2.3. Nanofluid Production

The nanofluid samples were fabricated at 0.001, 0.01, and 0.1 volume fraction (Φ). For calculating the Φ, the following equation was used:

where, V_np, m_np, and ρ_np are the volume, mass, and density of the silica nanoparticles, respectively, whereas the V_bf is the volume of the basefluid. The ρ_np was provided by the manufacturer as 2 g/cm³, and the m_np were measured using a highly accurate ae-ADAM PW 214 analytical balance (Adam Equipment Ltd., Perth, Western Australia) with 10⁻⁴ g readability and ±2 × 10⁻⁴ g accuracy. Furthermore, the suspensions were then prepared through two stages. In the first stage, a magnetic stirrer device was used for 1 h to provide initial mixing between the nanopowder and the base fluid. Next, a Sonics Materials VCX 750 ultrasonic microprocessor, which is a probe type sonicator obtained from Fisher Scientific company. (Hampton, NH, USA), was used to further disperse the nanoparticles within the base fluid for 3 h. It is important to note that the ultrasonic device operated at 750 W net power output and 20 kHz with a 19 mm solid probe that is made of a high-grade titanium alloy (Ti-6Al-4V). Furthermore, the mixture temperature was controlled throughout the dispersion process using a BUENO BIOTECH company cooling and heating water bath (Nanjing, China), of type BGDC, with a 0.1 °C accuracy while being monitored using the ultrasonic temperature probe accessory, which is made of stainless steel and has a 1 °C accuracy. The previous suspension fabrication technique is widely used in the field and is known as the two-step nanofluid production method [30]. It is important to note that surfactants were not used in preparing the dispersions.