Thermal convection from a localized heat source in a cylindrical layer was studied experimentally. Experiments were done for Rayleigh numbers from 3.4 . 10(5) to 4.5 . 10(7) and different Prandtl numbers (38, 67, 209). The main problem of the study was the impact of boundary layer flows on the heat transfer. We demonstrated that for the chosen interval of Rayleigh number secondary flows are characterized by remarkable variation of their structure and intensity. It was found that the power law that describes dependence of Nusselt number on Rayleigh number for the considered experimental configuration does not respond to the transformation of the boundary layer convective structures. Physical interpretation of this result is proposed. (C) 2019 Elsevier Ltd. All rights reserved.