What's more important in the mechanics of a fan blade? Speed, (RPMs) or the angle and/or curvature?

Question

Also, I was wondering how exactly a fan blade does its job- does it catch the air, does it create a vacuum effect, pulling the air forward, what exactly is that piece of plastic doing to move those air molecules? Does it work on the same principle of an airplane's wing?





ALSO: If the temperature is the average kinetic energy, why does the air feel COOLER when it is moving FASTER than the air around it? Is it that the air flow is absorbing the heat energy, and more air is coming to absorb more?

Oh yeah- If one is designing a fan blade, how should the air move around the blade when it is in a static position, shown withh a small wind tunnel?

Bibs, yes I have, on account of I designed both the wind tunnel i will attept to use and i am attempting to design a fan, since its so hot and it seems no fan is powerful enough. (because it's blowing air that is about 99 degrees) But there's a problem with getting that degree- still in high school

Answer 1

A fan isn't that complicated. It's just swinging a bat at air molecules to impart kinetic energy to them in a preferred direction. The Bernoulli effect doesn't play much of a part. As you send air molecules away, you locally reduce the air pressure, and surrounding air at higher pressure moves in to move toward equilibrium.

Fans are designed for various purposes with various criteria. A room fan just tries to move the air efficiently with minimum noise. Blade angle, shape, and speed are just design parameters traded off.

Air from a fan feels cooler if it's bringing you air that's cooler than the air that's currently around you, and because it increases the rate of evaporation of your perspiration. Fans are most effective if they can carry warmer air out of a room, to be replaced by cooler air from somewhere else.

Answer 2

Actually, the fan works by convection over your skin. The amount of heat removed by convection depends on the properties of the air (temperature, velocity, etc) and the temp of the surface its moving over.

if the temperature change due to convection is
dT = h*(T-T_inf)
T is your surface temp, and T_inf is the air temp.
so in this example, if T_inf is higher, less heat is exchanged.
Air moving at higher speeds has a higher h value and therefore also draws more heat away from your body than slower air would with a smaller h value, i.e. hotter air cannot remove as much heat as cooler air, and faster air removes more heat than slower air because h is bigger. Also, if the air is hotter than your skin temperature it will feel hot, which is cooler than 98 degrees...ignoring sweat.

But yes, it acts like an airplane wing / turbine / propeller
The air moves faster on one side than the other creating a pressure differential which moves the air. In a fan, it pushes the air forward, in a propeller it pushes it back to create thrust to move the boat/airplane.

Answer 3

1. Yes, it works on the same principal as the airplane wing.
2. Your body temperature is 98.6 F. If the air is cooler than that, the air passing over your skin will feel cool. If it is warmer than 98.6 F, it will feel hot.

Have you ever considered getting a college degree in engineering or the sciences?