# Effect of Nanofluids on Boiling Heat Transfer Performance
## 5 The Direction of Nanofluid Research
On the contrary, nucleating bubbles in SDS and Triton X-100 solutions rarely merged/coalesced. Accordingly, high-density small sized bubbles formed with these foaming solutions. Bottom view images of vapor bubbles at different subcooling and heat fluxes, for aqueous solutions and SDS at critical micelle concentration, during pool boiling on an inverted heater as shown in Figure 15. From the Figure 15, it can be suggested that the effective bubble size was found to decrease with the increase in subcooling due to enhanced condensation. Subsequently, vapor crowding was decreased and the CHF was found to increase with subcooling for ionic liquid and surfactant. Figure 14: (**a**) Snapshot of bubbles during near-saturated boiling with aqueous surfactant solutions at critical micelle concentration and pure water in the early nucleate boiling regime. (**b**) Schematic representation of the bubble behavior during pool boiling. Relatively large bubbles with higher terminal velocity were formed with water in comparison to surfactant solution [134]. [PERSON] [135] et al. found that unlike water the aqueous solution of surface active ionic liquid avoids coalescence to form multiple small bubbles with significantly large wet area on the heater surface. Resulting rewetting of the heater surface increases the critical heat flux to \(\sim\)950 kW/m\({}^{2}\), which is an enhancement of \(\approx 4:5\times\) in comparison to pure water. It can be seen from the above literature that the formation, size and detachment state of boiling bubbles have a significant influence on the boiling heat transfer performance. So the influence of nanofluids on boiling heat transfer can be studied by the following means. 1. By disposing the nanoparticles with different thermal conductivity on the heated surface and not escaping due to the severity boiling during the boiling process. The effects on the critical heat flux and boiling heat transfer coefficient in the pure solution are investigated and the bubbles around a single nanoparticle are observed. 2. The current boiling heat transfer devices are all boiling in a large container saturated pool boiling, so the influence of the multicomponent solution on the boiling heat transfer can be observed by externally condensing the device, and the relative movement between the multicomponent solutions can be clearly observed. The motion and the disturbance of the bubble were observed and analyzed, and the effects on the critical heat flux and boiling heat transfer coefficient were investigated. 3. By investigating the boiling heat transfer performance of mixed nanoparticles in multisolution, the relative motion between base liquids and the influence of micromotion of different nanoparticles due to their density difference and specific surface difference on the critical heat flux and boiling heat transfer coefficient were analyzed. 4. To classify the heat transfer between different nanoparticles and different base liquid nanofluids and to correlate the effects of nanofluids on boiling heat transfer to a general purpose test of boiling critical heat flux and boiling heat transfer coefficient. Subsequent further in-depth research laid the foundation. The excellent physical properties of nanofluids make it gradually applied to many fields of enhanced heat transfer, but the research and conclusions on its boiling heat transfer performance still lack a lot of experimental verification and convincing mechanism explanation. Therefore, it is necessary to examine the microscopic motion of nanoparticles and the operating state of bubbles from deeper and more diverse studies to reveal the mechanism of strengthening or suppressing heat transfer. Figure 15: Bottom view images of vapor bubbles at different subcooling and heat fluxes, for aqueous solutions and SDS at critical micelle concentration, during pool boiling on an inverted heater [135].