10 replies to this topic

[Stevo]

Hi,

 

Please I need assistance. I need a simple mathematical model or rule of thumb to calculate the outlet pressure of liquid from a combining manifold of four lateral flows each with different inlet pressures.

 

Thank you all.

[Steve Hall]

Stevo,

 

Variations of this question are posed periodically on this site. The answer always comes down to a hydraulic calculation. We need a flow diagram to answer your question - where are these "laterals," where are you measuring their pressures, what are their sources, are you pumping through the laterals or are they free-flowing, where does the outlet pipe from the manifold go, etc. But conceptually, the pressure at the manifold - and therefore at the end of each lateral - is a singular value. You can't have different pressures at each lateral. Your system will balance the flow rates to achieve the singular value. With a hydraulic calculation you can determine the flows through each of the laterals and the pressure in the manifold.

 

Steve

[Stevo]

Hi Steve,

 

Thank you so much. Please find the attached flow diagram of the problems. 

 

There are 4 flow lines (each 3 " diameter with different flowrates of 4.895, 13.60, 30.15 and 8.251 m3/h and equally spaced). 

 

Thank you.

Attached Files

•  Manifold.xlsx   14.38KB   26 downloads

[Steve Hall]

Where are the pressures measured - at the Well or at the manifold?

 

Are there any check valves in the laterals? Control valves?

 

What motivates the flowrates given -- pumps (centrifugal or positive displacement), well pressure, other?

 

Why are you able to state flow rates with so many significant figures?

 

What are the length and diameter of the proposed manifold?

[Stevo]

Pressure measured at the manifold station.

 

There are check valves in the laterals to prevent back flow

 

 Length of the manifold is 25m and Diameter of the manifold is 8 inches.

 

There are 4 flow lines (each 3 " diameter with different flowrates of 4.9, 13.6, 30.2 and 8.2 m3/h and equally spaced).

 

Centrifugal Pump motivates the flow rates given 

 

Thank you

[breizh]

Stevo , 

 

 

what about the fluid? properties (temperature, viscosity,...).

 

 

Breizh

[Stevo]

Hi,

 

 

The properties of the fluid are:

 

Temperature:  205 F

 

Viscosity: 0.3718 cP

Edited by Stevo, 11 July 2013 - 03:16 AM.

[breizh]

Stevo

What about the density @ temperature ?

This is to perform hydraulic calculation .

 

Breizh

[Stevo]

Hi,

 

density = 867kg/m3

 

Thank you.

[Steve Hall]

Stevo,

 

It isn't clear why the four flows have different pressures at the manifold. I have to assume that the pressures you report are taken one at a time (that is, with only one of the laterals flowing, measure the pressure). But if they each dump into the same header, the pressure for the highest flowing stream should be higher than the pressure for the lowest flowing stream. This is because the pressure in the manifold should be the downstream pressure (the main header?) plus frictional pressure drop and static head developed from the lateral through the manifold to the header. Your data shows the opposite.

 

With centrifugal pumps, here's what you should expect when flowing all four laterals into the manifold: The pressure in the manifold will equalize based on the total flow to the header; the centrifugal pumps will adjust their flow rates by moving along the pump curves. If the pumps aren't sized to accomplish the flow balance, then one or more of them could either shut off (back pressure too high to overcome so flow will drop to zero) or run out (backpressure too low so pump runs out on curve and overloads).

[Stevo]

Steve,

 

Thank you for your good response.