Thermal stability of graphene-oxide nanofluids during enhanced convective heat transfer in a spacecraft fluid loop

Abstract

Owing to their excellent thermal conductivity, nanofluids are widely used in solar collectors, automotive radiators, and spacecraft thermal management systems. However, the thermal stability and reliability of nanofluid systems limit their heat-transfer performance. This study investigated the stability and reliability of typical water-based graphene-oxide nanofluids under the simulated working conditions of a practical spacecraft fluid-loop system. Nanofluid stability was evaluated in the room-temperature static state, room-temperature flow state, heated static state, and heated flow state; the instability mechanism was also studied. The volume fraction of nano graphenes in the nanofluids decreased with increasing heating time and temperature and was independent of the motion state. The volume fraction remains above 90 % of the pristine sample between 298 K–358 K, showing a relatively stable state, and its stability decreased rapidly at 373 K. In the heated flow state, graphene-oxide sheet edges folded owing to the high temperature, decreasing the specific surface area and the contact area of the graphene-oxide sheets during convective heat transfer, which is responsible for the degraded heat transfer performance. Graphene-oxide sheet folding was mainly driven by the competition between the graphene–water binding energy and graphene-oxide bending energy. This study provides stability criteria for graphene oxide–deionised water nanofluids for practical applications and reveals the instability mechanism.