Clumping

DIMENSION NODE (MAXEL, DIMENSION CORD (MAXNP, DIMENSION MOOD (MAXDF DIMENSION IBC (MAXBC DIMENSION VEL (MAXDF DIMENSION CLUMP (MAXNP DIMENSION. /ET (MAXDF DIMENSION SIW (MAXEL,... 

VEL, MAXNP, MAXEL, ITAXST, RMATl, PHAT2, IRED, STRES, CLUMP)... 

VEL, MAXNP,MAXEL,MAXST,RMAT1,RMAT2,IRED, STRES,CLUMP)... 

CLUMP, NNP, 14AXNP,WEL, NGAUS, P, DEL IMPLICIT DOUBLE PRECISION(A-H,0-Z)... 

The process of smaller particles of precipitate clumping together to form larger particles. 

Soft-wheat flours are sold for general family use, as biscuit or cake flours, and for the commercial production of crackers, pretzels, cakes, cookies, and pastry. The protein in soft wheat flour mns from 7 to 10%. There are differences in appearance, texture, and absorption capacity between hard- and soft-wheat flour subjected to the same milling procedures. Hard-wheat flour falls into separate particles if shaken in the hand whereas, soft-wheat flour tends to clump and hold its shape if pressed together. Hard-wheat flour feels slightly coarse and granular when mbbed between the fingers soft-wheat flour feels soft and smooth. Hard-wheat flour absorbs more Hquid than does soft-wheat flour. Consequently, many recipes recommend a variable measure of either flour or Hquid to achieve a desired consistency. 

The direct microscopic count determines the number of viable and dead microorganisms ia a milk sample. A small amount (0.01 mL) of milk is spread over a 1.0 cm area on a microscope sHde and allowed to dry. After staining with an appropriate dye, usually methylene blue, the sHde is examined with the aid of a microscope (oil immersion lens). The number of bacterial cells and clumps of cells per microscopic field is determined and, by appropriate calculations, is expressed as the number of organisms per milliliter of sample. 

Disinfection. Ozone is a more effective broad-spectmm disinfectant than chlorine-based compounds (105). Ozone is very effective against bacteria because even concentrations as low as 0.01 ppm are toxic to bacteria. Whereas disinfection of bacteria by chlorine involves the diffusion of HOGl through the ceU membrane, disinfection by ozone occurs with the lysing (ie, mpture) of the ceU wall. The disinfection rate depends on the type of organism and is affected by ozone concentration, temperature (106), pH, turbidity, clumping of organisms, oxidizable substances, and the type of contactor employed (107). The presence of oxidizable substances in ordinary water can retard disinfection until the initial ozone demand is satisfied, at which point rapid disinfection is observed. 

Wetting Clumps. The density of a clump, Pi lump to the fraction of void space within the perimeter of the clump (porosity), SpQj, ... 

If the Hquid is nonwetting it does not enter the pores to displace the gas unless the hydrostatic pressure, bottom of the submerged clump,... 

Gravity, or centrifugation rarely provide enough hydrostatic pressure to force Hquid into nonwetting pores. If the Hquid wets the soHd the clump density increases as gas is displaced from the interior. It is best if submersion does not occur until the Hquid has completely displaced gas from the pores (Fig. 2). For wetting Hquids and pores with average diameter, D-pQ- y and tortuosity,the length, to which Hquid is pulled into a bed of powder by... 

Fig. 2. Problems in wetting A, Hquids that wet the exterior before displacing gas from pores leave gas trapped in the submerged clump B, fully wetted clumps of buoyant particles do not sink C, nonwetting Hquids do not penetrate and displace gas from pores, so clump remains buoyant and caimot submerge and D, foam produced from air is drawn under the surface, sheared into small bubbles, and stabilized by the wetting agent.

If the clump submerges in a wetting Hquid before all the gas has escaped, the Hquid continues to advance into the pores, compressing the trapped gas, until the gas pressure balances the force pulling the Hquid into the pores ... 

Complete wetting caimot occur until either the clump is broken up to let the gas escape or the trapped gas dissolves in the Hquid. A sudden decrease in hydrostatic pressure can help remove gas trapped in a submerged clump by expanding the bubble volume to break up the clump or extend the bubble past the clump s exterior so that it may escape. 

Fig. 3. Typical design elements for wet-in (a)a spinning disk deagglomerates powder just prior to wet-in (b) a rotor breaks clumps as they wet-in, andcentrifugal force helps submerge nonbuoyant powders and (c) a disk impeller provides a rapidly refreshedHquid surface. In (a) and (c), the system may...

Viscosity. Because a clump of particles contains occluded Hquid, the effective volume fraction of a suspension of clumps is larger than the volume fraction of the individual particles that is, there is less free Hquid available to faciHtate the flow than if the clumps were deagglomerated. The viscosity of a suspension containing clumps decreases as the system becomes deagglomerated. This method is not very sensitive in the final stages of deagglomeration when there are only a few small clumps left. 

An alternative mechanism involves a physical reorientation of particles at constant total volume to form clumps that have much larger pores (74). Electron micrographs of successive changes in morphology as a function of steeping time in hot water are offered in support of this interpretation. 

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