Packed Tower Design

Dear Friends

I know I'm not recommended to ask 1 question in 2 forum, but because it's important to me and also i didn't get any answer before, i'm asking my question again. so excuse me.
I, wanna design a packed tower for a sulphuric acid plant and one of parameters which should be considered for Enthalpy balance in absorbing and drying towers, is " Association heat" which is produced in High concentration of sulfuric acid and it is different from produced heat of classic reaction: H2O + SO3 = H2SO4 + Q . I wanna know what really Association heat is? and in which acid concentrations it should be considered? I have a empirical equation for SO3 association heat in Absorbing tower and I'd like to know weather there is any Association heat in Drying towers or not? if yes what will be the way to find it?is there any empirical ways to calculate it or any charts for this purpose?any information will be highly appreciated.

Thanks.