Tubes Collapsible

Figure 16.11. (a) Deposition of cladding and (b) tube collapse in optical fiber production. 

In the final step, the tube is removed from the lathe after sufficient layers have been deposited, and the entire preform is heated to the softening point of the quartz tube. The tube collapses and is drawn into fiber. In this process, the inner core that remains after MCVD layering is removed. Typical preforms are on the order of 1 m in length, from which hundreds of kilometers of continuous optical fiber can be fabricated. 

The tube is then filled with liquid paraffin, to stabilise the gradient and reduce tube collapse. The small vacuum seal Allen Screw is... 

Having set a base line for some 50 years ago, what was the state of packaging art up to yesteryear Glass and corks were supported by metal cans and tins, metal screw caps, thermoset caps, paperboard boxes and cartons, glassine and waxed papers, composite paper board containers, glass ampoules and cartridge tubes, collapsible metal tubes and the Aspro waxed paper strip. 

They reduce the possibility of having the tubing collapse at the bend. 

A similar effect was reported in a paper by Gao et al., who performed molecular mechanics calculations on separated SWCNTs. They indicated that for diameters of less than about 2 nm, only the cylindrical (circular cross section) geometries are stable, whereas a collapsed structure, which is flattened at the center with circular bulges at both ends, becomes more stable when the diameter of the CNTs exceeds about 6 nm. For diameters between 2 and 6 nm, both cylindrical and flattened structures were found to be stable. The authors pointed out that the flattening of the SWCNTs was actnally dne to the van der Waals atdaction between the opposing walls. At some point ( ) 6 nm), this attractive interaction becomes snfficient to overcome the increase in (angnlar) strain due to the circular bulges at the ends, which must form when the tubes collapse in the center. 

The stress calculations show resistance to crippling stress (kinking) and tube collapse due to outside pressure [22] with more than adequate safety margins. For instance, calculation shows the beam pipe able to withstand about 100 psi or about 6 atmospheres outside pressure. Resistance to stress grows nonlinearly with material thickness and with overall tube thickness. Thus, small increases in either dimension work to our advantage. The key question is whether or not this design can hold vacuum. Will there be any pin holes ... 

Cellulose fibers in plants are in the form of tubes (Fig. 1.18). When cellulose is removed from plants/trees, it dries and, because of residual stresses the tube collapses and buckles. This is seen in microscopy studies of cotton and wood fibers (Fig, 1.18(c)). 

For heat exchangers on seawater duty, where long life is required, titanium may be used. Alternatively, Cu/Ni alloys may be selected, provided that the fluid velocities are kept within the range given in the specifications. Normally, seawater is permitted only on the tube side of a heat exchanger. On some high-pressure gas coolers, however, this is not possible because of the risk of tubes collapsing under external pressure. In such cases titanium tubes and shells are necessary to allow seawater to be used on the shell side. 

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