Stack packing

Usually used stacked, and as first layers on support grids for smaller packing above. Pressure drop relatively low, channeling reduced for comparative stacked packings. No side wall thrust. 

For stacked packing the liquid usually has little tendency to cross-distribute, and thus moves down the tower in the cross-sectional area that it enters. In the dumped condition most packings follow a conical distribution down the tower, with the apex of the cone at the liquid impingement point. After about 12 ft vertical height, the liquid flow s vertically downward unless redistributed. For uniform liquid flow and reduced channeling of gas and liquid with as efficient use of the packing bed as pos.sible, the impingement of the liquid onto the bed must be as uniform as possible. 

Stacked packing is a hand operation and rather costly. It is avoided where possible except for the initial layers on supports. Liquid distributed on a stacked packing usually flows straight down through the packing immediately adjacent to the point of contact. There is very little horizontal liquid flow. Packing patterns perform differently, and are illustrated in Figure 9-16A-C. 

Figure 9-16A. Stacked packing square pattern (S). Used by permission of U.S. Stoneware Co. (now, Norton Chemical Process Products Corp.).

Fig. 17. Models of A/ (l-40) fibrils, viewed down the fibril axis. (A, B) Cartoon representations of the hairpin model proposed by Petkova et al. (2002). (A) The proposed /1-strands span residues 9-24 and 30-40, with a main-chain bend spanning residues 25-29. Aspartate 23 and lysine 28 are proposed to form a salt bridge (dotted line) based on distance constraints provided by ssNMR. The hairpins stack in-register to form two parallel //-sheets. (B) Two hairpin stacks pack together to form the smallest observed fibrils, or protofilaments, burying the hydrophobic residues of the C-terminal strand. Two or more protofilaments may pack together to form thicker fibrils. (C) Cartoon representation of the parallel /i-helix-like model proposed byj. T. Guo and Y. Xu (unpublished model shown in Fig. 1 of Shivaprasad and Wetzel, 2004). The gray oval highlights residues 17 and 34, proposed to sit in close proximity.

Mesophase in which board-shaped molecules assemble in stacks packed parallel to one another on a one- or two-dimensional lattice (see Figs. 17 and 18). 

Figure 11.45. Stacked packing used to support random packing...

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