Pipelines: Loss coefficiency on Clean Water VS Slurry

[Su Solberg]

Hi Guys, I have a problem about the loss coefficient.

Head loss = K * (v^2/2g)

Where K is the loss coefficients.

This equation is base on Darcy-Weisbach equation.

I wonder how is K varies for same flow rate, same device with a different viscosity and density.

Thanks a lots in advance.

 

[Q_Goest]

Good question. Normally, K isn't adjusted for viscosity or density. K is generally only used for minor losses such as entrance and exit losses, bends and other specific restrictions and is simply added to fL/D to come up with a total loss coefficient. Note that f takes into account viscosity and density, so these factors are accounted for on a typical piping system, but I've never seen K adjusted for these factors. I think you probably could, just as flow coefficient for a valve (C_v) is sometimes modified to account for viscosity, but unless it's an unusual system, the adjustment probably wouldn't be too significant.

 

[Su Solberg]

Good question. Normally, K isn't adjusted for viscosity or density. K is generally only used for minor losses such as entrance and exit losses, bends and other specific restrictions and is simply added to fL/D to come up with a total loss coefficient. Note that f takes into account viscosity and density, so these factors are accounted for on a typical piping system, but I've never seen K adjusted for these factors. I think you probably could, just as flow coefficient for a valve (C_v) is sometimes modified to account for viscosity, but unless it's an unusual system, the adjustment probably wouldn't be too significant.

Yes, only the frictional constant F relates to viscosity and density.

However, since my pipeline is a bit short, just 7m with numbers of fitting, so the only loss is K, minor loss coefficient.

I am curious whether I can estimate the head when system is feeded with slurry by the clear water head which majorly come from K by mutiplying Ratio of Slurry S.G. to Clear water.
(K is base on expermental method of clear water?? I think.)

Thanks for your kind help.

 

[Q_Goest]

I am curious whether I can estimate the head when system is feeded with slurry by the clear water head which majorly come from K by mutiplying Ratio of Slurry S.G. to Clear water.
(K is base on expermental method of clear water?? I think.)

I think what you're asking is can you multiply K by the ratio for your slurry divided by that of water. (ie: multiply K by specific gravity of your slurry.) I don't think that will work at all. Let's start over.

There are methods out there that allow adjusting K for viscosity. The simplest thing to do is to simply use the L/D ratio for your restrictions where available. For example, an elbow may have an L/D ratio of 5, so just use that and determine the friction factor normally. That way you eliminate the use of K and you use equivalent length instead for the various restrictions.

You might also consider using the two-K and three-K method as described http://www.cheresources.com/eqlength.shtml" . I'm not familiar with these methods but from what I understand, they are useful in correcting for actual Reynolds number. Probably the best thing to do would be to pull the original papers (listed below) and review them. I'd be interested in what you find out, so if you decide to do so, feel free to update us on what you find out.

One other web page looks promising http://www.cheresources.com/invisio...ethod-for-excess-head-loss-in-pipe-fittings/". If you download the Excel spread sheets, feel free to post them here so I don't have to join that site!

1. Hooper, W. B., The Two-K Method Predicts Head Losses in Pipe Fittings, Chem. Eng., p. 97-100, August 24, 1981.
2. Darby, R., Correlate Pressure Drops through Fittings, Chem. Eng., p. 101-104, July, 1999.

 

[GT1]

Hi Guys, I have a problem about the loss coefficient.

Head loss = K * (v^2/2g)

Where K is the loss coefficients.

This equation is base on Darcy-Weisbach equation.

I wonder how is K varies for same flow rate, same device with a different viscosity and density.

Thanks a lots in advance.

K is independent of those parameters if the flow is fully turbulent (high Reynolds numbers).
If you are not in the turbulent regime you can use the 3-K method.
Another thing to keep in mind - your slurry is probably a non Newtonian fluid (the viscosity depends on the shear rate). there are very limited data and correlations for minor losses of non Newtonian fluids.