# Effect of Nanofluids on Boiling Heat Transfer Performance
## 3 Effects of Nanofluid Physical Properties and Heated Surface on Boiling Heat Transfer
### Effect of Base Fluid Type on Boiling Heat Transfer  
When the nanoparticles are dispersed in different base fluids with different physical properties, the boiling heat transfer performance of nanofluids is also affected by the type of base fluid in addition to the influence of nanoparticles. Different base fluids exhibit different thermal conductivity [113; 114] and different viscosities [115; 116] (as shown in Figure 11), resulting in difference in convective heat transfer performance of the nanoparticles, and the bubble generation and escape rates as well as the surface tension. At present, the base fluids include deionized water, organic solvents, and refrigerants. The thermal conductivity of deionized water is higher than that of organic solvents and refrigerants, but some of the high specific surface area nanoparticles have very poor dispersibility in deionized water, so there are many studies on dispersing in organic solvents or refrigerants [93; 117], otherwise the nanoparticles are functionalized. Therefore, the influence of the physical parameters of the base liquid on the heat transfer has also received extensive attention and research. The viscosity increased with MWCNT concentration in the ethylene glycol and deionized water mixed liquid, but the viscosity decreased with increasing temperature [118]. [PERSON] [119], [PERSON] [83], [PERSON] [84], and others studied the physical properties and heat transfer properties of ethylene glycol and deionized water mixed liquid-based Al\({}_{2}\)O\({}_{3}\) nanofluids. The viscosity of the base liquid and the charge on the nanoparticles surface determine the degree of aggregation. Moderate aggregation of nanoparticles can make nanofluids more thermally conductive. In addition, it was found that the ethylene glycol and deionized water mixture has higher thermal conductivity than the single ethylene glycol or deionized water-based Al\({}_{2}\)O\({}_{3}\) nanofluid. As the heat flux increases, the boiling heat transfer coefficient increases remarkably. However, as the concentration increases, the surface roughness and heat transfer coefficient deteriorate significantly. There is an optimum concentration to enhance the boiling heat transfer performance. When the optimum volume concentration of the nanoparticles is 0.75%, the boiling heat transfer coefficient is increased by 64%. [PERSON] [100], [PERSON] [101], and others studied the boiling heat transfer of ethylene glycol-based ZnO nanofluids, ethylene glycol and water mixed liquid-based ZnO nanofluids respectively. The thermal conductivity increased by 40% when the volume concentration of nanoparticles is 3.75% dispersed in ethylene glycol. As can be seen from Figure 12, the volume fraction of 1.6% ZnO can increase the boiling heat transfer coefficient by 22%, and 2.6% ZnO can increase the critical heat flux by 117%. When ZnO nanoparticles with a mass fraction of less than 7.25% are dispersed in the 80 EG/20 DW (the volume ratio of ethylene glycol and deionized water is 80:20) mixed liquid, the critical heat flux and boiling heat transfer coefficient are enhanced due to the decrease in surface wettability. [PERSON] [93] then studied the boiling heat transfer performance of the graphene nanosheet in the 60 EG/40 DW mixed liquid. When the graphene concentration is less than 0.02%, critical heat flux increases with the increase of graphene concentration, because the deposition of graphene on the heated surface causes the wettability to increase. When the mass concentration is greater than 0.02%, the critical heat flux remains basically unchanged with the increase of concentration. In addition, SiO\({}_{2}\)[120], SiC [116], Fe\({}_{3}\)O\({}_{4}\)[92], CuO [91,121], and TiO\({}_{2}\)[122] were also studied with regard to the heat transfer characteristics of nanoparticles in a mixture of ethylene glycol and deionized water. In the same mixture of ethylene glycol and water, as the concentration of nanoparticles increases, the thermal conductivity of the nanofluid increases.