Effect of doping liquid organic chains and nanoparticles on heat capacity of commercial engine oil

A recent study discovered the heat capacity of non-polar liquid can be enhanced by in-situ formation of fabricated superstructure. However, the result of the study seems to vary significantly between samples. Therefore, a parallel study has been conducted in this article that utilizes more compatible materials for the development of more enhanced oil nanofluids with high repeatability and ease of manufacturing. To show the effect of the improved synthesis protocol 1) pre-dispersed nanoparticle solution and 2) liquid phase polar organic chains) were used in the new in-situ synthesis. SAE 30 grade non-surfactant oil was doped with Al₂O₃ nanoparticle dispersion in toluene (10% concentration by volume) and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (average M_n ~2,000), because the glass transition temperature of the organic chain is -20 °C and remains as a complete liquid during the synthesis. The average heat capacity was measured to be 2.812 kJ/kg°C, which is 19.68% enhanced heat capacity over the pure SAE 30 oil (2.349 kJ/kg°C). The random error of the measurement was reduced by 7 times with the new in-situ synthesis protocol. The average viscosity of pure SAE 30 oil was measured to be around 7.35 cP and almost independent of shear rates showing Newtonian behavior. On the other hand, the nanofluids showed a very high increase of viscosity value at 25 /s and the increase of the viscosity decreases with the increase of shear rates showing non-Newtonian behavior (i.e., shear-thinning). The increase of the viscosity at 25 /s is 168.9% and decreased to 55.2% at 1000 /s. The shear-thinning behavior observed in the nanofluids confirms the formation of spiny nanostructures in the nanofluids.