Screw flight lead

The SSE is an important and practical LCFR. We discussed the flow fields in SSEs in Section 6.3 and showed that the helical shape of the screw channel induces a cross-channel velocity profile that leads to a rather narrow residence time distribution (RTD) with crosschannel mixing such that a small axial increment that moves down-channel can be viewed as a reasonably mixed differential batch reactor. In addition, this configuration provides self-wiping between barrel and screw flight surfaces, which reduces material holdback to an acceptable minimum, thus rendering it an almost ideal TFR. 

L/D ratio See screw length-to-diameter ratio, leach To extract a soluble component from a mixture by the process of percolation. See percolation, leachate A contaminated liquid that drains from landfills and must be treated before entering the environment. It can contain decomposed wastes, decomposition byproducts, heavy metals, or bacteria. See geomembrane, lead 1. The distance in an axial direction from the center of an element such as a screw flight at its outside diameter to the center of the same flight. See directional property. 2. A heavy metal, Pb is hazardous to one s health if inhaled or swallowed. Its use is restricted. In plastics it is found in certain products, such as additives. Pb can be used in safe environments since it has excellent performance properties, such as resisting attack by many corrosive chemicals and is impervious to x-ray and gamma radiation. See hazard x-ray. 

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