Difference in flowrates depending on where the pipe splits.

[zjn12385]

Fluid Dynamics Question:

I have a 1.5" pipe that has water pumped through it. The pipe is immediately split by a manifold into 5 separate 0.75" pipes after exiting the pump. Each 0.75" pipe runs to an outlet at varying lengths from the manifold (15", 37", 52", 89", and 126"). I want to know if my flowrates will drop if I modify this set up so that the 1.5" pipe has a reducer fitting on it to drop the pipe size to 0.75" and then use a tee fitting to branch off an 8" long pipe such that the distance from the end of the branching pipe to the reducer is the same distance as stated before.

(FR = Flow Rate)

_____________________ FR
/_____________________ FR
______/______________________ FR
\_______________________ FR
\______________________ FR



VS


______________________________________________ FR
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| | | |
FR FR FR FR

 

[Q_Goest]

Hi zjn. I'm not sure I follow your diagram but I think you're saying you have a pump with a 1.5" outlet and that pipe extends out such that you have 5, .75" pipes branching off of it and you want to know if there will be a change in flow rate if you immediately reduce the 1.5" pipe to .75" and then have the .75" pipes branch off.

Assuming your pump is a centrifugal pump, yes, the flow rate will decay. There's an irrecoverable pressure drop through the reducer when going from 1.5" to .75" which isn't on the original set up. Given that most pumps have a discharge pipe fitting on them that is about as small as they can be without significant pressure drop, the reduction to .75" is very likely going to cause a large drop in the pump's output and a corresponding rise in discharge pressure on the pump.

You can determine pressure drop and flow through piping systems using the Darcey Weisbach equation as explained in most textbooks, the Crane Paper 410, or the manual called Pipe-Flo Pro I posted here.

 

[256bits]

zin12385
Yes your flowrate will drop if you branch off one line of same diameter as before rather than have 4 separate lines.

 

[256bits]

As an addendum, without the manifold and four separate exit pipes, the pressure the pump puts out would increase. If a positive displacement pump, you may end up producing a high enough pressure to blow a fitting or the pipre right after the pump.

If you want to do what you propose you would necessarily go to a larger pipe from the pump.

 

[alphy]

I would first analyze the factors that affect flowrates in a pipe system. These include the diameter and length of the pipe, the fluid viscosity and density, and the pressure difference between the inlet and outlet of the pipe.

In the first scenario, the flowrates in each 0.75" pipe will depend on the length of the pipe and the pressure difference between the manifold and the outlet. This is because the diameter of the pipes and the fluid properties remain constant.

In the modified scenario, the flowrates will also depend on the diameter of the branching pipe and the distance from the end of the branching pipe to the reducer. However, the flowrates may be affected by the reducer fitting and the tee fitting, which can cause turbulence and pressure drops in the system.

To accurately determine the difference in flowrates between the two scenarios, I would recommend conducting a fluid dynamics simulation or performing experiments in a controlled environment. This will allow for a more precise analysis of the changes in flowrates and any potential impacts on the overall system performance.

It is also important to consider the purpose and requirements of the system when making modifications. If the goal is to evenly distribute the flow between the outlets, the modified scenario may be more effective. However, if maintaining a certain flowrate in each outlet is crucial, the original setup may be more suitable.

In conclusion, the difference in flowrates between the two scenarios will depend on various factors and can only be accurately determined through further investigation and analysis. As a scientist, it is important to consider all relevant factors and use scientific methods to provide a comprehensive response to this question.