Enhanced settling area

Increasing the surface area of a combustible solid enhances the ease of ignition. Solid particles less than about 10 pm in diameter settle slowly in air and comprise float dust . Such particles behave, in some ways, similarly to gas and, if the solid is combustible, a flammable dust—air mixture containing a distribution of particle sizes can form within certain limits. 

Figure 6.6 shows a design for a decanter. After the two-phase mixture enters the decanter at the feed nozzle, the liquid jet must be diffused to prevent mixing of the two phases and promote settling of the dispersed phase. One way to accomplish this is to insert two closely spaced, perforated parallel plates across the jet, as shown in Figure 6.6. The first plate drops the pressine of the jet, and the second plate decreases its velocity. Jacobs and Penny [17] recommend that the flow area of the first plate be 3 to 10% of the decanter flow area, and the second plate 20 to 50% of the decanter flow area. Another way to disperse the entering liquid jet, and at the same time enhance coalescence of the dispersed phase, is to use a wire-mesh pad in front of the feed nozzle.

Highly active surface area causes particles to clump with each other, increasing particle size and settling velocity from the atmosphere, and binding with hpid cell membranes. This effect enhances its potential to remove microbes from the air, and to bind with lung epithehal cells in the lung interstitial space. 

Floe blanket clarification uses the floes themselves to form the fluidized bed, to enhance flocculation. In laboratory models a particulate suspension (such as polymer spherical beads) may be used to form the fluidized bed. In any case, the upflow rate is limited by the settling velocity of the fluidized suspension. This is affected linearly by the density of the suspension particles, and greater upflows (therefore more production per unit plan area of tank) can be passed through more dense particle suspensions. 

In some water supply areas, problems are experienced with the corrosion of old cast-iron water mains, such that iron (red-water) discolouration can become an aesthetic problem with iron concentrations exceeding several parts per million (mg/1). In such cases, the loose iron corrosion deposits can settle within a lead pipe and absorb lead it is likely that this absorption enhances lead dissolution from the lead corrosion deposit as the equilibrium concentration for the dissolved lead is given less opportunity to be realised. Any disturbance of the loose deposits, such as the scouring effect of high flow, can cause elevated concentrations of lead in the drinking water. As an approximation, lead concentrations can double as a consequence of the interaction with loose iron deposits. Particulate lead may also arise from the physical sheer of pieces of the lead corrosion deposit from within the lead pipe, as a consequence of physical damage (as can occur in partial lead pipe replacement). Vibration from heavy road traffic might also cause pieces of the lead corrosion deposit to sheer. There is some evidence (Cardew, 2009) that the lead... 

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