A novel empirical effective viscosity equation for hybrid nanofluids

• The proposed novel viscosity equation for hybrid nanofluids integrates theory and experiments. • Validation against extensive data confirms high accuracy across varied conditions. • Analyzed parameters include volume fraction, nanoparticle size, and temperature. • Previous models typically cover fewer variables than our comprehensive approach. • The study offers insights crucial for heat and mass transfer calculations. This study introduces a new viscosity equation for a wide range of hybrid nanofluids, combining theoretical insights and experimental findings. The equation integrates calculated Brownian motion with two correction factors, synthesizing individual contributions into a comprehensive model for effective viscosity. Validation against experimental data shows strong agreement. We explore the influence of key factors affecting hybrid nanofluid viscosity, such as volume fraction, nanoparticle characteristics (size, shape, density), temperature, nanoparticle, and base fluid types. Unlike existing models, which typically consider fewer factors, our equation provides a comprehensive approach validated against extensive experimental data across various conditions. The study reviews existing viscosity correlations and proposes a new equation based on analysis of 2300 experimental and 4000 theoretical data points, covering 50 types of nanofluids and 30 hybrid nanofluids, spanning temperatures from 273 K to 338 K and nanoparticle diameters from 2 nm to 300 nm. The current new formulation was designed based on available data from the literature for five base fluids and 14 nanoparticle pairings.