Burning downward

The capacity of a sintering strand is related direcdy to the rate at which the burning zone moves downward through the bed (78). This rate is... 

The produrtive capacity of a sintering strand is related directly to the rate at which the burning zone moves downward through the bed. This rate, which is of the order of 2.5 cm/min (1 in/min), is controlled by the air rate through the bed, with the air functioning as the heat-transfer medium. 

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

On the other hand, if a salvo of rockets is required, a fast-burning PIC can be uncoiled into the bottom of a flight-box (which is a box with a wire mesh floor containing rockets, whereby the sticks or tails protrude downwards). On ignition, the plastic fuse rapidly ignites each of the quickmatch fuses protruding from the nozzles of the rockets. 

Levy et al. (L5) have studied the effect of eccentricity on the bum-out flux in upward vertical annular flow. Eccentricity does not affect the burn-out flux until the annular separation is about 20% or less of its concentric value. Bum-out fluxes for great eccentricities are increased about 30%, which is ascribed to poor fluid mixing pressure-drop at the same conditions is reduced. The small effect of moderate eccentricity in downward annular flow of steam-water mixtures was also reported earlier by Stein et al. (Sll) in their study of pressure-drop and critical flow. 

One of the most useful laboratory flammability tests is the oxygen index (OI) test (ASTM-D2043). In this test, the specimen is burned as a candle in controlled mixtures of oxygen and nitrogen. The minimum oxygen concentration which produces downward flame propagation is considered the OI of ignitability for the polymer. 

Contrary to the general trend described above, hydroxyl terminated polybutadiene (a polyurethane) has a burning rate curve which bends concave downward below 0.3 atm. (Figure 16), and the extinction pressure of this propellant is rather high (0.18 atm.). The burned surface of extinguished samples of this propellant had a glistening black appearance. 

Fig. 6.20 Experimental particle paths in an opposed stagnation flow. A mixture of 25% methane and 75% nitrogen issues upward from the bottom porous-plate manifold and a mixture of 50% oxygen and 50% nitrogen issues downward from the top porous-plate manifold. The inlet velocity of both streams is 5.4 cm/s. Both streams are seeded with small titania particles that are illuminated to visualize the flow patterns. The upper panel shows cold nonreacting flow that is, the flame is not burning. In the lower panel, a nonpremixed flame is established between the two streams. Thermal phoresis forces the particles away from the flame zone. The fact that the flame region is flat (i.e., independent of radius) illustrates the similarity of the flow. Photographs courtesy of Prof. Tadao Takeno, Meijo University, Nagoya, Japan, and Prof. Makihito Nishioka, Tsukuba University, Tsukuba, Japan.

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