**3. Preparation and stability of metal oxide nanofluid**

#### **3.1 Preparation**

Preparation of NFs is the most challenging step, as far as the experimental studies with NFs are concerned. This is so because nanofluids need special requirements

**135**

**Figure 1.**

*Society.*

*Nanocomposite and Nanofluids: Towards a Sustainable Carbon Capture, Utilization, and Storage*

One-step technique (or direct approach) consists in formulating the nanofluid right after their synthesis. The literature reports two major approaches including direct evaporation and the laser ablation method. In either approach, the nanofluid

Two step approach is designed in a manner that the surface of MO-NPs is sufficiently wet so to mitigate the particle impingement [39]. This is done by either using mechanical mixing [40] or sonication or the combination of both [41, 42] as

During the mechanical mixing, the large flocs are broken down and the individual particles are kept separated from each other. During the sonication stage, the ultrasound waves, by stretching the molecular spacing of fluid, creates cavities within, which cause subsequently the chemical bonds to break [44]. However, due to the intrinsic properties of MO-NPs, a poor dispersion is often yielded which is mitigated by either extending the mixing time, adding few drops of acidifying

Sedimentation method is the simplest and most straightforward method to investigate the stability of a nanofluid. A fixed volume of nanofluid is transferred into a graduated test tube and observed over the time. **Figure 2** shows the sedimen-

The monitoring of the volume of deposited NPs showed that a load in alumina-NP of 0.05 wt.% was sufficient to give a stable nanofluid. The literature reports similar results, in which no or little visual sedimentation of particles can be

*Preparation of polymer-based NFs; Adapted with permission from [43]. Copyright (2019) American Chemical* 

including stable suspension, low agglomeration of particles, and no chemical

*DOI: http://dx.doi.org/10.5772/intechopen.95838*

*3.1.1 Preparation using direct method or one-step approach*

*3.1.2 Preparation using two-step method approach*

is obtained after a transition from the gas to solid phase [37, 38].

agents [45] or even bubbling gas during the preparation [43].

tation of alumina-based NFs upon increasing the load in NPs.

change of the fluid.

shown in **Figure 1**.

**3.2 Stability of MO-NFs**

*3.2.1 Monitoring the stability of NFs*

observed from the naked eye [46].

*3.2.1.1 Sedimentation and centrifugation method*

*Nanocomposite and Nanofluids: Towards a Sustainable Carbon Capture, Utilization, and Storage DOI: http://dx.doi.org/10.5772/intechopen.95838*

including stable suspension, low agglomeration of particles, and no chemical change of the fluid.
