Rayleigh and Nusselt numbers

  1. Hi

    Can anyone tell me anything about these numbers. I know the formulae I just want a qualitative description.

    As far as I have it the Rayleigh number tells you if you can have convection and how vigorous that convection is, and the Nusselt number tells you how efficient that convection is in transporting heat.

    I could well be wrong.....

  2. jcsd
  3. Check out the following reference:

    Natural Convection in Enclosures
    Book: Free-Convective Heat Transfer
    Publisher: Springer Berlin Heidelberg
    Pages: 279-343
  4. Andy Resnick

    Andy Resnick 6,143
    Science Advisor
    Education Advisor

  5. sorry, I had a brain fart ...

    Here's something I compiled for work:

    Rayleigh Number:
    Important in natural (free) convection
    Onset of natural convection occurs when the Rayleigh number reaches a critical value (~1700)

    Nusselt number:
    Ratio of convective to conductive heat transfer across a solid-fluid interface
    Used to calculate heat transfer coefficient at the interface
    Depends upon Re and Pr in forced convection
    Depends upon Gr and Pr in natural convection
    Sometimes also interpreted as the dimensionless temperature gradient at the surface.
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