Nonequilibrium in the transport of heat and reactants in combustion in porous media A.A.M. Oliveira 1 , M. Kaviany * DepartmentofMechanicalEngineeringandAppliedMechanics,UniversityofMichigan,2350HaywardAvenue,2250G.G.BrownLaboratory, Ann Arbor, MI 48109-2125, USA Received 17 August 1999; accepted 21 November 2000 Abstract Combustion in inert, catalytic and combustible porous media occurs under the in¯uence of a large range of geometric length scales, thermophysical and thermochemical properties, and ¯ow, heat and mass transfer conditions. As a result, a large range of phenomenologicallengthandtimescalescontroltheextentofdeparturefromlocalthermalandchemicalnonequilibrium.Theuseof intraphase and interphase nonequilibria have allowed for the design of new combustion processes and systems, such as, catalytic reactorsandconverters,porousradiantburners,directenergyandgasconversiondevicesandsystems,chemicalsensors,andmaterial synthesisprocesses.Improvementofcurrentanddesignofyetnewerandmoreinnovativesystemsrequiresfurtherinvestigationsinto the gas-phase and surface chemistry, solid-state and condensed-phase physics, transport in disordered structures, and mathematical and numerical methods. Here we summarize the processes leading to thermal and chemical nonequilibrium, their role in the combustion in porous media, their innovative uses and effects on applications, the current modeling of these processes and the modeling techniques that may allow for further improvements and developments. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: Combustion; Porous media; Heat transfer; Nonequilibrium; Heterogeneous media Contents 1. Introduction .................................................................. 524 2. Description and modeling ........................................................ 526 2.1. Modeling ................................................................ 526 2.2. Volume-averaging treatment .................................................. 528 3. Thermal nonequilibrium ......................................................... 530 3.1. Superadiabatic combustion ................................................... 530 3.2. Radiant porous burners ...................................................... 532 3.3. Thermal regeneration ....................................................... 533 4. Chemical nonequilibrium ......................................................... 534 4.1. Distributed porous burners .................................................... 534 4.2. Catalytic reactions ......................................................... 535 4.3. Solid pyrolysis ............................................................ 539 4.4. Powder combustion ......................................................... 541 5. Summary .................................................................... 542 References ...................................................................... 543 Progress in Energy and Combustion Science 27 2001) 523±545 PERGAMON www.elsevier.com/locate/pecs 0360-1285/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S0360-128500)00030-7 * Corresponding author. Tel.: 11-734-764-2694; fax: 11-734-647-3170. E-mail addresses: amirol@emc.ufsc.br A.A.M. Oliveira), kaviany@umich.edu M. Kaviany). 1 Present address: Department of Mechanical Engineering, Federal University of Santa Catarina, CEP 88040-900, Floriano Âpolis, SC, Brazil.