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I Can someone explain this equation for Reynolds' number?

  1. Mar 25, 2017 #1
    The following is quoted from British Standard 6891:2015, the standard for the installation of domestic gas pipework:

    "In the UK, the Reynolds number is taken to be equivalent to:
    25 043 x Q/d for natural gas; and
    83 955 x Q/d for LPG."

    [Q = flow rate, cubic metre per hour, d = pipe diameter, mm]

    In every internet source I've looked at, Reynolds' number is proportional to pipe diameter; in this BS 6891 formula it's inversely proportional. How can this be?
  2. jcsd
  3. Mar 25, 2017 #2
    I am not versed at all in fluid dynamics, but a brief scour of a few reliable (I believe( locations seemed to support that indeed the Re is proportional to the inverse cross-section area. This also makes sense, since less viscous material would flow 'better' in a wider pipe.
  4. Mar 28, 2017 #3

    Andy Resnick

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    Reynolds number Re = uL/ν can be re-written by substituting in an expression for the velocity u (say, Poiseulle flow) and integrating to obtain an expression in terms of the volume flow instead of the pressure gradient. When all is done, Re = 4Q/πνd for cylindrical pipes.
  5. Mar 28, 2017 #4
    This equation is correct, but no integration is required.
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