Surface-tension change of graphene-based water nanofluid and its effects on heat-transfer process

Abstract

Nanofluids with high thermal conductivities are gaining attention for heat-exchange applications, particularly in boiling processes. Nanofluid heat-transfer efficiency is significantly influenced by the surface tension (ST) and wettability patterns of the nanofluid. This study investigated graphene-based water nanofluids prepared from three different viscoelastic polymer solutions. The effects of the dispersant, graphene concentration, and temperature on the ST were investigated, and the wetting behavior of nanofluids on stainless steel and polypropylene random surfaces was determined. The results indicated that the ST of the nanofluids exhibited a negative correlation with the dispersant concentration and temperature. Additionally, the inclusion of graphene reduced the ST in xanthan-gum systems but increased it in sodium carboxymethyl cellulose and polyethylene-oxide systems. Overall, the nanofluids exhibited a lower ST than water. The decrease in the nanofluid ST is ascribed to the development of a rigid network resulting from the co-adsorption of graphene nanoparticles and the dispersant at the gas–liquid interface. Furthermore, graphene has been demonstrated to enhance the wettability of the base fluids of various materials. A decrease in ST led to increased frictional resistance; however, this was counteracted by an increase in the contact angle, resulting in an overall reduction in frictional resistance. Moreover, reducing the ST can improve the fluid boiling heat transfer. Therefore, these nanofluids exhibited the dual effect of reduced flow resistance and enhanced heat-transfer efficiency. This study offers valuable insights into the behavior of nanofluids and their potential applications in areas such as energy storage and spacecraft thermal management.