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How should the water flow in your condenser? From the flask to the top of the condenser, or from the top of the condenser back to the flask? I could imagine both: flask to top will fill the entire condenser with water, because of the resistance of gravity, enlarging cooling area, or top to flask, because this will generate counter current exchange increasing heat flow, but then it is almost impossible to get a decent cooling surface without extreme water pressure.

This picture suggests the first.


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up vote 5 down vote accepted

In general the cooling water is attached according to the countercurrent exchange mechanism to maximize the efficiency. Of course this doesn't work well for the Liebig condenser you pictured, but you generally wouldn't use this kind of condenser for reflux anyway. The most common condenser for reflux is the Dimroth condenser which can be used for countercurrent exchange without any problems as the entry and exit of the water are both at the top of the condenser.

Here is an image from Arbeitsmethoden in der organischen Chemie (page 43) that shows where to attach the cooling water for different condenser types.

enter image description here

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Water should always enter from the bottom of a condenser (the end closest to the flask) and exit from the top of the condenser. Doing it this way always ensures that your condenser will be full of cooling water. If you set it up the opposite way, and if for some reason the rate of water flow into the condenser decreased and became slower than the rate of water exiting the condenser, then the condenser would not remain filled with water. If the reaction were unattended, this could cause problems. BTW, here is a link you might enjoy. It contains a lot of lab tips, including "how to hook up the water tubing to a condenser".

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Yes, I thought that would be the case, but then I remembered counter current exchange and started to doubt. – Jori Jun 25 '14 at 17:58
Sorry, this is nonsense. How should an empty space suddenly appear in the water? Bubbles, OK, one of several reasons why a Liebig cooler is totally unsuitable as a reflux condensor. – Karl Nov 29 '15 at 22:40

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