Enhancing thermal performance in a magnetized square cavity: Novel insights from mixed convection of Ag-MgO nanofluid around a rotating cylinder

Abstract

This numerical investigation considers the mixed convection of a magnetically influenced hybrid nanofluid in a two-dimensional square cavity containing a centrally positioned rotating circle cylinder with a radius of R = 0.12. The nanofluid within the enclosure is water-based and incorporates Ag-MgO nanoparticles, the chemical and physical interactions between MgO nanoparticles and Ag molecules play an important function in determining the thermal conductivity and dynamic viscosity of MgO-Ag nanofluid. These findings exhibit that MgO-Ag nanofluid has the potential to be used as an advanced heat transfer fluid in cooling systems and heat exchangers. Two distinct cases are examined: firstly, with all walls of the square cavity and the rotating circle cylinder being adiabatic, except for the bottom side, and secondly, with the right side of the cavity being maintained at an isothermal condition. A finite element software package (FLEXPDE) is used in the present study. The governing partial equations, rendered dimensionless and encompassing various physical parameters, are solved utilising the Galerkin-based finite element method. Novelty is injected into the exploration through a meticulous parametric study, delving into the influence of key parameters, including the angular velocity spanning from -25 to 25, Reynolds number (10 ≤ Re ≤ 100), and Richardson number (0 ≤ Ri ≤ 35). The outcomes are vividly portrayed through visualisation of the flow structure via streamlines, the depiction of the heat transfer process through isotherms, and the computation of average Nusselt numbers. A discernible trend emerges, demonstrating that an increase in the Reynolds number, angular rotation speed, and Richardson number corresponds to an elevation in the average Nusselt number. Increasing Reynolds number (Re) from 10 to 50 intensifies streamlines, indicating fivefold higher flow resistance, with isotherms at Re = 50 showing 80 % concentration near the hot bottom wall compared to Re = 10. Counterclockwise rotation induces 90 % curvature near the bottom, clockwise rotation near the top, highlighting directional effects on flow resistance and streamlines. Remarkably, an intriguing observation surfaces as the angular velocity intensifies counterclockwise, revealing a 10 % augmentation in the average Nusselt values compared to a clockwise direction. Furthermore, the adoption of nanofluids as cooling agents, in lieu of pure water, is shown to enhance the cavity's thermal and overall performance, surpassing previous results. This underscores the novel insight into the advantageous utilisation of nanofluids in improving the efficacy of thermal systems.