# Effect of Nanofluids on Boiling Heat Transfer Performance
## 5 The Direction of Nanofluid Research  
At present, there are still many scholars who have conducted in-depth research on the boiling heat transfer performance of nanofluids. The innovative ideas include selecting nanoparticles with high thermal conductivity and increasing their properties by surface functionalization or dispersion in a base liquid with a high viscosity to improve boiling heat transfer performance. In terms of analytical methods, the following research methods are included. 1. Scanning electron microscopy is used to analyze the sedimentary morphology and atomic force microscopy is used to analyze the roughness of the deposited surface. 2. Analysis of the generation and detachment of boiling bubbles by high-speed cameras. 3. Analysis of the wettability of the heated surface. However, through the analysis in this paper, in terms of the thermal conductivity of the heated surface, the deposition of the low thermal conductivity nanoparticles on the heated surface reduces the heat dissipation rate of the heated surface and improves the wall superheat of the heated surface [70; 78]. Then, the enhancement of the boiling heat transfer coefficient of the nanofluid should be attributed to the thermal conductivity of the nanoparticle to the base fluid and the influence of the microscopic motion of the nanoparticle on the disturbance of the heated surface bubble. The nanometer particles can be appropriately labeled, and the compositional analyzer can be used to observe the motion path during the boiling process. The influence of the microscopic motion of the nanoparticles on the boiling heat transfer is deeply studied and analyzed. In addition, because the surface of the nanoparticle is deposited on the heating surface to change the bubble generation state, it is necessary to use a high-speed camera to observe and analyze the bubble generation state around the deposition of a single nanoparticle. [PERSON] [134] first experimentally studied the surface wettability-independent critical heat flux during boiling crisis with foaming solutions. Foaming solution refers to those aqueous surfactant solutions that are very effective in avoiding bubble coalescence and form vapor foam. The slowly rising small bubbles in the foam crowd the heater surface to inhibit rewetting and trigger boiling crisis. Similar to the typical relation between the terminal velocity and the bubble size, we observe a power law exponent of half between the CHF and the bubble size. Such a behavior suggests that the ability of buoyancy to remove bubble swarm away from the heater surface dictates the CHF during boiling with foaming solutions. Resulting premature dry-out not only reduces CHF significantly in comparison to boiling with pure water, but also renders the effect of wettability improvements from micro-/nanotexturing inconsequential to CHF enhancement. Terminal velocity of the rising bubbles is estimated to model the maximum vapor-removal capacity and successfully predict the CHF over a wide range of concentrations. Weakly foaming surfactants, or the strongly foaming surfactants but at lower concentrations, behave similar to water wherein they form large bubbles and wettability improvements via surface modifications exhibit CHF enhancements. The physical insights gained in this study can now be used to devise strategies for CHF enhancement with aqueous surfactant solutions. High-speed visualization of the nucleate boiling process illustrated a fundamental difference in bubble dynamics (Figure 14). It can be seen from the Figure 14, comparison to water and Tween 80, bubbles relatively large in number and small in size were formed with aqueous SDS and Triton X-100 solutions. Boiling videos further suggested that the size and the number of bubbles correlated with the bubble coalescence properties of these solutions. For example, pure water allows the formation of relatively large bubbles, but a few in numbers, due to significant coalescence. Similarly, coalescence also prevails in Tween-80 solution and hence the formation of large bubbles.