A mixture of diamond nanoparticles and mineral oil may be the most effective nanofluid for heat transfer applications, according to new research from Rice University.
Thermal fluids are used in a variety of applications, from protecting machine components from the effects of wear-and-tear to power transmission systems, solar cells, nanoelectronic mechanical systems and cooling systems. These fluids must balance the ability to flow with thermal transport properties in order to be effective; however, in many modern fluids one requirement is often emphasized in favor of the other. Thin fluids like water and ethylene glycol flow easily but don’t conduct heat well, while the flow rate of traditional heat-transfer fluids is often hindered by factors such as stability, viscosity, surface charge and agglomeration.
Since the late 1990s, researchers have been experimenting with nanosized particles in low concentrations in order to create a nanofluid that offers a middle ground between flow and thermal transport properties. According to the Rice University team, nanodiamonds have reportedly proven to be the best additive yet, offering 100 times better thermal conductivity than copper while still acting as an efficient lubricant.
“The great properties of nanodiamond—lubricity, high thermal conductivity and electrical resistivity and stability, among others—are quite impressive,” Taha-Tijerina said. “We found we could combine very small amounts with conventional fluids and get extraordinary thermal transport without significant problems in viscosity.”
In tests, the Rice scientists dispersed nanodiamonds in mineral oil and found that a small concentration—one-tenth of a percent by weight—raised the thermal conductivity of the oil by 70 percent at 373 kelvins (211°F). Dispersing the same amount of nanodiamonds at a lower temperature of 323 K still raised the thermal conductivity, albeit a smaller increase of about 40 percent.
“Brownian motion and nanoparticle/fluid interactions play an important role,” Taha-Tijerina said of the reason why the phenomenon occurred. “We observed enhancement in thermal conductivity with incremental changes in temperature and the amount of nanodiamonds used. The temperature-dependent variations told us the changes were due not just to the percolation mechanism but also to Brownian motion.”
The research is published in the American Chemical Society journal Applied Materials and Interfaces.