hist-brewing: Anyone using a "heat pipe" to cool fermenter? How about a peltier driven heatpipe?

Bill Velek billvelek at alltel.net
Mon Feb 20 15:09:46 PST 2006


I've been kicking an idea around for awhile and did a google-search but 
couldn't find anything directly on point.  A recent post about peltier 
devices made me think about this again.  What about coupling a peltier 
with a heatpipe?

For those who don't know, a 'heat pipe' is a very simple device with no 
moving parts and requiring no power, but which helps transfer heat from 
one place to another.  In its simplest form, it would be a length of 
straight copper pipe sealed at both ends, partially filled with alcohol 
or freon or some other liquid to act as a refrigerant.  To cool a 
carboy, it would be inserted into the neck of the carboy and extend from 
the bottom and protrude through the neck for some distance -- perhaps a 
foot (30cm) or a bit more.  The liquid refrigerant (alcohol, freon, or 
whatever) pools at the bottom of the pipe, picks up heat from the 
fermenting wort which causes some of the refrigerant to evaporate and 
rise to the top (into the part of pipe extending outside the carboy) 
where it condenses, releasing heat to the upper part of the pipe where 
it is dissipated into the air, and the condensed refrigerant runs back 
down the pipe into the lower portion within the carboy to repeat.  The 
cycle is continuous so long as there is a temperature differential, 
helping move heat from the inside to the outside of the carboy.  The 
thinnest gauge copper would be used to improve conductivity, and even 
convoluted pipe could be used to increase surface area and efficiency.

By itself, I'm not sure a heatpipe would help very much because it can't 
cool below ambient temperature, and I can do better than that with a fan 
and evaporative cooling.  But heatpipe performance should be improved 
immensely by adding a peltier device to the top portion of the pipe, and 
I think it would probably lower temps more than evaporative cooling, 
based on my readings.  For those who don't know, a peltier device uses 
solid state electronics and a flow of direct current to move heat from 
one side to the other; an example is those ice chests which can be 
plugged into a car's cigarette lighter socket.  Coupling a peltier to a 
heatpipe would also solve a couple of problems for people who want to 
use a peltier with a carboy: first, it solves the problem of how to 
connect to the carboy; second, it reaches to the center of the wort 
which is hardest to cool; third, because it runs up the center, 
convective currents should be uniformly distributed within the fermenter 
for greater efficiency and uniformity of temperature.  The pipe would be 
easy to sanitize and since it isn't permanently mounted, the whole thing 
could easily be moved to other fermenters such as a bucket or a conical, 
if they have a sufficient opening in their lids.  A thermostatic 
coupling for the peltier could run along the side of the pipe, thereby 
measuring temp at the center of the fermenter to regulate the peltier.

There are some downsides, but nothing significant in my mind.  First, 
you won't be able to use a Burton Union on your carboy, but I don't know 
anyone who does anyway, even though they are available.  Second, you 
won't be able to use a blow off tube or a conventional airlock.  How bad 
is that?  Well, if properly designed, the heatpipe should act as an 
airlock itself.  If the pipe has a flange or is widened at the point 
where it enters the fermenter so that the weight of the pipe rests on a 
sanitized rubber gasket between it and the lid or carboy neck, I think 
it will provide a sufficient seal.  Pressure inside the fermenter would 
merely lift the entire pipe and peltier device just enough to release 
CO2, and whenever it vents in that way, the positive pressure inside the 
fermenter should prevent oxygen and contaminants from entering.

Would that create too much pressure inside the fermenter, risking an 
explosion of the carboy?  Most of the weight of the portion of the pipe 
which is submerged in wort would be offset by buoyancy; in fact, 
depending upon the gauge of the pipe and how much it is filled with 
refrigerant, that portion of the pipe might even have a positive 
buoyancy.  That leaves the portion of pipe extending above the level of 
wort, plus the weight of the peltier, heat sink (if any), and fan.  I've 
tried to find some weight specifications to use as examples, but 
unfortunately haven't found any yet.  But some of these devices that are 
available are mounted on CPUs inside computers, and don't look like they 
could weigh much more than a pound -- but let's use 3 pounds (1.36kg) as 
an example and as an upper limit of total negative buoyancy, i.e., the 
weight on the gasket at the carboy neck or lid.  The inside diameter of 
the neck on my carboys is about one and an eighth inches (2.86cm), for a 
surface area of .994 square inches (6.41 square cm) -- "close enough for 
government work" to call one square inch.  Assuming three pounds of 
weight on that one square inch, it would require 3 psi to break the 
seal, causing a pressure of 3psi throughout the carboy.  I tried to 
research whether that was too much or not, and couldn't find an answer; 
I did find this thread -- http://tinyurl.com/fvned -- which was 
inconclusive.  But assuming that 3psi is not too much, the pipe and 
peltier should cause a good seal.  Now, another bad downside with not 
being able to use a blow off tube is that, with a really vigorous 
fermentation, each time the seal is momentarily broken to vent pressure, 
we're likely to have some kraeusen squirt out; this can at least be 
deflected downward by adding to the heatpipe a small sleeve which 
overhangs the neck of the carboy, but then we would still have a mess 
with kraeusen running down the sides of the carboy -- although it could 
be set inside a small pan or tub to minimize the mess.  However, if the 
heatpipe and peltier are successful in holding the temp of the wort down 
to a nice low temp of, let's say, 64F/18C, will fermentations really be 
that vigorous?  I don't know because I've never been able to ferment 
that low; I've had some pretty violent fermentations, but I've seldom 
been able to keep my temp down below 70F/21C.  With lower temps, 
fermentations will be slower, but I don't know how slow.

This is just some thinking on my part; I've never attempted any of this 
and don't know if it would work or not.  Seems to me like it would, and 
I'd love for some of the more knowledgeable engineering types here to 
comment on this.  If anyone thinks they can make this work and market 
it, you have my permission; just send me a 'beta' unit to try out. ;-) 
Also, if anyone tries this, please let me know how it works out.  I 
might give it a try myself, but I'll need to find out a lot more about 
how to make the heat pipe -- how much liquid to put in it, etc.  But 
there's no sense in even trying if calculations say it won't work.

I'm posting this to a lot of forums to try to get as many responses as 
possible.  Also, I'm sorry this is so long; I hope you folks don't mind.

Thanks.

Cheers, Bill Velek
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