A comparison of the gas-phase fire retardant action of DMMP and Br2 in co-flow diffusion flame extinguishment,

A one dimensional stagnation point diffusion flame stabilized next to a porous wick is studied using a numerical model. The bottom end of the one-dimensional wick is dipped inside a liquid fuel (ethanol) reservoir. The liquid is drawn towards the surface of the wick through capillary action against gravity. The model combines heat and mass transfer equations in the porous media with phase change and gas-phase combustion equations to investigate steady-state flow structure in the porous wick and flame characteristics in the gas phase. In one-dimensional system, the only steady solution in the porous wick that is stable is found to be in the funicular regime. There are two regions in the wick: a vapor-liquid two-phase region near the surface exposed to the flame and a purely liquid region deep inside the wick. The physics behind the two-phase flow driven by capillarity and evaporation has been studied in detail. The coupling between the flame and the porous transport involves three different length scales: flame standoff distance, wick height above the reservoir and capillary rise. Attempt is made to study the effect of the non-dimensional numbers that contains these scales. In the limit of fast chemical kinetics (large Damkohler number), the computed results depend only on two non-dimensional ratios: the ratio of wick height to capillary rise and the ratio of wick height to flame standoff distance. Thus, a simplified similitude has been identified.

Download Full-text

Deflagration Analysis of Aluminum Droplet Combustion

Volume 2: Heat Transfer Enhancement for Practical Applications; Fire and Combustion; Multi-Phase Systems; Heat Transfer in Electronic Equipment; Low Temperature Heat Transfer; Computational Heat Transfer ◽

10.1115/ht2012-58553 ◽

2012 ◽

Author(s):

Birce Dikici ◽

M. L. Pantoya ◽

B. D. Shaw

Keyword(s):

Gas Phase ◽

Flame Propagation ◽

Diffusion Flame ◽

Dominant Role ◽

Experimental Studies ◽

Droplet Evaporation ◽

Combustion Model ◽

Single Droplet ◽

Aluminum Particles ◽

Combustion Dynamics

The evaporation and combustion of nanometric aluminum particles with an oxidizer MoO3 is analyzed. The analysis was performed to correlate individual Al particle gasification rates to macroscopic flame propagation rates observed in flame tube experiments. Examination of various characteristic times relevant to propagation of a deflagration reveals that particles below about 1.7 nm in diameter evaporate before appreciable chemical reactions occur. Experimental studies use Al particles greater than 1.7 nm in diameter such that a diffusion flame model was developed to better understand the combustion dynamics of multiphase Al particles. The results showed that it is unlikely that droplets will fully evaporate before reacting in the gas phase. A droplet evaporation and combustion model was further applied to quantify single droplet reaction velocities in comparison to the bulk flame propagation measurements observed in the literature. The diffusion flame model predicted orders of magnitude slower propagation rates than experimentally observed. These results imply that another reaction mechanism is responsible for promoting reaction propagation or modes other than diffusion play a more dominant role in flame propagation.

Download Full-text

THE FORMATION OF TRIFLUOROMETHYL RADICALS IN THE GAS PHASE

Canadian Journal of Chemistry ◽

10.1139/v52-057 ◽

1952 ◽

Vol 30 (6) ◽

pp. 473-481 ◽

Cited By ~ 20

Author(s):

J. W. Hodgins ◽

R. L. Haines

Keyword(s):

Activation Energy ◽

Gas Phase ◽

Diffusion Flame ◽

Molecular Hydrogen ◽

Primary Reaction ◽

Atomic Sodium

Trifluoromethyl radicals were produced by the reaction between atomic sodium and iodo-, bromo-, and chloro-trifluoromethane in the diffusion flame apparatus. The results indicate that:(1). The primary reaction is CF3X + Na → NaX + CF3.(2). For the reaction between sodium and iodo-, bromo-, and chloro-trifluoromethane, the activation energy is 1.7, 2.3, and 7.4 kcal. per mole, respectively.(3). Some decomposition of trifluoromethyl radicals occurs, yielding chiefly tetrafluoroethylene.(4). Reaction occurs between molecular hydrogen and trifluoromethyl radicals yielding fluoroform.

Download Full-text