• Journal of the Korean Society of Safety
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• v.17 no.3
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• pp.43-49
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• 2002

The NOx emission characteristics of double-concentric diffusion flames and normal diffusion flames fueled with CH$_4$ were studied. Experimental and numerical investigations were carried out for double-concentric diffusion flame with varying central air flow rate and normal diffusion flame. The Emission indices of NOx(EINOx) were measured by chemiluminescent method and calculated by numerical model based on detailed chemistry. From the comparison between double-concentric diffusion flames and normal diffusion flames, the results show that EINOx of double-concentric diffusion flames are lower than normal diffusion flame, because of Prompt EINOx was decreased. EINOx of double-concentric diffusion flames increase with central air flow rate increasing.

• Journal of the Korean Society of Combustion
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• v.4 no.2
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• pp.75-83
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• 1999

The effect of temperature distributions on soot volume fraction in double-concentric diffusion flames have been investigated experimentally. Using fine thermocouple wires and a rapid insertion mechanism, we have measured temperature without the effect of soot particles attached to the thermocouple junction, which can lower the temperature signal about 100 K by increasing the heat loss from the junction by radiation. The temperature at the flame axis is higher in the double-concentric diffusion flames than in normal co-flow diffusion flames because of the inverse diffusion flame. However, it is almost the same as that at the periphery of normal flames, on which the inverse flame does not have an effect. Thus, the lower soot concentration found in the double-concentric diffusion flame can be explained by the effect of nitrogen diffusion from the central air jet.

• 한국연소학회:학술대회논문집
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• 1999.10a
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• pp.231-240
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• 1999

The temperature distribution in double-concentric diffusion flames have been investigated experimentally by rapid insertion technique. Using a fine thermocouple and rapid insertion mechanism, the temperature has been measured before soot particles attach the thermocouple junction which can affect the temperature signal by changing the radiation heat loss. For double-concentric diffusion flames, the temperature at the axis is higher than that of normal coflow diffusion flames because of the inverse diffusion flame at the center of the flame. However, it is almost same at the periphery on which the inverse flame does not have an effect.

• 한국연소학회:학술대회논문집
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• 2000.12a
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• pp.101-112
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• 2000

An Experimental study of oxygen enriched double inversed diffusion flame was conducted to understand the flame characteristics and radiation heat transfer. The infrared radiation meter was used to measure of various combination of fuel, air and pure oxygen. The results show that oxygen enriched double inversed diffusion flame is very effective to increase of thermal radiation and proper addition of pure oxygen in air flow can intensity thermal radiation of flame. And it can be found that oxygen enriched double inversed diffusion flame could give benefits of cost effective and very high energy saving.

• Journal of the Korean Society of Combustion
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• v.6 no.2
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• pp.50-64
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• 2001

An experimental study of oxygen enriched double inversed diffusion flame was conducted to understand the flame characteristics and radiation heat transfer. The infrared radiation meter was used to measure of various combination of fuel, air and pure oxygen. The results show that oxygen enriched double inversed diffusion flame is very effective to increase of thermal radiation and proper addition of pure oxygen in air flow can intensify thermal radiation of flame. And it can be found that oxygen enriched double inversed diffusion flame could give benefits of cost effective and very high energy.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1355-1362
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• 1999

An experimental study on a double-concentric diffusion flame(DDF) has been carried on in order to Investigate the characteristics of soot formation compared to a normal coflow diffusion flame(NDF). Laser extinction technique has been used for an ethylene($C_2H_4$) and air flame with various flow rates. Soot formation In the double-concentric diffusion flame was enhanced by the inner inverse diffusion flame due to the increase in flame temperature and also suppressed due to the nitrogen-dilution from the inner air. Soot concentration at the flame axis of DDF was higher than that of the NDF, mainly because of the increase of temperature by inner flame. However, the maximum soot volume fraction of DDF was lower than NDF at the outer side of the flame, mainly due to the effect of nitrogen-dilution from the inner air.

• Journal of Korean Institute of Industrial Engineers
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• v.38 no.4
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• pp.249-253
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• 2012

This paper suggests a numerical method for valuation of American options under the Kou model (double exponential jump diffusion model). The method is based on approximation of underlying asset price using a finite-state, time-homogeneous Markov chain. We examine the effectiveness of the proposed method with simulation results, which are compared with those from the conventional numerical method, the finite difference method for PIDE (partial integro-differential equation).

• Geomechanics and Engineering
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• v.32 no.5
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• pp.475-482
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• 2023

This paper studies the effect of the relaxation time on a two-dimensional thermoelastic medium which has a doubly porous structure in the presence of diffusion and gravity. The normal mode analysis is used to obtain the analytic expressions of the physical quantities, which we take the solution form in the exponential image. We have discussed a homogeneous thermoelastic half-space with double porosity with the effect of diffusion and gravity. The equations of generalized thermoelastic material with double porosity structure with one relaxation time have been developed. Moreover, the expressions of many physical quantities are explained. The general solutions, under specific boundary conditions of the problem, were found in some detail. In addition, numerical results are computed.

• Nuclear Engineering and Technology
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• v.56 no.4
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• pp.1296-1309
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• 2024

The aim of this work is to explore the effect of the double subdiffusion on the stability in BWRs. A BWR novel reduced order model with double subdiffusion effects: reduced order fractional model (DS-F-ROM) to describe the neutron and heat transfer processes was proposed for this study. The double subdiffusion was developed with a fractional-order two-equation model, and with different fractional-orders and relaxation times. The stability analysis was carried out using the root-locus method and change from the s to the W domain and were confirmed using the time-domain evolution of neutron flux for a unit step change in reactivity. The results obtained using the reduced fractional-order model are presented for different anomalous diffusion coefficient values. Results are compared with normal diffusion and P1 equations, which are obtained straightforwardly with DS-ROM when relaxation time tends to zero, and when the anomalous diffusion coefficient tends to one, respectively.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.1
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• pp.115-126
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• 2019

Recently, in order to solve the traffic congestion in urban areas and to improve the peripheral environment, research on the design and construction technology development of great depth underground double-deck tunnel is under way by using the underground space in the urban area. The network type double-deck tunnel is in the form of an intersection with a small cross section and a steep slope as per construction at the base of a flatland, so that the fire smoke spreads rapidly in case of fire, which is expected to cause damage of human life. Therefore, this study is analyzed the delay effect of fire smoke diffusion according to the installation and non - installation of delay system for fire smoke diffusion at the intersection. Fire fumes were delayed up to 270 seconds when the delay system for fire smoke diffusion was installed at the intersection and it is analyzed that the greater the operating area of the delay system for fire smoke diffusion, the more preventable the damage of human life of the intersection.