"Jeff" <dont_bug_me@all.uk> wrote in message
news:j3Upg.1891$PE1.260@newsread2.news.pas.earthlink.net...

Znod Grimpo wrote:

"Jeff" <dont_bug_me@all.uk> wrote in message
news:1Etpg.976$cd3.392@newsread3.news.pas.earthlink.net...

I'd like to build a few solar (water) collectors. With the price of
copper as high as it is, this makes steel conduit seem very attractive.
Thermal losses of using steel over copper would just be a bit less than
a degree F.

So... This is effectively a closed system where the working fluid is
recycled. How do I keep the steel from corroding, rusting or just
building up deposits? What treatment to the water would be effective? Is
this a case for a water softener?

Jeff

do a survey of the industry
most use copper for several reasons.

I only have one problem with copper. The cost of the copper tubing is
greater than the cost of all the other materials combined, by some margin!
Copper is 5 times the price it was a year and a half ago.

The loss due to the steel pipe is fairly small, figure steel at I think
26 BTU Ft/Ft2 F

corrosion, thermal conductivity, sealing via solder, fin attachment,

Actually wasn't planning on soldering the aluminum fins on. Heatsink
compound and rivits with a backing plate. Black etch primer on both to
prevent contact elctrolysis and for the collector surface.

higher

efficiency

water softener is a salt that causes corrosion

Good point.

I'm tempted to try the galvanized steel conduit and filtered tap water.
I'm thinking the amount of scale formation in a few hundred gallons of
water is small compared to what formed the scale in my old steel plumbing
over decades.


I don't care if this doesn't last years as I think the cost of selective
coatings will fall with the introduction of "Black Crystal". I can just
toss out the fin assemblies and upgrade, keeping the box and glazing.
There's a fair number of manufacturers that make replacement assemblies
for solar water collectors. Money is tight, for me, for a while...

the Israelis have cheap solar collector down cold.
you could use that black plastic pipe, not use fins, I have seen several
that just have lots of black plastic pipe stacked on the back.

(it is very cheap, low pressure stuff) No corrosion problems.
Guess if you make it out of very cheap stuff, it will be low cost to
replace items in it.
There are some good pumps out there too, cost $100 or so but use hardly any
electricity, could use DC from a panel, or use the self cirullating setup,
tank higher than the panel.
galvenized pipe will be heavy
there is AL pipe out there too, but I havent worked with it much.

I hope not. Solder doesn't work on aluminum at all. Aluminum coats
its own surface with a molecular layer of aluminum oxide, which
inhibits further reactions with air. Solder doesn't stick to *aluminum
oxide*. It is possible to weld aluminum, but it requires arc welding
in an inert atmosphere.

Jeff wrote:

I only have one problem with copper. The cost of the copper tubing is
greater than the cost of all the other materials combined, by some
margin! Copper is 5 times the price it was a year and a half ago.

Copper can corrode, too. This often occurs in copper pipes carrying
water:
http://www.southeastwater.com.au/sewl/index.asp?link_id=30.381

corrosion, thermal conductivity, sealing via solder, fin attachment,

Actually wasn't planning on soldering the aluminum fins on.

I hope not. Solder doesn't work on aluminum at all. Aluminum coats
its own surface with a molecular layer of aluminum oxide, which
inhibits further reactions with air. Solder doesn't stick to *aluminum
oxide*. It is possible to weld aluminum, but it requires arc welding
in an inert atmosphere.

Heatsink
compound and rivits

...either rivets or bolts. Simple sheet metal screws will work loose
as vibration reshapes the aluminum threads.

with a backing plate. Black etch primer on both to
prevent contact elctrolysis and for the collector surface.

Junction potentials are seen with dissimilar metals only. Stick with
only one metal for construction and you won't have to worry about
eletrolysis.

I'm tempted to try the galvanized steel conduit

Galvanized steel 'fights' corrosion by providing a more active metal
(zinc) which is guaranteed to corrode before the iron in the steel
begins to show corrosion. You will be adding zinc to your water.

and filtered tap water.

Filtering tap water will remove the solids and the particulates, but
very little of the dissolved gases (oxidizers) and mineral salts
(electrolytes) that will contribute to corrosion. If this is to be a
closed system I suggest using water that has been distilled *and*
degassed.

I'm thinking the amount of scale formation in a few hundred gallons of
water is small compared to what formed the scale in my old steel
plumbing over decades.

Scale often acts like seeds: once it is planted it grows. It's
'nutrients' are the metal, the air, and the water.

I don't care if this doesn't last years as I think the cost of
selective coatings will fall with the introduction of "Black Crystal". I
can just toss out the fin assemblies and upgrade,

Fin assemblies are a function of design, which is driven by function
and performance demands.

the need for fins in any application where they are required
(high-efficiency heat exchangers, especially systems in which one of
the working fluids is gas phase.)

Money is tight, for me, for a
while...

It is tight for most physicists, and has been for *quite* a while.

Tom Davidson
Richmond, VA