Column Height Vs Diameter ratio

[Lubavitcher]

MOD EDIT____Ive split this from --compact column design --- NOW PLAY NICE ---hmmm thanks lwtcs i guess the issues is best left until there is more data

on to a more productive question. Why is it that as diameter increases a taller height is needed to achieve the same purity all other things being equal like vapor rate, RR, packing, thermal heat loss, ect
for example if some one is useing a 2 inch er and they switch to a 4 incher why should they have to double the length of pipe to get the same purity? the vapor rate stays the same so the amount of time for the vapor and reflux to travel the length of the column doubles. which seams to knock out the theory that effective column height is determined by the distance reflux must travel, because if reflux was the main decider then a 4 incher should be the same height as a 2 incher.

the only way i can think to test this is to insert a thin strip of copper down the middle of a 4 inch with structured packing then then try the same experiment with a thin strip of wood this way we he can isolate weather the reason is because of reflux and vapor mixing or thermal gradient through the column

and to add fuel to the fire if you use the calculator on HD it seams that an increase in diameter of column does NOT demand an increase in height to get the same purity.. whats going on here? is a height to diameter ratio that every one is going on about (1:12-1:30) true or not?