Numerical investigation of flow boiling of refrigerant-based nanofluids and proposing correlations for heat transfer

The numerical simulation of subcooled flow boiling of R-113 working fluid has been done for two different nanofluids (R-113/Al2O3, R-113/TiO2) under different volume concentrations (0.5%, 1%, and 3%). The numerical results were compared with experimental results obtained by previous researchers, and the comparison shows that the numerical results are in good accordance. Nucleation site density, bubble departure frequency, and bubble departure diameter, which are three key parameters, are investigated in this study. The results express that these three parameters have the highest variation at low Reynolds numbers. The influence of different nanoparticles concentrations on the variation of the heat transfer coefficient is studied. The results indicate there is an insignificant difference between the effect of 1% and 3% concentrations on the heat transfer coefficient that means an increase of nanoparticles more than 1% concentration cannot improve heat transfer. The effect of different non-drag forces such as lubrication force, turbulent dispersion force, and lift force is also studied. Two correlations are proposed for predicting the convective heat transfer coefficient.