Flattened tubes

An example of a pneumatic PI controller is shown in Fig. 8-64 7. This controller has two stages of pneumatic amphfication and a Bourdon tube input element that measures process pressure. The Bourdon tube element is a flattened tube that has been formed into a cui ve so that changes in pressure inside the tube cause vertical motions to occur at the ungrounded end. This motion is transferred to the left end of the beam, as shown. 

Work on the production and oxidation of SWNT samples at SRI and other laboratories has led to the observation of very long bundles of these tubes, as can be seen in Fig. 2. In the cleanup and removal of the amorphous carbon in the original sample, the SWNTs self-assemble into aligned cable structures due to van der Waals forces. These structures are akin to the SW nanotube crystals discussed by Tersoff and Ruoff they show that van der Waals forces can flatten tubes of diameter larger than 2.5 nm into a hexagonal cross-sectional lattice or honeycomb structure[17]. 

Bourdon gauge A pressure gauge in which the sensing element is constructed from a coiled flattened tube closed at one end. 

FIGURE 6.6 High power density (HPD) SOFC, consisting of a flattened tube with two flat faces. The vertical struts between the two flat faces provide shorter paths for the electronic current collection, eliminating the need for all of the electronic current to travel around the circumference of the cathode, as in the standard tubular cell design shown in Figure 6.5 [48], Reprinted from [48] with permission from Elsevier. 

Blown film extrusion is perhaps the most widely used extrusion technique, by production volume. Billions of pounds of polyethylene are processed annually by this method to make products such as grocery sacks and trash can liners. In a blown film system (Figure 14-30), the melt is generally extruded vertically upward through an annular die. The thin tube is filled with air as it travels up to a collapsing frame that flattens it before it enters the nip rollers, which pull the film away from the die. The flattened tube then travels over a series of idle rollers to a slitter,... 

Bourdon gauge. A pressure gauge using a flattened tube (Bourdon tube), that straightens out under pressure. 

Tubing usually comes as a flattened tube 10 m long and 10 to 120 mm wide. Caution This is not the size of the opened tube. A 10 mm flat will produce a 6.4 mm diameter tube and a 16 mm flat will produce a 10 mm tube. Flat sheets are available, 200 x 200 mm. 

Attempts are being made at replacing the very expensive EVD process by other techniques. The cells are connected to bundles via nickel felts. The high ohmic resistance of this concept requires an operating temperature between 900 and 1000°C to reach power densities of about 200 mW/cm. To overcome this problem SWPC is working on a modified concept, using flattened tubes with internal ribs for reduced resistance (see Fig. 1). 

As the bubble moves upward and approaches the nip rollers, it is preflattened by the collapsing frame (Fig. 3.17). This device provides a smooth transition from a round tube shape to a flattened tube shape. Collapsing frames utilize wooden slats, metal rollers. Teflon-coated rollers, or an air cushion to perform the shape transition. 

FIGURE 2.7. Comparison of Hooker and Diamond cathode designs. A finger type construction (Hooker type S cell) B flattened tube-type construction (Columbia-Hooker Diamond, Hooker type T ). 

An extrusion system used extensively for thin films of polyethylene and polypropylene is the blown film process. In this process the polymer is extruded as a relatively thick tubular extrusion and is then blown up by internal air pressure to form a thin-walled tube. The tube is then sUt to form a sheet of film up to 10 ft in width or is left as a flattened tube known commercially as lay-fiat tubing. To improve gauge uniformity in this process, the circular extrusion die, the air cooling ring, or both are frequently rotated. Although low-density polyethylene and polypropylene are the materials most used for this process, polyvinyl chloride, polyamides (nylon), and some polystyrenes have all been used. (See also blown film lay-flat tubing.)... 

Pillai MR, Gostovic D, Kim I, Barnett SA (2007) Short-period segmented-in-series solid oxide fuel cells on flattened tube supports. J Power Sources 163 960... 

Improvement of sealless tubular cells. To improve the volume power density, flatten tube type or delta type designs have been investigated by Siemens... 

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

In an effort to further improve performance, power density, and cost, Siemens Westinghouse initiated the development of a variant on its technology with a flattened tube (also schematically shown in Figure 7-9a). By shortening the current path the power density, on an active area basis, is substantially increased. In addition, the volumetric power density is increased (Figure 7-13), (42). 

A Bourdon tube is a slightly flattened tube which is bent into a curve. One end of the tube is fixed and in response to pressure changes within the tube the free end moves. Repeated operation can cause the tube to stretch and distort and hence change the relationship between the pressure change and the movement. The effect was discoverd by a Monsieur Bourdon around 1850. 

Flattened tubes Anode-supported or cathode-supported tubes are flattened so that there is no need to seal the side of the tubes. When both ends are open, at least the entrances are sealed. When one end is closed, there is a need for an additional pipe to introduce air or fuel. Normally, interconnect materials are fabricated simultaneously. For this purpose, oxide interconnects are more appropriate. Figure 2.10 shows the flattened tube cells fabricated by Kyocera to be operated at 750°C. 

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