Fluids problem should be simple

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SUMMARY

The discussion focuses on calculating flow rates in a pipe system with multiple inlets and a single outlet. The setup includes two inlets with a diameter of 125mm and two with a diameter of 150mm, while the outlet has a diameter of 360mm and a flow velocity of 15 m/s. The user seeks to apply basic continuity and mass balance principles to determine the flow rates at each inlet. A key insight is that the assumption of infinite diameter for the pipe is incorrect, as internal flow dynamics must be considered for accurate calculations.

PREREQUISITES
  • Understanding of fluid dynamics principles, specifically continuity and mass balance.
  • Knowledge of pipe flow characteristics and how diameter affects flow rates.
  • Familiarity with centrifugal pump operation and its impact on fluid movement.
  • Basic mathematical skills for ratio and velocity calculations.
NEXT STEPS
  • Research the principles of fluid dynamics, focusing on the continuity equation.
  • Learn about the effects of pipe diameter on flow rates and velocity distribution.
  • Explore the behavior of centrifugal pumps in fluid systems.
  • Study internal flow network analysis to understand pressure variations in multi-inlet systems.
USEFUL FOR

Engineers, fluid dynamics students, and anyone involved in designing or analyzing piping systems will benefit from this discussion.

jd90
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Hi everyone.

So i have a simple problem and its really confusing me, although i think i might have been staring at the page too long.

I have a pipe which has 4 inlets and one outlet; via air being pulled through via a centrifugal pump. Think of the inlets as pulling air from atmosphere like in an air conditioning unit

The single outlet is 360mm diameter which is flowing at 15 m/s.

2 of the inlets are 125mm diameter
the other 2 are 150 mm diameter

Using basic continuity and mass balance is it possible to determine the flow rates?
I'm guessing it could be a simple ratio problem?


If they were all the same diameter (say 125) it would be simple as the flow would be the same at each inlet (31.1 m/s)






Please help me out, thanks.
 
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Welcome to PF.
You seem to be making an assumption that the pipe has infinite diameter. The flow, through the inlets, must combine in some way before reaching the outlet. That internal flow variation within the pipe will invalidate your assumption.

Maybe you are looking at it from outside, as a simple big box with 5 circular ports. It might be better to invert your view, then look at internal network flow, with 5 fixed pressure, circular ports.
 
Pls find the attached solution. Couldn't type the entire thing.. :-p
 

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