# Fan and venturi effect

A simple calculation shows the power $$P$$ you can get from wind at speed $$v$$ passing through an area $$A$$ is (in Watts) $$P = 1.23\,v^3 \frac{A}{2}.$$

Using the above equation and taking the Venturi Effect in a very simple way, we know that half the area would produce wind with twice the speed i.e. if you collect the fluid at $$v_1$$ through a tube of cross-section area $$A_1$$, then you get $$2v_1$$ if the cross-section area is reduced to $$A_1/2$$.

So instead of collecting from an area A, you could divide the area by ten for example, and get a 10 times faster wind speed. From there and the power get from wind you have infinite power :D. A fan could be an infinite source of energy (after it has been initiated).

So I suppose I am missing a point. My question is what am I misssing?

(I guess the pressure needed to "push" the air through a tunnel would be so much that the fan would just do nothing or you would need that much energy to fight that.)

• Wind speed is an independent variable for a wind turbine, meaning that you have no control over it, and you can't arbitrarily increase it with the geometry of the device that you are using. – David White Aug 27 '19 at 17:04
• I don't want to increase the wind speed of the device. I want to "push" the air trough a tunnel. And i want to know why the gain of speed from that cannot be a way to produce energy. (And i know it cant cause it would violate all the law of normality). And thanks @ohneVal for the edit, this post looks so beautiful). – PauZen Aug 28 '19 at 10:53