학회지
• /
• 제2권2호
• /
• pp.8-15
• /
• 1997

Combustion chamber systems using spray impinged on walls have been studied for improving combustion characteristics in high speed direct injection diesel engines. The fuel spray injected in a small combustion chamber may be easily impinged and deposited on the wall. The fuel deposit has been considered as the cause for unburned emission due to difficulty of fuel-air mixing. In this paper w-shaped combustion chamber which has four raised pips on the side wall is introduced and discussed by comparing with conventional chamber with no pips. The computer code employing new spray-wall interaction model in general non-orthogonal grids is used in here. The model is applied into the new chamber shape with raised pips. In this chamber system four-hole nozzle is used, and the sprays injected from the each hole impact on lands raised from the chamber wall surface. After impacting, the sprays break up into much smaller drops and distribute over all the chamber space, instead of distributing just near the wall surface in conventional omega-shape. The results showed the potential of the w-shaped chamber employing pips for dispersing droplets so as tn avoid the fuel deposit regions.

• Bulletin of the Korean Chemical Society
• /
• 제28권8호
• /
• pp.1358-1362
• /
• 2007

The structures, energetics and transfer integrals of the acene tetramers up to pentacene are investigated with the ab initio molecular orbital method at the level of second-order Møller-Plesset perturbation theory (MP2). Calculated geometries for the herringbone-style structures found in the crystal structure were characterized as local minima, however the geometrical discrepancy between crystal and MP2 theoretical structure is reasonably small. The binding energy of pentacene tetramer was calculated up to 40 kcal/mol (MP2/6-31G(d)) and about 90 kcal/mol (MP2/aug-cc-pVDZ), and the latter seems to be too much overestimated. The tendency of the hole transfer integrals computed with ab initio MP2/3-21G(d) geometry is well agreement with those estimated with crystal structure with some discrepancy, and the gradual increment of the transfer integrals at the crystal geometry is attributed to mainly packing structure rather than the intrinsic property of acene such as a size of acene.

• Water Engineering Research
• /
• 제2권3호
• /
• pp.179-185
• /
• 2001

The time consuming and expensive nature of experimental research on scouring processes caused by flowing water makes it attractive to develop numerical tools for the predication of the interaction of the fluid flow and the movable bed. In this paper the numerical simulation of scour by a wall jet is presented. The flow is assumed to be two-dimensional, and the alluvium is cohesionless. The solution process, repeated at each time step, involves simulation of a turbulent wall jet flow, solution of the convection-diffusion of sand concentration, and prediction of the bed deformation. For simulation of the jet flow, the governing equations for momentum, mass balance and turbulent parameters are solved by the finite volume method. The SIMPLE scheme with momentum interpolation is used for pressure correction. The convection-diffusion equation is solved for sediment concentration. A boundary condition for concentration at the bed, which takes into account the effect of bed-load, is implemented. The time rate of deposition and scour at the bed is obtained by solving the continuity equation for sediment. The shape and position of the scour hole and deposition of the bed material downstream of the hole appear realistic.

• 한국정보디스플레이학회:학술대회논문집
• /
• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
• /
• pp.108-111
• /
• 2009

We have determined the electronic energy level alignment at the interface between 4,4'-bis-N-phenyl-1-naphthylamino biphenyl (NPB) and 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HAT-CN) using ultraviolet photoelectron spectroscopy (UPS). The highest occupied molecular orbital (HOMO) of 20 nm thick HAT-CN film was located at 3.8 eV below the Fermi level. Thus the lowest unoccupied molecular orbital (LUMO) is very close to the Fermi level. The HOMO position of NPB was only about 0.3 eV below Fermi level at NPB/HAT-CN interface. This enables an easy excitation of electrons from the NPB HOMO to the HAT-CN LUMO, creating electron-hole pairs across this organic-organic interface. We also study the interaction of HAT-CN with a few metallic surfaces including Ca, Cu, and ITO using UPS and ab-inito electronic structure calculation techniques.

• 한국연소학회지
• /
• 제19권3호
• /
• pp.44-52
• /
• 2014

Solid oxide fuel cell(SOFC) makes electric power using hydrogen or reformed from methane and emits high temperature products that contain flammable species like hydrogen, carbon monoxide and methane which varies with operation condition. SOFC/gas turbine integrated system which uses thermal and chemical energy of the discharges is more efficient than SOFC itself. Burning character of the SOFC products will affect the efficiency and stability of the system. Experiments were conducted to know the characteristics of the flame for two typical composition of SOFC products, i.e. start-up and steady state composition. When coflowing air temperature was higher than $600^{\circ}C$, auto-ignitin occurred for both fuels. Though start-up fuel has higher contents of hydrogen, it makes longer flame than steady state composition. It was inferred that the amount of oxidizer necessary to burn makes this phenomenon. Steady state composition fuel was unstable since it contains lots of water. Nozzle that had 6 holes, distance between each hole was 16.7 times of hole diameter, improved the stability of the flame.