Abstract
In most results concerning bounds on the heat transport in the Rayleigh-Bénard convection problem no-slip boundary conditions for the velocity field are assumed. Nevertheless it is debatable, whether these boundary conditions reflect the behavior of the fluid at the boundary. This problem is important in theoretical fluid mechanics as well as in industrial applications, as the choice of boundary conditions has effects in the description of the boundary layers and its properties. In fact, different boundary conditions may inhibit or enhance heat transport. This review presents a selection of contributions in the theory of rigorous bounds on Nusselt number, distinguishing and comparing the results for no-slip, free-slip and Navier-slip boundary conditions.