# How does a ceiling fan blades redirect air throughout a room to cool you off?

I already know how a table fan works because of how the blades are angled. For a ceiling fan I am confused about how the blades cut through air to cool off things in a room?

• I am mostly confused about the blades cutting through and blowing air part of the question. – Ethan Sep 11 '15 at 6:46
• Ceiling fans don't cool rooms. The evaporation of sweat on your skin cools you. – CuriousOne Sep 11 '15 at 6:52

For a ceiling fan I am confused about how the blades cut through air to cool off things in a room?

See, basically it is an application of Bernoulli's Theorem if you already didn't know it. Bernoulli's Theorem states that $P + \rho gh + \frac{1}{2} \rho v^2$ = constant where the symbols have the usual meanings.You can check it here if you want. For constant $h$, we can say that $P + \frac{1}{2} \rho v^2$ = constant i.e. $P$ varies as $\frac{1}{v^2}$.

Now consider the blades of the fan to be rotating. The air column above the fan can be considered to have streamline flow and same elevation. So as the fan blades rotate, they are specially angled to make the air column move and this air column attains a high velocity. So from Bernoulli's Theorem, we can say the pressure of the air column decreases i.e. it has low air pressure.

However the air column below the ceiling fan has high pressure since it is not agitated by the fan blades and has low or no velocity.And we know air moves from high to low pressure. So air from above the fan rushes down and creates winds which increase the rate of evaporation of any liquid on any surface, creating a cooling effect.

• Kind of generates lift like an airplane. – Ethan Sep 11 '15 at 17:53
• @Ethan Yes you are right. It kind of acts like that – SchrodingersCat Sep 12 '15 at 10:44