On laminar natural convection inside multi-layered spherical shells

Laminar natural convection flow inside multi-layered spherical shells with internal hot and external cold boundaries was investigated. Direct numerical simulations (DNS), which were performed by utilizing the immersed boundary method, addressed the fully 3D natural convection flow inside spherical shells with concentric, eccentric, equi-spaced and non-equi-spaced zero-thickness internal baffles. The insulation efficiency of the spherical shell was studied for up to four equi-spaced concentric internal layers. A unified functional dependency correlating modified Nu∗ and Ra∗ numbers was derived for spherical shells with up to four equi-spaced concentric internal layers. The effects of both vertical and horizontal eccentricity of the internal layers and of the width variation of concentric layers on the overall insulating performance of the spherical shell were investigated and quantified in terms of the Nu-Ra functionality.