Stagnation point flow systems

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.

Compressible ID stagnation-point flow analysis forms the basis of the equation system presented below. It was found that the prediction of the effect of internal mass transfer limitations in the catalytic washcoat of the SFR configuration is crucial to derive microkinetic data from SFR experiments (Karadeniz, 2014 Karadeniz et al., 2013) our model is extended to include the diffusion limitations due to a porous layer. It should be noted that the CFiEMKIN code has no abihty to account for internal mass transport in the catalytic coating. 

Let us consider a solid spherical particle of radius o in a translational Stokes flow with velocity U and dynamic viscosity /i (Figure 2.1). We assume that the fluid has a dynamic viscosity /z. We use the spherical coordinate system. R, 9, ip with origin at the center of the particle and with angle 0 measured from the direction of the incoming flow (that is, from the rear stagnation point on the particle surface). In view of the axial symmetry, only two components of the fluid velocity, namely, Vr and Vg, are nonzero, and all the unknowns are independent of the third coordinate [Pg.58]

For a perfectly wetting system, i.e. for very small or zero contact angles, a continuous film of liquid is entrained on the solid substrate, creating a dip-coating flow pattern. The dip-coating pattern. Figure 10.5 (d), has a stagnation point on the gas-liquid interface. The liquid entrained on the solid surface comes from inside the liquid phase and the lower part of the interface moves away from the solid. Under these conditions, it has been shown (Diaz and Cerro, 2004) that LB deposition cannot take place. 

Surface tension variations affect the mobility of the fluid-fluid interface and cause Marangoni flow instabilities. Surfactant-laden flows exhibit surface tension variations at the gas-liquid or liquid-liquid contact line due to surfactant accumulation close to stagnation points [2,53]. For gas-liquid systems, these Marangoni effects can often be accounted for by assuming hardening of the gas bubble, i.e. by replacing the no-shear boundary condition that is normally associated with a gas-liquid (free) boundary with a no-slip boundary condition. It should be noted that such effects can drastically alter pressure drop in microfluidic networks and theoretical predictions based on no-shear at free interfaces must be used with care in practical applications [54]. 

Another two phase flow system, which can be used for the comminution /22/ and the measurement 723-27/ of particles in a gas stream originates from the movement of particles in a stagnation point... 

Winter et al. [119, 120] studied phase changes in the system PS/PVME under planar extensional as well as shear flow. They developed a lubrieated stagnation flow by the impingement of two rectangular jets in a specially built die having hyperbolic walls. Change of the turbidity of the blend was monitored at constant temperature. It has been found that flow-induced miscibility occurred after a duration of the order of seconds or minutes [119]. Miscibility was observed not only in planar extensional flow, but also near the die walls where the blend was subjected to shear flow. Moreover, the period of time required to induce miscibility was found to decrease with increasing flow rate. The LCST of PS/PVME was elevated in extensional flow as much as 12 K [120]. The shift depends on the extension rate, the strain and the blend composition. Flow-induced miscibility has been also found under shear flow between parallel plates when the samples were sheared near the equilibrium coexistence temperature. However, the effect of shear on polymer miscibility turned out to be less dramatic than the effect of extensional flow. The cloud point increased by 6 K at a shear rate of 2.9 s. ... 

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