Rayleigh number

The Rayleigh number (Ra, after Lord Rayleigh ) is a dimensionless parameter that describes the nature of the heat transfer within a fluid.

When the Rayleigh number is below a critical value for the fluid, the heat transfer is given primarily by conduction; if it exceeds the critical value, the heat transfer is given primarily by convection.

In which

  • Ra = Rayleigh number (dimensionless)
  • Gr = the Grashof number (dimensionless)
  • G = gravitational acceleration (eg gravity in SI units 9.81 m / s ² )
  • Ts = characteristic temperature ( in SI units K)
  • T ∞ = resting temperature ( in SI units K)
  • ν = kinematic viscosity of fluid ( in SI units m² / s)
  • A = thermal diffusivity ( in SI units m² / s)
  • β = coefficient of thermal expansion ( in SI units 1 / K)
  • L = characteristic length (m in SI units)
  • Code ( Fluid Mechanics )
  • Code ( thermodynamics)
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