# 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
#### 3.1.1 Effect of Nanoparticle Types on Boiling Heat Transfer
Therefore, it is proposed that the ordered porous structure surface structure of nanoparticle deposition changes the critical unstable wavelength [112], resulting in the critical heat flux increases. [PERSON] [112] et al. proposed a formula for the influence of modulation wavelength on the critical heat flux of a porous surface, as shown in Equation (6). \[\mathrm{q}_{\mathrm{porous}}^{\prime\prime}=\frac{\pi}{8}\mathrm{h}_{\mathrm{fg} }(\frac{\sigma\mathrm{g}_{\mathrm{g}}}{\lambda_{\mathrm{m}}})^{1/2} \tag{6}\]  
Figure 7a,b shows the contact angle and the wavelength of the porous surface for the critical heat flux of different types of nanofluids, respectively. The boiling heat transfer of nanofluids is not only affected by nanoparticle type, but also the thermal conductivity of the base liquid [106]. Because of the density [89] and specific surface area [107], the roughness of deposited topography on heated surface is different during the boiling heat transfer process. The wettability and contact angle of the deposited surface have a great influence on the formation, growth, and detachment of boiling bubbles [82; 103]. The type of nanoparticles and the size of the nanoparticles have a significant effect on the boiling heat transfer. Compared with the above literature, the thermal conductivity of nanoparticles is higher and the heat transfer performance is better [71; 80]. That is, the better the thermal conductivity of the prepared nanofluids, the better the heat transfer performance. However, in view of the long-term static or high temperature conditions, the stability of the nanofluid is affected, so that the thermal conductivity of the nanofluid is reduced while changing the morphology of the heated surface. The morphology of the heated surface changes the number of boiling vaporization core points and bubble formation and detachment, thereby further  
Figure 7: CHF phenomena and comparisons between models and experimental data. (**a**) Effects of a surface wettability (Kandlikar’s model with contact angle). (**b**) Effects of a geometrically determined critical instability wavelength [111]. affecting the boiling heat transfer performance. It can be concluded that the stronger stability and thermal conductivity of the prepared nanofluid, the stronger the heat transfer. However, when the nanofluid cannot guarantee the long-term stability under the test conditions, the deposition of the nanoparticles on the heated surface causes the influence about the change of the physical properties of the heated surface. Firstly, the different nanoparticles type causes the different morphology and thickness of the deposited layers at the same concentrations. Secondly, the different nanoparticle types cause different wettability of the heating surface, thereby affecting the formation and detachment of bubbles, which include the shape and the diameter of the bubbles. Finally, the different kinds of nanoparticles make the different running speed in base liquid. During the boiling process, the difference in the speed caused by the microscopic movement of the nanoparticles causes the frequency of the disturbance and the separation of the bubbles to be different, thus affecting the heat transfer performance.