What are the effects of pressure on Nafion dryers and humidifiers?
Aside from the purely physical effects of pressure on Nafion 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 essentia
