Air Displacement

Uglybb

I cant believe you think there isnt much information out there on ducted fans they are used by most of the jet fighter looking RC models

google "rc plane ducted fan" youtube will also show numerous designs and looks at operations.

And I was going to say someone was sure to have tried what you were talking about ... its petrol driven not human powered but same principle

http://www.youtube.com/watch?v=_AXuy...069B9F7A30CAFC

sophiecentaur

I wonder if the designs for rc models will scale usefully to 'full size'?

256bits

I am quite sure the extra fans will not impart extra momentum to the air.
They have to be of different design and /or rotate at different speeds.

Try you own experiment:
Take 2 fans exactly the same.
Power the first.
Put second fan in the airflow of the powered first fan.
Ideally, the second fan will now rotate at the same speed ( assume no energy losses) as the first.
Ereeka - you have just constructed a primitive "automatic transmission".

Now, mechanically have the second fan rotate at the same speed as the first with a connecting shaft for example. Do you now think that there will be an extra air flow displacemnt by adding axial fans in series in a duct?

The second fan has to be of different fin design and/or rotational speed to impart any extra momentum to the air flow. You could be up to a challenging task.

Note that if you add many many fans in series arranged with an offset of tip to tip, you will end up with an auger or archimedes screw.

Have you ever heard the low frequency thump thump beat of large ventilation systems? Ramp that up with a higher rpm system and that type of feedback may just blow your system apart as mentioned before in previous posts.

sophiecentaur

Certainly the pitch would need to be different.

Studiot

One point that has only been skirted round so far.

How do you propose to drive the fans, they will not turn on their own?

jakers82

sorry to interupt this thread without any help to anyone , but i had a question? can a fan/seperater, spinning at 25000 rpm powered by a 1.25 hp motor moving 70cuft of air per minute through water, clean a 2500 sq ft home in an hour?

russ_watters

Clean?

jakers82

yes. clean. if im able to pull the air in my home through water as a filtering system at 70cf per minute, how
lomg would it take to clean a sealed 4000 sgft home?

russ_watters

Well, water doesn't make for a good filter and 70cfm is not a lot of air (you should calculate how long it takes to run all of the air in your house through it), so I'd have to say never.

Also, that fan's performance is terrible. 70cfm should only take a tiny fraction of a horsepowe unless for some odd reason you use a rediculously high pressure.

sophiecentaur

As the pump performance is measured by volume, you would need to know the heights of the rooms in order to get a volume from the area measurement you give. I know this is important because the majority of rooms in my house are more than 3m high and the house we used to live in had somerooms that were were not much more than 2m high. Our heating bills are shameless!