CCW Fan for counter-rotating pair...

CoolROD · 08-20-2003, 10:46 PM

Does anyone know of a source for a CCW rotation 6" (150mm) muffin fan?

I want to set up a counter-rotating pair...the second fan should stall at a more favorable axial airspeed.

Thoughts? Suggestions?

bigben2k · 08-21-2003, 01:04 AM

Do you mean a blower, or an axial fan?

What for?

Why counter-rotate?

CoolROD · 08-21-2003, 07:33 AM

I am talking about axial fans in series, but counter-rotating.

One of the reasons that a fan stalls is that the angle of attack of the airfoil increases as the axial airflow slows (backpressure builds). As the fan approaches a "dead head" condition there is no laminar airflow over the top part of the airfoil.

1) An axial fan imparts a rotational velocity to the airstream (in essence the air corkscrews out of the fan). If fan1 imparts more axial velocity to the airstream than rotational velocity, fan2 will have a more favorable angle of attack. This will help shift the stall point of fan2.

2) The rotational velocity imparted on the airstream by a single fan is energy wasted. If you have a counter-rotating pair of fans then fan2 sees the rotating airstream at an apparently higher rotational velocity. This is a way of recovering some of the wasted energy from fan1 and increasing the efficiency of the system. There is a significant increases in the static pressure that a fan generates with increased rpm (DC voltage).

3) There may be another increase in fan2's efficiency if fan1 is oversped and pressurizes the inlet of fan2 and increases the air density. I just want to play with that, though.

CoolROD · 08-21-2003, 08:56 AM

I have an air-velocity and air-pressure meter and have started a page for my measurements. I measured static pressure behind my 12VDC 6" Rotron at full stall and between the fan and heatercore. I made multiple measurements in 1VDC increments.

Click Here if you are interested.

Gulp35 · 08-21-2003, 09:17 AM

I have seen a counter rotating 120mm fan on HardOCP.com's forums ( hint: search fan stacking)

Though what I have read there( I know that it probably isn't scienticifly based) is that if you use 2 fans that are running the same direction will cause more turbulence and therefore more noise but will increase airflow through a HSF (because of an increase in pressure) but not as much as 2 counter rotating fans.

So for those on the cheap may want to go for 2 normal fans glued together or whatnot instead of the more rare single casing counter rotating fans.

Since87 · 08-21-2003, 09:33 AM

I have Papst and Panaflow 120mm fans that rotate in opposite directions. (Don't know off the top of my head which fan spins which way though. I think the Papst might have the less common spin direction.)

One of them might sell the fan you want though.

CoolROD · 08-21-2003, 09:42 AM

Great -I will look into them and thanks for the info and the key words "fan stacking".

There are some counter-rotating assemblies available, but I doubt that I could afford one.

To recap: I am looking for a CCW 6" axial flow fan to stack on top of my 6" Comair Rotron Major DC. By CCW, I mean Left Hand Rotation as viewed from the inlet side.

bigben2k · 08-21-2003, 11:22 AM

Nice data set!

Do you plan on trying out various heights between two fans (with one that's counter-rotating), and running the same tests?

CoolROD · 08-21-2003, 02:03 PM

Thanks! I took the RPM readings with my trusty optical tach that uses reflective stickers. The pressure readings were from my (work's) combination air meter with a 0-1" W.C. pressure head installed. That is why I could not report pressures for the higher RPMs. I have a 10" W.C. pressure head, but did not want to change after I had taken so many measurements (I ran each test three times).

Quote:

Do you plan on trying out various heights between two fans (with one that's counter-rotating), and running the same tests?

Yes, if I get a 6" CCW (reverse rotation) fan then it would be a good idea to try a few different heights.

CoolROD · 08-21-2003, 02:47 PM

I updated the web page for my fan performance data linked above. I centered everything and added some pictures of my testing...

For the stall test I have a heavy steel chamber with a small hole to attach my pressure gauge.

To test the performance of the fan through my heatercore I used my shroud and -argh- put a hole in it to gauge through. I taped the corner seams on the inside to reduce leakage which would inflate my CFM predictions. I will silicone everything and retest for the final installation.

That is a friend of mine holding the optical tach and the pressure transducer against the steel pipe. The tach and pressure transducer are sensitive enough to see fluctuations when our hand was near the fan inlet. I had him conduct every test in a similar manner.

I did not use an air inlet or exit duct.

08-20-2003, 10:46 PM	#1
CoolROD Cooling Savant Join Date: Mar 2003 Location: North Carolina, USA Posts: 225	CCW Fan for counter-rotating pair... Does anyone know of a source for a CCW rotation 6" (150mm) muffin fan? I want to set up a counter-rotating pair...the second fan should stall at a more favorable axial airspeed. Thoughts? Suggestions? __________________ Jack of all Trades, Master of None.

08-21-2003, 01:04 AM	#2
bigben2k Responsible for 2% of all the posts here. Join Date: May 2002 Location: Texas, U.S.A. Posts: 8,302	Do you mean a blower, or an axial fan? What for? Why counter-rotate? __________________ WBTA (Water Block Testing Alliance) Nordic Hardware WC 101

08-21-2003, 07:33 AM	#3
CoolROD Cooling Savant Join Date: Mar 2003 Location: North Carolina, USA Posts: 225	I am talking about axial fans in series, but counter-rotating. One of the reasons that a fan stalls is that the angle of attack of the airfoil increases as the axial airflow slows (backpressure builds). As the fan approaches a "dead head" condition there is no laminar airflow over the top part of the airfoil. 1) An axial fan imparts a rotational velocity to the airstream (in essence the air corkscrews out of the fan). If fan1 imparts more axial velocity to the airstream than rotational velocity, fan2 will have a more favorable angle of attack. This will help shift the stall point of fan2. 2) The rotational velocity imparted on the airstream by a single fan is energy wasted. If you have a counter-rotating pair of fans then fan2 sees the rotating airstream at an apparently higher rotational velocity. This is a way of recovering some of the wasted energy from fan1 and increasing the efficiency of the system. There is a significant increases in the static pressure that a fan generates with increased rpm (DC voltage). 3) There may be another increase in fan2's efficiency if fan1 is oversped and pressurizes the inlet of fan2 and increases the air density. I just want to play with that, though. __________________ Jack of all Trades, Master of None.

08-21-2003, 08:56 AM	#4
CoolROD Cooling Savant Join Date: Mar 2003 Location: North Carolina, USA Posts: 225	I have an air-velocity and air-pressure meter and have started a page for my measurements. I measured static pressure behind my 12VDC 6" Rotron at full stall and between the fan and heatercore. I made multiple measurements in 1VDC increments. Click Here if you are interested. __________________ Jack of all Trades, Master of None.

08-21-2003, 09:17 AM	#5
Gulp35 Cooling Savant Join Date: Sep 2002 Location: Atlanta, GA Posts: 135	I have seen a counter rotating 120mm fan on HardOCP.com's forums ( hint: search fan stacking) Though what I have read there( I know that it probably isn't scienticifly based) is that if you use 2 fans that are running the same direction will cause more turbulence and therefore more noise but will increase airflow through a HSF (because of an increase in pressure) but not as much as 2 counter rotating fans. So for those on the cheap may want to go for 2 normal fans glued together or whatnot instead of the more rare single casing counter rotating fans. __________________ Epox 8RDA+ v1.1----------Tyan K8SDPro 1700+ JUIHB 0310XPMW (12.5x200Mhz@1.792v)--------2xOpteron246 (2Ghz 1MB L2) 2x256MB Kingston PC3000 (BH5?) 2-2-2-8 2.7v---2x512MB Corsair Reg.&ECC PC3200 ATi Radeon 9800Pro (stock, too hot)-----ATI RageXL WD800JB+WD2500JB-------WD1600JD Sony DVD/CDRW-------NEC 3520A Black Forton350W--------Antec TruePower2.0 550W EPS12v

08-21-2003, 09:33 AM	#6
Since87 Pro/Guru - Uber Mod Join Date: Sep 2002 Location: Indiana Posts: 834	I have Papst and Panaflow 120mm fans that rotate in opposite directions. (Don't know off the top of my head which fan spins which way though. I think the Papst might have the less common spin direction.) One of them might sell the fan you want though.

08-21-2003, 09:42 AM	#7
CoolROD Cooling Savant Join Date: Mar 2003 Location: North Carolina, USA Posts: 225	Great -I will look into them and thanks for the info and the key words "fan stacking". There are some counter-rotating assemblies available, but I doubt that I could afford one. To recap: I am looking for a CCW 6" axial flow fan to stack on top of my 6" Comair Rotron Major DC. By CCW, I mean Left Hand Rotation as viewed from the inlet side. __________________ Jack of all Trades, Master of None. Last edited by CoolROD; 08-21-2003 at 04:56 PM.

08-21-2003, 11:22 AM	#8
bigben2k Responsible for 2% of all the posts here. Join Date: May 2002 Location: Texas, U.S.A. Posts: 8,302	Nice data set! Do you plan on trying out various heights between two fans (with one that's counter-rotating), and running the same tests? __________________ WBTA (Water Block Testing Alliance) Nordic Hardware WC 101

08-21-2003, 02:47 PM	#10
CoolROD Cooling Savant Join Date: Mar 2003 Location: North Carolina, USA Posts: 225	I updated the web page for my fan performance data linked above. I centered everything and added some pictures of my testing... For the stall test I have a heavy steel chamber with a small hole to attach my pressure gauge. To test the performance of the fan through my heatercore I used my shroud and -argh- put a hole in it to gauge through. I taped the corner seams on the inside to reduce leakage which would inflate my CFM predictions. I will silicone everything and retest for the final installation. That is a friend of mine holding the optical tach and the pressure transducer against the steel pipe. The tach and pressure transducer are sensitive enough to see fluctuations when our hand was near the fan inlet. I had him conduct every test in a similar manner. I did not use an air inlet or exit duct. __________________ Jack of all Trades, Master of None.

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