Mechanistic insights of the surface contribution towards heat transfer in a nanofluid
Nanofluids play a very important role in thermal management and heat exchange processes and for a stable nanofluid, the surfactant is a salient material. There are many contrasting reports for the thermal conductivity of nanofluid and the associated heat transport mechanism in nanofluids. In this article, four different types of nanoparticles are synthesized using citric acid and oleic acid as a surfactant, followed by the assessments of their thermal conductivities. For a nanofluid of 3 wt% nanoparticle, coated with citric acid in water 67% reduction in thermal conductivity is observed, on the other hand, 4% enhancement in thermal conductivity is observed for oleic acid-coated nanoparticle in toluene. This anomaly in the thermal transport behaviour of the nanofluid can be related to the surface properties of nanoparticle and polarity of the base fluid. Theoretical calculation based on Molecular dynamics simulations shows that the reduction in long-range interaction and fluid structuration reduces the thermal conductivity in a polar fluid with a polar surfactant coated nanoparticle.