AbstractAn experimental study has been performed to determine the potential effect of buoyancy on the rate of propagation of a co‐current smolder reaction through a porous solid fuel, and the range of flow velocities where buoyancy effects are significant. In the co‐current smolder reaction, the fuel and oxidizer enter the reaction zone from the same direction. In the present experiments this is accomplished by initiating the reaction at the top of the fuel bed, α‐cellulose packed at a void fraction 0.85, so that the smolder wave propagates downward opposing an upward forced flow of air. Since in a stratified density field, buoyancy is proportional to the product of gravity and density difference, buoyancy can be controlled by varying either the gravity vector or the gas density. In this study the latter method is followed, varying gas density through the ambient pressure at which the experiments are performed. The smolder velocity is measured for air flow rates varying from 0.2 to 6 gm−2s−1at constant ambient pressures of 0.6, 0.8 and 1 atm. The results show that for flow rates larger than 1 gm−2s−1the smolder velocity increases linearly with the air flow rate but is independent of pressure. The reaction peak temperature is weakly dependent on flow rate and independent of pressure. For the present experimental conditions the effect of buoyancy is only observed at very low air flow rates. The mechanisms by which it affects the smolder process appears to be by altering the transport of air to the reaction zone from upstream and downstream o
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