Heat transport enhancement and flow transitions in partitioned thermal convection

Partitions are an essential part of industrial reactors and thermal management devices whose primary purpose is to increase transport rates by obstructing flow in one direction and promoting in the other via secondary and small-scale motions. Inspired by such applications, we have investigated thermal convection in a two-dimensional square enclosure heated at the bottom and cooled at the top, with four additional thin vertical partitions arranged parallel to facilitate organized plume motions in the range of Rayleigh numbers 106 to 109. The large-scale classical circulation observed in thermal convection breaks down into many roll configurations based on the constriction gap (S) between the partitions and the conduction walls. Due to their arrangement, we observed increased plume ejection, impact, and shear near the conduction walls when the partitions disturb the thermal boundary layers. The plume ejection and impact on either end of the constriction gap sets a pressure-driven forced convection on the conduction wall, thus increasing overall heat transport by at least an order of magnitude. We found the maximum heat transport when 0.2δRB<S<0.4δRB, where δRB is the time-averaged thermal boundary layer thickness in classical thermal convection. Using both the numerical simulations and a simple control volume-based analysis, we have estimated that the heat transport increases as S3 for small constriction gaps and as an inverse power of S for the large gap limit. With the help of energy dissipation, we have concluded that increasing plume intensity near the conduction walls leads to the observed high heat transport.