Particulate Functionalized Nanodiamond as a Low Concentration Additive to Liquid Systems to Enhance Their Thermal Extraction Capability

Abstract

Due to the inherently poor thermal conductivity of conventional heat transfer fluids such as water, ethylene glycol, mineral oils and their mixtures, they are substantially compromised in thermal management applications. In this paper, particulate deaggregated and functionalized nanodiamond (“detonation” nanodiamond), fND, is examined as a low concentration additive to traditional heat transfer fluids to enhance their thermal conductivity and hence, heat transfer capability while causing no major disruption in existing pressure drop or loop maintenance. The criticality of sufficient deaggregation and compatible functionalization chemistry of the nanodiamond to successful outcomes will be addressed. The tested fND fluids are prepared so that the functional group is specifically intended to have its terminal chemical bonding couple with the host matrix, resulting in their operational improvement. Because the effective diameter of molecular influence of the attached functional groups in the host matrix can be much greater than the 5 nanometers of the “core” nanodiamond, concentrations in the range of parts-per-million (ppm) of the fND have resulted in experimentally verified double digit improvements of key properties, such as thermal conductivity and heat transfer coefficient. The thermal conductivity of diamond nanofluids, described here as containing functionalized nanodiamond (fND) in water, was measured using a transient hot-wire method and a 15% increase over water in the thermal conductivity observed at nanodiamond concentrations below 100ppm. No increase of viscosity above that of the base fluid occurred. Practical comparisons of the cooling capability of only water versus the diamond nanofluid were performed at various concentrations of functionalized nanodiamond in water ranging from 50ppm to ∼ 100ppm over variable temperatures and pumping conditions. The nanofluid flowed in the closed-loop system with a conduction cold plate heated via six cartridge heaters with a constant heat flux. Results indicate that the convective heat transfer coefficient and Nusselt number of diamond nanofluid are higher than that of DI water at the same conditions, e.g., temperature and flow rate, and these properties increased further with increasing Reynolds number. The nanofluids have been stable for 22 months and no sedimentation is observed. Examples of these fND applications will be presented, such as, evaluation in an extensively instrumented water based cooling loop system, analogous to those used for electronics.