New formulations of lubricants and refrigerants mixed with nanoparticles could produce an increase in the energy efficiency of refrigerators, according to research from the National Institute of Standards and Technology (NIST). In the experiments, the heat transfer for the refrigerant R134a was increased by between 50% and 275% by the dispersion of copper oxide nanoparticles in a polyester lubricant that was added to the coolant. Copper oxide particles are 30 nanometers in diameter.
NIST scientists are still working to understand how the improvement in heat transmission dynamics happens, apparently the high thermal conductivity of copper oxide plays an important role. At sufficient concentrations, the nanoparticles also improve heat transfer by encouraging a stronger boiling of the mixture, causing the increased bubbles to carry heat away from the surface.
The research will focus on understanding the optimal combination of coolant, lubricant and copper oxide particles, as other interactions are likely to contribute to the huge performance improvements observed by NIST as well.
Successful optimization of recipes for refrigerants, lubricants and nanoparticle additives would yield significant short- and long-term benefits; Of course, if other aspects of equipment performance are not affected, nanoparticle mixtures could be introduced into existing cooling systems, resulting in immediate energy savings and in addition, next-generation equipment would be smaller and would require, therefore, fewer raw materials for its manufacture. This would represent a high environmental impact, as refrigerators account for about 13 percent of the energy consumed by U.S. buildings, and about 9 percent of global electricity demand, according to the Department of Energy.
The results of this work, which have recently been presented in a series of conferences, will be published in one of the upcoming issues of ASME's Journal of Heat Transfer.
