Time-dependent Rayleigh–Benard convection: Cell formation and Nusselt number

•We performed Rayleigh–Benard experiments as a fundamental study on severe accidents.•High Ra was achieved by using mass transfer experiments based on analogy.•Numerical analyses visualized time evolution of convection cell and Nusselt number.•Measured and calculated Nusselt numbers agreed with the existing studies.•Nusselt number varies little by the evolution of the cells after the square cell.

Rayleigh–Benard convection was investigated using experiments and numerical simulations for Rayleigh numbers in the range of 1.06 × 107–1.83 × 1010 and a Prandtl number of 2014. The plate separation and plate area were varied. High Rayleigh numbers were achieved using mass transfer experiments based on the heat and mass transfer analogy. The measured and calculated Nusselt numbers were in good agreement, and followed existing heat transfer correlations. The numerical analyses visualized the time evolution of the Rayleigh–Benard convection cell formation, as well as the time dependence of the Nusselt number.