Ken,
to avoid the tube bending business you can use a plate heat exchanger -
more compact but if DIY you have to do some welding. Cut two equally
sized pieces of *thin* stainless steel plate. Make about two dimples
about 2 mm deep on every square 10 cm of the plate with a ball-peen(sp?)
hammer (work on a wooden bench!). Weld the two plates together all around the
edges with the sides with the raised dimples facing each
other.
Grind
away the weld and cone out openings for the short pieces of pipes where the
fluid goes in and out (on opposite corners). The short pipe pieces
are welded in place.
Carefully pressurize the unit with very low air pressure - less
than 0.05 kg/cm2 - and test for leaks with soap water, remember to use
clamps or something to hold the plates together or you end up with a pressurized
'football'!
Make
two or more of these units and submerge in whatever storage tank you use, you
can connect them in series or in parallel as long as you avoid air
pockets.
The
size of the plates is as big as needed but keep in mind
that these DIY units are not meant to be used with internal
pressure! Pressure can maybe be used inside the storage tank but the
numbers of dimples have to be increased.
Also
beware of air pressure in large containers - even a small pressure can add up to
large forces and even blow the container!
Stainless steel rods for welding and a TIG welding equipment is also
needed - a skilled TIG welding buddy will make things easier if you
don't have the know-how.
-----Original Message-----Hi all,
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]On Behalf Of Ken Dunn
Sent: den 24 september 2005 08:02
To: Biofuel@sustainablelists.org
Subject: [Biofuel] Double wall heat exchange - Solar Hot Water Heater
Sorry for the long subject line but, I thought it may aid in archive searches... Is there a home remedy to creating a double wall heat exchange? I have contemplated buying two sizes of copper tubing, inserting the smaller inside the larger and bending the two simultaneously. I could see how the inner tubing might kink or flatten out but, I think that would be unlikely unless I tried to bend too tight of a radius. Is there a better home-builder solution? Perhaps there is an affordable storage tank commercially available that makes building a backyard heat exchange mute anyway.? I'm going to need to come up with a storage tank anyway. I understand the theoretical pros/cons to internal and external heat exchanges but, what are the real-world practical differences?
Thanks a bunch,
Take care,
Ken
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