Chillers

Since my carboys and equipment should arrive between tomorrow and the next day, and Saturday promises to be a brew day, I’m now thinking about chillers.  I’m fairly sure I could borrow one easily, and that is likely to be what I will do.  But at some point I’ll be doing my own brewing in my own garage, and will need a method to rapidly cool wort.  Making a few notes on some of the things I’ve run across while researching the topic so I can find them rapidly when the time comes.

• Thermodynamics of Chilling
• Counterflow provides optimal cooling; immersion is simpler and very likely cheaper.  Cleanliness and sterilization is a not insignificant concern in a counterflow chiller.
• Why?  Reduce dimethyl sulfide which is eliminated from the wort while boiling, but accumulates in the hot wort post-boil until it’s chilled to a level appropriate for fermenting; limit the amount of time wort is in the delicate stage between a sterilizing boil and fermentation with the protection of an airlock and a layer of CO2.
• Nice, simple build diagram for a basic immersion chiller (maybe use more tubing, had a few thoughts on the subject to increase surface area by possibly incorporating a few verticals.
• Is there enough variation in temperature to create convection within the wort?  Is there a good way to increase it if so?
• Chiller built from some thinner diameter tubing, but it doesn’t seem to cool as fast as some of the larger diameter tubing chillers I’ve seen referenced.  May be possible to overcome by pumping from an ice bath?
• Combination whirlpool/immersion chiller.
• An article with some of the formulas useful in calculating and improving the efficiency of the heat exchange.
  • Thinner walled tubing is better.  I had been pondering this, but now that I write it down it makes complete sense.  You want the heat to transfer from the wort to the coolant as quickly as possible, and any other medium that the heat has to travel through will impede that.
  • Other thoughts
    • As the wort and cooling medium approach an equilibrium, heat transfer becomes less efficient.  I’m not sure it’s logarithmic, but it’s true that the greater the difference in temperatures, the more efficient the transfer.
    • Only a small amount of the cooling medium within the chiller actually contacts the transfer medium (i.e., copper tube) itself.   Heat will equalize in the cooling medium very quickly due to turbulence.  Does this have an effect that would be relevant to the nominal diameter of the tubing and/or volume to surface area ratio of the tubing?
    • Assuming, I believe accurately, that the temperature of the cooling medium will very rapidly approach the temperature of the wort (i.e., in the first few inches of tubing submerged in the wort), would there not be a benefit to running a split system with several coils like the Hydra in addition to a couple of large volume short length exchangers to cool very rapidly during the initial phase?
    • Flow within the chiller itself – should the cooling medium flow from top-to-bottom or bottom-to-top through the chiller?  Much like a water heater, I would expect the wort temperature to vary from hottest at the surface to coolest at the base, with the exception of a whirlpool chiller which would tend to equalize temperature throughout.  I’m not sure how great this temperature variation would be, though it’s probably realistically too small to even bother considering in a homebrew scenario. (This could also be achieved to some extent by increasing the flow rate of the cooling medium if practical, but may still prove less effective, during the very early phases, over a 20 or 25′ length of tube.)