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Encyclopedia > Smoulder

Smouldering (or smoldering in American spelling) combustion is a flameless form of combustion, deriving its heat from reactions occurring on the surface of a solid fuel when heated in an oxidizing environment. It is of interest both as a fundamental combustion topic and as a practical fire hazard. Common examples of smouldering combustion are the initiation of upholstered furniture fires by weak heat sources, and the persistent combustion of biomass occurring in wildland fires behind the flaming front. To meet Wikipedias quality standards, this article or section may require cleanup. ... Combustion or burning is a complex sequence of chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. ... Fuel is a material with one type of energy which can be transformed into another usable energy. ... European Union Chemical hazard symbol for oxidizing agents Dangerous goods label for oxidising agents An oxidizing agent is a compound that oxidizes another substance in electrochemistry or redox chemical reactions. ... A large bonfire. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Ê™ For other uses, see Wildfire (disambiguation). ...


Fundamentals

The fundamental difference between smouldering and flaming combustion is that in smouldering occurs on the surface of the solid rather than in the gas phase. The characteristic temperature and heat released during smouldering are low compared to those in the flaming combustion. Typical values in smouldering are around 600 °C for the peak temperature and 5 kJ/g-O2 for the heat released; typical values during flaming are around 1500 °C and 13 kJ/g-O2 respectively. These characteristics make smoulder to propagate at low velocities, typically around 0.1 mm/s, which is about two orders of magnitude lower than the velocity of flame spread over a solid. In spite of its weak-combustion characteristics, smouldering is a significant fire hazard. Smouldering can be initiated by weak sources of heat; yields a high conversion of fuel to toxic products per unit mass smouldered (particularly CO and heavy gases); is difficult to detect and extinguish; and it can abruptly transition to flaming combustion. To meet Wikipedias quality standards, this article or section may require cleanup. ... In physics, heat is defined as energy in transit. ... CO can stand for: Carbon monoxide, molecular formula Central office, in telecommunications and telephony Chesapeake and Ohio Railroad Colombia, in various country codes Colorado, U.S. postal abbreviation Commanding officer, military Conscientious objector, military Continental Airlines, IATA airline designator Collaborative Browsing Chinese Orchestra Correctional Officer, Correctional Officer Co can stand...


Many materials can sustain a smouldering reaction, including coal, cotton, tobacco, paper, duff, peat, wood and most polymers. A burning cigarette or bit of charcoal is an example of smoldering combustion. In general, a smoulder fuel consists of an aggregate and permeable medium formed by particulates, grains, fibers forming a porous matrix. These aggregate fuel elements facilitate the surface reaction with oxygen by providing a large surface area per unit volume. They also act as thermal insulation that reduces heat losses but, at the same time, permit oxygen transport to the reaction sites by convection and diffusion. From the chemical point of view, smouldering generates flammable and toxic gas products and leaves behind a significant amount of solid combustible char. This char is considerably richer in carbon % content than the original fuel and has a high enthalpy of oxidation. As a result, char oxidation represents an important source of heat release in smouldering. Hence, it is considered that any material that forms char during thermal decomposition can potentially sustain a smouldering process. The combustion reaction in smouldering is characteristically incomplete and so it emits toxic gas compounds at a higher yield than flaming fires. These gas compounds are also flammable and could later on be ignited in the gas-phase, triggering the transition from smouldering to flaming. From a fundamental point of view, smouldering is a basic combustion problem involving heterogeneous chemical reactions, and the transport of heat, mass and momentum in the gas and solid phases. Smouldering initiation requires the supply of heat flux to the solid fuel. The subsequent temperature increase of the solid triggers its thermal-degradation reactions (endothermic pyrolysis and exothermic oxidation) until the net heat released is high enough to balance the heat required for propagation. This net heat released by the reactions is partially transferred by conduction, convection and radiation ahead of the reaction and partially lost to the surrounding environment. The oxidizer is transported to the reaction zone by diffusion and convection, in turn feeding the oxidation reactions. Once ignition occurs, the smoulder reaction propagates through the material in a creeping fashion. It has been observed that for most materials and typical conditions, the two limiting factors in smouldering propagation are the oxidizer flux to and the heat losses from the reaction zone. Coal (previously referred to as pitcoal or seacoal) is a fossil fuel extracted from the ground by underground mining or open-pit mining (surface mining). ... Cotton ready for harvest. ... Species Nicotiana acuminata Nicotiana alata Nicotiana attenuata Nicotiana benthamiana Nicotiana clevelandii Nicotiana excelsior Nicotiana forgetiana Nicotiana glauca Nicotiana glutinosa Nicotiana langsdorffii Nicotiana longiflora Nicotiana obtusifolia Nicotiana paniculata Nicotiana plumbagifolia Nicotiana quadrivalvis Nicotiana repanda Nicotiana rustica Nicotianasuaveolens Nicotiana sylvestris Nicotiana tabacum Nicotiana tomentosa Ref: ITIS 30562 as of August 26, 2005... Piece of paper Paper is a thin, flat material produced by the compression of fibers. ... Duff may refer to: Persons See Duff (surname) As given name: Duff Green Duff McKagan, former bassist for the hard rock band Guns N Roses, current bassist for Velvet Revolver Hilary Duff, a pop artist. ... This article or section does not cite its references or sources. ... A tree trunk as found at the Veluwe, The Netherlands Wood derives from woody plants, notably trees but also shrubs. ... A polymer is a long, repeating chain of atoms, formed through the linkage of many molecules called monomers. ... A lit cigarette A full ashtray. ... Charcoal is the blackish residue consisting of impure carbon obtained by removing water and other volatile constituents of animal and vegetable substances. ... A pore, in general, is some form of opening, usually very small. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... Convection is the transfer of heat by currents within a fluid. ... Schematic drawing of the effects of diffusion through a semipermeable membrane. ... Flammable or Flammability refers to the ease at which a substance will ignite, causing fire or combustion. ... Char may mean: A piece of charred substance A character Certain fish in the genus Salvelinus The Char 2C, a tank Char (StarCraft) Tea This is a disambiguation page — a navigational aid which lists pages that might otherwise share the same title. ... Enthalpy (symbolized H, also called heat content) is the sum of the internal energy of matter and the product of its volume multiplied by the pressure. ... Look up Heterogeneous in Wiktionary, the free dictionary. ... In physics, heat is defined as energy in transit. ... Mass is a property of a physical object that quantifies the amount of matter and energy it contains. ... In classical mechanics momentum (pl. ... Simple sketch of pyrolysis chemistry Pyrolysis usually means the chemical decomposition of organic materials by heating in the absence of oxygen or any other reagents, except possibly steam. ... The most fundamental reactions in chemistry are the redox processes. ... Conduction Please update this page Science The term is most commonly used in scientific contexts: Heat conduction -- the conduction of heat through matter Electrical conduction -- the conduction of charged particles through matter Nerve conduction -- the conduction of signals along nerve cells This is a disambiguation page—a list of articles... Convection is the transfer of heat by currents within a fluid. ... Radiation in physics is a process of emission of energy or particles. ... Schematic drawing of the effects of diffusion through a semipermeable membrane. ... Convection is the transfer of heat by currents within a fluid. ...


References and External links:

  • "Smoldering Combustion" by T.J. Ohlemiller, SFPE Handbook of Fire Protection Engineering (3rd Edition),2002.
  • Microgravity smouldering (NASA-funded) research facility at the University of California at Berkeley.

  Results from FactBites:
 
Spartanburg SC | GoUpstate.com | Spartanburg Herald-Journal (1151 words)
Smouldering (or smoldering in American spelling) is a flameless form of combustion, deriving its heat from oxidations occurring on the surface of a solid fuel.
Smouldering combustion of the forest ground does not have the visually dramatic impact of flaming combustion; however, as the cause of the killing of roots, seeds, and plant stems at the ground level, it is an important component of forest fires.
In wildland fire management, controlled smouldering fires aiming at reducing the load of ground fuels are useful due to the fact that they are easy to control and propagate, and because of their reduced effect on the ecosystem.
Smoldering - Wikipedia, the free encyclopedia (302 words)
Smoldering (or smouldering in British spelling) is slow combustion without generating flame, spreading slowly and steadily along a segment of a spherical surface.
Temperature may or may not be high enough to produce a visible glow at the advancing edge of the smoldering region.
Smoldering is a very great hazard within space vehicles, where the absence of weight and therefore buoyancy of heated vapors and extremely toxic combustion biproducts makes this type of combustion extremely difficult to detect even in later stages.
  More results at FactBites »

 
 

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