Nanoscale Investigations of Thermal and Momentum Transport in Graphene – Water Systems

Demand for miniaturized electronic devices has given rise to new challenges in thermal management. Integration with graphene, a two-dimensional (2D) material with excellent thermal properties, allows for further reduced sizes and combats thermal management issues within novel devices. Moreover, due to its wide availability and adequate thermal properties, liquid water is commonly used within traditional thermal systems to enhance cooling performance; as such, water is expected to yield similar performance in smaller-scale applications. However, at reduced sizes descending to the nanoscale realm, system behaviors deviate from traditional macroscale-based theory as interfacial effects become amplified. Employing insight provided by molecular dynamics simulations, this thesis investigates momentum and thermal transport characteristics, stemming from interfacial interactions, of graphene/water systems to unravel their nanoscale contributions on system-wide thermal performance.

The convective heat transfer process for a laminar flow of liquid water in graphene nanochannels is emphasized as a joint assessment of momentum and thermal transport, with understandings obtained from initial investigations. In preliminary momentum transport analysis, wettability assessments identified graphene/water system behavior as highly dependent on interfacial surface interactions. Extension to flow simulations further revealed that surface interactions significantly impact momentum transport of flowing water behavior and slip development; attributing to the anatomically smooth nature of 2D graphene, slip flow is observed even in cases of extreme hydrophilicity. In thermal transport assessments, increasing surface interactions are shown to enhance heat transfer due to decreased interfacial thermal resistance. In convection heat transfer analysis, momentum and thermal transport are found to be strongly correlated; however, thermal transport was determined to be more influential on resultant system characteristics than momentum transport. Additionally, system size dependence on momentum and thermal transport is observed, with convective performance suggested as the ratio of thermal slip length to system size.

Findings presented in this thesis are expected to enhance knowledge of the physics behind solid/liquid interfacial phenomena and establish more accurate descriptions of nanoscale momentum and thermal transport. Although constrained by limited dimensional/time scales, this work is anticipated to aid in laying the ground work for understanding nanoscale thermal characteristics, with aim at developing novel thermal systems.