Talk:Rayleigh number

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What is x? It is not defined.

x is the position. The article does mention this. The parameter changes along the length of the wall, so you need a local value at a particular x position. There is no fixed characteristic length. —Preceding unsigned comment added by 129.162.1.42 (talk) 18:42, 7 January 2008 (UTC)

The critical Rayleigh number's interpretation is not as simple as saying "conduction dominates" or "convection tominates". Under certain geometries, the critical Rayleigh number may be define in a way which considers Prandtl's Number's influence for determining whether the boundary layer is laminar or turbulent. I believe it's empiracle how you define Ra_c for a particular geometry and thermohydraulic conditions, which may be Gr or Pr sensitive.