Natural convection in cylindrical containers with isothermal ring-shaped obstacles

The -dependence of the critical roughness height in two-dimensional turbulent Rayleigh–Bénard convection

“…2017; MacDonald et al. 2019; Emran & Shishkina 2020) further revealed that at height the exponent decreases back to the exponent in the smooth cell, due to the competition between the turbulent bulk and BL flow.…”

“…Numerical results of Stringano, Pascazio & Verzicco (2006) and Salort et al (2014) also reported an increase of heat transfer when the mean thermal BL thickness becomes smaller than the roughness height. In a cylindrical cell with a set of isothermal obstacles attached to the plates, Emran & Shishkina (2020) recently showed that the global heat flux can be several times that in the traditional smooth cell when the obstacle rings are very tall and the gaps between them are sufficiently wide. On the other aspect, Ciliberto & Laroche (1999) experimentally found that the scaling exponent of heat transport between Nu and Ra increases if the roughness has power-law distributed heights and the thermal BL thickness is smaller than the maximum roughness size.…”

Vibration-induced boundary-layer destabilization achieves massive heat-transport enhancement

“…Recently, many strategies (6,7) were proposed to achieve high heat flux. The most widely used method is to disturb the boundary-layer structures, such as by creating roughness on the conducting plates (8)(9)(10)(11)(12), which enables a notable increase of heat flux (8,12) but may suppress the global heat transport in some parameter ranges (13). Geometrical confinement provides an additional way to enhance heat transfer via plume condensation (14,15), despite an intermediate range of the cell aspect ratio only.…”

“…As an example, the introduction of wall roughness has been widely adopted to disrupt boundary layers by enhancing the detachment of the thermal boundary layer from the tips of rough elements (8)(9)(10)(11). As the analog to pressure drag is absent in the temperature advection equation (18), however, the system settles back to the boundary-layer-controlled regime for large imposed temperature differences (9,12). Another attempt is to perform the lateral confinement of turbulent flows (14,15), which has been successful in manipulating the flow structures in the convective bulk, yet the laminar boundary layers still limit the global heat flux.…”

Periodically Modulated Thermal Convection

“…In particular, we calculate the transition between the different regimes in phase space and show how they depend on the Rayleigh and Prandtl numbers, which represent the ratios between buoyancy and viscosity and between momentum diffusivity and thermal diffusivity, respectively. Our modulation method is complementary to hitherto used concepts of using additional body force or modifying the spatial structure of the system to enhance heat transport, for example, adding surface roughness [30][31][32], shaking the convection cell [33], including additional stabilizing forces through geometrical modification [34][35][36], rotation [37], inclination [38,39], or a second stabilizing scalar field [40].…”