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Measurement of the local convective heat flux in thermally-driven turbulence with rough surfaces

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We report experimental measurements of the local convective heat flux in a cylindrical Rayleigh-B\'{e}nard convection cell with rough top and bottom plates. The Rayleigh number $Ra$ is from $6.1\times 10^8$ to $5.3\times 10^9$ and the Prandtl number is $Pr=5.3$. Simultaneous measurements of velocity and temperature in the centre of the cell are made using a thermal probe and one-dimensional laser Doppler velocimetry (LDV). It is found that the normalised vertical heat flux $J_z$ in the centre of the rough cell scales with $Ra$ as $J_z=0.46 Ra^{0.18\pm 0.01}$. The Reynolds number $Re$ based on the rms velocity scales with $Ra$ as $Re=1.8\times 10^{-2} Ra^{0.49\pm 0.01}$. Compared to the smooth case, it is found that the enhancement of the convective flux in the centre of the rough cell is due to more thermal plumes passing through the centre.

Author(s):

Yi-Chao Xie    
Department of Physics, The Chinese University of Hong Kong
Hong Kong

Rui Ni    
Department of Physics, The Chinese University of Hong Kong
Hong Kong

Xiao-Ming Li    
Department of Physics, The Chinese University of Hong Kong
Hong Kong

Ping Wei    
Department of Physics, The Chinese University of Hong Kong
Hong Kong

Ke-Qing Xia    
Department of Physics, The Chinese University of Hong Kong
Hong Kong