Gas-solid nonequilibrium in filtration combustion.

摘要

To analyze gas-solid nonequilibrium in filtration combustion (FC), a two temperature model, with separate temperature fields for the solid and gas particles, is employed. Heterogeneous combustion in a porous sample with an incoming gas flux at the inlet is considered. If the reaction is initiated at the inlet (outlet) of the sample and the combustion wave travels in the direction of (opposite to) gas filtration it is referred to as coflow (counterflow) FC.;In coflow FC, the gas infiltrating through the product region enhances the propagation of combustion waves. For a relatively small gas flux, the infiltrating gas delivers heat from the hot product to the combustion layer, thus increasing the combustion temperature, and hence, the reaction rate. Propagation of such FC waves is controlled by conduction of heat released in the reaction to the preheat zone. Conductively driven FC waves have been studied extensively using one temperature models, which assume a large interphase heat exchange rate, so that the phases rapidly attain thermal equilibrium.;For a relatively large gas flux, an alternative mechanism of enhancement occurs, in that the combustion temperature is increased as a result of increasing the effective initial temperature of the unburned solid fuel. Propagation of such FC waves is controlled by convection of heat stored in the product to the preheat zone. Convectively driven FC waves depend on a pronounced temperature difference between the phases, and therefore, require a two temperature model. In the appropriate limits, the model can describe both conductive and convective FC waves. I describe solutions in each of the limits and compare and contrast the structures, combustion characteristics, and parameter dependences of the two modes of propagation. I determine how gas-solid nonequilibrium affects such features as the wave velocity, the extinction limit, net gas production in the reaction, and energy accumulation near the reaction site. Though forced coflow FC is the main focus, other FC configurations, such as forced counterflow and buoyancy driven FC, are considered as well. Finally, a stability analysis of forced FC (coflow and counterflow) is presented and the effects of gas-solid nonequilibrium is discussed.