Cooling management

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Old style CM head

Cooling Management This is (unfortunately) a very common design. The cooling management still features cooling of the column before the product takeoff. This condenses a portion of the vapor and sends it back down the column as reflux. It is controlled via the manipulation of cooling water to the reflux condenser. If water flow is reduced, the reflux ratio drops and output increases. If cooling water is increased, the reflux ratio is increased. It is possible to completely stop output by increasing water flow (total reflux). The CM designs has a lot of variations. This is one of the oldest, yet most seen:

The main feature of this design are the cooling lines that travel through the column on their way to the product condenser. The reasons this design is pretty much the worst of the lot have been summed up nicely by rad:

rad14701 wrote: First, the reflux will drip off the entire length [of the tube through the column] and unless perfectly vertical the reflux will end up running down one side of the column rather than dropping into the center... Through tubes would probably perform better if the had a sag in the center so all reflux drips off into the center of the column...

Second, by having the tubes separated, with one at the top and one at the bottom, you are trying to force reflux separation within a small area... If that is the goal then you would need to be able to control the amount of water flow to each individual tube because if the bottom tube gets too cold no vapor will make it to the top, and if it does the top tube might reflux the balance of the vapor... With your design the bottom tube has more surface area than the top which further adds to the complexity...


Because of these problems, a newer design is now being built that is preferred by those people that have them as it gives them more flexibility in their product selection than both the LM and VM. People that want one still that will make both a vodka and a whiskey or rum have turned to this design. It allows you to do both. And with a CM still since it’s nothing more than a pot still with reflux added. They make a great whiskey and rum similar to a pot still. When you use the reflux option it makes an ok neutral.

CM Head - Dephlagmator StyleHead

A debate will always arise between the people that believe you make your best whiskey with a pot still and those that are now making whiskey from their CM stills.

This design avoids some of the problems of the older one above by generating all the reflux at the top of the column. The condenser here can be tubes (such as a dephlagmeter), a coldfinger, a jacket, or even a coil mounted inside the column. all will have similar results, as long as the reflux is centered somehow.

The CM still has gotten a bad reputation from the design mentioned above. Because the two through tubes disrupts equilibrium of the column and isn't enough cooling for good reflux. The fact that the reflux condenser can't be controlled separate from the product condenser makes that design an inferior one as well.

Consistent results can be had once good control is added to the cooling system and with a proper designed reflux condenser it is possible to attain 100% reflux that negates the negative reputation the original designs had. Also having two valves, one to control flow to reflux condenser and the other to the product allows you to make many different products.

One good thing about CM is they achieve great tails compression. To control the reflux ratio, you have to tweak the level of coolant flow to the reflux condenser. It takes some practice to run but like all stills one needs to learn to operate it. Coolant settings are not predictable, either - a hotter day could mean your water supply is warmer, or the still charge could be different. If you are recirculating your water, then it will get warmer, requiring constant attention.


Original Post by Kiwistiller, edited by Bushman, Can be found here.