New equation fits nitrogen to a T

As a molecule with only two atoms, which are identical, nitrogen is simple. As the stuff of 76 percent of our atmosphere, by weight, it’s an important gas whose properties have been minutely measured since the 1890s. It’s also a substance widely used in industry, so can there be anything new to learn about its characteristics?

Yes, say researchers who develop equations that describe thermodynamic properties of fluids.

A team of scientists at the National Institute of Standards and Technology (NIST) in Boulder, Colo., and three other institutions is getting ready to release the first major remake in 27 years of such an equation for nitrogen. Its benefits include more accurate density figures for given temperatures and pressures. “Nitrogen is now ‘less dense,'” says Eric W. Lemmon of NIST. For example, at 77 kelvins and atmospheric pressure, its density is nearly 0.3 percent less than that from the old formula. Uncertainty drops overall from the prior 0.1-0.2 percent to 0.01 percent.

For physics laboratories, the change should lead to greater precision in experiments, he says. For the $37 billion cryogenic-fluids industry, however, it means that the amount of liquid nitrogen a customer will receive now is different from that under the old equation.

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