• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.28 no.2
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• pp.164-170
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• 1992

In order to understand and explain the spary combustion, it was necessary to understand the disintegration mechanisms of liquid jet. To understand the disintegration mechanisms of liquid jet, the disintegration phenomena and uniform droplet production regions of testing liquid jet was investigated by means of longitudinally vibration capillary nozzle, which was injected the testing liquids. The testing liquids were light oil and light oil and light oil blended with 25wt% fish oil (File fish oil, Sardine fish oil, Alaska pollac oil) The results can be summarized as follows: 1. The uniform droplet phenomena have been changed according to the frequency of capillary tube, the jet velocity and physical properties of testing oils. 2. Within the region of uniform droplet, Reynold number was increased as Weber number increases. 3. The lower limit of wave length in which uniform droplet was produced 0.8d which was lower than Rayleigh wave length 4. The light oil blended with file fish oil which has lower viscosity and surface tension had the widest uniform droplet production region on the frequency and velocity among testing oils. But light oil blended with sardine fish oil were similar with light oil in the uniform production region.

• Journal of the Korean Society of Visualization
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• v.13 no.1
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• pp.49-53
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• 2015

Recently, researches for droplet impact phenomena have been faced a new phase in the direction of studying the effect of complex external conditions (e.g. wettability, temperature, morphology, electric field, etc.) for depth understanding and precise controlling in various applications. Hence, here we investigated the electrified droplet impact phenomena, because there were few quantitative researches for electrified droplet impact when we considering many real applications such as electrospray, electrohydrodynamic (EHD) jet printing. To observe interaction effect of surface charge between substrate and droplet simultaneously, micro-droplets with various Reynolds number (Re) and Weber number (We) were dripped on super-hydrophobic surface with existence and nonexistence of electrical surface charge. It shows three kinds of impact behaviors, fully bouncing, partial bouncing, and splashing with different We. Also, charged droplet bounced higher on electrically charged surface than on non-charged surface. Additionally, transition regions of three impact behaviors were classified quantitatively with water hammer pressure value, which means instant pressure inside droplet at the impact moment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.1
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• pp.45-54
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• 2002

The breakup phenomena of a vertical laminar jet issuing from capillary tubes in a quiescent ambient air are investigated using a forced vibration analysis of the surface wave. Using a linear approach to the transient jet velocity, an approximate solution fur the longitudinal motion of a vertical liquid jet is theoretically derived, thus performing an instability analysis by a vibration method. The damping term of this equation is nonlinear as it depends on dimensionless parameters, a Weber number, and an Ohnesorge number. The instability condition is determined based on whether the coefficient of the damping term is less than zero or not. Uniform drop formation is dependent on the vibration frequency fur the forced vibration case.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.301-308
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• 1999

The present study investigates numerically particle laden flow through compressor cascades and a rocket nozzle. Engines are affected by various particles which are suspending in the atmosphere. Especially in the case of aircraft aviating in volcanic, industrial and desert region including many particles, each components of engine system are damaged severely. That damage modes are erosion of compressor blading and rotor path components, partial or total blockage of cooling passage and engine control system degradation. Numerical prediction and experimental data, erosion rates are predicted for two materials - ceramic, soft metal - on compressor blade surface. Aluminum oxide ($Al_2O_3$) Particles included in solid rocket propelant make ablative the rocket motor nozzle and imped the expansion processes of propulsion. By the definition of particle deposition efficiency, characteristics of particles impaction are considered quantitatively Stoke number is defined over the various particle sizes and particle trajectories are treated by Lagrangian approach. Particle stability is considered by definition of Weber number in rocket nozzle and particle breakup and evaporation is simulated in a rocket nozzle.

• Food Science and Preservation
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• v.30 no.4
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• pp.589-601
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• 2023

Malaysian honey is rich in nutrients and bioactive compounds, which can be a healthy alternative to refined sugar in food production. However, liquid honey's viscous and sticky nature makes it unpreferable in industrial handling. This study, an atomization system coupled with vacuum drying to produce honey powders to overcome the problem. Three types of Malaysian honey, namely Acacia, Gelam, and Tualang, were encapsulated in Ca-alginate gel beads using the atomization system. The density viscosity, and surface tension of the honey-alginate solutions were measured, and the concentration of honey and alginate influenced the physical properties of the solutions. Honey-encapsulated gel beads in the size range of 2.16-2.92 mm were produced using the atomization system with the air-liquid mass flow rate ratios of 0.22-0.31, Weber number (We) of 112-545, and Ohnersorges number (Oh) of 0.35-10.46. Gel bead diameter can be predicted using a simple mathematical model. After vacuum drying, the honey gel powder produced was in the size range of 1.50-1.79 mm. Results showed that honey gel powders with good encapsulation efficiency and high honey loading could be produced using the atomization system and vacuum drying.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.2
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• pp.141-147
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• 2015

The contrast of a display is generally evaluated by using the ratio of the minimum luminance to the maximum luminance of the display. However, this contrast ratio is not matched with perceived contrast because it uses only physical characteristic of display without considering human perceptual characteristics. In this paper, the proposed contrast measure that considers perceptually discriminable brightness within the range of display brightness is suggested. First, the range between the minimum and maximum brightness of display in CIECAM02 color space is calculated to measure the length of perceived brightness for the display. Next, brightness ranges which are perceptually same at each brightness level are determined by applying Weber-Fechner ratio and then, the number of brightness values within each brightness range is counted. Finally, perceptually discriminable brightness is defined as the sum of ratio between the number of brightness values in each brightness range and the perceptual contrast length of the display. In the experiments, preference test using various displays with random brightness patches is performed to evaluate perceived contrast. As a result, the proposed measure is more consistent with human perception than the previous contrast measures.

• Korean Journal of Cognitive Science
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• v.24 no.3
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• pp.271-300
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• 2013

Human and animals are born with an intuitive ability to determine approximate numerosity. This ability is termed approximate number sense (hereafter, number sense). Evolutionarily, number sense is thought to be an essential ability for hunting, gathering and survival. According to previous research, children with mathematical learning disability have impaired number sense. On the other hand, individuals with more accurate number sense have higher mathematical achievement. These results support the hypothesis that number sense provides a basis for the development of mathematical cognition. Recently, researchers have been examining whether number sense training can lead to enhancement in mathematical achievement and changes in brain activity in relation to mathematical problem solving. Numerosity which basically represents discontinuous quantity is expected to be closely related to continuous quantity such as representations of space and time. A theory of magnitude (ATOM) states that processing of number, space and time is based on a common magnitude system in the posterior parietal cortex, especially the intraparietal sulcus. The present paper introduces current literature and future directions for the study of the common magnitude system.

• Journal of computational fluids engineering
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• v.21 no.4
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• pp.90-95
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• 2016

Leidenfrost drops with ellipsoidal shaping can control the bouncing height by adjusting the aspect ratio(AR) of the shape at the moment of impact. In this work, we focus on the effect of the AR and the impact Weber number(We) on the non-axisymmetrical spreading dynamics of the drop, which plays an important role in the control of bouncing. To understand the impact dynamics, the numerical simulation is conducted for the ellipsoidal drop impact upon the perfect non-wetting solid surface by using volume of fluid method, which shows the characteristics of the spreading behavior in each principal axis. As the AR increases, the drop has a high degree of the alignment into one principal axis, which leads to the consequent suppression of bouncing height with shape oscillation. As the We increases, the maximum spreading diameters in the principal axes both increase whereas the contact time on the solid surface rarely depends on the impact velocity at the same AR. The comprehensive understanding of the ellipsoidal drop impact upon non-wetting surface will provide the way to control of drop deposition in applications, such as surface cleaning and spray cooling.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.2
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• pp.87-92
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• 2008

The breakup processes and spray plume characteristics of liquid jets injected in subsonic air cross-flows were experimentally studied. The behaviors of column, penetration, breakup of plain liquid jet and droplet sizes, velocities have been studied in non-swirling cross-flow of air. Nozzle has a 1.0 mm diameter and Lid ratio=5. Experimental results indicate that the breakup point is delayed by increasing air momentum, the penetration decreases by increasing Weber number and the split angle is increased by increasing air velocity or decreasing injection velocity. SMD increases according as increasing height or decreases in accordance with increasing air velocity. This phenomenon is related to the momentum exchange between column waves and cross-flow stream. Droplet vector velocities were varied from 11.5 to 33 m/s. A higher-velocity region can be identified in down edge region at Z/d=40, 70 and 100. Lower-velocity region were observed on bottom position of the spray plume.

• Journal of ILASS-Korea
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• v.5 no.2
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• pp.53-60
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• 2000

An aerodynamically progressed model, which is called APTAB model. has been proposed for more accurate prediction of the deformation and breakup of a spray. Especially, the effects of the droplet deformation on the droplet aerodynamic external force are considered in this model, which was neglected in TAB model. It is found that the predicted droplet deformation using APTAB model shows better agreement with experimental data than those of other models for the droplets in both bag-type and shear-type breakup regimes. A new breakup criterion has been proposed to predict more reasonable breakup quantities, such as breakup deformation length, time and so on; i.e., it is defined that the breakup occurs when the internal liquid phase pressure of the deformed droplet at the equator is greater than that of the pole. The proposed breakup criterion shows more physical relationship between the degree of droplet deformation at breakup and the corresponding breakup Weber number as compared with the results with TAB and DDB models. Therefore, it provides better predictions of the experimental data than TAB and DDB models for the droplet deformation and time in both bag-type and shear-type breakup regimes.