Investigation of the flow and thermal fields in square enclosures: Rayleigh-Benard's instabilities of nanofluids

The Rayleigh-Benard instability phenomenon corresponds to the unstable state in which there is a horizontal layer of an expandable fluid subjected to a temperature gradient. The present work investigates the development of laminar convection flow at different Rayleigh numbers (10(3) < Ra <10(5)) in a rectangular Rayleigh-Benard cell. The enclosure is differentially or partially heated, and it is filled with air or nanofluid. The aspect ratio is changed between 1 and 6. A mathematical model based on the stream function and vorticity approach (psi-omega) is used. The study is performed numerically by using the finite difference method and a program created by Python. The obtained results revealed the formation of different structures of rotating flows. In the Rayleigh-Benard configuration, the increase in the Rayleigh number intensifies the velocity and temperature fields, resulting in a transition from the conduction mode to a convection mode. For Rayleigh numbers between 10(3) and 10(4) , the presence of solid nanoparticles in the fluid reduces the flow velocities, while the heat transfer is particularly improved. The convection is also delayed by the addition of nanoparticles.

Automated summary

The study investigates the development of laminar convection flow in a rectangular Rayleigh-Benard cell at different Rayleigh numbers, revealing the formation of different rotating flow structures. Increasing the Rayleigh number intensifies the velocity and temperature fields, while the presence of solid nanoparticles in the fluid reduces flow velocities but improves heat transfer efficiency.