Most efficient fan speed rpm

[green0273]

What is the speed of the cooling fan that it is most efficient? How do I figure the amount of torque or energy to run it at that speed? I'm thinking about using a small electric motor to turn the fan.

[bbodie52]

Click on the link below and read through that material...

viewtopic.php?f=55&t=15422

[66vairguy]

What is the speed of the cooling fan that it is most efficient? How do I figure the amount of torque or energy to run it at that speed? I'm thinking about using a small electric motor to turn the fan.

It's been tried a few times with dismal results. Bottom line --- the old fan belt is more efficient than an electric drive. GM did a fairly good job and the only improvement is revise the fan itself and then the only advantage is at higher RPM. Contrary to "opinions" the Corair cooling fan does not waste any power to meet cooling demands. Using the engine to run a generator and then route that to a motor is inefficient and adds more weight for the car to move.

Most want to increase cooling for racing or the turbo motors and that requires moving more air and higher pressures. Sorry no easy fix. Even GM's multifan overhead cam engine used a lot of HP for cooling at full power. The real fix is liquid cooling that is more efficient, ask Porsche.

[joelsplace]

I would agree with most of that except the wasted hp. The Corvair fan uses a lot more than needed as proven by other members. Did you mean the way it is driven doesn't waste power? That is true. Belts are very efficient.
http://corvaircenter.com/phorum/read.ph ... 610,page=1

[66vairguy]

I would agree with most of that except the wasted hp. The Corvair fan uses a lot more than needed as proven by other members. Did you mean the way it is driven doesn't waste power? That is true. Belts are very efficient.
http://corvaircenter.com/phorum/read.ph ... 610,page=1

The GM SAE papers show that under full power the cooling system is just adequate for the 140HP engine. Yes if you are cruising at high RPM at light load you are wasting HP on unneeded cooling. So the trick is a variable system, but electrical solutions are too inefficient and negate any variable advantage. Mechanical systems have been proposed, but cost and complexity have been negatives too big for anyone to solve. The real goal by most is to have adequate cooling using less HP at maximum power. Improvements are possible and time will tell if the cost justifies the HP gain.

BTW at one of the old conventions someone documented GM engineer Benzinger talking about the fact the Corvair cooling system was inadequate for the turbo motor, BUT as Benzinger pointed out --- it would take longer to overheat the engine than it would to reach the top speed of the Corvair and of course that was not a legitimate use of the car. Needless to say GM's approach was that quick acceleration to legal speeds and passing created no cooling issue with Turbo Corvairs - True! For those going racing --- water spray injection into the fan inlet is a cost effective fix.

[63Turbo]

The peak efficiency for the 61-63 fan is 32% and occurs at around 3000 engine rpm, the peak efficiency for the mag fan is around 25% and is occurring at roughly the same rpm... it is all down hill after this engine rpm, by 5000 rpm, both fans are down to around 16% or less.

[63Turbo]

It should be noted any good centrifugal fan should have absolutely no problem hitting 50-60%, and can often get in the 70%+ range. The reason the Corvair fans can't do this is because they are all the wrong type to be used in an "open" housing and are HIGHLY dependant on being in a "blower housing" to hit the peak efficiency that is expected for those types, roughly 60-65%. Backwards curved fans like mine mostly don't care about being in this special housing or not, and their efficiency doesn't change much when run "open". The reason the 140 and turbos "barely' have enough cooling is BECAUSE of the poor efficiency... basically the fans are not putting out the airflow they should be doing and belt slippage has zero to do with it.

[63Turbo]

[Nashfan]

The efficiency graph shows the mag fan (green curve) getting to 25-28% just past 3000 engine rpm, and the 61-63 fan (purple curve) at 32% at roughly the same rpm, and the Nashfan prototype hits 56% at approximately 4000 engine rpm.
I have started the process all over again with my production Nashfan and I'm testing it with one of the best guidevane bell mouths. The output of this combination is AMAZING, and appears to be in the ballpark of 7% more flow than the 61-63 fan.
At 4000 engine rpm, this combo generates 11.5" of water pressure, compared with 10 inches for the 61-63 fan, and 8.4" for the mag fan. The flow at 11.5" at 4k is 1673 cfm, compared to 1550 cfm for the 61-63 fan and 1510 for the mag fan.

My first and only efficiency data point for this set-up is at 3765 engine rpm (5950 fan rpm) the pressure is 10.2", the flow is 1575cfm, and is using only 2.93 hp for a efficiency of 86!

My previous testing with the prototype seemed to indicate that the airflow gain when the lower shrouds off was 30% more
so instead of 1673cfm the output with the lower shrouds off it would be 2174 at 4000 engine rpm, and at 5k it would be roughly 2700 cfm, and more if its revved higher.