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 (via a laminar flow).
(fluid dynamics,measure,turbulence)
Further reading:
https://en.wikipedia.org/wiki/Rayleigh_number
https://en.wikipedia.org/wiki/Thermal_diffusivity
https://en.wikipedia.org/wiki/Rayleigh%e2%80%93B%c3%a9nard_convection
https://www.oxfordreference.com/display/10.1093/oi/authority.20110803100406166
https://www.thermopedia.com/content/1076/
https://resources.wolframcloud.com/FormulaRepository/resources/Rayleigh-Number-Using-Thermal-Conductivity
https://www.quora.com/What-is-the-physical-significance-of-Rayleigh-number
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