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Heat pipes for use in greywater heat recovery

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Posted by Solar Mike (NZ) on August 12, 2009, 11:28 am
I'm playing around designing a greywater heat recovery system and am
thinking of using heat pipes as the double wall heat exchange

I have built a test heat pipe using an evacuated copper tube with
acetone as the phase change media. It works very well, but not at a
low enough temperature to be efficient. Acetone normally boils at 55c,
when the heat pipe is evacuated the liquid to vapor phase change
starts around 16c but only at a low rate; at 40c or above you can hear
the stuff boiling in the tube and it is very efficient at transferring
I require an efficient rate of heat transfer around 10 to 30c as it is
in this range that the waste water say from a shower occurs.

Next is to try a refrigerant gas like R410a or similar or even
propane, here the pipes will be under pressure as the normal bp is in
the order of  -20c. Has anyone done this or experimented along these

Mike (NZ)

Posted by daestrom on August 12, 2009, 9:01 pm
Solar Mike (NZ) wrote:

Have you considered these:

I have one and am pleased with its performance.  Although prices vary by
distributer so shop around.


Posted by Martin Riddle on August 13, 2009, 2:25 am

Interesting, They are in my neck of the woods. Maybe I'll pay them a


Posted by Solar Mike (NZ) on August 13, 2009, 4:02 am

I have, take up too much space to retrofit and are too expensive here
in NZ.

Currently I have 6m 15mm copper tube wound in a tight spiral fitted
inside a piece of waste pipe, greywater flows across this to drain,
cold water flows through copper tube.
Not double wall, so not really legal so to speak. But it works really
well, cold water to shower mixer gains approx 10 degrees C

I want to use a heat pipe as it gives me double wall and I can make
the device much more compact.
Have discovered R410a refrigerant isn't suitable as it is a mixture of
gasses and they fractionate.
Possibly propane or butane will be suitable.

Mike (NZ)

Posted by dow on August 13, 2009, 7:23 pm
Have you thought of diethyl ether? It's pretty easily available, and
boils at atmospheric pressure at about 35C.


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