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[HKk]

I am trying to figure out a design for a humidifier / direct contact cooler using gas liquid contact over a packed bed / tray column.The gas to the inlet is bone dry .So i am trying to utilise the latent heat of vaporisation for getting the cold water at bottom .

Can any body suggest me the method for the same & if it is better to use packed or tray column

regards

[siretb]

The method would be very similar to what you need for cooling towers.

YOu need to calculate the number of transfer units you need, and size accordingly.
The calculation of the number of transfer units can be found in Perry's handbook.
The heigth of a transfer unit must be calculated either from the vendor's data or using correlations.
You may refer to Billet and Schultes, Prediction of Mass transfer columns with ... pckings Tans IChemE vol 77 part A, sept 1999. Typical would be a HTU of 0.4 to 0.7 meters. Be careful however this depends much upon the hydrodynamics you have and the kind of packing.

If the gas is air, you can also do a heat transfer approach, and use a Lewis numnber of 1

I think that a packing will be more appropriate for that than trays, assuming the gas is almost dust-free. If the gas is real hot, then a conditioning tower, using air assisted nozzles is a good option.
If you need more help, supply details about waht you want to do.