Enhanced heat transfer by a slower flow in highly confined turbulent natural convection

Comparing to laminar flows, the most important effects of fluid turbulence are the greatly enhanced transport of mass, momentum and heat. With increased frictional drag from the container walls, one would ordinarily expect decreased transport of these quantities. Therefore, it comes as a surprise when heat transfer enhancement was observed as the cell width is reduced in a turbulent natural convection experiment [1]. In this paper, we use highly-resolved direction numerical simulations to provide abundant information of both temperature and velocities in such highly-confined geometries with much wider Rayleigh number Ra and width-to-height aspect ratio ranges. Our simulations reveals that in spite of largely suppressed velocity field due to viscid sidewalls, the Nusselt number Nu can increase substantially by 20%, over our explored parameters, due to much more coherent thermal plumes as clearly demonstrated by the temperature fields. Our study sheds new light on turbulent heat transport and has potential applications in passive heat management, which is critical for many microelectronic devices.