Burning upward

The flame spread rate depends on the orientation of the specimen which can be horizontal, vertical or at some angle to the horizontal direction. A vertically mounted specimen can burn upward or downward, so that two categories of results can be obtained. When the edges of the specimen are exposed, the combustion is more rapid than that of a specimen with inhibited edges (i.e. the edges are covered by a noncombustible material). 

About 8(1 percent of the electric energy used in the United States is derived from stored energy in coal. The stored energy has its origin in photosynthesis. Coal is the end product of the accumulation of plant matter in an oxygen-deficient environment where burning is thwarted. Formation takes millions of years. Proven reseiwes of coal in the United States are upwards of 500 billion tons, a reserve so great that even if coal continues to be burned at a rate of over one billion tons per year, the reserves will last for hundreds of years. 

Burn-out data and descriptive details of 24 different rod-bundle geometries, representing all known published work up to 1965, have been compiled and analyzed by Macbeth (M4). Data that have subsequently appeared are given by Matzner (M10), Janssen (J2), Edwards and Obertelli (El), Becker et al. (B11), Moeck (M14), and Hesson (H3). All these data refer to water, and in most of the bundles the direction of water flow is vertically upwards, parallel to the heated rods however, a few tests have also been made with the bundles horizontal, also using parallel flow. Nearly all the experiments have been performed at around 1000 psia, so that the correlation of rod-bundle data must be restricted to this pressure alone. 

One result of nonuniform heating is that burn-out does not always occur at the channel outlet as it does with uniform heating, provided instabilities are avoided and the flow is vertically upwards. Consequently, the problem of analysis is made that much more difficult. The obvious first step is to see if... 

Limit burning velocity as a function of the equivalence ratio for (a) downward propagation (symbol V) and (b) upward propagation (symbol A). 

Calcining. In the calcining process, the lime mud removed from the white liquor is burned to regenerate lime for use in the lime mixing step. The vast majority of mills use lime kilns for this process, although a few mills now use newer fluidized bed systems in which the reactants are suspended by upward-blowing air. 

Orloff, L., DeRis, J., Markstein, G. M.,Upward Turbulent Fire Spread and Burning of Fuel Surfaces", 15th Symposium (International) of Combustion, 1975. 

The Ahmad and Faeth [18] data encompass alcohols saturated into an inert wall of xp up to 150 mm and xf up to 450 mm. Typically, qf is roughly constant over the visible flame extension (4) with values of between 20 and 30 kW/m2. The same behavior is seen for the radiatively enhanced burning of solid materials - again showing q values of 20-30 kW/m2 over 4 for Xf up to 1.5 m. These data are shown in Figure 8.13. Such empirical results for the flame heat flux are useful for obtaining practical estimates for upward flame spread on a wall. 

---