Twisted tubes appearance

Under a microscope, a cotton fiber appears as a very fine, regular fiber, looking like a twisted ribbon or a collapsed and twisted tube. These twists are called convolutions there are about 60... 

At one Midwest refinery, on a 180,000 BSD crude unit, two parallel, 6000 square ft, titanium twisted tube bundles have been in service for a number of years. Crude tower overhead vapors plus steam are condensing on the shell side. Crude is on the tube side. Fouling on both the shell side and the tube side appears to be quite minimal. However, the heat-transfer coefficient is bad only about 20-25 Btu/hr/ ft /°F, even when the exchanger is clean. 

The evolution of dispensers into a yet stronger point-source-emission mode and further away from the original uniform fog mode occurred in the mid-1980s with the commercial appearance of the Shin-Etsu ropes. These were made up of the pheromone of the target species residing in sealed polyethylene tubes that were hand-applied in a twist-tie manner around plant stems. The reduction in the number of point sources per hectare from tens of thousands (fibers) to now only 1,000 or even 500/ha was achieved with fewer, but higher-strength point sources with no loss of efficacy. 

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