Structured-type packing, liquid

For structured-type packing, a liquid holdup of 4 to 5 percent corresponds to this optimum packing fractionation efficiency. For 1-in Raschig rings, this optimum holdup would be roughly 10 to 12 percent. 

The process engineer who draws the conclusion from the above data that structured-type packing is superior to trays is correct. However, he should also note that the performance of packing can be no better than the initial liquid distribution provided by the spray headers. 

Earliest type, usually cheaper per unit cost, but sometimes less efficient than others. Available in widest variety of materials to fit service. Very sound structurally. Usually packed by dumping wet or dry, with larger 4-6-inch sizes sometimes hand stacked. Wall thickness varies between manufacturers, also some dimensions available surface changes with wall thickness. Produce considerable side thrust on tower. Usually has more Internal liquid channeling, and directs more liquid to walls of tower. Low efficiency. 

In 1978, Bryan [11] reported on crystal structure precursors of liquid crystalline phases and their implications for the molecular arrangement in the mesophase. In this work he presented classical nematogenic precursors, where the molecules in the crystalline state form imbricated packing, and non-classical ones with cross-sheet structures. The crystalline-nematic phase transition was called displacive. The displacive type of transition involves comparatively limited displacements of the molecules from the positions which they occupy with respect to their nearest neighbours in the crystal. In most cases, smectic precursors form layered structures. The crystalline-smectic phase transition was called reconstitutive because the molecular arrangement in the crystalline state must alter in a more pronounced fashion in order to achieve the mesophase arrangement [12]. 

The possibility that IPMS can occur in lipid systems as a structure of microemulsions or liquid-crystalline phases was first pointed out by Scriven (1976). The concept of IPMS and the possibilities of cubic phases consisting of lipid bilayers curved as an IPMS has attractive features that merit consideration. The lipid bilayer is the dominating structure type in lipid systems. In most cases there is an L -phase on one side of the cubic phase in the phase diagram. The IPMS is intersection free, so that the main difference compared to the infinite bilayer structure of the L -phase is the curvature, which can allow for wedge-shaped molecules (see further discussions in Section 8.2.8). The hydrostatic pressure is the same everywhere in an IPMS structure. All molecules can in fact have an identical close-packing environment, with lateral diffusion freedom similar to that of the L -phase. 

Figure 8-5 shows the configuration at the top of the tower. The reflux was distributed by an orifice plate chimney type, pan liquid distributor. Vapor flowed up through the chimneys reflux was supposed to be evenly distributed by the /2-in. holes drilled in the pan across the top of the packed bed. To determine if the reflux was truly being equally distributed across the structured bed, I proceeded as follows ... 

It has been well established that the efficiency of random packings is significandy affected by the quality of liquid distribution onto the packed bed. As was true when saddle-type packings first were developed, initially structured packings were assumed to be able to rectify the initial inferior liquid distribution quality. More recent work has shown that liquid distribution quality also is critical to achieving high mass transfer efficiency with structured packings [9]. 

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