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Originally Posted by: firewaterburn QUESTION: How do I maintain the temp at the top of the column? It seems that I was constantly turning the water flow on and off and never relly saw the temperature hold.
You really can't control the vapor temperature. The temp at the top of the column will be whatever the temp of the vapor is, period. When you turn on the cooling water, it'll knock those vapors back down into the column & your temp will drop to whatever the temp of the air is above the column condenser tubes is. This is IMO, one of the issues you have to deal with using this design, given the location of the thermometer.
Think of the column condenser in this design as a sort-of valve -- it either lets vapors through (no cooling = valve open), or it knocks the vapors down (cooling water flow = valve closed). If you can control the temp and volume of the cooling water precisely enough, you'd be able to control the _volume_ of vapors passing through (and hence the volume of what gets knocked back down) ... which will affect the ratio ... not the temperature of the actual vapor itself.
Based on what I've seen so far, I noticed that if I'm driving the column too hard (too much heat) the vapor temp is higher -- much like what happens during my stripping runs -- lot's of smearing, so the temps are higher. If you keep experimenting with your heat you'll find that sweet spot. Based on what (I think) you're describing, I would try bringing things up until you get some output, then backing off heat (with no column cooling water flowing) until the output stops. Then bring up the heat _slowly_ until you get some output again. Then start some cooling water (just a small amount) until output stops again, Then again with heat, etc.
Basically, you only need enough heat for your column to do what it's designed to do -- separate the fractions -- while giving you some control over the output _volume_. There _is_ such a thing as too much heat. ;-)
Anyway, that's my two cents from my observations.
--JB"