So… we’re trying to cope with the heat just like the rest of the country.
I set up two desktop fans. One is about 5” in diameter. The other is about 10” in diameter.
My son set up the 5” fan behind the 10” fan as a sort of turbocharger thinking that the resulting airflow out of the second fan would be faster if the air flow in was faster.
My wife and I told him we didn’t think it would work the way he thought it would.
And, of course, the answer came back “Why not?”
Um, er, well….
My wife said, “It can’t work or, at least, the net effect can’t be significant. Otherwise, we’d use the principle everywhere.”
My response: “Just because it isn’t practical (i.e. an efficient use of energy) doesn’t mean it might not work in principle
So, I throw the question to you scientists and armchair scientists…. Would this increase the speed of the air flow or not? If so, how does it do so? If not, why doesn’t it? What are the relevant principles to consider here?
2006-07-25 07:28:28 · 7 answers · asked by Richard S 1 in Science & Mathematics ➔ Physics
Yep--I'm with the kid on this one. The speed of the fan is partial limited by air resistance. The design of the motor is obviously the major limiting factor, but less resistance means the motor can spin the blades that much faster in the front fan with the same amount of power. Smart kid.
2006-07-25 07:48:59 · answer #1 · answered by Pepper 4 · 0⤊ 0⤋
If you look at the compressor on say a jet engine it is in fact a series of 'fans' in series. (with velocity energy converted to pressure energy by stators in between each stage) Of course it is generating pressure and each 'fan' is designed for the specific aerodynamic conditions that pertain to the flow. A domestic fan is a constant speed device driven by an electric motor in which the air flow is governed to a large degree by the velocity at which air is thrown off the blades ie a function of blade velocity which will be constant. My feeling is that the aerodynamics characteristics would likely result in some increase in air flow as the airflow would more nearly match blade velocity characteristics but it could also perhaps upset the flow creating extra turbulence.
2006-07-25 15:14:51 · answer #2 · answered by Robert A 5 · 0⤊ 0⤋
This isn't a well thought out answer, but it seems to me that the airflow would be the same as if you only had the front fan running. Since the blades interrupt the air, they would likely interrupt the air flowing out of the previous fan and either slow it down or speed it up to the same speed as the front fan.
2006-07-25 14:33:39 · answer #3 · answered by canejacket 2 · 0⤊ 0⤋
yes it does increase the volume/speed of the air coming out , kinda like a turbocharger in a way but not the same as a turbocharger since a t.b.chrgr. works on waste gases that are a byproduct of combustion and the fans in series is working on extra energy that is not the result of combustion. It is more analogous think of the little fan as a pre amplifier for an electric guitar.
2006-07-25 14:41:25 · answer #4 · answered by Anonymous · 0⤊ 0⤋
I am no scientist, only a ninth grader, but it seems it wouldn't work because the blades of the fan in front are still going at the same speed, so they're going to force air out at the same speed. Having another fan behind it will do nothing. If you sped up the blades somehow, it would force more air out, but speeding up the air won't do anything.
2006-07-25 14:34:13 · answer #5 · answered by Anonymous · 0⤊ 0⤋
A fan makes air move by scooping it up from the surroundings and throwing it forward. Air in motion say a wind whether natural or from another fan will make no difference as the net work done is randomly distributed.
2006-07-25 14:34:33 · answer #6 · answered by ag_iitkgp 7 · 0⤊ 0⤋
no it would only change the air volume to increse the speed you would have to speed up the rpms on the motor
2006-07-25 14:49:29 · answer #7 · answered by terry s 1 · 0⤊ 0⤋