• Journal of the Korean Institute of Gas
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• v.26 no.6
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• pp.37-44
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• 2022

In this study, two low-swirl nozzles with the same SN (Swirl Number) but different mass ratio (m) of the core part and the swirler part were designed to perform an atmospheric pressure combustion test. For each nozzle, a combustion test was conducted according to the adiabatic flame temperature, and the flame structure, emissions, and combustion instability mode were identified. Although the flame structure was significantly different, the CO emission was similar, and the NOx emission was also more related to combustion dynamics than the flame structure. Combustion dynamics and NOx emission were identified while adjusting the convection delay time by changing the position of the fuel injection nozzle. It was confirmed that when the convection delay time is in the region of (3+4n)/4T±1/4T (n=0,1,2,...), the combustion instability is strong, and in the opposite case, the combustion instability is very weak.

• Journal of ILASS-Korea
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• v.22 no.2
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• pp.55-61
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• 2017

This study has investigated the relationship between heat release fluctuations and the flow perturbations in a partially premixed gas turbine combustor using a commercial CFD code. Special focus of the current work is placed on the effect of equivalence ratio on the flame dynamics in a partially-premixed system. As the first step for this combustion dynamics study in the non-perfectly premixed combustor, flame behaviors are modeled and then compared with measured results under both steady and unsteady conditions. The calculated results of the flame transfer function with equivalence ratio fluctuation are found to well capture the main qualitative characteristics of the combustion dynamics for the partially-premixed flames.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.247-252
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• 2001

In this paper, dynamic modeling and its analysis for the PIG flow through $90^{\circ}$ curved pipe with compressible and unsteady flow are studied. The PIG dynamics model is derived by using Lagrange equation under assumption that it passes through 3 different sections in the curved pipeline such that it moves into, inside and out of the curved section. The downstream and up stream flow dynamics including the curved sections are solved using MOC. The effectiveness of the derived mathematical models is estimated by simulation results for a low pressure natural gas pipeline including downward and upward curved sections. The simulation results show that the proposed model and solution can be used for estimating the PIG dynamics when we pig the pipeline including curved section.

• Journal of the Korean Institute of Gas
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• v.21 no.3
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• pp.70-76
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• 2017

Although various methods have been tried to measure the safety culture of firms, they are limited to derive the qualitative analysis results according to the subjective criteria that are not formalized according to the evaluation method. We developed a questionnaire that can be applied to a combined power plant, quantified the evaluation results using the system dynamics model based on the results, and conducted simulation through various scenarios. And to present the criteria for safety cultural policy.

• Journal of Industrial and Engineering Chemistry
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• v.68
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• pp.24-32
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• 2018

Nanocellulose was surface-functionalized toward the applications in enhanced oil recovery (EOR) as a green alternative. The focus of this paper is on the effect of this material based nanofluid (NF) on foam lamella stabilization through studying its bubble breakup dynamics and flow behaviors in constricted mircofluidic devices. The NF stabilized foam produced an improved flow resistance across the capillary largely due to the capillary trapped bubbles at the contraction. The "snap-off" caused the NF stabilized foam to produce finer textured bubbles, which can migrate readily forward to the deep porous media, as revealed by the pressure profiles.

• Journal of Electrical Engineering and Technology
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• v.10 no.2
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• pp.625-633
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• 2015

The effect of altitude on thermal conduction, surface temperature, and thermal radiation of partial arc was investigated on the basis of molecular gas dynamics to facilitate a deep understanding of the pollution surface discharge mechanism. The DC flashover model was consequently modified at high altitude. The validity of the modified DC flashover model proposed in this paper was proven through a comparison with the results of high-altitude simulation experiments and earlier models. Moreover, the modified model was found to be better than the earlier modified models in terms of forecasting the flashover voltage. Findings indicated that both the thermal conduction coefficient and the surface thermodynamics temperature of partial arc had a linear decrease tendency with the altitude increasing from 0 m to 3000 m, both of which dropped by approximately 30% and 3.6%, respectively. Meanwhile, the heat conduction and the heat radiation of partial arc both had a similar linear decrease of approximately 15%. The maximum error of DC pollution flashover voltage between the calculation value according to the modified model and the experimental value was within 6.6%, and the pollution flashover voltage exhibited a parabola downtrend with increasing of pollution.

• Journal of ILASS-Korea
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• v.18 no.4
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• pp.202-208
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• 2013

The present study aims to investigate the flow characteristics with respect to fuel type and equivalence ratio in the flame spray coating process. The flame spray flow is characterized by much complex phenomena including combustion, turbulent flows, and combined heat transfer. The present study numerically simulated the flam spray process and examined the gas dynamics involving combustion, gas temperature and velocity distributions in flame spray process by using commercial computational fluid dynamics (CFD) code of FLUENT (ver. 13.0). In particular, we studied the effect of fuel type and equivalence ratio on thermal and flow characteristics which could substantially affect the coating performance. From the results, it was found that the gas temperature distributions were varied with different fuels because of reaction times were different according to the fuel type. The equivalence ratio also could change the spatial flame distribution and the characteristics of coated layer on the substrate.

• Journal of the Korean Society of Visualization
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• v.10 no.2
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• pp.32-38
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• 2012

In recent years a unique drug delivery system named as the transdermal drug delivery system has been developed which can deliver drug particles to the human skin without using any external needle. The solid drug particles are accelerated by means of high speed gas flow through a shock tube imparting enough momentum so that particles can penetrate through the outer layer of the skin. Different systems have been tried and tested in order to make it more convenient for clinical use. One of them is the contoured shock tube system (CST). The contoured shock tube consists of a classical shock tube connected with a correctly expanded supersonic nozzle. A set of bursting membrane are placed upstream of the nozzle section which retains the drug particle as well as initiates the gas flow (act as a diaphragm in a shock tube). The key feature of the CST system is it can deliver particles with a controllable velocity and spatial distribution. The flow dynamics of the contoured shock tube is analyzed numerically using computational fluid dynamics (CFD). To validate the numerical approach pressure histories in different sections on the CST are compared with the experimental results. The key features of the flow field have been studied and analyzed in details. To investigate the performance of the CST system flow behavior through the shock tube under different operating conditions are also observed.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.1
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• pp.156-163
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• 2010

A nonequilibrium molecular dynamics(NEMD) simulation method is developed and applied to study shock waves propagating through argon gas. In this simulation method, shock waves are generated by pushing a piston at a constant speed from one side of a simulation box filled with argon molecules. A linear relationship between piston speeds and shock speeds is observed. Thermodynamic properties including density, temperature, and pressure before and after the shock front are obtained from the simulations and compared with the well-known Rankine-Hugoniot equations based on ideal gases. The comparison shows an excellent agreement, indicating that this NEMD simulation method can be employed to investigate various physical properties of shock waves further.

• Journal of the Korean Vacuum Society
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• v.19 no.2
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• pp.121-127
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• 2010

Neutral gas in a Hall-effect thruster in a small satellite is simulated using a molecular dynamics code. Investigated are neutral density, pressure, axial average velocity, and temperature for the variation of diffusive reflection ratio, initial gas temperature, and channel length. Expected through this research are improving of discharge simulation through the neutral simulation and understanding of real system.