HW 1 - p 3.14 - Effective Film Thickness Over Water Evaporating Into Air - 4 pts
Water in an open dish exposed to dry air at 25oC is found to vaporize at a constant rate of 0.04 g/h-cm^2. Assuming the water surface to be at the wet-bulb temperature of 11.0 oC, calculate the effective gas-film thickness (i.e., the thickness of a stagnant air film that would offer the same resistance to vapor diffusion as is actually encountered at the water surface).
posted by Dr. B at 2:12 PM
6 Comments:
I was trying to find the Fuller, Shettler, Giddings method of estimating Dab but couldn't find it anywhere in the chapter. I thought it best to ask what it was rather than search for it online or use a different equation.
Eqn 3-36/3-37 (the name is in the text before it)
How to calculate the effective gas file thickness?
gwydion 2:42 PM & green @3:28 PM
Green is exactly correct.
Amy 10:06 PM
This process is a UMD process in which water diffuses through stagnant air.
Eqn 3-33 gives the flux of water through air in this case. We know the water flux and we can determine DAB (see comments, above). So, we can solve for the film thickness, z2-z1.
Cross out the words "the wet-bulb temperature" in the problem statement. They are confusing. The T of the liquid is 11 degC.
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