• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.8
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• pp.1040-1047
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• 1999

The characteristics of flame propagation in inert particle-laden $H_2$/Air premixed gas are numerically investigated on this study. The 2nd order TVD scheme is applied to numerical analysis of governing equations and multi-step chemical reaction model and detailed transport properties are sued to solve chemical reaction terms. Radiation heat transfer is computed by applying the finite volume method to a radiative transfer equation. The burning velocities against the mole fractions of hydrogen agree well with results performed by different workers. The inert particles play significant roles in the flame propagation on account of momentum and heat transfer between gas and particles. Gas temperature, pressure and flame propagation speed are decreased as the loading ratio of particle is increased. Also the products behind flame zone contain lots of water vapor whose absorption coefficient is much larger than that of unburned gas. Thus, the radiation effect of gas and particles must be considered simultaneously for the flame propagation in a mixture of $H_2$/Air and inert particles. As a result, it is founded that because the water vapor emits much radiation and this emitted radiation is released at boundaries as radiant heat loss as well as reabsorbed by gas and particles, flame propagation speed and flame structure are altered with radiation effect.

• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.88-97
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• 2001

The present study numerically investigates the fuel-air mixing characteristics, flame structure, and pollutant emission inside a double-swirler combustor. A PSR(Perfectly Stirred Reactor) based microstructural model is employed to account for the effects of finite rate chemistry on the flame structure and NO formation. The turbulent combustion model is extended to nonadiabatic flame condition with radiation by introducing an enthalpy variable, and the radiative heat loss is calculated by a local, geometry-independent model. The effects of turbulent fluctuation are taken into account by the joint assumed PDFs. Numerical model is based on the non-orthogonal body-fitted coordinate system and the pressure/velocity coupling is handled by PISO algorithm in context with the finite volume formulation. The present PSR-based turbulent combustion model has been applied to analyze the highly intense turbulent nonpremixed flame field in the double swirler combustor. The detailed discussions were made for the flow structure, combustion effects on flow structure, flame structure, and emission characteristics in the highly intense turbulent swirling flame of the double swirler burner.

• Fire Science and Engineering
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• v.23 no.6
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• pp.111-115
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• 2009

Acetone LIF and Rayleigh scattering measurements were performed to identify the entrainment of ambient air in the buoyant jet qualitatively. The air entrainment near nozzle exit was enhanced with increasing both an axial distance and Reynolds number. The results supported that the air entrainment had to be considered in isothermal model for the development of its accuracy. Also, this paper provided an isothermal model based on the ideal plume, of which radiative heat loss fraction was assumed to 0.35 and the entainment of isothermal jet was considered. This simple model could be used in compartment or semi-enclosure fires such as tunnel, and it is more reliable because of introducing entrainment effect in isothermal jet.

• KIEAE Journal
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• v.17 no.1
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• pp.69-75
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• 2017

Purpose: Heat transfer analysis of recently developed 'slim type double-skin system window' were presented. This window system is designed for curtain wall type façade that main energy loss factor of recent elegant buildings. And the double skin system is the dual window system integrated with inner shading component, enclosed gap space made by two windows when both windows were closed and shading component effectively reflect and terminate solar radiation from outdoor. Usually double-skin system requires much more space than normal window systems but this development has limited by 270mm, facilitated for curtain wall façade buildings. In this study, we estimated thermophysical phenomena of our double-skin curtain wall system window with solar load conditions at the summer season. Method: A fully 3-Dimentional analysis adopted for flow and convective and radiative heat transfer. The commercial CFD package were used to model the surface to surface radiation for opaque solid region of windows' frame, transparent glass, fluid region at inside of double-skin and indoor/outdoor environments. Result: Steep angle of solar incident occur at solar summer conditions. And this steep solar ray cause direct heat absorption from outside of frame surface rather than transmitted through the glass. Moreover, reflection effect of shading unit inside at the double-skin window system was nearly disappeared because of solar incident angle. With this circumstances, double-skin window system effectively cuts the heat transfer from outdoor to indoor due to separation of air space between outdoor and indoor with inner space of double-skin window system.

• Fire Science and Engineering
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• v.26 no.4
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• pp.55-62
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• 2012

The suppression mechanisms of carbon dioxide ($CO_2$) as a representative fire suppression agent were revisited using a counterflow diffusion flame which could be applied the concept of a local application system. To end this, the low strain rate $CH_4$/air counterflow diffusions with $CO_2$ addition in either fuel or oxidizer stream were examined numerically using detailed-kinetic chemistry. Radiative heat loss due to radiating gas species including $CO_2$ added was considered by the optically thin model (OTM). As a result, the critical $CO_2$ volume fractions in the oxidizer stream required to extinguish the flame were in good agreement with the experimental data reported in the literature, while somewhat under-prediction was observed with $CO_2$ added in the fuel stream. The surrogate agents were adopted to estimate the quantitative contribution with changing in global strain rate ($a_g$) on the flame extinguishment among pure dilution effect, thermal effects including radiation heat loss and chemical effect due to the $CO_2$ fire suppression agent.

• Journal of the Korean Society of Combustion
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• v.21 no.1
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• pp.38-45
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• 2016

Flame characteristics and NO emission behavior in $CH_4$/air-air premixed counterflow flames with applying FIR and FGR with $CO_2$ and $H_2O$ were investigated numerically by varying the ratios of FIR and FGR as well as global strain rate. Chemical effects of added $CO_2$ and $H_2O$ via FIR and FGR were analyzed through comparing flame characteristics and NO behaviors from real species($CO_2$ and $H_2O$) with those from their artificial species($XCO_2$ and $XH_2O$) which have the same thermochemical, radiative, and transport properties to those for the real species. The results showed that flame temperature and NO emission with FIR varied much more sensitively than that with FGR. Those varied little irrespective of adding $CO_2$, $H_2O$, and their artificial species to the fuel stream via FIR. However, Those were varied complicatedly by chemical effects of added $CO_2$ and $H_2O$ via FGR. Detailed analyses for them were made and discussed.