Abstract
A numerical study of flow boiling has been performed with R134a refrigerant flowing inside a horizontal tube. Flow pattern has been captured using VOF methodology in OpenFoam software up to mass flux of 150 kg/m2s. The various stages of bubble dynamics like nucleation, growth, merging and departure has been observed for ranges of heat and mass fluxes. The phase fraction variations during flow boiling have also been observed at two different saturation temperatures and the differences in interfacial features have been reported. An attempt has been made to estimate the number of nucleation sites and the bubble departure diameter for R134a in the case of flow boiling inside the smooth tube. With the help of numerical simulations, the study has also been made by providing artificial nucleation sites in the form of indentations/cavities inside the tube. An increase in nucleation sites has been observed for the dimpled tube as compared to the plain tube and the corresponding change in bubble departure phenomenon has been reported. The heat transfer coefficients at different heat flux, mass flux, saturation temperature and tube configurations have been evaluated to link observed interfacial phenomenon with enhancement factor.
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