# 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  
The concentration of the nanoparticles largely determines the deposition morphology of the heated surface. Appropriate nanoparticle concentration can increase the number of vaporization core sites and increase the wettability of the heated surface. If the concentration is too high, the surface roughness of the deposited surface will be reduced or the deposited layer will be too thick, resulting in a decrease in the boiling heat transfer coefficient. [PERSON] [74], [PERSON] [78], and others studied the boiling critical heat flux curve and boiling heat transfer coefficient of water-based Al\({}_{2}\)O\({}_{3}\) nanofluids with different concentrations. It can be seen from Figure 8a that the addition of Al\({}_{2}\)O\({}_{3}\) nanoparticles makes the boiling curve move to the right and the heat transfer performance is weakened. As the concentration of nanoparticles increases, the heat transfer performance of Al\({}_{2}\)O\({}_{3}\) nanofluids first decreases, and then increases. It can be seen from Figure 8b that the addition of Al\({}_{2}\)O\({}_{3}\) nanoparticles to deionized water, in addition to moving to the left in boiling curve of the Al\({}_{2}\)O\({}_{3}\) nanofluid with a volume concentration of 0.001%, right with the concentration. However, it can be seen from the literature that the addition of Al\({}_{2}\)O\({}_{3}\) nanoparticles increases the boiling critical heat flux of the base liquid. The literature also points out that the increase of the critical heat flux of nanoparticles is due to the enhanced wettability of the porous surface formed by the deposition of Al\({}_{2}\)O\({}_{3}\) nanoparticles on the heated surface, and the increase of the wettability causes the bubble contact angle to decrease. The decrease of the boiling heat transfer coefficient is due to the porous deposition layer formed by the deposition of the nanoparticles, which increases the thermal resistance of the heat conduction, as shown in Figure 9.  
Figure 8: Boiling heat transfer curves and boiling heat transfer coefficient curves of different nanofluids. (**a**) Al\({}_{2}\)O\({}_{3}\) nanofluid boiling curve [74]. (**b**) Al\({}_{2}\)O\({}_{3}\) nanofluid boiling curve [78]. [PERSON] [70], [PERSON] [74], [PERSON] [76], and [PERSON] [78] et al. experimentally studied the boiling heat transfer performance of water-based Al\({}_{2}\)O\({}_{3}\) nanofluids with different concentrations. The literature [76] also studied the boiling heat transfer of water-based CNTs and water-based Fe\({}_{2}\)O\({}_{3}\) nanofluids. [PERSON] [79] et al. studied the boiling heat transfer of water-based SiO\({}_{2}\) nanofluids and finally reached the same conclusion. That is, the deposition of the nanoparticles causes an increase in wettability, which in turn increases the critical heat flux. However, the porous deposition layer causes an increase in the thermal resistance of the heat conduction, thereby increasing the wall superheat and reducing the boiling heat transfer coefficient. [PERSON] [92] et al. studied the boiling heat transfer characteristics of ethylene glycol and deionized water mixed with a liquid-based Fe\({}_{3}\)O\({}_{4}\) nanofluid on the Ni-Cr wire surface. The volume concentration was 0.01%, 0.05%, and 0.1%. The volume ratio of ethylene glycol to deionized water is 50:50. The results show that as the concentration increases, the deposition of nanoparticles increases and the critical heat flux increases. At a concentration of 0.1%, the critical heat flux is 100% higher than that of the mixed base liquid.