# Homework Help: Fan Selection for air cooling of a computer

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1. Apr 3, 2017

### mech-eng

• Moved from a technical forum, so homework template missing
2. Apr 3, 2017

### CivilSigma

I'm not familiar with the equations, but at point 3 the air will be sucked in at some velocity 'v' and just at 4 it will be pushed out at the same velocity 'v' excluding any energy losses.

3. Apr 3, 2017

### rcgldr

Because the tube diameter is constant between 3 and 4, and assuming in-compressible fluid, the density does not change. Mass flow is constant or else mass would be accumulating. So from point 4 to the end of the exhaust tube, velocity and pressure ideally remain constant. Afterwards, the pressure would normally decrease and velocity would increase, affected by viscous reaction with the surrounding air.

4. Apr 4, 2017

### mech-eng

Can we say as one consequence that when fans sucking airs, they just change their pressures at first by fan work?

Thank you.

5. Apr 6, 2017

### rcgldr

Looking at the diagram, the funnel shaped tube intake would correspond to accelerating air. Within the cylindrical part of the tube, there would be no net acceleration in the direction of the tube.

Last edited: Apr 7, 2017
6. Apr 7, 2017

### mech-eng

Yes, this can be another result from directly looking the scheme but what about deriving a result for pressures?

Thank you.