Numerical simulation on single bubble behavior during Al2O3/H2O nanofluids flow boiling using Moving Particle Simi-implicit method

In this study, regression analysis on the thermal properties of Al2O3/H2O nanofluids was made firstly. The growth and departure of a single bubble behavior in Al2O3/H2O nanofluid and pure water flow boiling process were then numerically simulated by an improved Moving Particle Semi-implicit method in different flow boiling conditions. The results indicate that the bubble in Al2O3/H2O nanofluids grows faster and the bubble departure frequency of Al2O3/H2O nanofluids is greater than that in pure water. The flow boiling heat flux is also improved by dispersing nanoparticles of Al2O3/H2O in pure water. This work initially reveals that nanofluids can enhance flow boiling heat transfer from the point of view of bubble dynamics behavior. The effects of nanoparticle concentrations and diameters of Al2O3/H2O nanofluids on the bubble behavior were also investigated and compared under the same flow conditions. It is found that the increasing of nanoparticle volume concentration may increase the bubble departure frequency and departure diameter, while the increasing rates of departure frequency and departure diameter are lessened with the increasing of nanoparticle volume concentration. It is suggested that the suitable nanoparticle volume concentration of nanofluid for flow boiling heat transfer enhancement should not be too large, especially regarding the negative effect of flow resistance increase due to the increasing of nanoparticle volume concentration. The interesting finding is that in the same nanoparticle volume concentration condition, the bubble departure frequency for the nanofluid with nanoparticle diameter of 29 nm shows a maximum value. The increasing of nanoparticle diameter leads to the decreasing of bubble departure diameter. It is boldly to predict that an optimal nanoparticle diameter range between 20 and 38 nm should be beneficial to flow boiling heat transfer enhancement of Al2O3/H2O nanofluids.