Measured spatial distribution of the local thermal dissipation rate in turbulent Rayleigh-B{\'e}nard convection

The timed-averaged local thermal dissipation rate $\epsilon_{N} ({\bf r})$ in turbulent convection is obtained from simultaneous measurements of three components of the temperature gradient vector in convection cells filled with water. It is found that the measured $\epsilon_{N}({\bf r})$ contains two contributions; one is generated by thermal plumes and occupies mainly in the plume-dominated bulk region. The other contribution comes from the mean temperature gradient and is concentrated in the thermal boundary layers. The experiment provides new insights into the mechanism of heat transport in turbulent convection. \newline \newline *Work supported by the Research Grants Council of Hong Kong SAR.