# Effect of Nanofluids on Boiling Heat Transfer Performance
## 4 Effect of Nanofluid on Critical Heat Transfer and Boiling Heat Transfer Coefficient  
This paper discusses the boiling heat transfer performance from the four aspects including nanoparticle types, concentrations, base fluids, and heating surfaces. Considering the divergence of nanofluids on boiling heat transfer performance, the differences between the enhancement of  
Figure 13: Boiling curves of deionized water on nanocoated and uncoated surfaces and comparing with 0.0025 vol.% nanofluid at various inclination angles of the heater [PERSON] et al. (2019). critical heat flux and the boiling heat transfer coefficient of nanofluids are considered. The addition of nanoparticles can enhance the critical heat flux, and this conclusion is well supported. The strengthening factor is mainly due to the following two reasons. 1. The addition of nanoparticles increases the thermal conductivity of the base fluid. 2. The deposition on the heated surface during boiling process reduces the contact angle and changes the wettability, so that the liquid is quickly replenished to the dry spots formed after the bubbles are detached. When the concentration of the nanoparticles is too large and the heating surface roughness begins to decrease, the critical heat flux no longer increases and begins to deteriorate gradually. In addition, the deposition morphology of different nanoparticles increases the capillary force and enhances the liquid replenishing ability after the bubbles are detached. From the current research literature, it is concluded that the influence of nanofluids on the boiling heat transfer coefficient is mainly affected by the following factors. 1. The influence of the deposition morphology of the nanoparticles on the heated surface. 2. The size of the bubble diameter. 3. Liquid convection effect on the heated surface. It is certain that the higher concentration nanoparticles deteriorates the boiling heat transfer coefficient. Since there are many cavities in the deposited layer formed on the heated surface and the contact thermal resistance increases. It can be known from the boiling theory that the amount of bubble detachment from the heated surface determines the boiling heat transfer coefficient in a certain period of time. The number of gasification core points on nano-heated surface plays an important role, so the boiling heat transfer coefficient can be enhanced by grooving [130; 131; 132] and polishing [129]. In addition, the diameter and detachment state of the bubble are changed by changing the pressure of the boiling environment, and the addition of magnetic fields, electric fields, and gravitational fields enhances the microscopic motion of the nanoparticles. The frequency of the bubble's detachment determines how quickly the heat on the heated surface is carried away. To some extent, the external field changes the perturbation effect of the microscopic motion of the nanoparticles on the boiling bubbles, thereby enhancing the detachment of the bubbles and enhancing the heat transfer. The low pressure effect is beneficial to the detachment of bubbles [85]. In addition to making the nanofluid more stable, the surfactant can reduce the surface tension, so that the bubble detachment diameter is reduced, the heated surface cannot easily form a film, and the boiling heat transfer performance is enhanced [87; 88]. The reasons for the current boiling heat transfer coefficient are presumed to include the following factors. 1. The thermal conductivity of nanoparticles compared to heated surfaces. 2. Bubble detachment. 3. Microscopic motion between multiple solutions. Copper blocks are used as electronic components with high thermal conductivity, and there are relatively many studies on heating surfaces. However, the thermal conductivity of metal oxides such as Al\({}_{2}\)O\({}_{3}\), CuO, and Fe\({}_{2}\)O\({}_{3}\) is much lower than that of copper, resulting in an increase in thermal resistance at the deposition point of the heated surface and the heat cannot be taken away in time, which increased the wall superheat.