A Perspective Review on Thermal Conductivity of Hybrid Nanofluids and Their Application in Automobile Radiator Cooling

Table 2

Summary of the method of preparation of hybrid nanofluids.

S/N	Techniques	Some hybrid nanoparticle syntheses by the method	Main advantages	Disadvantages
(a) Chemical synthesis methods
1	Chemical reduction (CR)	Au-Pd-Pt, Au/TiO2, and Au-ZnO	Nanoparticles’ size and concentration can be tuned by controlling the synthetic.	Inability of both pure noble metals (NM) nanoparticles and hybrid nanoparticles to mix properly.
2	Photoreduction (PR)	Pd/TiO2, Ag/TiO2, Au/TiO2	Simplicity of steps and versatility of application.	Presence of impurities
3	Sol-gel	Au/SiO2, CNT-Fe3O4, and silica-MWCNT	Obtaining a high surface area and stable surfaces thus improves adhesion between the substrate and the topcoat.	High cost of precursor.
			Low processing temperature (energy saving).	Long duration of the process.
			The aspect ratio.	Relatively low yield.
			Precisely controlled in size and internal structure.
4	Hydrothermal	Pt/TiO2, Ag-ZnO	Ease in controlling the size and shape of nanoparticles.	High pressure and reaction temperature
5	Thermal decomposition	Pd-Fe3O4, Ag-TiO2		High cost of equipment
6	Coprecipitation method	Au-Fe2O3, Au-NiO, Au-Co3O4, and Au-ZnO	Simple and effective.	It is inappropriate for the synthesis of a highly untainted, precise stoichiometric phase.
7	Sonochemical synthesis	Pd-CuO, Pd-TiO2	It is faster, safer, less complicated, and eco-friendly.	Still, the mechanism is not well understood
		Au-TiO2	Size distribution in narrow particles.
8	Seeding growth	Ag-Fe3O4	It is a very effective method, especially in the case of dumbbell-like hybrid nanoparticles.
9	Electrodeposition (ED)	Ni-graphene, Ni-TiN, Pt-Ru, Ni-TiO2, Ni-ZrO2, Ni-AlN, Ni-Al2O3, and Ni-Si3N4	Process of rapid solidification.	Low temperature can lead to poor crystallinity.
			Cost-effectiveness and method adaptability.
			It is quick and has high purity.
			Low processing temperature (room temperature).
(b) Physical fabrications of hybrid nanoparticles
10	Laser-induced heating (laser ablation)	Ag-Al2O3, Cu-Cu2O	Highly pure colloids are produced with unique surface characteristics and without any by-products.	It requires a great amount of energy.
				NP colloids is often low, hence difficult to implement them on an industrial scale.
				Lack of control of the size and shape of the particles.
11	Atom beam cosputtering	Au-ZnO, Au-Ag	High purity	It is difficult to control the morphology of the formed nanoparticles
				Extensive energy requirement.
12	Ion implantation	Au-TiO2, Ag-TiO2		High energy demands.
(c) Biological fabrications of hybrid nanoparticles
13	Microbial incubation and plants extract	Fe-Pt, Co-Pt, Co-Fe, and Cd-Se.	Good reproducibility and scalability, high yield, and low cost	Slow and laborious

Source: Mohapatra et al. [92]; Ali et al. [93].