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Rayleigh number

(Ra)
(measure reflecting a fluid system's propensity to convection)

A Rayleigh number (Ra) is a measure of a condition within a fluid that might cause convection, a ratio between a tendency toward conduction and a tendency toward convection, each tendency represented by a timescale. Sufficiently low, there is no convection, sufficiently high, there is turbulent convection, and between, there is smoother convection (laminar flow).


(fluid dynamics,measure,turbulence)
Further reading:
https://en.wikipedia.org/wiki/Rayleigh_number
https://en.wikipedia.org/wiki/Thermal_diffusivity

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