Stagnation point flow

Figure 4.1.2 is a photograph of a coimterflow burner assembly. The experimental particle paths in this cold, nonreacting, counterflow stagnation flow can be visualized by the illumination of a laser sheet. The flow is seeded by submicron droplets of a silicone fluid (poly-dimethylsiloxane) with a viscosity of 50 centistokes and density of 970 kg/m, produced by a nebulizer. The well-defined stagnation-point flow is quite evident. A direct photograph of the coimterflow, premixed, twin flames established in this burner system is shown in Figure 4.1.3. It can be observed that despite the edge effects.

Sheu, W.J. and Sivashinsky, G.L, Nonplanar flame configurations in stagnation point flow. Combust. Flame, 84, 221,1991. 

Figure 1. Schematic of the stagnation point flow conflguration.

A number of theoretical (5), (19-23). experimental (24-28) and computational (2), (23), (29-32). studies of premixed flames in a stagnation point flow have appeared recently in the literature. In many of these papers it was found that the Lewis number of the deficient reactant played an important role in the behavior of the flames near extinction. In particular, in the absence of downstream heat loss, it was shown that extinction of strained premixed laminar flames can be accomplished via one of the following two mechanisms. If the Lewis number (the ratio of the thermal diffusivity to the mass diffusivity) of the deficient reactant is greater than a critical value, Lee > 1 then extinction can be achieved by flame stretch alone. In such flames (e.g., rich methane-air and lean propane-air flames) extinction occurs at a finite distance from the plane of symmetry. However, if the Lewis number of the deficient reactant is less than this value (e.g., lean hydrogen-air and lean methane-air flames), then extinction occurs from a combination of flame stretch and incomplete chemical reaction. Based upon these results we anticipate that the Lewis number of hydrogen will play an important role in the extinction process. 

Ribe NM Smooke MD (1987) A stagnation point flow model for melt extraction from a mantle plume. J Geophys Res 92 6437-6443... 

Fig. 2 Reported growth rate of tin oxide, prepared from (Ctf3)4Sn + O2, as a function of temperature. Borman et al. [39] used a hot wall reactor with various diameters shown in the legend, [TMT] = 99-390 ppm. Ghostagore [32,33] used a horizontal cold wall reactor with [TMT] = 117-310 ppm. Chow et al. [54] used a stagnation-point flow reactor, and Vetrone et al. [55] a horizontal hot-wall reactor with a tilted substrate...

V. Giovangigli and M.D. Smooke. Calculation of Extinction Limits for Premixed Laminar Flames in a Stagnation Point Flow. J. Comp. Phys., 68 327-345,1987. 

M. Murayama, S. Kojima, and K. Uchida. Uniform Deposition of Diamond Films Using a Flat Flame Stabilized in the Stagnation-Point Flow. J. Appl. Phys., 69 7924-7926,1991. 

The ignition criteria for stagnation-point flow Semenov-Frank-Kamenetski or van t Hoff (with X, Song and L.D. Schmidt). Combust. Sci. Tech. 75, 311-331 (1991). 

Vertical reactor or stagnation point flow reactor at atmospheric and reduced pressure conditions... 

Vertical CVD Reactors. Models of vertical reactors fall into two broad groups. In the first group, the flow field is assumed to be described by the one-dimensional similarity solution to one of the classical axisymmetric flows rotating-disk flow, impinging-jet flow, or stagnation point flow (222). A detailed chemical mechanism is included in the model. In the second category, the finite dimension of the susceptor and the presence of the reactor walls are included in a detailed treatment of axisymmetric flow phenomena, including inertia- and buoyancy-driven recirculations, whereas the chemical mechanism is simplified to a few surface and gas-phase reactions. 

For m = 1, which corresponds, as previously indicated, to stagnation point flow, the values ofja given in the table can be closely represented by... 

The flow profiles with H > 2.591, correspond to velocity distributions with inflection point and these are the decelerated flows or flows with adverse pressure gradient. On the contrary, the flow profiles with H < 2.591, correspond to - < 0 (the accelerated flows). The figure with = 0 and H = 2.59, corresponds to the Blasius profile. The profile with j3h = I and H = 2.22 corresponds to the stagnation point flow. The other two profiles in Fig. 2.7 are for flows with adverse pressure gradient and the crosses on the profile indicate the locations of the inflexion point. The profile for /3h = —0.1988 H = 4.032) corresponds to the case of incipient separation. 

Fig. 18. CO coverage (H) as a function of the Pt substrate temperature measured during CO oxidation at a pressure of 20 mbar. (D) indicate temperatures where equilibrium CO surface coverage was too low to be detected. CO2 production (A) simultaneously measured by mass spectrometry in the exhaust gas. The measurement were carried out under laminar flow conditions in a stagnation point flow onto the Pt catalyst surface. Solid lines are results of a numerical reactive flow simulation for a CO/02/Ar-stagnation point flow onto the Pt foil corresponding to the experimental flow conditions (CO 15 seem O2 30 seem Ar 105 seem).

Figure 10-8. A sketch showing streaming flow past a circular cylinder. On the right is the flow as seen with a course level of resolution. On the left is the flow in the immediate vicinity of the front-stagnation point, as seen from a much finer resolution. It is evident that the local flow examined in a region close enough to the stagnation point reduces to a classic stagnation point flow as described by the Falkner-Skan equation for, 8 = 1.

Dijt JC, Cohen Stuart MA, Hofman JE, Fleer GJ. Kinetics of polymer adsorption in stagnation point flow. Colloids Surfaces 1990 51 141—158. 

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