Flame attachment

A link between laminar and turbulent lifted flames has been demonstrated based on the observation of a continuous transition from laminar to turbulent lifted flames, as shown in Figure 4.3.13 [56]. The flame attached to the nozzle lifted off in the laminar regime, experienced the transition by the jet breakup characteristics, and became turbulent lifted flames as the nozzle flow became turbulent. Subsequently, the liftoff height increased linearly and finally blowout (BO) occurred. This continuous transition suggested that tribrachial flames observed in laminar lifted flames could play an important role in the stabilization of turbulent lifted flames. Recent measurements supported the existence of tribrachial structure at turbulent lifted edges [57], with the OH zone indicating that the diffusion reaction zone is surrounded by the rich and lean reaction zones. 

Figure 18.4 Propane-air premixed flame attached to suction coUar rim for — U2IU1 = 0.0 (a), and to nozzle exit for —U2/U1 = 0.022 (6)...

Figure 19.7 also shows that the amplitude of oscillations decreased with equivalence ratios greater than around 0.8 for swirl numbers up to 1.35, and at smaller values of equivalence ratio for larger swirl numbers. This is in contrast with results for ducted flames behind steps and bluff bodies, where the amplitude is nearly always a maximum near stoichiometry. This appears to be due to a shift in the location of flame stabilization by up to 50 mm, from close to the exit of the swirler to the end of the expansion section, since the amplitude of oscillations depends strongly on the intensity of heat release near the acoustic pressure antinode. This shift in flame location may have been related to the movement of the flame attachment with pressure oscillations. 

Pressure oscillations in the first arrangement depended on the equivalence ratio of the flow in the annulus and decreased with velocities in the pilot stream greater than that in the main flow due to decrease in size of the recirculation zone behind the annular ring and its deflection towards the wall. Increase in swirl number of the second arrangement caused the lean flammability limit to decrease, and the pressure oscillations to increase at smaller values of equivalence ratio. Unpremixedness associated with large fuel concentrations at the centre of the duct increased the pressure oscillations. Pressure oscillations caused the position of flame attachment to move downstream in both flows with a decrease in amplitude of oscillations. 

Tests for carboxylic acids were made by paper chromatography using 95% ethanol (100 ml.) and concentrated ammonium hydroxide (1 ml.) as solvent and aqueous bromothymol blue as indicator (1). Tests for pyridines were made on their hydrochlorides using butanol-.acetic acid water (4 1 5) as solvent and ammoniacal iron chloride or cysteine-sulfuric acid as indicators. Phenol tests were made using the same solvent and ammoniacal silver nitrate as indicator. Preliminary separations by gas chromatography were attempted using a 15-foot silicone gum column and a hydrogen flame attachment. 

Conditioning of the manganese oxide suspension with each cation was conducted in a thermostatted cell (25° 0.05°C.) described previously (13). Analyses of residual lithium, potassium, sodium, calcium, and barium were obtained by standard flame photometry techniques on a Beckman DU-2 spectrophotometer with flame attachment. Analyses of copper, nickel, and cobalt were conducted on a Sargent Model XR recording polarograph. Samples for analysis were removed upon equilibration of the system, the solid centrifuged off and analytical concentrations determined from calibration curves. In contrast to Morgan and Stumm (10) who report fairly rapid equilibration, final attainment of equilibrium at constant pH, for example, upon addition of metal ions was often very slow, in some cases of the order of several hours. 

The stability of open flames attached to flame holders (burners) is also complicated by the hydrodynamics associated with the divergent gas stream from the burner nozzle, heat losses to the burner, and convection of the surrounding air. The stability of such flames relative to their burners and the related phenomena of flash back and blow-off are outside the scope of this book. 

Because of the importance of boundary-layer theory to problems related to flame attachment and to flame spread, we shall begin with a presentation of this subject as applied to reacting flows. It will be seen that formulations base(f on coupling functions (Section 1.3) are particularly useful for reacting boundary layers. A general theoretical framework will be... 

The first commercially available flame photometer was introduced in the 1940s by the Perkin-Elmer Corporation. In 1948, Beckmann Instruments, Inc., introduced a flame attachment that could be used with their popular model D.U. spectrophotometer. By the late 1950s, instruments had been developed that used lithium as an internal standard to maximize precision. Autodilution features and microprocessor-controlled operations became widely used options in the 1970s. The most recent significant development was the introduction of cesium as the internal standard, by Instrumentation Laboratory, Inc. (Figs. 1-3). This development makes concurrent lithium determinations more practical. 

Procedure (a) Adjust a small burner flame attach a funnel over the flame and connect a wash bottle which has been filled with a few mis of limewater. Mount the water aspirator to the correct end of the wash bottle, and suck the combustion products through the bottle, (b) Put several spoonfuls of copper oxide into the combustion tube and hold it with pieces of glass wool. Fill one syringe with 20 ml of butane from the butane burner and attach to one side of the combustion tube connect the other syringe to the opposite side of the tube... 

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