Thursday, August 11, 2011

Beer Chiller

Due to popular demand I've decided to do a writeup on the beer chiller I created for the Beer Chilling Contraption Contest at DEFCON 19.

In previous years I had used a coiled pipe submerged in a chilled liquid consisting of a mixture of dry ice, alcohol, lN2, water, and salt. These chillers where very effective at getting beer cold but could not particularly fast or capable of handling capacity.

This year the rules changed to include scores for speed, capacity, and reaching a target temperature of 36 degrees. Unfortunately, the contest became a cluster fuck and the winner was chosen on lowest temperature so I didn't win.

Deviant has decided to stop hosting beer chilling so I'll be taking over the contest next year. Stay tuned if you want to participate for updated rules, sponsor opportunities, and other shit useful information.

Onto the meat of this post. The team Ad-Hoc DEFCON 19 beer chiller.

Description and General theory of operation.

This chiller operates with a similar concept as a water jacketed pipe. However, unlike the water jacket which relies on flowing liquid to move heat this chiller uses a stagnant reservoir of of liquid CO2 in the jacket cavity which it boils off to move thermal energy away from the center pipe (where the beer is) and into the operators face. I'll be moving the vent location on the next revision.

Operating the chiller is the simple process of filling the liquefaction chamber with dry ice. Melting the dry ice under pressure, and then transferring the liquid CO2 into the cooling cavity. In reality this ends up being a lot harder then it sounds. Just figuring out if you have a chamber of liquid CO2 ready for transfer is very difficult.

Beer chiller operation overview.

Why / How it works.

In a liquid only chiller the wall temperature of the inner pipe is dependent on the thermal conductivity of the cooling liquid and the rate which it can be moved from the edge of the pipe. Most systems rely on the thermal conductivity of the fluid rather then circulating. It is difficult to find a pump which operates at cryogenic temperatures. This greatly limits the cooling capacity of the system as most fluids don't conduct heat very well and rely on convection.

The phase change CO2 solution solves the removal of cooling mass from the edge of the pipe through boiling action. This greatly increases the thermal transfer capacity of the unit. Further, unlike the liquid coolers the wall temperature is regulated to the boiling point of the CO2 under the pressure set by the operator. Therefor if liquid is freezing in the pipe the pressure can be increased thus increasing the boiling point and the temperature of the inner pipe.


In the end we where able to chill a beer from 90 degrees to 45 degrees in about 4 seconds. I feel we can get lower temperatures if more care is taken when charging the unit to ensure all the dry ice has melted before starting a transfer.

Future Work.

The biggest changes I will be making are to the pipe's connecting the two chambers. There was significant leaking at the compression fittings. Normally they would have worked but as the unit was moved around they started to leak.

A way to determine the fill level of the cooling cavity and the liquid state of the liquefaction chamber would be extremely helpful. We still have no idea when the chamber is ready for transfer or if all the CO2 has been moved to the cooling cavity.

I feel it was a good first run and I look forward to giving this thing another go next year at DEFCON 20.

All in all the whole thing cost me about $300 and resulted is tones of fun. Totally worth every penny and now I have a beer chiller which looks like a weapon of mass destruction.


Now for pictures. Ill try to get more from other people who have them.