*2.1. Materials*

Nanoparticles of γ-Fe2O<sup>3</sup> and functionalised MWCNTs were used in this work. The γ-Fe2O<sup>3</sup> nanoparticles (20–30 nm diameter as specified by the manufacturer) were sourced from Nanostructured and Amorphous Materials Inc., TX, USA, while the f-MWCNT nanoparticles (length: 10–30 µm; outer diameter: 10–20 nm and inner diameter: 3–5 nm) were purchased from MKnano Company, ON, Canada. Sodium dodecyl sulphate (SDS) with the purity of ≥98.5% bought from Sigma-Aldrich, Berlin, Germany was used as a surfactant to affect the stability of the studied hybrid nanofluids. The thermal properties of the base fluid and nanoparticles used in this study are provided in Table 1. It is noted that some properties and parameters of nanomaterials are provided in the company's product datasheets.

**Table 1.** Thermophysical properties of studied materials at room temperature.

