Height of packing for both natural and mechanical draught towers

Height of packing for both natural and mechanical draught towers 

The height of a water-cooling tower can be determined by setting up a material balance on the water, an enthalpy balance, and rate equations for the transfer of heat in the liquid and gas and for mass transfer in the gas phase. There is no concentration gradient in the liquid and therefore there is no resistance to mass transfer in the liquid phase. 

The five basic equations for an incremental height of column, dz, are  

Integration of this expression over the whole height of the column, on the assumption that the physical properties of the materials do not change appreciably, gives  

These equations cannot be integrated directly since the conditions at the interface are not necessarily constant nor can they be expressed directly in terms of the corresponding property in the bulk of the gas or liquid. 

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