For example, putting copper oxide particles, each about 30 nm in diameter, into a common polyester lubricant, then combining it with R134a refrigerant improved heat transfer by 50 to 275%. Though the phenomenon is not completely understood, scientists speculate that nanoparticle of materials with high thermal conductivities improve heat-transfer rates for some systems. NIST experiments do show that when in sufficient concentrations, nanoparticles enhance heat transfer by encouraging more vigorous boiling. The small particles seem to stimulate double bubbles — secondary bubbles forming atop bubbles initiated at the boiling site. Bubbles carry heat away from the surface. And because they form more readily due to the nanoparticles, heat is being transferred more efficiently.
National Institute of Science and Technology
If the researchers are successful, more-efficient refrigerants could be used in current chillers and HVAC equipment resulting in immediate energy savings. (Chillers consume about 9% of the nation’s electricity.) And future chillers could be made smaller and lighter.
Nanoparticles added to refrigerants create double bubbles like these when the mixture boils, a sign of higher heat transfer. It’s also a sign the modified refrigerant would be more efficient in industrial-sized cooling systems.