Big Increase in Chillers' Efficiency Seen from Nano Additives

An infusion of the right amount of nanoparticles to standard mixes of lubricants and refrigerants can boost chillers' performance substantially, suggesting huge energy savings are possible, the National Institute of Standards and Technology (NIST) announced July 25. Chillers, used to cool factories, office buildings, hospitals, and other structures, account for about 13 percent of the electricity consumed by the nation's buildings and 9 percent of overall U.S. demand for electrical power, according to NIST.

NIST researcher Mark Kedzierski found that dispersing sufficient amounts of copper oxide particles 30 nanometers in diameter in a common polyester lubricant and combining it with the refrigerant R134a improved heat transfer by 50 to 275 percent. "We were astounded," he said in a NIST news release.

Results of this work have been presented at recent conferences and will be reported in an upcoming issue of the ASME Journal of Heat Transfer. Exactly how nanomaterial additives improve the dynamics of heat transfer in refrigerant/lubricant mixtures is not thoroughly understood, according to the agency, which said its research work aims to fill gaps in knowledge and eventually predict optimal combinations of the substances.

"As with all good things, the process is far from foolproof," Kedzierski said. "In fact, an insufficient amount or the wrong type of particles might lead to degradation in performance."

NIST research also indicates that, in sufficient concentrations, nanomaterials enhance heat transfer by encouraging more vigorous boiling of the mixture. The tiny particles stimulate "double bubbles," which are secondary bubbles that form atop bubbles initiated at the boiling site. Bubbles carry heat away from the surface, and the fact they're being formed more efficiently because of the nanoparticles means the heat is transferred more readily.

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