# Fluids problem should be simple

1. Jun 23, 2014

### jd90

Hi everyone.

So i have a simple problem and its really confusing me, although i think i might have been starring 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)

2. Jun 24, 2014

### Baluncore

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.

3. Jun 29, 2014

### sci-phy

Pls find the attached solution. Couldn't type the entire thing.. :tongue:

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