Cooling pipes in the column

[partsbill]

I've read and read and read, searched and searched and searched, and still can't seem to find a decent answer. I know this is a simple first question for a newbie but here goes. Why are the cooling pipes on some internal reflux stills routed through the column? Is this what is causing the internal reflux? And then some stills that aren't thru-piped have copper mesh in the column for reflux? Once I wrote this I think I answered it myself.

Partsbill