Computational Study of Thermal Performance of Shape-Dependent CNT/ Titanium Dioxide/Aluminum OxideSodium Alginate Hybrid Nanofluids for Solar Annular Collectors

Abstract

Solar direct absorber collectors are increasingly deploying more complex working nanofluids to enhance thermal performance. Hybrid nanofluids with non-Newtonian base fluids offer great promise in this regard. Motivated by these developments, the present article examines theoretically and numerically the thermal convection in a ternary hybrid nanofluid comprising an incompressible non-Newtonian sodium alginate base fluid in the annular gap between a pair of infinite concentric cylinders, as a model of a solar annular collector system. Sodium alginate (C6H9NaO6)n exhibits distinctive thermophysical characteristics, including enhanced versatility and viscoelasticity, rendering it appropriate for solar energy applications when integrated with hybrid nanoparticles. The Reiner-Rivlin third-grade viscoelastic model is therefore deployed to simulate the non-Newtonian characteristics. Three categories of nanoparticles are featured in the hybrid nanofluid: Carbon nanotubes (CNTs), Titanium dioxide (TiO2), and Aluminum oxide (Al2O3). The nanoparticles are categorized by their specific shapes: Carbon nanotubes exhibit a cylindrical form, Titanium dioxide exhibits a spherical configuration, and Aluminum oxide takes on a platelet shape. The presence of hybrid nanofluids influences both the internal transport characteristics and the heat flux towards the curved boundary and the behavior of nanoparticles with varying shapes is also a critical factor. Both linear and quadratic convection, along with viscous dissipation and heat generation/absorption, are also taken into account. The transformed boundary value problem is solved numerically with a finite difference method. Validation of the computational scheme with previous studies is included. Graphical results are provided for the impact of all emerging parameters on transport characteristics. Nusselt number is observed to be elevated with higher Grashof number (thermal buoyancy parameter) and heat generation parameter, whereas this trend is reversed with larger volume fractions of nanoparticles (CNTs, TiO2, Al2O3) and greater values of the quadratic convection parameter. The larger volume fraction of CNTs, TiO2, and Al2O3 nanoparticles strongly modifies viscosity and suppresses velocity magnitudes. The skin friction profile shows an increasing trend, which is greatly influenced by the Grash of number, heat generation parameter, and third-grade fluid parameter. In contrast, the quadratic convection parameter and the introduction of nanoparticles (CNTs, TiO2, Al2O3) tend to reduce skin friction magnitudes

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