2017/01/24 by Paolo Orlandi, Orlandi, Paolo, Sergio Pirozzoli +1 · 1 citation
Engineering · #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #Fluid Dynamics and Turbulent Flows #Heat Transfer Mechanisms #Nanofluid Flow and Heat Transfer
paper · pdf · doi:10.48550/arxiv.1701.06912
openalex publication_date 2017/01/24 · openalex created_date 2022/10/04 · openalex updated_date 2026/07/28
We study turbulent natural convection in enclosures with conjugate heat\ntransfer. The simplest way to increase the heat transfer in this flow is\nthrough rough surfaces. In numerical simulations often the constant temperature\nis assigned at the walls in contact with the fluid, which is unrealistic in\nlaboratory experiments. The DNS (Direct Numerical Simulation), to be of help to\nexperimentalists, should consider the heat conduction in the solid walls\ntogether with the turbulent flow between the hot and the cold walls. Here the\ncold wall, 0.5h thick (where h is the channel half-height) is smooth, and\nthe hot wall has two- and three-dimensional elements of thickness 0.2h above\na solid layer 0.3h thick. The independence of the results on the box size has\nbeen verified. A bi-periodic domain 4h wide allows to have a sufficient\nresolution with a limited number of grid points. It has been found that, among\nthe different kind of surfaces at a Rayleigh number Ra \≈ 2 \⋅ 106,\nthe one with staggered wedges has the highest heat transfer. A large number of\nsimulations varying the Ra from 103 to 107 were performed to find the\ndifferent ranges of the Nusselt number (Nu) relationship as a function of\nRa. Flow visualizations allow to explain the differences in the Nu(Ra)\nrelationship. Two values of the thermal conductivity were chosen, one\ncorresponding to copper and the other ten times higher. It has been found that\nthe Nusselt number behaves as Nu=\α Ra^\γ, with \α and \γ\nindependent on the solid conductivity, and dependent on the roughness shape.\n