# Effect of Nanofluids on Boiling Heat Transfer Performance
## 3 Effects of Nanofluid Physical Properties and Heated Surface on Boiling Heat Transfer
### Effect of Heated Surface on Boiling Heat Transfer of Nanofluids  
The effect of the roughness of the heated surface on the boiling heat transfer performance is to increase the heat transfer surface area, thereby increasing the influence of the vaporization core on the boiling heat transfer. However, the different heating surfaces and the surface roughness are also different for the heat transfer performance of the nanofluid. In addition, in order to further explore the influence of nanofluids on boiling heat transfer, it is necessary to study the boiling heat transfer of the pure base liquid on the deposition surface formed by the nanofluid boiling heat transfer test. Compared with deionized water, Al\({}_{2}\)O\({}_{3}\) nanoparticles with a volume concentration of 0.001% can enhance the boiling heat transfer performance of a smooth surface with an average roughness of 25 nm, but the effect on the heat transfer of a rough surface with an average roughness of 420 nm is not obvious [52]. [PERSON] [53] et al. further promoted the boiling heat transfer of water-based Al\({}_{2}\)O\({}_{3}\) nanofluids on different roughness heating surfaces. The volume concentration was 0-0.05% and the heating surface roughness was 177.5 nm and 292.8 nm, respectively. The results show that when the concentration is increased from 0% to 0.05%, the critical heat flux increases by 224.8% and 138.5% on the surfaces of roughness 177.5 nm and 292.8 nm, respectively. The boiling heat transfer performance of Al\({}_{2}\)O\({}_{3}\) nanofluid with a concentration of 0.05% is lower than that of deionized water at Ra = 177.5 nm, but the maximum boiling heat transfer coefficient increases due to the increase of critical heat flux. The weakening of the boiling heat transfer coefficient is mainly caused by the deposition of nanoparticles on the heated surface, which increases the heat transfer resistance, but the wettability of the deposited surface is enhanced and the critical heat flux is increased. By welding the foam metal on a smooth surface, the boiling heat transfer surface area can be increased. In addition, there is an influence on bubble growth and detachment during boiling process. In order to further enhance the boiling heat transfer of the foam metal surface, [PERSON] et al. [126] investigated the effect of nanoparticles concentration and nanoparticles size on the boiling heat transfer of copper foam. The nanoparticles were Al\({}_{2}\)O\({}_{3}\) and SiC. The foam copper thickness was 7 mm; the pore density was 5 PPI, 60 PPI, 100 PPI; and porosity was 0.9, 0.95, and 0.98. Preliminary studies have found that the addition of nanoparticles can enhance the boiling heat transfer performance of low porosity foamed copper, and the deposition of nanoparticles on the surface of foamed copper can increase the capillary force of copper foam, in addition to increasing the number of vaporization core points. In addition, the boiling heat transfer performance of nanofluids on the gradient hole surface was also studied, because the addition of nanoparticles blocked the voids of high density foam copper (100 PPI), and the bubble escape resistance increased, so that the heat transfer performance decreased [127]. [PERSON] et al. [128] found that the ethanol-based MWCNT nanofluids increased the boiling heat transfer rate by 59% on the surface of the disk with laser inscribed square column texture. It can be seen that the boiling heat transfer performance of nanofluids is affected not only by the nanofluids themselves, but also by the heating surface. Besides the roughness of the heated surface,the ratio of the average particle size to the roughness of the heated surface is also related to the boiling heat transfer performance. Using larger ratios, the deposition of nanoparticles can further increase the roughness of the heated surface, and, on the contrary, reduce the roughness. However, the boiling heat transfer performance will be significantly deteriorated by the formation of porous deposits on the surface of nanoparticles with high concentration.