Experimental study on cooling performance of water-based hybrid nanofluid with PCM and graphene nanoparticles

In this work, experimental study is performed to explore the cooling performance of water-based hybrid nanofluid with PCM and graphene nanoparticles in a tube to enhance energy efficiency of heat exchanger. The forced convection experiments have been performed for the cases of pure water and the hybrid nanofluids. The experiments are conducted for the volumetric flow rates of Q˙ = 60, 90 and 180 cm³/min, the mass fractions of tetracosane PCM nanoparticles of ω_pcm = 2, 5, and 10%, and the mass fractions of graphene nanoparticles of ω_np = 0 and 0.006%. The measured results show clearly that for the appropriate flow rate and heating power, using the nanoemulsion with the PCM nanoparticles as coolant can effectively reduce the wall temperature and enhance the heat dissipation effectiveness as compared with the case of pure water. However, the highly increased viscosity of the nanoemulsion with the PCM nanoparticles would drastically downgrade its highest figure of merit (FOM). The maximum average heat transfer effectiveness ratio of 1.044 can be achieved by using the PCM nanoparticles at l_h⁺/(d_i⁺Pe_f) = 0.033, [Formula presented]=0.0942, and Q˙ = 90 cm³/min. In addition, adding the graphene nanoparticles with the mass fraction of ω_np = 0.006% to the nanoemulsion to form the hybrid nanofluid leads to significant enhancement in the heat transfer.