Two regimes of flux scaling in axially homogeneous turbulent convection in vertical tube

Two regimes of the flux scaling in axially-homogeneous turbulent convection are observed. In one, the scaling exponent is \textonehalf{}, similar to the one expected in the so called `ultimate regime' of turbulent convection and in the other, it is 0.3, similar to the one observed in Rayleigh-Benard convection. However, the flow is different from the Rayleigh-Benard convection, in particular, very high fluxes and Reynolds numbers are obtained in this case. Results from different studies for three Prandtl numbers nearly collapse with the proposed unified flux scalings for the two regimes