Nanofluids

Above: Wen Yu (left) and David France (right) measure the heat transfer of a nanofluid, a fluid containing nanoparticles in suspension.

Nanofluids are fluids containing nanoparticles (nanometer-sized particles of metals, oxides, carbides, nitrides, or nanotubes). Nanofluids exhibit enhanced thermal properties, amongst them; higher thermal conductivity and heat transfer coefficients compared to the base fluid. Simulations of the cooling system of a large truck engine indicate that replacement of the conventional engine coolant (ethylene glycol-water mixture) by a nanofluid would provide considerable benefits by removing more heat from the engine.

Additionally, a calculation has shown that a graphite based nanofluid developed jointly by Argonne and Valvoline could be used to eliminate one heat exchanger for cooling power electronics in a hybrid electric vehicle. This would obviously reduce weight, and allow the power electronics to operate more efficiently. The benefits for transportation would be:

• Radiator size reduction
• Pump size
• Possible of elimination of one heat exchanger for hybrid-electric vehicles
• Increased fuel efficiency

Using silicon carbide nanoparticles from partner Saint Gobain, the team has created an ethylene glycol/water fluid with silicon carbide nanoparticles that carries heat away 15 percent more effectively than conventional fluids. And working with industrial partner Valvoline, they’ve developed a graphite-based nanofluid that has an enhanced thermal conductivity of 50 percent greater than the base fluid, which would, under specific conditions, eliminate the need for a second heat exchanger for cooling power electronics. Read the paper.

To develop nanofluids for heat transfer (i.e., cooling), the team used a systems engineering approach. This method enables scientists to look at how nanofluid systems work by analyzing the behavior of the whole system, which is different than looking at each individual property of the system, such as nanoparticle material, concentration, shape, size and more. Using this scheme, the team discovered that particle size and concentration are important factors in designing nanofluid systems. Read the paper.

Part of the current research focuses on a nanolubricant based on poly-alpha-olefin (or PAO). When combined with nanoparticles of molybdenum disulfide and a surfactant, the resulting lubricant shows reduced friction and wear for a cast iron cylinder-liner segments reciprocating against piston-skirt segments at 100 degrees Celsius, thus increasing the lifetime and fuel efficiency of vehicle components.

Using Raman spectroscopy, Routbort’s team showed that the interaction between the nanoparticles and rubbing surfaces produced a very thin film between contacting parts. This “tribofilm” is responsible for the improved properties.

Future work will concentrate on further development of carbon-based nanofluids for hybrid electronic cooling having higher heat transfer coefficients while keeping the viscosity low.

More

• TransForum article: Nanofluids Improve Performance of Vehicle Components

February 2012