For the benefit of the back of the class:- No not OT, nor a joke (note no laughter).... FFS ;>)
Q if I were to install say 3 duct fans in series (yers in the same duct) should I expect almost 3 X their stated airflow ??
Jim K
Why? First fan shifts air - second fan shifts THE SAME air etc. If the ducts are too small a cross section to be shift, what you want you may somewhat increase the speed of the air and thus increase airflow marginally I suppose.
AWEM
Jim K wrote in news: snipped-for-privacy@googlegroups.com:
You could try designing multi-stage Axial Flow Compressors for Jet Engines.
I don't see any joke. Can you explain what you hoped we wouldn't see?
I presume you mean fluidically in series, not electrically?
I don't know. They have multiple fans at intervals along tunnels so there must be some advantage.
If the second runs twice as fast, and the third three times as fast, as the first one, then yes, maybe. These two will also draw more current, as they are doing more work. Now, if you split the duct, put a fan in each branch, and then brought them back together in a duct with three times the cross-sectional area of the original, that might work. Is it worth it?
Why? - er well 1st fan say 0-20mph, i.e. fed into 2nd fan at 20mph which might get us upto 20-40mph? etc or am I missing something?
Jim K
With industrial vacuum cleaners, having the vac motors in parallel e.g. side by side, gives roughly twice the airflow with the same suction.
With commercial carpet extraction machines that have two vacs in series e.g 1 sucking through the exhaust of the other, gives greater suction with the airflow staying roughly the same.
Assuming the same thing applies - and I can't see why it wouldn't - they would be better in parallel.
In message , Jim K writes
Funnily enough I've been considering putting two in series because the run from the shower to the outside is too long really for the single fan. However I wouldn't expect double the airflow. I would be happy to restore the flow to the maximum that a single fan could provide with no or short exit duct. My current fan is a Mantrose 100T and I planned to add another Mantrose
100 described on their website as suitable for running in tandem So I contacted Mantrose to ask if I could link it in to the timer output on the 100T and could they supply wiring diagram. I was taken aback by their reply. They said that the 100 was not suitable for connecting in series and recommend another 100 high output fan. Next step is to get back to them and ask the obvious question.
Fan packs for some servers have them in series. I think some of the 1U rack servers have fan packs with 4 fans in them - 4 across, 2 deep.
In message , bert writes
It was pointed out some time back that cheap flexible ducting (corrugated internally) is hugely lossy in terms of air turbulence. If you could do any straight runs in rigid you might get away with the existing fan.
t was pointed out some time back that cheap flexible ducting (corrugated internally) is hugely lossy in terms of air turbulence. If you could do any straight runs in rigid you might get away with the existing fan.
End quote.
Neither duct nor fan(s) currently exist...
Jim K
Too true - and also with vacs.
A couple of expensive hoses for cryogenic ue (lN2) were useless as the drop due to the corrugations resulted in vapourisation before the chamber (cooling with lN2 is just arefined version of 'throw in a bucketful) and also an unbearable noise.
No. Only slightly more. You would be able to get the same air down a smaller duct. (Though not three times smaller, the relationship is not linear.).
I use plastic drain pipe. Much quieter too. Also condensation doesn't accumulate. "Horizontal" pipe work should run slightly down hill in the direction of flow to clear it.
In article , bert writes
I'd expect to find them redirecting you from an axial fan (which is not suited to operation at pressure - the long duct) to a centrifugal one which will not suffer from that problem. The advantage will be greater reliability (1 fan instead of 2) and lower noise but at greater cost.
ps: Manrose (no 't').
But they will presumably be designed for that, with appropriate fan specifications.
Axial fans don't generate a very significant pressure difference at max flow, and any resistance in the air path will severely dent their throughput capability. Two fans in series will nearly double the dynamic resistance in the air path they can handle whilst retaining full flow.
Paired up axial fans are common in 1U servers. Air paths in 1U servers do generally have quite high dynamic resistance and need more than one fan in series to overcome this. The small 1U axial fans are inefficient and have to spin very fast (hence their noise) and have limited lives. A pair of fans enables the system to continue running with a lower power profile until a failed fan is replaced.
Indeed, at work we allow a maximum of 1 metre of flexible ducting and that is only for the final connection to the grilles.
Erm no.
What about in parallel?
So it seems you are being taught well.
Have you been taught about insulated ducting yet?
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