Abstract
The multi-phase Rayleigh–Bènard convection has been weakly investigated, even though it plays a leading role in the theoretical and applied physics of the heat transfer enhancement. For the case of moderate turbulent convection, a rather unexpected result is an unusual kind of wind reversal, in the sense that the fluid is found to be strongly influenced by the bubbles, whereas the bubbles themselves appear to be little affected by the fluid, despite the relative smallness of the Stokes numbers. The wind reversal induced by the bubbles dispersed in the fluid is a new and remarkable phenomenon in multi-phase flows that provides further perspectives in understanding the complex physics leading the enhancement of thermal convection. For this reason, the fundamental research proposed in this paper aimed to identify a space of control parameters and the physical mechanisms responsible for the wind reversal induced by dispersed bubbles in a confined convective flow. The strength of the following description lies in an innovative numerical approach, based on the multi-scale physics induced by the coupling of the local thermal and mechanical mechanisms arising between each bubble and the surrounding fluid. The continuous phase has been solved numerically using the direct numerical simulation (DNS) technique and each bubble has been tracked by means of a particle Lagrangian model.
Highlights
The standard Rayleigh–Bénard convection occurs in a Newtonian single-phase fluid, bounded by lower and upper horizontal plates both at constant temperature, and an adiabatic side-wall.The thermal-induced buoyancy force pushes the stream toward the hotter region where the fluid is lighter.In the colder region, it happens in exactly the opposite way
The thermal convection undergoes significant changes with phase transitions [1,2] and when polymers [3], bubbles [4,5], and particles [6] disperse in the continuous phase
The Jakob number is a dimensionless parameter that takes into account the bubble ability to increase its own volume due to the heat transfer with the surrounding fluid
Summary
The standard Rayleigh–Bénard convection occurs in a Newtonian single-phase fluid, bounded by lower (hot) and upper (cold) horizontal plates both at constant temperature, and an adiabatic side-wall.The thermal-induced buoyancy force pushes the stream toward the hotter region where the fluid is lighter.In the colder region, it happens in exactly the opposite way. The standard Rayleigh–Bénard convection occurs in a Newtonian single-phase fluid, bounded by lower (hot) and upper (cold) horizontal plates both at constant temperature, and an adiabatic side-wall. The thermal-induced buoyancy force pushes the stream toward the hotter region where the fluid is lighter. The most relevant effect is the heat transfer enhancement of the multi-phase convection respect to the case of single phase convection. The multi-phase Rayleigh–Bénard convection plays a leading role in a wide range of physical phenomena such as the formation of atmospheric precipitation [7], magma chambers [8,9] boiling of liquid [10], and counterflow cooling towers [11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
