# Effect of Nanofluids on Boiling Heat Transfer Performance
## 3 Effects of Nanofluid Physical Properties and Heated Surface on Boiling Heat Transfer
### Effect of Nanoparticles on Boiling Heat Transfer
#### 3.1.2 Effect of Nanoparticle Concentration on Boiling Heat Transfer
Firstly, the concentration of the nanoparticles increases, resulting in enhanced wettability of the heated surface, as shown in Figure 9. Secondly, the enhanced surface wettability results in an increase in the detachment diameter of the bubble, and the bubble detachment frequency is lowered, as shown in Figure 10.  
The study on boiling heat transfer of nanofluids, including Al\({}_{2}\)O\({}_{3}\) nanofluids from [PERSON] [71], [PERSON] [72], [PERSON] [75], [PERSON] [79], [PERSON] [84], [PERSON] [85] and others; CuO nanofluids from [PERSON] [87], [PERSON] [88], [PERSON] [89], [PERSON] [90], [PERSON] [91], and others; as well as GNs [92], Fe\({}_{3}\)O\({}_{4}\)[67], ZnO [101], SiO\({}_{2}\)[99], and CNT [71; 80; 95; 97] nanofluids, indicated that nanofluids  
Figure 10: These two aspects cause a decrease in the boiling heat transfer coefficient. Figure 9: Schematic diagram of the deposition of nanoparticles on a heated surface [78]. enhance the boiling heat transfer coefficient. The current explanation for this phenomenon is that nanoparticles increase the number of vaporization core points on the heated surface [67; 71; 72; 84; 92] and increase the thermal conductivity of the solution whose stability of the solution enhanced [75; 84; 95; 86]. Decreased surface tension [87; 91] leads to a decrease in the diameter of the bubble, which is conducive to detachment of the bubble. While a decrease in the wettability of the heated surface is also advantageous for the detachment of the bubble [101]. The boiling heat transfer coefficient is increased under the same heat flux by reducing the wall superheat. However, [PERSON] [74] pointed out that the boiling heat transfer performance of water-based nanofluids is weaker than that of deionized water. However, because the critical heat flux is faster than the wall superheat, the maximum boiling heat transfer coefficient is enhanced. It can be seen from the above influence of the nanoparticles concentration on the boiling heat transfer that there have an optimum value of the nanoparticles concentration making the maximum critical heat flux or the boiling heat transfer coefficient. A low concentration of nanoparticles can increase the thermal conductivity of the base liquid, and can increase the number of gasification core points, so that the generation of bubbles increases and the heat transfer is enhanced under the premise of the same bubble overflow frequency. However, high nanoparticle concentration causes a decrease in the operating frequency of the bubbles, which increases liquid viscosity and increases the thickness of the deposited layer. Under the premise of increased roughness of the surface deposited layer, the critical heat flux increases with the increase of the nanoparticles concentration. As the surface roughness begins to decrease as the concentration increases, the critical heat flux begins to decrease. The presence of a certain cavity in the deposited layer formed by the nanoparticles on the heated surface causes the heat to be not dissipated in time, resulting in an increase of wall superheat, so that the critical heat flux increases ratio less or less than the wall superheat, which causes a decrease in the boiling heat transfer coefficient. Therefore, it can be concluded that there is an optimum nanoparticles concentration dispersed in the base liquid, which can increase the number of boiling vaporization core points and the microscopic motion disturbance of the bubbles. At the same time, the formation of the nanoparticle deposition cavity does not cause the wall superheat to rise too fast. Thereby the maximum boiling heat transfer coefficient is improved.