Nanofluids as power savers
doi:10.1038/nindia.2011.136 Published online 26 September 2011
Researchers have produced a new viscous nanofluid containing magnetic nanoparticles that conducts heat efficiently when under an intense magnetic field. This magnetic nanofluid could be useful as a super-coolant or for damping unwanted vibrations in optoelectronic devices.
Magnetic nanofluids exhibit both liquid and magnetic properties. Such fluids can be easily tailored using external magnetic fields for applications such as optical switches and drug-delivery devices. However, existing magnetic nanofluids exhibit low thermal conductivity.
The researchers produced their magnetic nanofluid by first capping magnetite nanoparticles with oleic acid and then dispersing the resulting nanoparticles in kerosene and hexadecane. They studied the thermal conductivity and viscosity of their nanofluid by varying the strength of the external magnetic field while also changing the size and concentration of the nanoparticles.
Nanofluids with a higher concentration of nanoparticles exhibited larger thermal conductivity when under a strong magnetic field. Applying the magnetic field parallel to the nanofluid aligned them along the direction of the field, forming chain-like structures with lengths ranging from tens of nanometres to several micrometres.
Increasing the magnetic field strength increased the chain length, resulting in the formation of evenly spaced single-nanoparticle chains throughout the nanofluid volume. This reduced the space between the nanoparticle chains, thus allowing for efficient heat flow.
Increasing the magnetic field strength also caused the viscosity of the nanofluid to rise. The nanofluid with the largest nanoparticle size (9.5 nm) exhibited the largest enhancement in thermal conductivity.
"This magnetic nanofluid could be used to design multifunctional smart materials for cooling-cum-damping applications," says lead researcher John Philip. Such fluids can also be used to improve the heat transfer of solar collectors used to harness solar energy, he adds.
- Shima, P. D. et al. Tuning of thermal conductivity and rheology of nanofluids using an external stimulus. J. Phys. Chem. C doi: 10.1021/jp204827q (2011)