Effect of Preparation Temperature, Surfactant, and Nanoparticles Concentration on the Effective Thermophysical Properties of Multi-walled Carbon Nanotubes’ Nanofluids

This research investigates the thermophysical properties and physical stability of multi-walled carbon nanotubes (MWCNTs)–water nanofluids that are manufactured through the two-step controlled sonicator bath temperature method. The nanofluids are prepared with water as the basefluids, and MWCNTs of 0.01–0.10 vol%. A bath-type ultrasonicator was employed to disperse the nanomaterials within the as-prepared basefluid. The sonication process, for all as-fabricated suspensions, lasted for 90 min and the device bath temperature was controlled in the range of 10 °C–50 °C. Furthermore, the samples were then characterized in terms of their thermophysical properties as well as their short and long physical stability. The results have indicated that the effective density of the suspension was higher than that of the basefluid, and that this property decreases with the increase in the production temperature. As for the effective specific heat capacity, that property was shown to be highly sensitive to the MWCNTs and SDS concentrations. Furthermore, the fabrication temperature was shown to be a dominant parameter when it came to both the effective thermal conductivity and viscosity, where it caused the first property to increase while reducing the second one. In terms of the surfactant concentration, the physical stability results have shown that low surfactant concentration can only physically stabilize the dispersion for 24 h, whereas the concentrations higher than 1:1 surfactant to MWCNTs ratio caused the nanofluids to maintain their stability for up to 7 days.