• Journal of the Korean Society of Combustion
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• v.11 no.2
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• pp.28-36
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• 2006

A constant volume combustion chamber was used to investigate the combustion characteristics. of homogeneous charge of methane-air mixture under various initial pressure, equivalence ratio and ignition times. The constant volume combustion chamber(CVCC) mostly has been studied by the experiments of visualization until now. So it is needed the numerical analysis of fluid and combustion characteristics in chamber by the more detail simulation. In this paper, the numerical analysis is tried to approach basically the homogeneous charge combustion phenomena under the various conditions, and the combustion phenomena in chamber is numerically analyzed by the commercial FIRE code. As a results, the combustion phenomena which were mean temperature, OH radical and reaction rate in chamber were investigated and it showed that the smallest flame growth occurs for the lean state and the increase of initial charged pressure condition due to the reduced OH radical.

• Journal of Animal Reproduction and Biotechnology
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• v.35 no.2
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• pp.177-182
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• 2020

The present study aimed to investigate the conceptus-related changes during early pregnancy in the Black Bengal breed of goat. A total of 22 gravid genitalia of the Black Bengal goats were collected from local slaughterhouses. The crown-rump lengths (CRL) of the conceptuses were determined to estimate the gestational age (GA). The length and diameter of uterine horn and amniotic sac were measured, and volume of amniotic and allantoic fluid formed by individual conceptus were recorded. The results reveal that the CRL is positively correlated with GA of the conceptus (R² = 0.89, p < 0.05); however, CRL was not influenced by number of conceptus. Both the left and the right uterine horn gradually increased in size with the advancement of pregnancy irrespective of conceptus number present in the horn. The size of the amniotic sac of conceptus gradually increased with the conceptus age but maintained spherical shape from 5 to 7 weeks of pregnancy. The amniotic fluid formed by individual conceptus rapidly increased from 5 weeks (3.4 ± 0.3 mL) to 7 weeks (21.0 ± 2.0 mL) and 9 weeks (111.5 ± 4.0 mL). The volume of allantoic fluid formed by individual conceptus was steadily increased until 7 weeks (60.0 ± 5.0 mL) and began to decline slowly thereafter (50.0 ± 5.0 mL at 9 weeks). Notably, there was no effect of conceptus number per pregnancy on individual amniotic and allantoic fluid volume. The cotyledons have first appeared on the allanto-chorionic surface from 4 to 5 weeks of pregnancy. The closed eye, nostril and hooves of the conceptus became visible at 7 weeks of pregnancy. The present study has shown the basic information on conceptus-related developmental changes during early pregnancy up to 9 weeks in Black Bengal goat.

• Journal of the Korean Society of Visualization
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• v.18 no.2
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• pp.46-50
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• 2020

On-demand droplet generation with tunable droplet volume is fundamental in many droplet microfluidic applications. In this work, we propose an acoustofluidic method to produce water-in-oil droplets with prescribed volume in an on-demand manner. Surface acoustic waves produced from a slanted interdigital transducer are coupled with parallel laminar streams of dispersed and continuous phase fluids. Acoustic radiation force acting on the fluid interface enable generation of droplets in a microfluidic chip. We expect that the proposed acoustofluidic droplet generation method will serve as a promising tool for on-demand droplet generation with on-chip droplet volume control.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1857-1862
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• 2004

EK pumps packed with particles inside capillaries are involved in the mixed electroosmotic flow and pressure driven flow. For analysis in the porous EK pumps, the volume-averaging technique is applied to derive the volume-averaged equations for momentum and electrical potential. By using the volume-averaged equations, analytical solutions for electric potential and velocity distribution due to the mixed electroosmotic and pressure driven flows are obtained. The present analysis is validated by comparison with numerical and experimental results for the case of microchannel EK pumps.

• Nuclear Engineering and Technology
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• v.56 no.6
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• pp.2029-2038
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• 2024

A deep understanding of the characteristics and mechanism of geyser boiling and capillary pumping is necessary to optimize a high-temperature sodium heat pipe. In this work, the Volume of Fluid (VOF) two-phase model and the capillary force model in the mesh wick were used to model the complex phase change and fluid flow in the heat pipe. Computational Fluid Dynamics (CFD) simulations successfully predicted the process of bubble nucleation, growth, aggregation, and detachment from the wall in the liquid pool of the evaporation section of the heat pipe in horizontal and tilted states, as well as the reflux phenomenon of capillary suction within the wick. The accuracy and stability of the capillary force model within the wick were verified. In addition, the causes of geyser boiling in heat pipes were analyzed by extracting the oscillation distribution of heat pipe wall temperature. The results show that adding the capillary force model within the wick structure can reasonably simulate the liquid backflow phenomenon at the condensation; Under the horizontal and inclined operating conditions of the heat pipe, the phenomenon of local dry-out will occur, resulting in a sharp increase in local temperature. The speed of bubble detachment and the timely reflux of liquid sodium (condensate) replenishment in the wick play a vital role in the geyser temperature oscillation of the tube wall. The numerical simulation method and the results of this study are anticipated to provide a good reference for the investigation of geyser boiling in high-temperature heat pipes.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.5
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• pp.405-414
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• 2015

Fluid transport is a key issue in the development of microfluidic systems. Recently, Myong (2014) has proposed a new concept for droplet transport without external power sources and numerically validated the results for a hypothetical 2D, initially having a hemicylindrical droplet. In this paper, the movement of an actual water droplet, initially having a 3D hemispherical shape, on horizontal hydrophilic/hydrophobic surfaces is simulated using a commercial computational fluid dynamics (CFD) package, Fluent, with VOF (volume of fluid) method. The results are compared with the 2D analysis of Myong (2014), and the transport mechanism for the actual water droplet is examined based on the numerical results of the time evolution of the droplet shape, as well as the total kinetic, gravitational, surface free and pressure energies inside the droplet.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.12
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• pp.1555-1569
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• 2000

Numerical simulation of fluid flow with moving free surface has been carried out. For the free surface flow, a VOF(Volume of Fluid)-based algorithm utilizing a fixed grid system has been investigated. In order to reduce numerical smearing at the free surface represented on a fixed grid system, a new free surface tracking algorithm based on the donor-acceptor scheme has been presented. Novel features of the proposed algorithm are characterized as two numerical tools; the orientation vector to represent the free surface orientation in each cell and the baby-cell to determine the fluid volume flux at each cell boundary. The proposed algorithm can be easily implemented in any irregular non-uniform grid systems that are usual in finite element method (FEM). Moreover, the proposed algorithm can be extended and applied to the 3-D free surface flow problem without additional efforts. For computation of unsteady incompressible flow, a finite element approximation based on the explicit fractional step method has been adopted. In addition, the SUPG(streamline upwind/Petrov-Galerkin) method has been implemented to deal with convection dominated flows. Combination of the proposed free surface tracking scheme and explicit fractional step formulation resulted in an efficient solution algorithm. Validity of the present solution algorithm was demonstrated from its application to the broken dam and the solitary wave propagation problems.

• Journal of Biomedical Engineering Research
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• v.28 no.6
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• pp.768-776
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• 2007

A new type of the fluid circulation blood pressure simulator was proposed to enhance the blood pressure simulator used for the development and evaluation of automatic sphygmomanometers. Various pressure waveform of fluid flowing in the pipe was reproduced by operating the proportional control valve after applying a pressure on the fluid in pressurized oil tank. After that, appropriate fluid was supplied by operating the proportional control valve, which enabled to reproduce various pressure wave of the fluid flowing in the tube. To accomplish this work, the mathematical model was carefully reviewed in cooperating with the proposed simulator. After modeling the driving signal as input signal and the pressure in internal tube as output signal, the simulation on system parameters such as internal volume, cross-section of orifice and supply pressure, which are sensitive to dynamic characteristic of system, was accomplished. System parameters affecting the dynamic characteristic were analyzed in the frequency bandwidth and also reflected to the design of the plant. The performance evaluator of fluid dynamic characteristic using proportional control signal was fabricated on the basis of obtained simulation result. An experimental apparatus was set-up and measurements on the dynamic characteristic, nonlinearity, and rising and falling response was carried out to verify the characteristic of the fluid dynamic model. Controller was designed and thereafter, simulation was performed to control the output signal with respect to the reference input in the fluid dynamic model using the proposed proportional control valve. Hybrid controller combined with an proportional controller and feed-forward controller was fabricated after applying a disturbance observer to the control plant. Comparison of the simulations between the conventional proportional controller and the proposed hybrid simulator indicated that even though the former showed good control performance.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.5
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• pp.611-618
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• 2018

In this study, numerical analysis of solid-liquid two-phase flow was conducted as a preliminary step to analyze the flow characteristics of drilling fluid using the commercial CFD code, ANSYS CFX 14.5. The homogeneous model and separated flow model were used to simulate solid-liquid two-phase flow phenomena. In the separated flow model, Gidaspow's drag force model was applied with the kinetic theory model was applied for solid particles. The validity of the numerical model used in this study was verified based on the published experimental results. Numerical analysis was carried out for volume fractions of 0.1 to 0.5 and velocities of 1 to 5 m/s in a horizontal tube with a diameter of 54.9 mm and a length of 3 m. The Pressure drop and volume fraction distribution of solid particles were confirmed. The pressure drop was predicted using the homogeneous model and separated flow model within the MAE of 17.04 % and 8.98 %, respectively. A high volume fraction was observed in the lower part of the tube, and the volume fraction decreased toward the upper part. As velocity increased, variations in volume fraction distribution at varying heights were decreased, and the numerical results predicted these flow characteristics well.

• The Journal of the Acoustical Society of Korea
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• v.32 no.1
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• pp.14-21
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• 2013

The erosion, suspension, and transport of sediment frequently occur in the coastal waters and estuarine. These processes often generate the so-called fluid mud layer, which is defined as a high-concentration aqueous suspension of fine grained sediment (> 10 g/l), consisting mainly of silt and clay-size particles. Therefore the high-resolution ultrasound is mostly used to detect or monitor the fluid mud layer. Because the sound attenuation tends to increase rapidly with the suspended sediment concentration, it is necessary to consider the accurate attenuation correction to estimate the backscattering strengths from the suspended sediment layers. In this paper, the volume backscattering strengths with various suspended sediment concentrations were measured using 5-MHz ultrasound signal in a small-scale water tank. The sound attenuation due to the viscosity and scattering from suspended sediment particles was predicted by the Richard's model and applied to the sonar equation to estimate the volume backscattering strengths from the suspended sediment concentrations. For the case that the additional attenuation was not considered, the volume backscattering strengths increased to the concentration of 20 g/l, and over this point, the backscattering strengths were roughly constant. However, for the case that the attenuation due to the suspended sediment concentration was considered, the backscattering strengths increased with the concentration.