A comprehensive review of double diffusive convection: Effects of flow geometries, external forces, and porous media

This review investigates Double Diffusive Convection (DDC), a phenomenon where heat and solute concentration diffuse at differing rates, resulting in complex flow dynamics influenced by temperature and concentration gradients. DDC plays a crucial role in various natural and engineered systems, including oceanography, energy systems, and astrophysical contexts. This article synthesizes recent research on flow, heat, and mass transfer in DDC, emphasizing the effects of diverse flow geometries and external forces, including porous media. It examines critical parameters such as buoyancy ratio ($\mathrm{BR}$), aspect ratio ($\mathrm{AR}$), Prandtl ($\mathrm{PR}$), Reynolds ($Re$), Rayleigh ($\mathrm{Ra}$), and Lewis ($\mathrm{Le}$) numbers, alongside the Hartmann ($\mathrm{Ha}$), Soret ($\mathrm{Sr}$), and Dufour ($\mathrm{Du}$) numbers, highlighting their influence on velocity profiles, entropy generation, and heat/mass transfer rates quantified by Nusselt ($\mathrm{Nu}$) and Sherwood ($\mathrm{Sh}$) numbers. The review underscores the significant impact of geometry on DDC outcomes, demonstrating that configurations like rectangular and porous cavities enhance heat transfer efficiencies at elevated Rayleigh numbers. The introduction of nanofluids and variable porosity in porous media further optimizes thermal performance. Additionally, magnetic fields and rotation introduce complexities in flow stability and transfer efficiency, with higher Hartmann numbers leading to a transition from convection-dominated to conduction-dominated heat transfer. The interaction of thermal and solutal diffusion in porous media reveals transitions in stability, influencing flow patterns and convective currents. This comprehensive analysis highlights the vital role of geometrical configurations, fluid properties, and external forces in advancing DDC applications across diverse contexts.