Author Topic: LWR variables  (Read 3265 times)

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AEROSTATIC3

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LWR variables
« on: November 01, 2004, 09:23:00 PM »
Greets Beez...  after much reading on the attributes of the LWR and the HDR, and having a few LWR successes, SWIA's friend wonders about condensor length and/or diameter in relation to the efficiency of a LWR (or even a HDR).  In SWIA's prior dream I heard she used a 45cm long inner-coiled reflux condensor (approx. 12cm in diameter) on a 36 hr LWR; came out w/ beautiful gear. Now all her friend can obtain are some short fat Allihns, go figure. So I guess the question really is... Does size matter? (please no one with an inferiority complex lash out at me lol)--diameter, size, length, all of the above... Though she knows the little Allihns will perform efficiently, is it viable to throw 2 condensors together lengthways? Hell, or just opt for buying a real lengthy sumbitch?  Why or why not? SWIA's friend was told the longer AND wider the better, even for nanos or small reactions...

Amnesia

  • Guest
A condensor is there to condense the vapours...
« Reply #1 on: November 02, 2004, 02:50:00 AM »
A condensor is there to condense the vapours back into liquids, so as long as it keeps the vapours from escaping and condenses it back into the RXN it doesnt matter what the hell you use.

But of course a bigger one will do the job better, but overkill wont do anything of course.

Its just common sense.

AEROSTATIC3

  • Guest
so the answer....
« Reply #2 on: November 02, 2004, 05:10:00 AM »
Thanks for the reply and time; yet you only offered that 'big' may be better, to wit: is or is'nt 'longer' necessarily better? SWIA's friend has witnessed 36+ hr refluxes w/ extra lengthy Allihns and watched the height of condensation SLOWLY rise during the 36 or so hour course of the reaction.  Was curious if that was a positive indicator of a more proficient reflux or not... or whatever. Any elaboration would be welcomed, Beez.

Amnesia

  • Guest
Well it all depends on the surface area.
« Reply #3 on: November 02, 2004, 07:47:00 AM »
Well it all depends on the surface area.
One that brings the most vapours into contact with the cool surface that is being cooled by the coolent will do the best job.

Whether that surface area is increased by an extra long condensor or whatever means you can think of then the condesation will be better.

Of course you could always decrease the temp of the coolent being used, which will increase the rate the vapours droping boiling the critical point and condense and drop back down.

So is longer better? yes because it gives the vapours more time to condense before they escape and more time to come into contact with the surface, but you should also be looking at the other factors.

geezmeister

  • Guest
Doesn't take much
« Reply #4 on: November 02, 2004, 04:11:00 PM »
The LWR doesn't place a heavy demand on a condenser. IF you circulate cold or even cool water through it a 200 ml Liebig is enough of a condenser for cooks up to the two ounce range. Over that I usually use a 400 ml Liebig which is more than enough condenser for reactions up to four ounces. I can't recall ever needing to stack condensers, even with phos acid cooks.


AEROSTATIC3

  • Guest
is Amnesia correct Geez?
« Reply #5 on: November 02, 2004, 05:22:00 PM »
So if Amnesia is correct, Allihn's (short or long), with their bulbous inner tube, would be a plus due to more surface area and more contact of vapours on cooling surface?  Last idle question, I promise.

geezmeister

  • Guest
more than enough condenser
« Reply #6 on: November 02, 2004, 06:19:00 PM »
An Allihn condenser is more than sufficient. There will be no detriment to its use, but that does not imply an advantage to its use, either. The reaction takes place in the flask, not the condenser. Any condenser that returns the vapor to the flask as a liquid is sufficient for the purpose of the reaction.


NMR

  • Guest
The purpose of the reflux condenser in a ...
« Reply #7 on: November 03, 2004, 02:05:00 PM »
The purpose of the reflux condenser in a reaction that requires one is to condense those constituents that can be condensed and return them to the reaction flask while at the same time allowing unwanted gases that are formed as the reaction progresses to escape.  That is why the reflux condenser is not sealed at the top.

If one has a short condenser, then just turn down your heat so that the reflux miniscus only travels half way up the condenser.  Therefore, is the miniscus is less than half way up the condenser, turn up the heat a little, if above half way, turn down the heat.

If one is running a hypothetical reaction that refluxes at between 100 and 125 degrees centigrade, then a simple short West condenser is more than adequate.

If you still have a difficult time regulating your heat so that your miniscus is right in the middle of the condensor, then you can artificially increase the efficiency of your condenser by running ice water through it instead of tap water by using a small submersible fountain pump submerged in a 5 gallion bucket of ice water to circulate through it and return to the bucket.  Just keep adding ice as needed.