A review of carbon and aluminium nanofluids and elastocaloric materials for heating and cooling applications

Nanofluids, suspensions of nanoparticles (NPs) in base fluids, enhance heat transfer in heating and cooling applications. Carbon and aluminium based nanofluids are the most promising materials owing to high stability, excellent thermal properties, low cost and high sustainability. This review critically examines the use of aluminium and carbon-based nanofluids, focusing on their synthesis, stability, thermal properties, and practical applications. Incorporating Al₂O₃, AlN, graphene, or C NPs into base fluids like water, methanol and ethylene glycol significantly enhances thermal conductivity and heat transfer performance. Carbon-based NPs added to water can result in up to 5000 W/m.K in thermal conductivity from 0.607 W/m.K. The two main synthesis methods namely one-step and two-step processes are discussed. The review also addresses challenges such as sedimentation, agglomeration, and channel blockage, providing insights into strategies for enhancing nanofluid stability and performance. Another limiting factor is the increased viscosity with increasing NP loading, with studies reporting up to a 138 % rise in fluid viscosity, which substantially raises the pumping power required. Future prospects such as using elastocaloric Ni-Ti alloys together with nanofluids for enhanced and sustainable heat transfer are reviewed.