Very viscous slurry

[Homayun]

Hi.
We are having this very visous (1000 cP) slurry that needs to be pumped. We are using a progressive cavity pump for that. Although the pump vendor knows about this viscosity, and has ensured us that his pump is the right pump, I was wondering how I could calculate the power requirement to bring this mass in motion.
I know how to calculate the hydraulic power, but the question is how do you calculate the power required to bring a mass sitting in the pipe into motion?
Thanks

 

[BigInch]

Go back to basics,
force = mass * acceleration + viscous shear
Work = force * distance
Power = Work/time


**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Homayun]

Thanks BigInch.
I had already gone this way too and have determined the WOrk..But what is my time? I know I have 40000 Lb material sitting in my Drum. So maybe in the Force equation, I can simply use mass/time (which is my flow rate)...

FOrce = (mass/time) * accelaration..

What about the viscous shear? what is that term?

 

[Homayun]

Big Inch,

I guess I can't simply add the vicsous shear with the product of mass*acceleration! THe units don't match!

Mass * acceleration = kg.m.S-2
Viscous SHear = kg.m-1.s-1

 

[BigInch]

That would be shear times inside area of pipe = force. In EGS, lbs/in2 * in2 = lbs... no problem. The trickey part is evaluating the shear at all points along the pipe and integrating from beginning of pipe to end of pipe for time step over which the accelaration takes place, which BTW you also have to do for mass * accelaration. Acceleration will not be the same at beginning of pipe to end of pipe, as there is some compression going on as the velocity at the beginning of the pipe starts to increase, but still remains at zero at the end of the pipe. Of course mass changes as the pressure increases and the fluid compresses as well.

Best to find a good computer program to handle all that bookkeeping for you.

Maybe you want the easier solution,
Calculate the power you need for steady state flow.
Accelaration of fluids in piping is provided for by any excess power available from the pump driver at any given time.

For a simplified example of starting just a water pipeline, the pump has a driver with 100 HP rating, but at 10% of BEP flow when starting, power required for maintaining that low flowrate would be say 5 HP, therefore you would have 95 HP available for accelerating to a higher flowrate. Power required increases with the ^3 of flow velocity, so you would have much less power available for accelerating the flowrate from there to 100% velocity and the acceleration from that velocity to BEP velocity takes relatively a much longer time as you near rated power, if it wern't for the torque delivery characteristics of the driver, which I'll get to in a minute. So, if you need to still have rapid changes of velocity at BEP flowrate, you should provide a driver that gives much higher torque as its speed drops from sycronous speed as it would when being called upon to provide additional acceleration, which BTW most electric drivers do, reaching about 150% of rated torque with relatively little drop in sycronous speed. Any EEs out there, feel free to help ... now.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[BigInch]

A good dynamic simulation program can help show exactly how well operation of the system will be as it comes up to speed or as you make changes to flowrates.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/