Thermal convection in a cylindrical layer heated from below and cooled at the top and side boundaries.*

Motivated by nuclear safety issues, we study heat flux exchanges in a thin cylinder with an imposed flux at the bottom and top (not necessarily equal) and a fixed temperature on the side. We combine Direct Numerical Simulations and a theoretical approach to derive scaling laws for the temperature difference between top and bottom and for the mean temperature of the system. We find two scaling laws depending on the flux aspect ratio. The first one is controlled by heat exchanges on the side, for which we recover classical laws of the vertical convection (George & Capp 1978). The second one is driven by top-bottom heat transfers analogous to Rayleigh-Bénard convection (Grossmann & Lohse 2000). In addition to averaged quantities, we show that heat flux fluctuations at the side wall are large and highly intermittent, which might impact safety protocols.