title: Effect of boundary layers asymmetry on heat transfer efficiency in turbulent Rayleigh-Bénard convection at very high Rayleigh numbers [corrected].
abstract: The heat transfer efficiency in turbulent Rayleigh-Bénard convection is investigated experimentally, in a cylindrical cell of height 0.3 m, diameter 0.3 m. We show that for Rayleigh numbers 10(12) < or approximately equal to Ra < or approximately equal to 10(15) the Nusselt number closely follows Nu is proportional to Ra(1/3 if the mean temperature of the working fluid-cryogenic helium gas-is measured by small sensors directly inside the cell at about half of its height. In contrast, if the mean temperature is determined in a conventional way, as an arithmetic mean of the bottom and top plate temperatures, the Nu(Ra) is proportional to Ra(γ) displays spurious crossover to higher γ that might be misinterpreted as a transition to the ultimate Kraichnan regime.
authors.affiliation: Institute of Scientific Instruments ASCR vvi, Brno, Czech Republic.
authors.forename: P
authors.initials: P
authors.lastname: Urban
authors.forename: P
authors.initials: P
authors.lastname: Hanzelka
authors.forename: T
authors.initials: T
authors.lastname: Kralik
authors.forename: V
authors.initials: V
authors.lastname: Musilova
authors.forename: A
authors.initials: A
authors.lastname: Srnka
authors.forename: L
authors.initials: L
authors.lastname: Skrbek