Mixing Enhancement

FIG. 18-48 Mixing enhancers for single-screw extruders a) Maddock (straight), (h) Maddock (tapered), (c) pineapple, (d) gear, (e) pin,... 

One of the significant innovations in control of pressure oscillations and supersonic mixing enhancement has been very simple, namely using nonaxisym-metric nozzles. Simple triangular, square, rectangular, and elliptic nozzles have been shown to effectively decrease combustion pressure oscillations, as well as increase supersonic mixing [7]. 

Gutmark, E. J., K. S. Schadow, and K. H. Yn. 1997. Mixing enhancement in snper-sonic free shear flows. Annual Reviews Fluid Mechanics 27 375-417. 

Strykowski, P. J., and R. K. Wilcoxon. 1993. Mixing enhancement due to global oscillations in jet with annular counterflow. AIAA J. 31 3. 

Supersonic combustion depends considerably (along with the kinetics) on the intensity of turbulent mixing. The significant factors in supersonic mixing enhancement are (1) the decrease in mixing intensity in supersonic flows, and... 

Haimovitch, Y., E. Gartenberg, and A. S. Roberts, Jr. 1994. Investigation of rump injector for supersonic mixing enhancement. NASA-CR-4634. 

T. Brouwer, D. B. Todd, and L. P. B. M. Janssen, Flow Characteristics of Screws and Special Mixing Enhancers in a Co-rotating Twin Screw Extruder, Int. Polym. Process., 18, 26 (2002). 

Extensive analysis and experimentation on dip-pipe design has been carried out by Penney and co-workers (Jo et al. 1994), and the reader is referred to this work for specific design recommendations for diameter and flow rate. Their recommendations are summarized in Table 6-3 for six-blade flat-blade and three-blade high-efficiency down-pumping impellers. These recommendations should be followed to prevent dip-pipe back-mixing, enhance local blending, and prevent solids plugging. 

Due to the nature of the dynamical system, chaotic advection requires either time-dependent flow in simple 2-D geometries or complex 3-D geometries [9, 12]. T q)ically, active chaotic micro-mixers which are actuated externally by time-dependent energy sources (i.e., pressure, electric and/or magnetic fields) use time-dependent 2-D flow to achieve chaotic advection for mixing enhancement. 

Sundarsan et al. [95, 127] reported two improved 2D serpentine micromixers, namely the planar spiral micromixer [127] and the asymmetric serpentine micromixer (ASM) [95] (Fig. 11a). Both the micromixers were able to produce effective mixing at low Re number. The mixing enhancement was due to the symergistic effect of Dean and expansion vortices, where the latter were introduced by abrupt expansions of the microchannels. 

Lim C, Lam Y, Yang C (2010) Mixing enhancement in microfluidic channel with a constriction under periodic electro-osmotic flow. Biomicrofluidics 4 014101... 

Noncircular nozzle Gutmark and Grinstein [3] reviewed experimental and numerical work of noncircular nozzle jets including rectangular and elliptic shapes. These nozzles cause a vortex evolution mechanism called axis switching which is responsible for mixing enhancement. 

Two mixing enhancement controllers with a similar feedback law were simulated. The controller consists of a pair of actuators acting in the streamwise direction at the jet exit in an antisymmetric fashion and a pair of sensors measuring the pressure difference across the original jet diameter. The control laws are ... 

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