Tilted flames

Figure 5.3 shows a moment of flame propagation in an unconfined propane cloud. On the left side, a flame is propagating through a premixed portion of the cloud its flame is characteristically weakly luminous. In the middle of the photograph, fuel-rich portions of the cloud are burning with characteristically higher flames in a more-or-less cylindrical, somewhat tilted, flame shape. 

If, however, the flow velocity is gradually reduced, this configuration reaches a condition in which the flame speed is greater than the flow velocity at some point across the burner. The flame will then propagate down into the burner, so that the flashback limit is reached. Slightly before the flashback limit is reached, tilted flames may occur. This situation occurs because the back pressure of the flame causes a disturbance in the flow so that the flame can enter the burner only in the region where the flow velocity is reduced. 

Because of the constraint provided by the burner tube, the flow there is less prone to distortion so further propagation is prevented and a tilted flame such as that shown in Fig. 4.30 is established [1],... 

FIGURE 30 Formation of a tilted flame (after Bradley [1]). 

Combustion behavior differed in some respects between continuous and instantaneous spills, and also between LNG and refrigerated liquid propane. For continuous spills, a short period of premixed burning occurred immediately after ignition. This was characterized by a weakly luminous flame, and was followed by combustion of the fuel-rich portions of the plume, which burned with a rather low, bright yellow flame. Hame height increased markedly as soon as the fire burned back to the liquid pool at the spill point, and assumed the tilted, cylindrical shape that is characteristic of a pool fire. 

A flame under the influence of wind will tilt in the direction that the wind is blowing and will change the location of the flame center. API RP 521 (2007) presents two methods for estimating the required flare height when the flame is tilted. 

To disintegrate the filter paper, the rinsed filter paper containing the precipitate is folded and placed into a preweighed porcelain crucible and the crucible is heated, first cautiously with a cooler Bunsen burner flame, so as to dry and char the filter paper, and then with the full heat of a Meker burner. For this final ignition step, the crucible should be tilted to one side and partially covered with the crucible lid so that the burner flame can be directed to the bottom of the crucible, thus avoiding engulfing the... 

FIGURE 3.9 A crucible tilted to one side, with lid partially covering the opening. This allows the burner flame to be directed to the bottom of the crucible and air to circulate into the crucible. 

When determining flame height, an assumption that the flame is a solid gray emitter with a well-defined cylindrical shape is made for ease of calculation. The cylinder may be straight or tilted as a result of wind. For pool fires, the flame height above the fire source can be determined by (Heskestad, 1981 1983) ... 

The effect of wind and tilt on flame geometry has been addressed in the SPFE Handbook (Beyler, 2002). The angle of tilt can be determined from the following equation and used to calculate the vertical and horizontal components of the flame length (see Figure 5-7) ... 

Additional discussion on the effect of wind and tilt of flame can be found in the SPFE Handbook (Beyler, 2002). 

Sublimation. Perform the experiment in a fume cupboard ) Put the beryllium oxyacetate crystals into a test tube. Slightly tilt the tube with its mouth downward and carefully heat it in the flame of a burner. What happens What is the composition of the substance deposited on the tube walls Examine the crystals of the precipitated and sublimed beryllium oxyacetate under a microscope. What can this compound be used for in the technology of beryllium ... 

You can pour the carbon dioxide over the flame of a birthday candle. As the carbon dioxide flows out of the bottle, it falls onto the candle and extinguishes the flame. (Don t tilt the bottle too far or some water will pour out.) At times, you may see the motion of the carbon dioxide by the streaming of the smoke from the extinguished candle. This is all evidence that carbon dioxide is heavier than air. 

The tube is now placed in a furnace possessing a flame surface of 75 cms. The furnace should be tilted so that the sealed end of the tube is somewhat higher than the other, and the 5 cms. free space should just lie outside the furnace. This arrangement prevents any moisture which collects in the protruding part of the tube from running back into the heated portion. In order to protect the rubber stopper, a square of asbestos board, having a circular hole in the centre, is placed over the tube between the furnace and the stopper. 

C. Remove the dilution bottle cap, flame and remove a sample with sterile pipette. Transfer this to a flamed dilution bottle or a sterile petri dish. The petri dish cover should not be fully removed, just tilted up enough that the pipette can be inserted. 

A laminar flame propagates through a combustible mixture in a horizontal tube 3 cm in diameter. The tube is open at both ends. Due to buoyancy effects, the flame tilts at a 45° angle to the normal and is planar. Assume the tilt is a straight flame front. The normal laminar flame speed for the combustible mixture is 40 cm/s. If the unbumed gas mixture has a density of 0.0015 gm/cm, what is the mass burning rate of the mixture in grams per second under this laminar flow condition ... 

The end of a 5 mm soda glass rod, selected for freedom from airlines, is melted in an oxy-gas flame. When the end has gatheced back and is about 6 mm in diameter, the flame is directed on to the rod just behind the hot blob, at the same time the rod is tilted up, almost vertically. A drop of molten glass will fall away from the rod but remain attached to it by a long tail. The hot glass drop is allowed to fall into a 500 ml beaker of cold water. The long tail is melted off so that about 3 cm of it is left attached to the drop, as shown in Fig. 5.4. 

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