Water evaporating from a pond does so as if it were diffusing across an air film 0.15 cm thick. The diffusion coefficient of water in 20 C air is about 0.25 cm2/sec. If the air out of the film is fifty percent saturated, how fast will the water level drop in a day

1.25 cm/day

Explanation:

An air thickness , (l) = 0.15 cm

Air Temperature =

Mass Diffusion coefficient (D) =

If the air pressure

We are to determine how fast will the water level drop in a day.

From the property of air  at T = 20° C

from saturated water properties.

The mass flow of  can be calculated as:

where:

R(constant) = 8.314 kJ/mol.K

Since 1 mole = 18 cm ³ of water

will be:

Again:

Converting the above value to cm/day: we have:

= 1.25 cm/day

∴ the rate at which  the water level drop in a day = 1.25 cm/day

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explanation:

answer:

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