## 2 Materials and Methods
### CuO Nanofluids Production  
In CuO particle production, 3.633 g (0.02 mol) of Copper Acetate was dissolved in 100 mL ethanol for 30 min in an ultrasonic bath. Then, 8 g (0.2 mol) of NaOH (Carlo Erba Reagents, Val de Reuil, France) and 200 mL of pure water were added to the resulting mixture and dissolved in an ultrasonic bath for 30 min. Then, the resulting mixtures were combined and stirred in the fish mixer for 1 h. In order to obtain the mixture at different pH ratios, ammonia was added to the mixture with a 10 mL beaker. The mixture was allowed to precipitate for 20 h after preparation. After the waiting process, filter paper was placed in the funnels and the material was subjected to the drying process at 50 \({}^{\circ}\)C. Finally, the material obtained was heat-treated at 450 \({}^{\circ}\)C for 1 h. SEM image analyses were performed to determine whether the material produced was a nanoparticle and whether nanoparticle production was successful.  
After the production of CuO nanoparticles, the materials used for the production of nanofluids are 57.1% Pure Water, 28.6% Ethylene Glycol and 14.3% Ethanol. 0.1%, 0.2%, and 0.3% CuO nanoparticles were added to the solution of pure water, ethylene glycol and ethanol and then stirred for 45 min in an ultrasonic mixer. The nanofluids formed as a result of the mixture is ready for use in the experimental setup. After determining the density of the produced nanofluids, pH values were determined using a pH measuring device. Experiments were performed for 5 different Reynolds values between 846 and 2292 for the produced nanofluids.  
Scanning Electron Microscope Analysis  
Basically, the scanning electron microscope (SEM), Tungsten, Lantana hexane boron cathode or the field emission (FEG) from the day of the use of the electrons emerging from the surface to be examined (as a result of the interaction) is based on the interaction. In general, this electron energy in SEM can range from 200-300 eV to 100 keV. For this purpose, the electron beam, which is collected by the concentrator electromagnetic lens (condenser lens), focuses on the lens and perform scanning on the sample surface with electromagnetic deflector coils. The formation of images in a scanning electron microscope is basically based on the principle of collecting and examining the signals resulting from the physical interactions with the surface of the electron beam (elastic, non-elastic collisions and others). In the SEM device, the electrons in the electron bundle are the secondary electrons that emerge as a result of the non-elastic collision with the atoms in the material (i.e., transferring their energies to the electrons in the atoms on the sample surface). These electrons emerge from a depth of about 10 nm of the sample surface, and their typical energies are at most 50 eV. Secondary electrons are collected by means of the photomultiplier tube and associated with the scan signal location, for example, to obtain a surface image [19].  
The nanoparticle images at different pH values taken with the SEM display device (JSM-7001F, Tokyo, Japan) are shown in Figure 1 respectively.  
The nanoparticles, defined as dusts, whose dimensions are less than or equal to 100 nm, form the basis of nanoscale materials and, thus, nanotechnology [20]. According to SEM analysis images in Figure 1, the morphological structure and dimensions of the CuO nanoparticles produced at various pH were found to be successful in the production of nanoparticles.  
Figure 1: The scanning electron microscope (SEM) image of CuO, (**a**) CuO pH 7 nanoparticle; (**b**) CuO pH 10 nanoparticle; (**c**) CuO pH 12 nanoparticle; (**d**) CuO pH 14 nanoparticle.