Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Rayleigh and Nusselt numbers

  1. Jan 25, 2007 #1

    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. Jun 11, 2009 #2
    Check out the following reference:

    Natural Convection in Enclosures
    Book: Free-Convective Heat Transfer
    Publisher: Springer Berlin Heidelberg
    Pages: 279-343
  4. Jun 11, 2009 #3

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor

  5. Jun 12, 2009 #4
    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook