Hey Ken;
Liquids are almost uncompressable. Fill the tube with water and put a
cap on each end with a compression fitting (swagelok etc) (underwater
of course no bubbles allowed - you could probaly fill the tube and then
tilt it up at one end and tape a bag around it with the tube poked
through and fill the bag with water to put the remaining cap on) and
then go ahead and bend your tubing. I have not tried this but have
been told that it works. Filling with sand can be a problem in getting
the sand out of the bend afterward. With a reducing union it should be
able to be done with coaxial pipe as well.
Hope it helps.
Joe
Mike Weaver wrote:
Maybe I'm losing my mind but I swear I used to have a kit w/ different
head and a long bar that I used to bend copper pipe. I remember it as being
very cheap (under 100.00 USD) at someplace like Norther Tool or Harbor
Freight. Of cource I haven't done any plumbing in over 20 years - maybe
the don't make it any more.
-Mike
Kjell Löfgren wrote:
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-----
*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
Hi all,
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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