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km987654
Joined: 25 Jul 2007
Posts: 2874
Location: Australia
TV/Projector: Barco BG809s
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| Posted: Wed Mar 21, 2012 6:39 am Post subject: |
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| CasetheCorvetteman wrote: | | rosenbush wrote: | | The Fig 2 clearly shows two fan in serie will deliver the same airflow as one. |
Yep, it does... Which is what ive been saying since the start of the thread... 
Anyway KM, i think you should just drop this sh** and come over for a cold beer mate  |
Careful what you wish for I just might be there
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CasetheCorvetteman
Joined: 09 Nov 2008
Posts: 6326
Location: Australia
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| Posted: Thu Mar 22, 2012 7:39 am Post subject: |
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Hahaha!! Will be your shout too 
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km987654
Joined: 25 Jul 2007
Posts: 2874
Location: Australia
TV/Projector: Barco BG809s
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| Posted: Sun Apr 08, 2012 8:50 am Post subject: |
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| CasetheCorvetteman wrote: | Well they wont, they are moving the same air arent they. If they were side by side they would move more air, but the blades are still pushing the same air through the same space at the same speed. Same air flow as a single half speed fan or very close to it. More resistance and more energy used at the same time.
Its very logical really. If you put one water pump straight into another water pump and turn them on half way do you get double the water flow? No. Youd be lucky to get half the water flow. |
OK I have finally had time to try a little experiment because I found this statment unrealistic.
The idea of the below is to show that airflow does improve when you put two fans in series so what I did was create a crude but effective wind tunnel and place a fan at either end. One fan produced airflow and was connected to a 12v power source the other was connected to a meter to record the fan rotation which again was measured in V. I then added a second fan at the same end as the one producing the air flow and this fan was placed as close as I could get it without hitting the blades on the first fan.
Its clear that there was a greater voltage and therefore greater airlow with two fans driving air through the tunnel. Both fans were running a max speed.
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| This is the volt meter reading with 2 fans driving the airflow. |
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| This is the volt meter reading with one fan driving the airflow. |
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HK-Steve
Joined: 15 Jul 2006
Posts: 849
Location: Switzerland
TV/Projector: Marquee 9500, Epson 8100
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| Posted: Sun Apr 08, 2012 8:57 am Post subject: |
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The idea is correct, but what you are seeing is more pressure to spin the unpowered fan blades faster, not more air flow.
If I get some time this week, I will do the same experiment, with my air flow meter.
Cheers
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km987654
Joined: 25 Jul 2007
Posts: 2874
Location: Australia
TV/Projector: Barco BG809s
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| Posted: Sun Apr 08, 2012 9:05 am Post subject: |
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| HK-Steve wrote: | The idea is correct, but what you are seeing is more pressure to spin the unpowered fan blades faster, not more air flow.
If I get some time this week, I will do the same experiment, with my air flow meter.
Cheers |
Hey Steve if the fan rotates faster (producing a higher voltage) how can there not be more air moving through the blades actually you only have to stand behind the unit and you can feel a greater air flow but hey please try the air flow meter I don't have one of those.
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HK-Steve
Joined: 15 Jul 2006
Posts: 849
Location: Switzerland
TV/Projector: Marquee 9500, Epson 8100
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| Posted: Sun Apr 08, 2012 9:14 am Post subject: |
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Think of the fan blades as a resistance, along with the fan bearings, with a certain amount of air flow, the blades will spin.
With more pressure they will spin faster.
Yes, with more air flow also, they will spin faster.
I agree, with 2 fans there will be a small increase in air flow, but a very small increase, very small.
An air flow meter would show a true result.
A better way to test this is a fixed size hole at the end of the tunnel, with an air flow meter.
I picked mine up for about $100
Cheers
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CasetheCorvetteman
Joined: 09 Nov 2008
Posts: 6326
Location: Australia
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| Posted: Sun Apr 08, 2012 10:17 am Post subject: |
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It wouldnt matter what we told you, you dont seem to want to see it for what it really is. You dont seem to understand what is being put to you, nor do you understand your test results.
By all means, go ahead and do this if you personally think it will work. You can find my statements as unrealistic as you want, and at the end of the day, it doesnt matter at all what either of us thinks. The facts will remain the same.
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km987654
Joined: 25 Jul 2007
Posts: 2874
Location: Australia
TV/Projector: Barco BG809s
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| Posted: Sun Apr 08, 2012 10:51 am Post subject: |
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| CasetheCorvetteman wrote: | It wouldnt matter what we told you, you dont seem to want to see it for what it really is. You dont seem to understand what is being put to you, nor do you understand your test results.
By all means, go ahead and do this if you personally think it will work. You can find my statements as unrealistic as you want, and at the end of the day, it doesnt matter at all what either of us thinks. The facts will remain the same. |
Its all a bit of fun really.
Seems simple more air over the blades causes the fan to rotate faster therefore a higher voltage is produced therefore two fans in series move more air than one.
How do you explain the higher voltage or faster rotation of the unpowered fan?
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CasetheCorvetteman
Joined: 09 Nov 2008
Posts: 6326
Location: Australia
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| Posted: Sun Apr 08, 2012 2:12 pm Post subject: |
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Oh i can see youre having fun with this, and believe me i am all for science experiments in the home 
What kind of fan are you using here to get a generated voltage? An electronically commutated computer fan? Did you check rotational speed with an optical tachometer or are you just assuming it is going faster cause the voltage is different?
If the motor youre using is an EC type, which if its a computer fan i reckon it will be, then your readings are not overly indicative of much at all, because youre talking about what is essentially an AC syncronous motor of sorts, it electronically converts DC into AC to turn the motor.
Id be interested to see what voltage readings you get with the meter on AC, or at least see what sort of wave form is coming out of this motor, cause i dont think it will be ripple free DC, hence, you could start that test 3 different times with the same air flow and get 3 different voltage output readings.
Try these things i mension above and see what you can find.
Its good that youre thinking here and trying these things out, but youve got a very long way to go before you convince me
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rosenbush
Joined: 14 May 2010
Posts: 94
Location: Brownsville Texas
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| Posted: Sun Apr 08, 2012 3:53 pm Post subject: |
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| km987654 wrote: | Seems simple more air over the blades causes the fan to rotate faster therefore a higher voltage is produced therefore two fans in series move more air than one.
How do you explain the higher voltage or faster rotation of the unpowered fan? |
You're not considering Airflow Impedance. Putting two fans on series in one side of your wind tunnel, will deliver de same Airflow. If you put one fan at each end will low the Airflow Impedance and will deliver more airflow (You have a fan in the middle wich create impedance). If there is no fan in the middle there won'tl be no diference on the air flow if you put both fans on one end or on each end.
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km987654
Joined: 25 Jul 2007
Posts: 2874
Location: Australia
TV/Projector: Barco BG809s
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| Posted: Sun Apr 08, 2012 10:24 pm Post subject: |
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| rosenbush wrote: | | km987654 wrote: | Seems simple more air over the blades causes the fan to rotate faster therefore a higher voltage is produced therefore two fans in series move more air than one.
How do you explain the higher voltage or faster rotation of the unpowered fan? |
You're not considering Airflow Impedance. Putting two fans on series in one side of your wind tunnel, will deliver de same Airflow. If you put one fan at each end will low the Airflow Impedance and will deliver more airflow (You have a fan in the middle wich create impedance). If there is no fan in the middle there won'tl be no diference on the air flow if you put both fans on one end or on each end. |
Ok but why do we have an increased voltage.
Case
Its good to see you are considering this. Steve has has instruments to measure airflow we should see what that achieves.
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CasetheCorvetteman
Joined: 09 Nov 2008
Posts: 6326
Location: Australia
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| Posted: Mon Apr 09, 2012 12:50 am Post subject: |
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Did you try an AC measurement on that output?? Dont spose you have a CRO there do ya? What im getting at here is there is no rectifier on the output side of your little generator, so this is why i dont think your DC measurements are much of an indication of rotational speed.
Im not sure how much you know about wave forms, but there is DC, and there is ripple free DC. That meter you have there isnt bad, but im not sure how accurate it would be for measuring DC with a high ripple to it. It could almost be said that it will have a frequency to it, which may or may not be alternating. Its all abit of speculation really cause ive never tried to use an electronically commutated motor as a generator
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km987654
Joined: 25 Jul 2007
Posts: 2874
Location: Australia
TV/Projector: Barco BG809s
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| Posted: Mon Apr 09, 2012 2:16 am Post subject: |
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| CasetheCorvetteman wrote: | Did you try an AC measurement on that output?? Dont spose you have a CRO there do ya? What im getting at here is there is no rectifier on the output side of your little generator, so this is why i dont think your DC measurements are much of an indication of rotational speed.
Im not sure how much you know about wave forms, but there is DC, and there is ripple free DC. That meter you have there isnt bad, but im not sure how accurate it would be for measuring DC with a high ripple to it. It could almost be said that it will have a frequency to it, which may or may not be alternating. Its all abit of speculation really cause ive never tried to use an electronically commutated motor as a generator |
Well I am sure I don't know what you do. At this time I would like to see Steve air flow meter results.
I would say though that this works because none of these fans move air at the maximum capable for its cross section but lets see the air flow meter results.
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CasetheCorvetteman
Joined: 09 Nov 2008
Posts: 6326
Location: Australia
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| Posted: Mon Apr 09, 2012 3:43 am Post subject: |
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Im an electrician.
Where are you from? How far from Sunshine Coast?
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km987654
Joined: 25 Jul 2007
Posts: 2874
Location: Australia
TV/Projector: Barco BG809s
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| Posted: Mon Apr 09, 2012 3:52 am Post subject: |
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| CasetheCorvetteman wrote: | Im an electrician.
Where are you from? How far from Sunshine Coast? |
Newcastle NSW. 1000Km approx.
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CasetheCorvetteman
Joined: 09 Nov 2008
Posts: 6326
Location: Australia
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| Posted: Mon Apr 09, 2012 4:00 am Post subject: |
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F*** itd be a long drive for a beer mate eh!!!
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km987654
Joined: 25 Jul 2007
Posts: 2874
Location: Australia
TV/Projector: Barco BG809s
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| Posted: Mon Apr 09, 2012 4:08 am Post subject: |
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| CasetheCorvetteman wrote: | | F*** itd be a long drive for a beer mate eh!!! |
yeah you're not kidding. We do get up that way from time to time. I will give you a yell if we are. I would like to say hello.
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CasetheCorvetteman
Joined: 09 Nov 2008
Posts: 6326
Location: Australia
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| Posted: Mon Apr 09, 2012 6:29 am Post subject: |
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No worries mate yeah, im always around
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Ile
Joined: 09 Mar 2006
Posts: 1491
Location: Jyväskylä, Finland
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| Posted: Mon Apr 09, 2012 9:06 am Post subject: |
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It's not that black and white with two fans in parallel or series, airflow depends about static pressure fans see.
http://www.nmbtc.com/fans/engineering/multiple-fan-use.html
Your higher airflow with two series operating fans should be correct result when you connect those to high static pressure enclosure. Same airflow that one fan is only true in free air.
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CasetheCorvetteman
Joined: 09 Nov 2008
Posts: 6326
Location: Australia
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| Posted: Mon Apr 09, 2012 9:50 am Post subject: |
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Ile, inside the projector, they are mounted pretty much in free air are they not?
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