FAQ - Technical

What are the effects of pressure on Nafion™ dryers and humidifiers?

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Aside from the purely physical effects of pressure on Nafionv tubing, total pressure has essentially no effect on Nafion™ dryers.

Nafion™ tubing is relatively tough but quite flexible. The tubing has a relatively high burst point when subjected to a positive pressure. Positive pressure inside the tubing causes it to swell slightly, exposing the maximum surface area and slightly improving performance.

Because the tubing is flexible, negative pressure inside the tubing can cause it to collapse like a soda straw. This collapse will prevent sample flow and cause dryer failure. Negative sample pressure should be limited to 5 inches of water or less if the dryer is heated. Greater negative pressures will constrict the tubing, reducing active surface area and thus reducing performance, or will totally collapse the tubing.

Although total pressure has only physical effects on Nafion™ performance, the fundamental driving force of the process is the water vapor pressure gradient. Functioning essentially as a semi-permeable membrane to water vapor, Nafion™ equilibrates the water vapor pressure across the tubing wall. Since doubling the pressure of a sample doubles the partial pressure of the water vapor component of that sample, increased pressure on the sample side of the tubing wall or decreased pressure on the purge side of the sample wall can be used to stimulate the process.

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