Effects of different thermal conductivity models and ? sphericity on mixed convection for hybrid nanofluids

Abstract

This work focuses on the combined effects of different thermal conductivity formulas for hybrid nanoparticles and the sphericity of these nanoparticles on the thermal behavior of a laminar flow of hybrid nanofluids in mixed convection through a partially heated pipe. The governing equations are solved by the finite volume method and using a structured and non-uniform mesh. This method used allows the behavior of nanofluids, which are complex mixtures of base fluid and nanoparticles, to be modeled. Simulations can take into account aspects such as the Brownian motion of particles and interactions between particles and fluid, thus improving the understanding of heat transfer phenomena. A percentage selection was made for a wide range of copper (5 %, 10 %, 15 %, 25 %, 40 %, 50 %) and three nanoparticle volume fractions (phi = 0.5 %, 2 %, 5 %). It was found that the effect of Cu is notable in the upper part of the section, where free convection is dominant in the presence of forced convective heat transfer due to the flow. We can also say that the percentage of copper and aluminum in nanofluids is a variable parameter and adjusted according to the application. There is no single value, but rather a range of concentrations that allows the desired performance to be achieved. A comparison between the numerical results and the experimental measurements available in the literature is carried out in order to validate the chosen numerical procedure. The Brownian model is associated with higher thermal conductivity, which means a greater ability to transfer heat. The Maxwell and Hamilton models show heat transfer characteristics very close to each other, which makes them less efficient than the Brownian model. This observation is crucial for choosing the most suitable model for an application where efficient heat transfer is sought, indicating that the processes describing the motion of particles in the Brownian model are the most efficient for moving thermal energy. Moreover, there is an increase in the average coefficients hup and hlow as the volume fraction of the nanoparticles in the fluid increases, for all values of the shape factor n1 of the alumina oxide particles, which represents 90% of the total volume fraction phi. Furthermore, the sphericity of nanoparticles affects the thermal properties of nanofluids by altering the interaction between the particles and the base fluid, as well as the particle arrangement. More spherical particles tend to maintain greater fluidity, reducing friction and aggregation, which can improve the thermal conductivity and stability of the nanofluid. The increase in thermal conductivity, one of the key properties of nanofluids, is directly influenced by this morphology.