# A Review of Pool-Boiling Processes Based on Bubble-Dynamics Parameters
## 7 Conclusions  
In this work, the mechanisms and mathematical correlations of each period of bubbles were reviewed and analyzed. The conclusions were made as follows:  
1. Whether bubbles can nucleate or not depends upon solid surface conditions and the wall superheat. Hydrophilic walls have higher critical heat flux, while hydrophobic surfaces have lower initial nucleation criteria. The density of nucleation sites is affected by a variety of factors (e.g., cavity shape and size, wall wettability, heat flux, wall temperature, and system pressure). There is no correlation formula yet that can predict all surfaces, which is important as more and more complex surfaces emerge.
2. Bubbles in the growth period and detachment period are mainly affected by the surface tension and the differential pressure between the inside and outside of the bubble. The bubble force analysis is of importance for the prediction of bubble  
Figure 14: Comparison of multiple heat flux prediction models with experimental results [120]: (**a**) comparison of heat flux prediction models from [PERSON] et al. [132], [PERSON]’s [130], and [PERSON] and [PERSON]’s. [131] with [PERSON] and [PERSON]’s [35] experimental boiling heat flux; and (**b**) comparison of the [PERSON] [132] boiling heat flux density prediction model with experimental boiling heat flux density results given by [PERSON] and [PERSON] [35], [PERSON] and [PERSON] [133], and [PERSON] and [PERSON] [134].  
detachment diameters. The influence of ambient pressure is proposed to be considered in the force analysis. Accurate mathematical descriptions of the drag force \(F_{d}\) and the inertial force \(F_{i}\) are still missing, and how to capture the center-of-mass trajectory of the bubble remains to be solved as well.
3. The growth rate of bubbles is mainly determined by the various properties of liquids and walls, and the growth of bubbles mainly comes from the evaporation of the thermal boundary layer. The difficulty in accurately predicting growth rates stems from the need for correct mechanistic analyses at different time periods. There is a lack of research on the flow physics of bubbles in existing studies, which we believe plays an important role in the refinement of bubble-growth models.
4. Most of the studies on the relational equations for the bubble detachment frequency \(f\) need to be calculated by the boiling heat transfer coefficient \(h\) and the heat flux \(q\), which is contrary to the commonly expected need to calculate the above two parameters with the help of \(f\). So, it is worthwhile to exclude the above two parameters from the correlation equations and replace them with other factors such as the wall superheat.  
In the current study, the bubble-dynamics correlations are always highly specific to the experimental data observed by themselves, and the agreement always reduces when these expressions are used for other boiling conditions. This is attributed to the fact that these correlations depend on a variety of influential parameters. However, usually only some of the highly correlated factors were selected to make the correlation guess based on their own experimental data, and other factors were ignored. Therefore, it is necessary to conduct a full range of experiments and to take all factors into account in the correlations, which requires a very sophisticated experimental design.  
Conceptualization, formal analysis, investigation and methodology, L.X.; resources, X.W., Y.Z., J.Y. and Y.L. ([PERSON]); supervision, X.W., Y.L. ([PERSON]), J.Y. and X.H.; writing--original draft, L.X.; writing--review and editing, X.H. All authors have read and agreed to the published version of the manuscript.  
This work has been supported by the National Natural Science Foundation of China (No. 52076185), and the Natural Science Foundation of Zhejiang Province (No. LZ19E060001).  
No new data were created or analyzed in this study. Data sharing is not applicable to this article.  
The authors declare no conflict of interest.