Question Regarding Placement of takeoff in a 3'' VM Column
Posted: Mon Mar 28, 2011 8:34 am
As I am waiting for bits I have had way too much time to think about the layout of 3'' reflux column heads. Now, I am not an expert in fluid dynamics, my knowledge of hydraulic behaviour comes form the fire service and my knowledge of the movement of air/vapour comes from parachuting and paragliding.
So with that disclaimer out of the way; My question concerns what happens when you reduce a 3'' column into a 2'' equal tee. My understanding is that as the vapour enters the reduction in the 2'' tee it accelerates but reduces in pressure. It is at this point that we place our takeoff aperture. Although ethanol vapour is denser than air or steam I would have thought that the reduction in pressure caused by the vapour acceleration would make the takeoff less efficient. In effect, the column would attempt to draw air up the leibeg to compensate for the reduction in pressure. If on the other hand the column widened back to 3'' velocity would reduce, pressure would rise and if a takeoff was placed in the 3'' it would be more efficient.
Having read as much as my wee brain can take, the only evidence I could find on the forum regarding this was Minime (I think) who noticed that when he placed an inverted funnel in the column below takeoff, product collection improved markedly.
Now, I am no expert and I know that nothing is truly new; just rediscovered or covered by someone else. Has anyone done work that would back up my thinking or am I way off the mark. If no one has I may build a head just to see how things pan out.
Over to the experts.
So with that disclaimer out of the way; My question concerns what happens when you reduce a 3'' column into a 2'' equal tee. My understanding is that as the vapour enters the reduction in the 2'' tee it accelerates but reduces in pressure. It is at this point that we place our takeoff aperture. Although ethanol vapour is denser than air or steam I would have thought that the reduction in pressure caused by the vapour acceleration would make the takeoff less efficient. In effect, the column would attempt to draw air up the leibeg to compensate for the reduction in pressure. If on the other hand the column widened back to 3'' velocity would reduce, pressure would rise and if a takeoff was placed in the 3'' it would be more efficient.
Having read as much as my wee brain can take, the only evidence I could find on the forum regarding this was Minime (I think) who noticed that when he placed an inverted funnel in the column below takeoff, product collection improved markedly.
Now, I am no expert and I know that nothing is truly new; just rediscovered or covered by someone else. Has anyone done work that would back up my thinking or am I way off the mark. If no one has I may build a head just to see how things pan out.
Over to the experts.