Boiling and two-phase flow phenomena of refrigerant-based nanofluids: Fundamentals, applications and challenges

The study of refrigerant-based nanofluid boiling and two-phase flow phenomena is still in its infancy. This field of research provides many opportunities to study new frontiers but also poses great challenges. To summarize the current status of research in this newly developing interdisciplinary field and to identify the future research needs as well, this paper presents a comprehensive review of nucleate pool boiling, flow boiling, condensation and two-phase flow of refrigerant-based nanofluids. The effects of nanolubricants on boiling and two phase flow phenomena are presented as well. Furthermore, studies of applications and challenges of refrigerant-based nanofluids are presented and future research needs are identified. For the limited studies done so far, there are some controversies from one study to another. Conclusions and contradictions on the available refrigerant-based studies of physical properties, boiling and two phase flow are presented. According to this review, it has been realized that the physical properties have significant effects on the refrigerant-based nanofluid boiling and two-phase flow characteristics but the lack of the accurate knowledge of these physical properties has greatly limited the study in this interdisciplinary field. Furthermore, the limited available experiments and quite contradictive results have limited the understanding of the fundamentals of boiling and two phase flow phenomena. Flow regimes are very important in understanding the phenomena but less investigated so far. Apparently it is still a long way to go to achieve systematic fundamental knowledge and theory in the relevant subject. Therefore, effort should be made to contribute to the physical property database of nanofluids as a first priority. Secondly, systematic accurate experiments and flow regime observations on boiling and two-phase flow phenomena under a wide range of test conditions and nanofluid types should be emphasized to understand the fundamentals. Finally, physical mechanisms and prediction methods for boiling heat transfer and two phase flow characteristics should be targeted and applied research should also be focused on in the future.