Why are there large blades in my computer's fan but only three skinny blades on a modern windmill?

Question

I looked it up and the best answer I found was that the tower might fail in high winds. If that is true, why not make many smaller windmills?

Answer 1

Nice speculation by the previous answerers but all wrong or incomplete. Excellent question though.

It has to do with the speed of the blade you want versus how much power you're delivering and how much space you ahve to fit it into.

A computer fan obviously must be small in diameter to fit in your PC and to keep the air flow close to the chip. A wind turbine blade is trying to capture energy from a lot of air, and size isn't nearly the same problem (though as pointed out the bigger the wind turbine the higher the cost, but also the more power produced and sold so usually bigger turbines are more cost effective in the long run, to a point).

Now think of safety. A small plastic fan in a computer rotating 1000s of times a min can be stopped with your finger tip due to its low inertia and diameter. If you put such large blades on a wind turbine it would be very dangerous due to weight storing more energy so that if it broke loose it would be much worse.

Another more subtle point is the pattern of wind. The optimal energy comes from the wind if you reduce its speed to 1/3 its original value - called the Betz limit (59.3% efficient is the highest efficiency theoretically possible from a wind turbine - real ones get 30%, maybe). Factor in smaller, lighter blades would be cheaper to assemble high up, I think we have an answer.

Compare this to a fan - you're taking air standing still outside the computer and greatly accelarating it to cool the processor. YOu don't give a rats *** about the efficiency of the wind conversion since you want your processor cold. Big blades help this.

Once again, excellent question -a real thinker I'll pose to my class.

Answer 2

Here is a quote from the link that says that bigger is much better. It is therefore better to make one large windmill rather than several smaller units.

"The bigger the windmill, the more power you get. The power is proportional to the square of the radius of the windmill. Double the radius and you quadruple the power."

Answer 3

i friend! to know the reason in difference in their design first lets take their function into consideration.
1)computer fan works on electricity and pushes out the hot air from inside the cpu(tower of ur computer). on the controry, wind mill does not work on electricity but they produce it.
2)computer fan needs to handle hot air which is rarer(less denser). so, it needs to be heavy. however, wind mill handles relatively cool air.

now lets consider their dsign.
computer fans are not aerodynamically designed. they just have the contour and helix angle to create a motion in the fluid in which they move. if they are moved in water, they can be used as propeller for small toy boats. also, both the surface of the blade are parallel to each other.
on the other hand, blade of a wind mill is aerodynamically designed. it has a camber. this means that its both surface are not parallel to each other. upper surface is a bit curved. this design helps it in generating reaction as the wind passes through it. as a result of this reaction, the fan moves and rotates the generator and electricity is produced.

so, as per the function, their design is made. also, if wind mill blades are made too heavy, it would need stronger wind to rotate it. so, lesser amount of current will be produced.

hope that i have answered ur querry!!
good luck!

Answer 4

Because they don't want your computer to feel inferior to a gigantic windmill's fan. The windmill might call your computer a girly fan. It's not politically correct.

Answer 5

If the windmill were identical in scale to your PC fan:

The torsional force on a device that large in a system where the forces are unregulated and unpredictable-- would likely just knock the device over.

And the resulting cow deaths would feed families everywhere, so we should build them-- who needs power when you can eat?

Happy researching! :)

Answer 6

i think its because it wont be profitable if we use heavy huge blades in windmills.and also Ur PC fan is moving the blades.the windmill's blades has to be moved by the air.it isn't the same thing.

Answer 7

You need something to rotate fast due to external power. Wind mills need not generate wind. They should consume wind to convert into mechanaical energy. While on your computer it is the opposite. They need to generate wind (air) from electrical energy. So are they designed.

Answer 8

Ever seen the wind generators out west?