How does viscosity effect HPSHr? 2

[keaand]

If the NPSHr of a pump is normally measured using water, how does the actual viscosity of the pumped fluid effect the NPSHr? I would have thought that increased fluid velocity would have increased the pressure drop between the pump suction and impellar and as such the NPSHr of a pump would increase with increasing viscosity. I can't find any details of viscosity correction for NPSHr. Anyone able to confirm if NPSHr should be corrected for viscosity.

 

[ebermudez]

Generally NPSH values given in the performance curve sheets are measured values which correspond to a loss of discharge head of 3%.
The total heads and the performance characteristic shown on these curves, apply to media with a density of 1 kg/dm3 and a kinematic viscosity up to 20 mm2/s. If the density is other than 1 the friction must be multiplied by rho.

You can learn a little bit more of viscosity correction on pumps here:

http://www.mcnallyinstitute.com/14-html/14-04.htm

Also, the following link has an excel datasheet that uses the Hydraulic Institute method to predict how a centrifugal pump will perform with higher viscosity fluids:

http://www.chemengsoftware.com/pipesize/pumpds.htm

Hope you find it useful,

EB

 

[ebermudez]

i have the performance correction chart, if you need it i could mail it to you!. Just let me know

EB

 

[WebWizz]

Further to Ebermudez' info, you can also use the website

http://www.engineeringpage.com

The link to the calculator:

http://www.engineeringpage.com/calculators/pumps/viscosity_correction.html

An explanation of how it works is on:

http://www.engineeringpage.com/technology/pumps/viscosity_correction.html

Hope this helps

Wim