• 한국연소학회:학술대회논문집
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• 한국연소학회 2002년도 제25회 KOSCI SYMPOSIUM 논문집
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• pp.11-17
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• 2002

The first-order conditional moment closure (CMC) model is applied to $CH_4$/Air turbulent jet diffusion flames(Sandia Flame D, E and F). The flow and mixing fields are calculated by fast chemistry assumption and a beta function pdf for mixture fraction. Reacting scalar fields are calculated by elliptic CMC formulation. The results for Flame D show reasonable agreement with the measured conditional mean temperature and mass fractions of major species, although with discrepancy on the fuel rich side. The discrepancy tends to increase as the level of local extinction increases. Second-order CMC may be needed for better prediction of these near-extinction flames.

• Journal of the Korean Wood Science and Technology
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• 제26권1호
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• pp.76-86
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• 1998

Effects of processing variables and MAPP (maleic anhydride polypropylene) coupling agent on the properties of composite were discussed for turbulent-air-mixed woodfiber-polypropylenefiber composites. In this research, density, composition ratio, and mat moisture content were established as processing variables, and emulsified MAPP prepared by direct pressure method was incorporated as the coupling agent. And the turbulent air mixer, which was improved in function through alteration of our previous fiber mixer, was used to mix wood fibers and polypropylene fibers. At the addition level of 1% MAPP, based on oven-dried wood fiber weight, woodfiber-polypropylenefiber composites generally showed enhanced the physical and mechanical properties. And composites with low to medium densities of 0.6 to 0.8g/$cm^3$ greatly increased in these property values than with high densities of 1.0g/$cm^3$ or more by adding 1 % MAPP. Thus, MAPP addition was thought to be an effective way of enhancing properties for nonwoven web composites. At the mat moisture contents of 5 to 20%, however, the physical and mechanical properties were not enhanced by adding 1% MAPP. In the composites containing 15% polypropylene fibers, the lowest thickness swelling and water absorption values were observed at the 1% MAPP level. The addition of more than 1% MAPP had the adverse effect on the physical and mechanical properties of composites.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제28회 KOSCO SYMPOSIUM 논문집
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• pp.15-20
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• 2004

Characteristics of turbulent lifted flames in coflow jet have been investigated by varying initial temperature through the heating of coflow air. In the turbulent regime, liftoff height increases linearly with fuel jet velocity and decreases nonlinearly as the coflow temperature increases. This can be attributed to the increase of turbulent propagation speed, which is strongly related to laminar burning velocity. Dimensionless liftoff heights are correlated well with dimensionless jet velocity, which are scaled with parameters determining local flow velocity and turbulent propagation speed. This implies that the turbulent lifted flames are stabilized by balance mechanism between local turbulent burning velocity and flow velocity. Blowout velocity can be obtained from the ratio of mixing time to chemical time. Comparing to previous researches, thermal diffusivity should be evaluated from the initial temperature instead of adiabatic flame temperature.

• 한국연소학회지
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• 제9권1호
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• pp.32-38
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• 2004

Characteristics of turbulent lifted flames in coflow jet have been investigated by varying initial temperature through the heating coflow air. In the turbulent regime, liftoff height increases linearly with fuel jet velocity and decreases nonlinearly as the coflow temperature increases. This can be attributed to the increase of turbulent propagation speed, which is strongly related to laminar burning velocity. Dimensionless liftoff heights are correlated well with dimensionless jet velocity, which are scaled with parameters determining local flow velocity and turbulent propagation speed. This implies that the turbulent lifted flames are stabilized by balance mechanism between local turbulent burning velocity and flow velocity. Blowout velocity can be obtained from the ratio of mixing time to chemical time. Comparing to previous researches, thermal diffusivity should be evaluated from the initial temperature instead of adiabatic flame temperature.

• 오토저널
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• 제12권1호
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• pp.33-39
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• 1990

This study has been conducted by experiments for distribution of concentration of helium gas, which is jetted into stationary atmosphere at the normal temperature and pressure. It is able to obtain the data for concentration of helium and air mixtures by the use of hot wire probe which has fast response. At an up stream, the concentration gradient which is attained is steep. At a down stream, the mixing time of helium and air is gradually shortened with the lapse of time in front of a jet. The arrival frequency of a jet in an unsteady area is mostly constant from 0% to 100% up to 80mm, but the time which is reaching to 100% is gradually to lengthen as a descending downstream. After starting a jet and the point of 90%, the mixing time is especially to lengthen. This reason comes from the turbulent intensity which causes for mixing of helium and air. This time difference which causes according to lengthen a jet should be considered in the design of combustion chamber.

• 대한기계학회논문집B
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• 제33권9호
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• pp.699-708
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• 2009

To understand hydrogen jet liftoff height, the stabilization mechanism of turbulent lifted jet flames under non-premixed conditions was studied. The objectives were to determine flame stability mechanisms, to analyze coexistence of two different flame structure, and to characterize the lifted jet at the flame stabilization point. Hydrogen flow velocity varied from 100 to 300 m/s. Coaxial air velocity was changed from 12 to 20 m/s. Simultaneous velocity field and reaction zone measurements used, PIV/OH PLIF techniques with Nd:YAG lasers and CCD/ICCD cameras. Liftoff height decreased with the increase of fuel velocity. The flame stabilized in a lower velocity region next to the faster fuel jet due to the mixing effects of the coaxial air flow. The flame stabilization was related to turbulent intensity and strain rate assuming that combustion occurs where local flow velocity and turbulent flame propagation velocity are balanced. At the flame base, two different flame structures were found that was the partial premixed flames and premixed flame.

• 대한기계학회논문집B
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• 제20권3호
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• pp.1028-1039
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• 1996

This study was focused on the examination of the flame structure and the combustion characteristics of diffusion flame which was formed the turbulent shear flow of a double coaxial air jet system. The shear flow was formed by the difference velocity of surrounding air jet(U$\_$s/) and center air jet (U$\_$c/). So experimental condition was divided S-type flame (.lambda. > 1) and C-type flame (.lambda. < 1) by velocity ratio .lambda. (=U$\_$s//U$\_$c/). For examination of the flame structure and the combustion characteristics in diffusion flame, coherent structure was observed in flame by schlieren photograph method. We measured fluctuating temperature and ion current simultaneously and accomplished the statistical analysis of its. According to schlieren photograph, the flame was stabilized in the rim of the direction of lower velocity air jet, coherent eddy was produced and developed by higher velocity air jet. The statistical data of fluctuating temperature and ion current was indicated that reaction was dominated by higher velocity air jet. The mixing state of burnt gas and non-burnt gas was distributed the wide area at Z = 100 mm of C-type flame.

• 한국연소학회지
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• 제10권1호
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• pp.13-19
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• 2005

Measurements of flame length and NOx emissions have been conducted to investigate the effects of acoustic excitation on flame structure in turbulent hydrogen diffusion flames with coaxial air. When the acoustic excitation of a specific frequency is applied to coaxial air stream, flame length is dramatically reduced, resulting in reduction of flame residence time. Consequently, EINOx could decrease up to 35 % and this shows that acoustic excitation is effective in reducing NOx emissions. Mie scattering technique has been used to visualize the vortex structure induced by acoustic excitation and vortex formation, development and destruction were observed quantitatively. As a result, vortex entrains coflow air into fuel stream and mixing rate between fuel and air is significantly enhanced, which may contribute to reduction of NOx emissions.

• 설비공학논문집
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• 제4권4호
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• pp.253-262
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• 1992

A numerical procedure is introduced to calculate local ventilation effectiveness using the definitions of local decay rate and local mean age. A low Reynolds number $k-{\varepsilon}$ model is implemented to calculate steady state turbulent velocity distributions, and a step-down method is used to calculate transient concentration distributions. Simulations are carried out for several different values of air change rates and several different diffuser angles in a two-dimensional model of a half scale office room. The results show that the local ventilation effectiveness within a room could vary significantly from one location to another. The nominal air change rate based on the assumption of complete mixing of room air does not provide the local ventilation effectiveness information. It is numerically proved that the local mean age distribution obtained from the transient calculation is equivalent to the steady state concentration distribution with homogeneously distributed contaminant sources.

• Journal of Mechanical Science and Technology
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• 제15권7호
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• pp.895-905
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• 2001

This paper presents vector fields, three dimensional mean velocities, turbulent intensities, turbulent kinetic energy and Reynolds shear stresses measured in the X-Y plane of the gas swirl burner with a cone type baffle plate by using an X-type hot-wire probe. This experiment is carried out at the flow rates of 350 and 450ℓ/min which are equivalent to the combustion air flow rate necessary to release 15,000 kcal/hr in a gas furnace. The results show that the maximum axial mean velocity component exists around the narrow slits situated radially on the edge of a burner. Therefore, there is some entrainment of ambient air in the outer region of a burner. The maximum values of turbulent intensities occur around the narrow slits and in front of a burner up to X/R=1.5. Moreover, the turbulent intensity components show a relatively large value in the inner region due to the flow diffusion and mixing processes between the inclined baffle plate and the swirl vane. Consequently, the combustion reaction is expected to occur actively near these regions.