air absorbing moisture by blowing across pond

winnie_t

Hi,

Does anyone know how I can find out how much water the air can pick up by blowing across a pond?

If the wind speed is 20m/s and the air has is 15 degree Celsius at the relative humidity level of 70% (absolute humidity of 9 g/m cube). How can I find out how long it would take to bring the humidity level of the incoming air to a saturation level and what is its relationship of the area of contact of the air and the pond?

Thanks

Chestermiller

The boundary condition between the air and the water at the interface is always going to be 100% humidity. The water vapor in the air has to diffuse through a concentration boundary layer near the interface, under the concentration driving force 100% - 70%. The faster the air is moving, the thinner the boundary layer, and the higher the rate of mass transport. But, you don't expect for the humidity to rise to 100% all that way up to the top of the atmosphere. Unless the air is nearly stagnant, most of the air will pass over the pond with essentially no change in its humidity. Only the air very close to the surface will pick up water.

winnie_t

Thanks.

So if it is in a confined environment, it would be a different case?

If I were to have a water surface of 1 msq (1m x 1m), the wind would travel through this body of water at a speed of 20m/s in a tunnel of a height of 0.1m (hence the volume of air in the tunnel across the body of water would be 0.1 m cube. How would I be able to find out how much of the air (at 15 degree Celsius, 70% relative humidity) leaving the tunnel would be saturated?