Flowrate through reduced pipe diameter 1

[bakal28]

Hi all.

I have a slurry pipeline 150dia Steel Pipeline 40 km long which will need to tie in to a 90dia Steel pipeline 12 metres long at the discharge end to make use of existing valves and instrumentation. Im now trying to calculate whether there will be any changes to the flowrate.

Pump Q = 16 Lps
Slurry SG = 1.94

Am I expecting any change of flowrate? How do I calculate this? Tried treating this as an orifice flow but doesnt give a convincing result. Is the reduction in pipe diameter significant enough to impact the pump performance?

Thanks everyone!

 

[BigInch]

Assuming you hold steady state, the velocity will go up in inverse proportion to the change in area. V2 = A1 * V1/A2
Calculate your pressure drop over the 12 meter long section using that velocity and hope your pump can provide the same flowrate at the new total differential pressure of both the 46 Km + 12 m lengths. Check your pump curve at the same flowrate and new differential pressure to be sure.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[bakal28]

Thanks BigInch.

To clarify, V2 will be calculated on the assumption that Q1 = Q2. I would have thought at some point the flowrate will change. How do we determine this?

Thanks.
Nimajoef

 

[BigInch]

The flow could change if your pump cannot move Q1 at the new differential pressure. Q1 will tend to reduce and Q2 will eventually = Q1. If you pump can move more than Q1 at the new differential pressure, Q1 will increase and Q2 will eventually = Q1.

The study of how long it will take Q2 to equal Q1 is transient flow.. or a temporary unsteady state flow.



Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[bakal28]

To close this out, I understand we need to check the pump curve on the resulting Q (Q2) based on the new pressure head requirement. Correct me if I'm wrong but any 'significant' change in the head (in this case due to additional fitting loss caused by the reducer) will have a corresponding change in flow. And the pump should be able to deliver flow as long as it does not fall beyond the minimum continuous flow.

Thanks a lot for your input.

Nimajoef

 

[BigInch]

A large change in flow may cause only a small change in head, or quite a large one, depending on where you are on the pump curve and how the system curve intersects it at the new flowrate vs where it was at the old flowrate.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso