Characterization of Carbon Nanotube-Enhanced Water as a Phase Change Material for Thermal Energy Storage Systems

Innovation in electronics and directed energy technologies is accelerating as the 21st century progresses. The requirement to process, store and interpolate information and signals faster and with compact electronic units has led
to the engineering of high power electronics. As the power density of these electronic systems increases, the demand for cooling increases. Development of directed energy systems also requires the dissipation of large heat loads. If the heat generated by high power electronics and other high energy systems is not reduced or transferred efficiently and quickly, resultant pre-mature equipment failure, individual component failure or the inability to operate the equipment will occur.
Carbon nanotube enhanced fluids have shown increases in the thermal conductivity from 20% to 250% when compared to the base heat transfer fluid. This study focuses on the stability of static, water-based, carbon nanotube
enhanced mixtures during thermal cycling (i.e., freezing and thawing) of the nanofluid using various types of carbon nanotubes, loading percentages and surfactants. Electrical resistance measurements were recorded over a series of
phase changes in order to assess the stability of the nanofluid. Experimental results showed that static, carbon nanotube enhanced nanofluids are stable between three to five freeze and thaw cycles before the carbon nanotubes start to agglomerate and subside. This resulted in an increased electric conductivity, and validated the use of electrical resistance measurements as a viable means of assessing the stability of the nanofluid. However, ultrasonication of the nanofluids after the instability recovers the original electric
conductivity of the nanofluid.