Dynamic thickeners

In turbulent reacting cases the Dynamically Thickened Flame model [311 321 355 361] is used, where a thickening factor F is introduced to thicken the flame front and the efficiency function developed by Colin et al. [269] is used to account for subgrid scale wrinkling. 

J.-Ph. Legier, T. Poinsot, and D. Veynante. Dynamically thickened flame LES model for premixed and non-premixed turbulent combustion. In Proc. of the Summer Program, pages 157-168. Center for Turbulence Research, NASA Ames/Stanford Univ., 2000. 

Dynamic thickeners have become a popular machine option. Special dynamic elements housed inside a thickening chamber keep the slurry continuously moving hence, a concentrate of a paste-like consistency is possible without the danger of filter blocking. High flowrates per unit area, resulting from very thin cake formation, allow such units to be designed of relatively small size. 

Figure 20. Typiccd operating scheme for a dynamic thickener.

Figure 21. Op nuan wash curves for a dynamic thickener Wash at feed concentration (top) wash at Aickened concentration (middle) wos A at semithickened concentration A bottom), is a function of rate yvian inverse function of solids concentration.

Washing by successive dilution is used when the soHds are separated into a slurry, such as in filter thickeners. The soHds, thickened into a small amount of mother Hquor, are diluted into a wash Hquid and then separated again, diluted, separated, etc until clean of mother Hquor. The consumption of the wash Hquid can be reduced in countercurrent washing systems, sometimes referred to as countercurrent decantation. Cocurrent dilution washing, however, can be built into some dynamic filter-thickeners such as the Escher-Wyss filter. 

Because the batch flux data are obtained in a closed system with no outflow, the net solids flux is zero in the batch system and Eq. (14-40) reduces to FL = —(pV%/ 1 — cp). Note that FL and Vs are of opposite sign, because the displaced liquid moves upward as the solids settle. The relative velocity between the solids and liquid is Vr = Vs — VL which, from Eq. (14-20), is Vr = Fs/(1 — relative velocity that controls the dynamics in the thickener. If the underflow draw-off rate from the thickener is gu, the additional solids flux in the thickener due to superimposition of this underflow is qu = Qu/A = Vu. Thus, the total solids flux at any point in the thickener (qs) is equal to the settling flux relative to the suspension (i.e., the batch flux qsb) at that point, plus the bulk flux due... 

This transition has profound effects in all fluid dynamics, and certainly so in aerodynamics. The velocity profile in (he boundary layer becomes fuller neat the surface on account of Ihe higher average kinetic energy of the layer created by turbulent energy exchange from layer lo layer. The effective viscosity is therefore larger in turbulent than laminar flow, ihe turbulent boundary layer thickens more rapidly downstream, the skin friction increases. 

Block copolymers are widely used industrially. In the solid and rubbery states they are used as thermoplastic elastomers, with applications such as impact modification, compatibilization and pressure-sensitive adhesion. In solution, their surfactant properties are exploited in foams, oil additives, solubilizers, thickeners and dispersion agents to name a few. Particularly useful reviews of applications of block copolymers in the solid state are contained in the two books edited by Goodman (1982,1985) and the review article by Riess etal. (1985). The applications of block copolymers in solution have been summarized by Schmolka (1991) and Nace (1996). This book is concerned with the physics underlying the practical applications of block copolymers. Both structural and dynamical properties are considered for melts, solids, dilute solutions and concentrated solutions. The book is organized such that each of these states is considered in a separate chapter. 

Azam F (1998) Microbial control of oceanic carbon flux the plot thickens. Science 280 694-696 Azam F, Long RA (2001) Oceanography - sea snow microcosms. Nature 414 495-498 Barlow RG (1982) Phytoplankton ecology in the Southern Benguela Current. 3. Dynamics of a bloom. J Exp Mar Biol Ecol 63 239-248... 

Annealing of the nascent powder sample passed through Process 1, and above 90 °C, dynamic molecular motion started, as defined by Process 2. This critical temperature is slightly higher than that of the solution-crystallised sample. This difference indicates the restricted crystalline chain motion for the domain network structure crystallised during polymerisation. In Process 2, the crystallinity remained at a constant level for the nascent powder sample. This shows that the lamellar thickening is limited for the nascent powder morphology. 

A quahtative understanding of shear thickening is that hydro-dynamic forces (the Magnus force) drive particles close to physical contact such that hydrodynamic lubrication forces and frictional... 

Vertical in-tube condensers are often designed for reflux or knock-back application in reactors or distillation colnmns. In this case, vapor flow is upward, countercurrent to the liquid flow on the tube wall the vapor shear acts to thicken and retard the drainage of the condensate film, reducing the coefficient. Neither the flnid dynamics nor the heat transfer is well miderstood in this case, bnt Soliman, Schuster, and Berenson [/. Heat Transfer, 90, 267-276... 

---