• Current Optics and Photonics
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• v.6 no.3
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• pp.332-336
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• 2022

Given a cubic space, it is easy to uniformly illuminate the floor with light sources placed on top. However, little has been reported about uniform illumination on walls with the same configuration of light sources. Here we present a luminaire consisting of nine light-emitting diodes (LEDs) with perfect Lambertian distribution, placed on the top as a 3 × 3 rectangular LED array. The distances between LEDs and tilt angles of each individual LED are adjustable and optimized by an annealing algorithm. After optimization, the array produces a rectangular illumination pattern on one wall with a uniformity of about 89%. Analysis shows that the tilt angles of individual LEDs are key parameters for uniform side illumination. In a scenario that is more practical, the tilt angles of all the LEDs are set to be the same, only decreasing the uniformity to 83%.

• Journal of computational fluids engineering
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• v.15 no.1
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• pp.56-63
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• 2010

Since emission regulations for vehicles have become more stringent, SCR technology has drawn a strong attention in order to reduce NOx emissions. Optimal design of a reductant injection nozzle and a multi-hole plate located between the cone and catalyst is critical in that the uniform distribution of reductant is necessary to maximize the NOx conversion efficiency and minimize the slip of reductant in SCR. In this work, an LPG fuel(C3H8 in vapor state) was used as a reductant for LPG vehicles. A Realizable k-$\varepsilon$ model is used for turbulence, and SCR body is defined as porous media with inertia and viscous resistances measured in this work. Effect of the number of nozzle holes on the flow mixing index was analyzed, which revealed that a four hole nozzle shows the best performance in terms of uniformity of flow. An installment of a multi-hole plate at the entrance of catalyst was evaluated with flow mixing index, uniformity of flow, and pressure drop. A multi-hole plate with gradual hole diameter change in three steps showed the best uniformity of flow within the conditions suggested in this work.

• International Journal of Control, Automation, and Systems
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• v.2 no.2
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• pp.256-262
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• 2004

Conventionally, profile non-uniformity has been characterized by relying on approximated profile with angle or anisotropy. In this study, a new non-uniformity model for etch profile is presented by applying a discrete wavelet to the image obtained from a scanning electron microscopy (SEM). Prediction models for wavelet-transformed data are then constructed using a back-propagation neural network. The proposed method was applied to the data collected from the etching of tungsten material. Additionally, 7 experiments were conducted to obtain test data. Model performance was evaluated in terms of the average prediction accuracy (APA) and the best prediction accuracy (BPA). To take into account randomness in initial weights, two hundred models were generated for a given set of training factors. Behaviors of the APA and BPA were investigated as a function of training factors, including training tolerance, hidden neuron, initial weight distribution, and two slopes for bipolar sig-moid and linear function. For all variations in training factors, the APA was not consistent with the BPA. The prediction accuracy was optimized using three approaches, the best model based approach, the average model based approach and the combined model based approach. Despite the largest APA of the first approach, its BPA was smallest compared to the other two approaches.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.3
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• pp.16-23
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• 2008

Flow analyses have been performed to investigate the uniformity of propellant flow through the oxidizer manifold of a 30 tonf full-scaled combustor. Injectors were simulated as porous medium layers of equivalent pressure drops. The uniformity of oxidizer propellant has been analyzed for various diameters of holes in vertical/horizontal distributors and configurations of oxidizer inlet to propose an improved design solution. It has been proven that the mass flow uniformity were improved by adjusting the holes in vertical/horizontal distributors.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.127-130
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• 2009

The uniform gas distribution between anode channels of the indirect internal reforming type molten carbonate fuel cell (MCFC) is crucial design parameter because of the electric performance and the durability problems. A three-dimensional computational fluid dynamics (CFD) analysis is performed to investigate flow characteristics in the anode channels and manifold under different pressure drop and channel temperature conditions. The combined meshes consists of hexadral meshes in the channels and polyhedral meshes in the manifold are adopted and chemical reactions inside the MCFC system are not included because of computational difficulties associated with the size and geometric complexity of the system. Results indicate that the uniformity in flow-rate is in the range of $\pm$ 0.048 % between the anode channels when the pressure drop of anode channel is about 150 Pa. A gas flow-rate uniformity decreases as the pressure drop of anode channels decreases and as the temperature difference between indirect internal reforming (IIR) channels and anode channels increases.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.4
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• pp.108-114
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• 2007

This research represents the catalytic converter for application in the motorcycle. We have to consider about catalytic converter for reducing exhaust gas strength regarding the displacement volume enlargement. The catalytic converter has been widely used to satisfy the regulations of pollutant emissions from automobiles. Recently, all catalytic converter researches are about automobile. Study about motorcycle catalytic converter has not been conducted yet. In this study, flow uniformity and pressure distribution were simulated in the monolithic inlet of catalytic converter for motorcycle. Exhaust pulsation pressure was set as transient condition about. It was found that flow uniformity shown in base model (0.85) was lower than megaphone model (0.98).

• Journal of the Semiconductor & Display Technology
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• v.20 no.2
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• pp.19-24
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• 2021

As the size of semiconductor devices decreases, the etching pattern becomes very narrow and a deep high aspect ratio process becomes important. The cryogenic etching process enables high aspect ratio etching by suppressing the chemical reaction of reactive ions on the sidewall while maintaining the process temperature of -100℃. ESC is an important part for temperature control in cryogenic etching equipment. Through the cooling path inside the ESC, liquid nitrogen is used as cooling water to create a cryogenic environment. And since the ESC directly contacts the wafer, it affects the temperature uniformity of the wafer. The temperature uniformity of the wafer is closely related to the yield. In this study, the cooling path was designed and analyzed so that the wafer could have a uniform temperature distribution. The optimal cooling path conditions were obtained through the analysis of the shape of the cooling path and the change in the speed of the coolant. Through this study, by designing ESC with optimal temperature uniformity, it can be expected to maximize wafer yield in mass production and further contribute to miniaturization and high performance of semiconductor devices.

• Journal of the Korean GEO-environmental Society
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• v.14 no.5
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• pp.41-47
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• 2013

Well-graded and dense soils have good engineering properties. Unsaturated soil properties such as shear strength, compressibility and permeability are closely related to the soil-water characteristic curve of the soil. Therefore it is important to study the effects of the coefficient of uniformity and the porosity on the soil-water characteristic curve of the sandy soils, which are also related to the grain size distribution and the density of the soil, respectively. In this study soil-water characteristic curves (SWCCs) for six sandy soil specimens were investigated using Tempe pressure cells. The test data were best-fitted to Fredlund and Xing equation. The obtained fitting parameters and the characteristic points of SWCCs were discussed and correlated with the porosity and the coefficient of uniformity of the specimens. The results show that the smaller the porosity of the specimen becomes, the larger the value of the residual matric suction becomes, whereas the larger the coefficient of uniformity of the specimen becomes, the larger the value of the residual matric suction becomes. Regardless of the coefficient of uniformity, the smaller the porosity of the specimen, the flatter the max. slope of SWCC.

• Journal of the Semiconductor & Display Technology
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• v.21 no.3
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• pp.101-104
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• 2022

Mist-CVD is known to have advantages of low cost and high productivity compared to ALD and PECVD methods. It is capable of reacting to the substrate by misting an aqueous solution using ultrasonic waves under vacuum-free conditions of atmospheric pressure. In particular, Ga₂O₃ is regarded as advanced power semiconductor material because of its high quality of transmittance, and excellent electrical conductivity through N-type doping. In this study, Computational Fluid Dynamics were used to predict the uniformity of the thin film on a large-area substrate. And also the deposition pattern and uniformity were analyzed using the flow velocity and particle tracking method. The uniformity was confirmed by quantifying the deposition cross section with an FIB-SEM, and the consistency of the uniformity prediction was secured through the analysis of the CFD distribution. With the analysis and experimental results, the match rate of deposition area was 80.14% and the match rate of deposition thickness was 55.32%. As the experimental and analysis results were consistent, it was confirmed that it is possible to predict the deposition thickness uniformity of Mist-CVD.

• KSTLE International Journal
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• v.2 no.2
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• pp.114-119
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• 2001

The distribution of magnetic flux density of electro-magnetic chucks may clarify the clamping characteristics, which is strongly related to the machining efficiency and machining accuracy in surface grinding machine. Therefore the distribution of the normal and the tangential components of magnetic flux density have been analyzed theoretically. It appears that the normal component of magnetic flux density increases and the tangential component of magnetic flux density increases as the ratio of the separator width to the pitch, e/p decreases. The results seem to increase the stability and uniformity of normal component of magnetic flux density for the decreased e/p.