29 July 2008
folder [featCategs]
"Double bubble" technology boosts chiller efficiency
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NANOTECHNOLOGY used in a refrigeration lubricant additive could significantly boost the energy efficiency of chillers, according to US research.
The government-run National Institute of Standards and Technology (NIST) has found that dispersing the right amount of copper oxide particles in a standard polyester refrigerant lubricant and combining it with R134a improves heat transfer by between 50% and 275%.
The particles, which are just 30 nanometers in diameter, are thought to encourage secondary nucleation bubbles on top of bubbles. This 'double-bubble' effect is said to enhance boiling heat transfer and, ultimately, could help to boost the energy efficiency of industrial-sized cooling systems.
Just how nanomaterial additives to lubricants improve the dynamics of heat transfer in refrigerant/lubricant mixtures is not thoroughly understood, but the right concentration of nanoparticles appears to be crucial.
On the basis of work so far it appears that 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.