ScienceDaily (July 28, 2008) —
Adding just the right dash of nanoparticles to standard mixes of
lubricants and refrigerants could yield the equivalent of an
energy-saving chill pill for factories, hospitals, ships, and others
with large cooling systems, suggest the latest results from National
Institute of Standards and Technology (NIST) research that is pursuing
NIST experiments with varying concentrations of nanoparticle
additives indicate a major opportunity to improve the energy efficiency
of large industrial, commercial, and institutional cooling systems
known as chillers. These systems account for about 13 percent of the
power consumed by the nation’s buildings, and about 9 percent of the
overall demand for electric power, according to the Department of
NIST researcher Mark Kedzierski has found that dispersing
“sufficient” amounts of copper oxide particles (30 nanometers in
diameter) in a common polyester lubricant and combining it with an
equally pedestrian refrigerant (R134a) improves heat transfer by
between 50 percent and 275 percent. “We were astounded,” he says.
Results of this work have been presented at recent conferences and
will be reported in an upcoming issue of the ASME Journal of Heat
Just how nanomaterial additives to lubricants improve the dynamics
of heat transfer in refrigerant/lubricant mixtures is not thoroughly
understood. The NIST research effort aims to fill gaps in knowledge
that impede efforts to determine and, ultimately, predict optimal
combinations of the three types of substances.
“As with all good things, the process is far from foolproof,”
Kedzierski explains. “In fact, an insufficient amount or the wrong type
of particles might lead to degradation in performance.”
On the basis of work so far, the researcher speculates several
factors likely account for nanoparticle-enabled improvements in
heat-transfer performance. For one, nanoparticles of materials with
high thermal conductivity improve heat transfer rates for the system.
Preliminary results of the NIST research also indicate that, in
sufficient concentrations, nanomaterials enhance heat transfer by
encouraging more vigorous boiling of the mixture. The tiny particles
stimulate, in effect, double bubbles–secondary bubbles that form atop
bubbles initiated at the boiling site. Bubbles carry heat away from the
surface, and the fact that they’re being formed more efficiently
because of the nanoparticles means the heat gets transferred more
Other interactions, Kedzierski says, also are likely to contribute
to the dramatic performance improvements reported at NIST and elsewhere.
Success in optimizing recipes of refrigerants, lubricants and
nanoparticle additives would pay immediate and long-term dividends. If
they did not harm other aspects of equipment performance,
high-performance mixtures could be swapped into existing chillers,
resulting in immediate energy savings. And, because of improved energy
efficiency, next-generation equipment would be smaller, requiring fewer
raw materials in their manufacture.
Adapted from materials provided by National Institute of Standards and Technology.