Functionalization and exfoliation of graphite into mono layer graphene for improved heat dissipation

Abstract

A novel synthesis procedure is presented for preparing single layer graphene (SGr) with high specific surface area (SSA). The SGr has been introduced as a promising additive for preparing super conductive nanofluids for high performance heat transfer applications. Owing to high SSA and unique degree of functionalization with hydrophilic groups, the SGr demonstrates an excellent colloidal stability and thermo-physical properties as an additive in aqueous media. Using UV–vis spectrometer, a highest dispersion stability of 0.866-relative concentration was reached after 30 days from preparation. Water-based SGr nanofluids illustrated fairly Newtonian behavior. Nanofluid containing SGr sheets with SSA of 761 m2/g and weight concentration of 0.01% showed the largest increase in thermal conductivity, i.e., from 0.748 to 0.795 W/m K as the temperature increased from 20 to 50 °C. The average heat transfer coefficient ratio (hnf/hbf)ave showed a downward trend with increasing of Reynolds number, decreasing from 233.5% at Re of 2000 to only 83.8% at Re of 16,000 at the constant weight concentration of 0.01%. Finally, the water-based SGR nanofluids were shown to be dramatically more effective in the duct with a backward-facing step in terms of overall thermal performance e.g., performance index and pumping power, and rheological properties including effective viscosity in comparison to distilled water.