Two-phase forced convection of nanofluids flow in circular tubes using convergent and divergent conical rings inserts

Numerical investigations are conducted using finite volume method to study the thermal and hydraulic characteristics of turbulent forced convection of nanofluid flow in a circular tube equipped with conical ring inserts. Four nanofluids with different types of nanoparticles, Al ₂ O ₃ , CuO, SiO ₂ , and ZnO with 1–4% volume fraction and particle diameters from 20 to 50 nm in base fluid (water) are tested. Two different approaches for simulating nanofluids viz., a single-phase and two-phase mixture are implemented. The effects of Reynolds number (2000–10,000) and conical rings type (convergent and divergent) are studied to test the heat transfer enhancement. The results revealed that the highest performance enhancement criteria based on the same pumping power is provided by the divergent ring inserts with 365%. Among the four tested nanofluids, those with SiO ₂ particles have achieved the highest heat transfer enhancement in terms of Nusselt number and the friction factor. The Nusselt number is enhanced with the increase of the particle volume fraction and Reynolds number, and with the decrease of nanoparticle diameter. It is found that the comparison of calculated results for different models with the experimental and numerical values shows that the two-phase mixture model is more precise than the single-phase model.