5 replies to this topic

[djack77494]

This problem is one of simultaneous heat and mass transfer. Water droplets falling through the hot air are evaporating and effecting the heat transfer. There are many variables that would need to be defined in order to fully solve this problem. Just a few are the initial droplet sizes, the distance the droplets fall, and the rate of water circulation. The worst case is that the water and air immediately reach equilibrium. I would be very inclined to start with this, and to reduce water flowrate until you get an acceptable solution. If this is not acceptable at all, then you will have to jump into the (messy) simulataneous mass and energy transport equations. Have a big pad of paper handy.
Doug

[djack77494]

If you don't want to do the calculations, then you can conservatively assume instantaneous heat transfer. As each droplet of water enters, assume it immediately mixes with the air and totally evaporates. The air and water vapor reach an equilibrium temperature. Think of that process continuing until the vapor mixture reaches saturation (which will probably happen fairly quickly). While this is not a very realistic approach, it is quick and it is conservative.
Doug

[djack77494]

[/quote]
is it reasonable to assume, that water droplets will have wet bulb temperature on surface?[/quote]

The very simple method I mentioned (but don't really endorse) is NOT all that reasonable. It is predicated on there being thermal equilibrium, which is NOT the case. It's advantages are that it's easy and quick; they come with a loss of accuracy which may be quite significant. The correct way was earlier described. You must make the decision on how much of a compromise you are willing to make.
Doug