View Full Version : Pipe Roughness coefficient for Darcy-Weisbach

SivaB

February 8, 2016, 07:40 PM

Hi ,

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

DICL (Ductile Iron)

Cast Iron

UPVC

AC

Copper

Thanks

Patrick Moore

February 9, 2016, 08:38 AM

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)

208

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)

209

Table found on this web page: http://www.brighthubengineering.com/hydraulics-civil-engineering/55227-pipe-flow-calculations-3-the-friction-factor-and-frictional-head-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

Claulo

September 24, 2018, 03:27 PM

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?

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)

208

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)

209

Table found on this web page: http://www.brighthubengineering.com/hydraulics-civil-engineering/55227-pipe-flow-calculations-3-the-friction-factor-and-frictional-head-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

Patrick Moore

September 24, 2018, 05:02 PM

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)

540

Patrick Moore

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?