Microtubular Cells Design

Microtubular cells were first made in 1990 by Michaela Kendall which were 1-5 mm in diameter, possessed 100-200 pm wall thickness and were made from extruded yttria-stabilised zirconia. After this achievement, Kendall and his co-workers demonstrated 20 cell, 200 cell, and 1000 cell reactors. Only a hot-air-fed reactor could heat up to the desired operating temperature and the cell could withstand an increase of temperature up to 200°C/min. Professor Kendall set up the first company in 1996 for microtubular (MT) cells known as Adelan (UK) Ltd. It was demonstrated by Bujalski that the operational temperature of these MT cells could be ramped at a rate of 4000°C/min, which indicates the rapid start-up time of 12 s for SOFC without any operational or structural damage to these cells. Second, these cells could be cooled extremely fast without any damage. The typical design of MT-SOFC and a 50 W portable MT is shown in Fig. 4.19a, b. The YSZ tube of thickness 150 pm and 

2 mm diameter is a support for the electrodes. In addition to this, the electrolyte tube also serves as a gas inlet tube and combustor outlet tube. The length of the tube may vary between 100-200 mm whereas the occupancy of the cell region is about 30 mm towards the outlet end of the tube. 

Group Cell diameter (mm) Operational temp. (°C) Heat up time (°C/min) Support Stack power (W) 

Upper Austria University of Applied Science 850 Anode 7 cells— 3.5 W 

3 Planar Cell Design (Bipolar/Flat-Plate Design) 

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Co-extruding a strip of lanthanum chromite based interconnect along the length of a YSZ microtube has also been demonstrated [45], although a number of difficulties remain. Firstly, the tubes are much weakened by the interconnect strip, and secondly the mixing of lanthanum chromite and YSZ at the boundary of the co-extruded materials leads to a dead-zone of material, about 350 pm in extent. Thus any microtubular cell design with co-extruded interconnect will require much further development to be successful. 

Other cell designs, such as radial configurations and more recently microtubular designs, have also been developed and demonstrated [21]. The microtubular designs can achieve lower operating temperature, since it has long been recognized that thinner electrolyte and electrode layers promote operation at lower temperature [22]. 

In 2000, Acumentrics Corp built a 1000-cell stack to illustrate the possibility of providing reliable power for computer systems back up. Since then, Acumentrics has designed and built several 2-5 kW systems using microtubular cells for use as back up power sources for broadband and computer systems. 

Table 4.1 Microtubular cells stack designs by various firms...

The cytoplasm of the cell is designated hyaloplasm in electron microscopy and cytosol in biochemistry. It constitutes about 51% of the cell volume and shows a microtubular lattice, (s. fig. 2.17) Basophilia, caused by ribonucleic acid, is the histochemical index for increased functional activity of the hepatocytes. The smooth endo-... 

Another approach is to adopt a design similar to the lead acid battery and to use wires brought out from the electrodes and connected externally. This is the approach adopted by Adelan in their microtubular design. Clearly, the design of the cells and how they fit into the overall stack is vitally important in deciding such issues. 

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