Friday, August 04, 2006

Gnitrogen gnomes back for advantages in tire pressure

Further to earlier IPBiz posts in in January 2006 and October 2005, the "nitrogen in tires" gnomes are back.

This time the information is courtesy of AP.

George Bourque of Fairfield is one of those who's driving around on tires filled with pure nitrogen, the same stuff that NASCAR racers use.

Bourque, an engineer, said he has seen a 1 to 1.5 mile-per-gallon increase since he began filling his tires with nitrogen, which is touted as maintaining tire pressure longer and resisting heat buildup on hot summer days.

Nationwide, fewer than 10 percent of tire dealers offer nitrogen, but the number is growing, said Bob Ulrich, editor of Modern Tire Dealer magazine in Akron, Ohio. Most dealers charge $2 to $5 per tire for the nitrogen fill-up, he said. The dealers generally offer free lifetime refills.

Bourque got his tires — filled with nitrogen — in Waterville, Maine at Tire Warehouse, which has 50 tire dealerships across New England. The nitrogen was part of an installation package when Bourque bought a set of tires.

***Here's the good part***

Nitrogen molecules are bigger than oxygen molecules, so nitrogen seeps out more slowly from tires than air; nitrogen resists heat buildup better than air, which contains moisture; and nitrogen reduces oxidation, which can damage the tire from the inside out, proponents say. Nitrogen is an inert gas, so there are no safety or environmental issues.

***Nitrogen weighs 28 gram/mole, and oxygen 32 gram/mole, so that oxygen is "heavier" than nitrogen (see October 2005 for Channel 10 in Philadelphia to the contrary).

***The parameter "b" in the van der Waals equation for gases gives an estimate of volume.

Since the constant b is an indication of molecular volume, it could be used to estimate the radius of an atom or molecule, modeled as a sphere. Fishbane et al. give the value of b for nitrogen gas as 39.4 x 10-6 m3/mol. This implies a volume of
0.654 X 10-28 m3/molecule.

(b for oxygen is lower than for nitrogen, 0.0318 liter/mole, but does this matter for seepage from tires?)


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