Tubular stacks

D.Seebach, J, L. Matthews, A. Meden, T. Wessels, C. Baerlocher, L. B. McCusker, Cyclo-P-peptides Structure and Tubular Stacking of Cyclic Tetramers of 3-Aminobutanoic Acid as Determined from Powder Diffraction Data , Helv. Chim. Acta 1997, 80, 173 - 182. 

Figure 9.5.4 Model of a tubular stack of cyclic peptides. Note the presence of l- and D-configured amino acids. (From Ghadiri et al., 1992.)...

Sccbach, D. Mathews, J.L. Meden, A. Wessels, T. Baerlocher, C. McCusker, L.B. Cyclo-[(3]-peptides Structure and tubular stacking of cyclic tetramers of 3-aminobutanoic acid as determined from powder diffraction data. Helv. Chim. Acta 1997, 80. 173-182. 

The above results were for SOFC buttrui cells, and more work is needed to demonstrate direct-methane utilization in stacks. One step towards this goal is simulation of stack operation. Such results indicate that in a tubular stack with a barrier layer over the first 30 % of the fuel-flow field, the anode-gas composition is maintained in the thermodynamically non-coking regime. Furthermore, the direct-methane feed case yielded overall stack performance nearly as good as the anode recycle case [33]. 

To form tubular stacks, there are four main motifs. First, a motif where a number of preformed disks self-associate to form a tube. Second, where wedges come together to form a ring that then further associates to form a tube. Third, where rigid rods are held together lengthwise to form a channel, a barrel-stave motif. Fourth, where the channel is defined by a winding of a polymer chain. The fourth motif is explained in Chapter 2 and beyond the scope of this chapter. In addition, there are countless examples of natural systems that form transmembrane channels, tubes, or disks that will not be presented here. 

To avoid the packing density limitations associated with cylindrical cells, some tubular stack designs use flattened tubes. 

Adopting a sealless tubular stack design to avoid usage of sealant materials. 

In Figs. 2.12 and 2.13, some characteristic features of SOFC stacks and SOFC systems are compared. In Fig. 2.12, the volumetric power density is plotted as a function of stack power. In this evaluation, the gas manifold parts are excluded. It is apparent that high volumetric power density can be achieved in a rather small stack. For tubular stacks aiming at larger systems. 

Figure 7.7 SOFC tubular stack bundle. (Image courtesy of Siemens Power Generation.)...

Fig. 7.58 The tubular stack esign of SOFC cells (a segment of a tube is shown) ( Westinghouse design ). The modules of stacked tubes do not require any high temperature seals. FVom Ref. [663].

---