Enhancement of natural convection of a nanofluid by stress-free patches in an L-shaped enclosure

PurposeThis study aims at investigating the heat transfer characteristics of a nonsquare enclosure when hydrodynamic resistance is altered discontinuously along its inner surface. Particularly, it focuses on investigating how several essential factors collaboratively influence the natural convection, including the Rayleigh number (Ra), the aspect ratio (AR), the nanoparticle volume fraction (phi) and the locations of changing hydrodynamic resistance. Design/methodology/approachTo achieve these objectives, an L-shaped enclosure of various AR is adopted, while zero local shear resistance is applied and modeled by stress-free (SF) patches of four distinct arrangements (corresponding to Cases 1-4). The nanofluid is modeled by Buongiorno's two-phase model. The effects are explored using an in-house numerical framework based on a hybrid lattice Boltzmann-finite difference method with the total variation minimization scheme. FindingsThe results show that when Ra is sufficiently large, i.e. Ra = 10(5), SF patches can generally enhance the heat transfer performance regardless of other factors. However, the ways of achieving those enhancements are different, which mainly depend on the arrangement of the SF patches and AR but are nearly independent of phi. The maximum improvement of heat transfer can be achieved in Case 3 with AR = 0.6, Ra = 10(5) and phi = 0.04, where the averaged Nusselt number is enhanced by 8.89%. Originality/valueThis study presents a new scenario where the SF patches of various arrangements are applied to enhance the nanofluid natural convection of a nonsquared enclosure, and it reveals how the improvement is achieved and cooperatively affected by several important factors.

Automated summary

This study investigates the heat transfer characteristics of a nonsquare enclosure with discontinuous hydrodynamic resistance on its inner surface. It explores the effects of several factors, such as Rayleigh number, aspect ratio, and nanoparticle volume fraction, on natural convection. The results show that the arrangement of stress-free patches and aspect ratio have significant impacts on heat transfer performance, while the nanoparticle volume fraction has minor influence.