Analytical and experimental investigation of the transition from low-velocity to high-velocity regime of filtration combustion

Combustion of gases under filtration in porous media, or filtration combustion (FC), is characterized with complex heat and mass transfer and interphase interaction and may be utilized in multiple thermo-chemical applications. The work studies filtration combustion of gases at transition from low-velocity (LV) to high-velocity (HV) regime under gas pressure growth. As shown, the transition regime of FC is characteristic for conditions of technological and experimental set-ups, at least at body pore size of d(0) > 1.5 to 2 mm. When increasing working pressure by 1-2 atmospheres higher than atmospheric one, critical size of pores decreases 2-2.5 times. Theory and estimation method for velocity and temperature of stationary FC waves under the transition regime is proposed, where dimensionless complex Phi - beta Pe(Su)(2)/Re-1/6, (beta = RTad/E-1 Pe(Su) = S(u)d(0)/kappa, Re = u(g)d(0)/nu, S-u - normal laminar flame velocity, u(g) - gas filtration velocity) constructed on turbulent combustion to thermal relaxation rate, is used as governing parameter. It is shown that satisfactory description of transition regime as well as of high-velocity FC cannot be obtained by using characteristics of normal laminar flames. Hence, theory of turbulent premixed flames is to be used. (C) 2000 Elsevier Science Inc. All rights reserved.