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Thread: Pipe Roughness coefficient for Darcy-Weisbach

  1. #1

    Join Date
    Jan 2014
    Posts
    7

    Pipe Roughness coefficient for Darcy-Weisbach

    Hi ,

    Could someone reply me the roughness coefficient (Darcy-Weisbach) for the following pipes:

    DICL (Ductile Iron)
    Cast Iron
    UPVC
    AC
    Copper

    Thanks

  2. #2
    Forum Moderator

    Innovyze Employee



    Join Date
    May 2015
    Posts
    386
    Siva,

    Here is a table from the InfoWater User guide that may be helpful as a starting point:
    Roughness table (click for larger image if necessary)
    C-factor-Darcy Weisbach.jpg

    You can also do a quick search for other recommended tables on the internet
    here is a DW roughness table (click for larger image if necessary)
    C-factor-Darcy Weisbach-web1.jpg

    Table found on this web page: http://www.brighthubengineering.com/...d-loss/#imgn_1

    One word of caution, 1) make sure to check the units used as different tables use different units - 2) Make sure to use the units expected in your model, and 3) Pipe materials like Cast Iron with no lining will generally have a roughness that will typically worsen over time (due to internal corrosion) and the tables usually show roughness values for new pipe only so be aware you may need to make adjustments to the table values used. For Darcy Weisbach roughness the higher the roughness coefficient number the greater the roughness will be.

    There are many other resources out there on this subject, but these should give you a starting point in deciding what to use in your model.

    Patrick Moore
    Last edited by Patrick Moore; February 9, 2016 at 08:42 AM.

  3. #3

    Join Date
    May 2018
    Posts
    1

    entering Darcy-Weisback

    Hi Patrick,

    When I go to enter in the roughness factor for modeling with the Darcy Weisback equation, there are only two significant figures available for entery.
    ie..
    0.00
    This is too large of a number to enter a f factor of 10^-6.
    Any help with this?



    Quote Originally Posted by Patrick Moore View Post
    Siva,

    Here is a table from the InfoWater User guide that may be helpful as a starting point:
    Roughness table (click for larger image if necessary)
    C-factor-Darcy Weisbach.jpg

    You can also do a quick search for other recommended tables on the internet
    here is a DW roughness table (click for larger image if necessary)
    C-factor-Darcy Weisbach-web1.jpg

    Table found on this web page: http://www.brighthubengineering.com/...d-loss/#imgn_1

    One word of caution, 1) make sure to check the units used as different tables use different units - 2) Make sure to use the units expected in your model, and 3) Pipe materials like Cast Iron with no lining will generally have a roughness that will typically worsen over time (due to internal corrosion) and the tables usually show roughness values for new pipe only so be aware you may need to make adjustments to the table values used. For Darcy Weisbach roughness the higher the roughness coefficient number the greater the roughness will be.

    There are many other resources out there on this subject, but these should give you a starting point in deciding what to use in your model.

    Patrick Moore
    Attached Images Attached Images

  4. #4
    Forum Moderator

    Innovyze Employee



    Join Date
    May 2015
    Posts
    386
    Clinton,

    This is caused because your 2 decimal places is what your current model defaults are using.

    If you simply change the InfoWater -> Tools -> Project preferences and go the the "Display Settings" tab, you can change the default decimal places in the "decimal placement" field from 2 to 4, or 6 or 8, etc if you so desire that would allow you greater flexibility in assigning a Darcy Weisbach roughness more than your current 2 decimal places.

    All model values by default are stored as double precision values which is 9 decimal places, but the model rounds the values to your current decimal places shown when viewed in the DBEditor. So to resolve, you just edit your decimal places to a higher number of "displayed" decimals so that you can enter more decimals and you should no longer have this difficulty.

    (click if you need a larger image)
    How to change the significant figures in a model.jpg

    Patrick Moore

    Quote Originally Posted by Claulo View Post
    Hi Patrick,

    When I go to enter in the roughness factor for modeling with the Darcy Weisback equation, there are only two significant figures available for entry(sic).
    ie..
    0.00
    This is too large of a number to enter a f factor of 10^-6.
    Any help with this?
    Last edited by Patrick Moore; September 25, 2018 at 04:26 PM.

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