I'm thinking about using a recent Taurus auto radiator or a Ford or GMC
pickup radiator to heat water with hot sunspace air, but I'm concerned that
a) it's hard to find specs for radiator performance, and b) a mechanic says
an aluminum core radiator might crud up with corrosion in less than a year
with oxygenated water and no antifreeze.
How many Btu/h can an auto radiator move from 150 F air to 140 F water,
using its electric fan, with no wind? An engine that makes 200 HP at 25%
efficiency (unlikely with no motion :-) would burn 800 HP of gas. If 25%
of the heat leaves from 200 F water to 100 F air via the radiator, the air-
water thermal conductance is 0.25x800x746x3.41/(200-100) = 5100 Btu/h-F,
good compared to a 2'x2' all-copper $200 MagicAire 2347 duct heat exchanger
that moves 45K Btu/h from 125 F water to 1400 cfm of 68 F air with a 0.1
"H20 pressure drop.
Antifreeze would be expensive for a 1000 gallon heat storage tank, and
an antifreeze heat exchange loop would add to the cost and lower efficiency.
How much antifreeze do we need just to prevent corrosion? Is there some
corrosion inhibitor we can use at a low concentration?
Why use Aluminium? I wouldn't have thought it would be hard to find an old
copper one which will.
A. Be a little more efficient
B. Won't have the corrosion problems Aluminium may have.
As you wont be running it under pressure even a leaky one should be easy
enough to patch up.
As for Aluminium corroding, if it's the only metal in the system I don't
think you will have a problem. If I was making something like this (and
someday I'd like to) and using second hand stuff I think I'd suck it and see
Be patient Nick, George will answer all.
Until then, consider the following. The radiator is based on the
constant flow of the water pump and the thermostat, which opens and
closes on a regular basis. If one were to take the engine, measure the
block and head temperatures, as well as the radiator fluid
temperatures, one would find the relationship between all of them.
Now, we know that a automobile engine with a failed thermostat will
malfunction in some way. If the thermostat is stuck open, the engine
will never ever warm up, thus giving us an indication that a typical
auto radiator is over designed for the application with a wide open
flow. If stuck closed, it will overheat.
Another similar way would be to take say, 200 degree water heated at
an even rate and flow it through the radiator and measure the
difference between the inlet and outlet at a given flow of fluid and
air through the radiator. I would suspect that you will need a much
lower flow than you expect to extract a given BTU without flow
Feel free to take all of that out of context in any way you see fit.
For some detailed answers you might look at
Parametric studies on automotive radiators
Applied Thermal Engineering, Volume 27, Issues 11-12, August 2007, Pages
C. Oliet, A. Oliva, J. Castro and C.D. Pιrez-Segarra
My gut feeling is performance won't be very good w/ only a 10F
temperature differential. In round numbers, an automotive radiator
operates on roughly a 100F difference or greater and except at idle, has
a pretty high airflow rate. Somebody else noted already they're well
over-designed for the minimum capacity in order to account for idling in
traffic on hot days w/ full A/C load, etc., but still the temperature
differences are around 200F for coolant and 100F for air temperatures
for the most part. Coolant flow rates are pretty high, as well.
One quick google suggests at least 25% ethylene glycol...
But that's still pretty high if you're talking about the whole storage tank
Another suggests that it isn't (corrosion) very bad if you can be sure to
use water that doesn't have any halides in it. But filling a whole storage
tank with demineralized water is probably about as expensive as doping it
A general rule to reduce corrosion is to use water that has a low electrical
conductivity and not connect dissimilar metals. So if you use an Al
radiator, you might consider using short sections of hose to connect it to
copper piping. This helps minimize forming a galvanic cell that will
corrode the metal with a more negative potential.
We can do that, but mechanics say an electrically-isolated aluminum radiator
with rubber hoses and insulating brackets can still corrode (oxidize?) soon,
with nothing but water inside. My old boy scout canteen ended up heavily
pitted with white crud on the inside. I think this was oxidation vs mineral
deposits or galvanic corrosion, since there were no other metals involved.
So far, I've only found Gunk anti-rust and water pump lube for car radiators,
$2 for 11 oz to protect 5 gallons or so, ie about $400 for 1000 gallons, and
a KPR VCI powder that costs about $20/lb and needs 0.25% concentration, ie
about $400 for 1000 gal. The tank will have a pressurized single-wall copper
pipe coil inside to make hot water for showers, so it would be nice to avoid
toxic tank water.
How long would it last? I gather it needn't be "fitted," just touching
the water and electrically connected to the aluminum. The 170 F tank water
won't change, so it won't have new minerals. It can absorb fresh oxygen,
esp since the radiator will drain down every day for freeze protection.
But it can't hold much oxygen, since it is hot. Then again, the corrosion
rate probably increases with temperature. The Farwest site mentions a 500
Wh/lb capacity for Mg rods used in pipelines, ie so many coulombs. How can
we turn that into a lifetime in a water heater with fresh O2 but no new
minerals? I've read that the oxide layer slows the corrosion rate, in air.
Nick, here's what I've been using in the heat storage system I built from your
suggestion of using old fuel oil tanks, some years ago. 2 parts to it, a rust
inhibitor, which costs about $15 a gallon and treats 300 gallons and an oxygen
scavenger, at about the same price per gallon. They have a chemical engineer
available, who may be able to answer any questions.
and Stop-Rust #200 oxygen scavenger which is the very last item on the page.
Hope you find this helpful.
Thanks. It was.
After talking with Modine and Farwest and Galvotec
this seems very empirical. A Galvotec engineer said they use about 5 mA/ft^2
(a lot) to protect steel in seawater, vs 2 in freshwater. They use more if
the water is flowing fast, as daestrom implied. The engineer didn't have
a value for aluminum.
The current can come from a sacrificial anode "battery" or a DC power supply.
The Farwest site has graphs to predict the lifetime of a pipeline-protection
anode as a function of soil conductivity. This seems to be a simple energy
calc. One of their products is 17 lb of magnesium inside conductive coke
inside bentonite clay inside a cotton bag, which disappears over time. This
can provide 1 amp for 1 year, ie about 1.7Vx1Ax8760h/17lb = 876 Wh/lb...
Galvotec said an anode wouldn't help much in this case (although there's
a 1996 patent for a radiator cap attached to a magnesium anode.) Modine
tried this unsuccessfully. Like chrome plating, it can protect the outside
of a tube, or the inside of a tank with a simple geometry, but it only
protects a few diameters into a tube. This seems to be a matter of water
conductivity and geometry. It might work if the deep insides of the radiator
tubes were directly connected to the anode and the parts closer to the water
hoses were connected via resistors with increasing values :-)
As to oxidation, an oil layer or oxygen getter may be useless if the radiator
is exposed to oxygen every day when it drains down to avoid freezing. STSS
EPDM-lined tank manufacturer Sven Tjernagel said "Don't use oil. That will
destroy the liner." He says just keep the water slightly alkaline. Modine says
their radiators should do fine if dielectrically isolated from other metals,
eg a bronze pump and a pressurized copper pipe DHW coil. The 12V radiator fan
could have an isolated DC supply. They say put a pan under the radiator and
make it inspectable and replaceable, in case it ever leaks.
Davies Chief Chemist Pat Fogerty recommends 0.5-2% of their "ACI 100" Al
corrosion inhibitor, listed in the "industrial" part of their web page.
A 5 gallon pail (0.5%) costs $41.80 + shipping and should last forever.
It's 42% sodium silicate, which may be essentially non-toxic when diluted.
It has a "2 mg/m^3" OSHA TLV (Threshold Limit Value) for human toxicity,
which seems to be a limit for the undiluted solution in a fog, vs a tank.
I wonder if it's still legal to preserve raw eggs in an undiluted solution.
Pat Fogerty says the MSDS says [the undiluted solution?] is non-toxic to
fish and has a "2,0,0" toxicity/flammability/corrosiveness safety rating...
Section P2902.5.2 of the 2006 ICC residential code for 1 and 2 family
Heat exchangers using an essentially toxic transfer fluid shall be
separated from the potable water by double-wall construction [unlike our
copper pipe coil.] An air gap open to the atmosphere shall be provided
between the two walls [which raises the cost and kills efficiency--
where's the GFX air gap?]
Section R202 defines an essentially toxic transfer fluid as
Soil, water, or graywater and fluids having a Gosselin rating of 2 or
more, including ethylene glycol, hydrocarbon oils, ammonia refrigerants
and hydrazine. [The scale runs from 2 (mildly-toxic, meaning 50% of 70 kg
humans would die if they drank 1 quart of it) to 6 (a few drops...)]
If the "2" ACI rating is a Gosselin number for the undiluted solution,
the worst-case toxic dose would be 1 pint, and diluting to 1% makes
the toxic dose 100 pints, well over 1 quart, so it would be fine
with a single wall heat exchanger.
Gosh that takes me back :-) I worked for an older guy when I was a kid that
kept a couple of cans of 'water glass' around from the depression. Said
they used to dip eggs in it and let them dry. The eggs would last for
months if not years without refrigeration.
Otherwise, thanks for sharing your findings.
I can only surmise that since the tubing is wrapped around the separate
drain pipe and soldered to it, the supply tube wall and the drain pipe wall
are the 'double-wall'construction. I doubt that an 'air gap' is required in
all installations, maybe you better go read that again. Another typical
heat exchanger design is two pressurized coils (one for toxic and one for
potable) mounted in a vented tank filled with non-toxic. If either tubing
leaks, the vented tank overflows and is detected before the opposite tubing
develops a leak. If potable pressure drops while the tubing fails, you
merely syphon the non-toxic water from the tank.
In that regard, the GFX is similar in that since the grey-water is vented to
atmosphere and the potable is pressurized. Any leakage of either will be
detected before a second failure can occur (you either get potable or grey
water all over the floor).
My limited experience in sewage treatment (couple of summers while in school
many years ago) ISTR that all potable to sewage connections had to have a
positive break such that if potable pressure fails and sewage backs up,
there should be no way for sewage to be syphoned into potable.
You could still get contamination with a multiple simultaneous failure of
two walls while the potable pressure fails. But that's pretty remote if you
can be reasonably sure you'd detect a single failure soon after it began
Quite right. Al forms a nice oxide layer that inhibits further corrosion,
*BUT* that oxide layer can be interrupted by several things. Physical
abrasion is an obvious one, but to a lesser extent erosion from very fast
moving fluids (sometimes called 'flow-accelerated corrosion'). But I don't
think you'll have trouble there.
The minerals in the water can have an affect too. From what I've read, any
with halogens (chlorides, flourides, bromides, etc...) will cause rapid
pitting of the surface. Carbonates (CaCO3, Mg2CO3, et.al.) are not so bad.
But this ends up being you either have 'bad water' or you don't. Oxygen
also plays a part and you're drain down system will have some problems with
that (each night the wet surfaces will be exposed to air, each morning
I've also read that there are dozens of different alloys of Al with
different corrosion resistance. No idea what version a radiator would have.
It may be significant that the interior is protected by anti-freeze with
corrosion inhibitors and the outside (exposed to rain, road salt, and storm
water) is protected by paint.
The carbonates combine with the oxygen to form carbonic acid. At
your typical 900 F steam operation, it is a SEVERE headache. This is
why steam plants use active dearation to acheive 7 parts per billion
oxygen in the feedwater.
I was only talking about carbonates and their affect on Al corrosion. The
link I found pointed out that dissolved halides were much worse at removing
the protective oxide layer than dissolved carbonates.
Carbonates in a boiler are bad news for several reasons and you don't need
900F to suffer. When you heat water the solubility for CaCO3, Mg2CO3 and
others drops off and they come out of solution. This is what forms scale on
heat transfer surfaces (even in home water heaters, and LP boilers). The
really bad part is that once the CaCO3 plates out, it will not re-dissolve
into the boiler water when you shutdown the boiler. You can't get the scale
back off with out 'mechanical' cleaning or 'chemical' cleaning. One way to
combat this in the old days was to add tri- and di-sodium phosphates. The
Na would combine with the CO3 to form a scale that was easier to remove.
The first trade name of such boiler-chemistry control was 'CalGon' (same as
the retail soap) which stood for 'calcium-gone'. But the large amount of
phosphates wasn't so good for the environment so phosphates have been
In steam plants it is now common to use 'polishers' (ion-exchange resin
beds) to continuously demineralize the condensate/feed-water. Keeping total
conductivity down well below 0.1 micromhos/cm is quite common. This slows
the buildup of TDS in the boiler water.
Dissolved oxygen in boiler is also bad for Cl-stress corrosion. But modern
low-carbon steels have a problem with too-low an O2 content as well. Yes,
O2 levels are controlled with several techniques (deareating feed tanks,
contact feed-water heaters and such). We actually have to keep O2 levels
between 10 and 50 ppb for best results.
On 24 Aug 2007 13:46:41 -0400, email@example.com wrote:
Radiator performance is readily available from the manufacturers, if not in their
catalogs then from an inquiry. Have you looked at, say, Modine's website.
Coolant anti-corrosion/passivation chemical packages are available separate from
antifreeze. These are used to maintain the anti-corrosion protection in large
coolant systems where one wouldn't change many gallons of antifreeze just
protection package is depleted. Stationary diesels, locomotive engines, things
Additionally, the aluminum can be completely protected from corrosion by fresh
using cathodic protection. There are many thousands of RV water heaters out
with aluminum tanks that handle all sorts of tap water without corrosion. The
is the magnesium anode screwed into the tank. I would think that an RV
anode could easily be fitted to an aluminum radiator.
John De Armond
See my website for my current email address
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
I'm going crazy. Wanna come along?
Aren't there also some active systems that do the same thing using electric
power instead of relying on cathodic action to provide the low voltage
differential? Of course they would stop working when the power went out, but
hopefully the amount of damage caused during the short power failure would not
amount to much.
Yes. Active service naval ships use cathodic protection with zinc anodes
that have to be replaced every year or two. But *inactive* ships in the
'mothball' fleet are protected by suspending separate electrodes in the
water around the ship. A small voltage impressed on these (only need about
1-2 V) will protect the hull from corrosion. It's much simpler to replace
the suspended electrodes (a single sailor can pull one up and replace it)
than to put the whole ship in drydock.
You can also find these 'active systems' in marinas for private yachts as
well. Same idea. If the power goes out for a couple hours, you don't see
any real damage. After all, the hull is designed to stand up to seawater
corrosion for many years, the 'active systems' just extend that further.
I'm in active service in the Dept of the Navy as a shipriding Marine
Engineer. I live in a world where we pay a lot of attention to the
things that really could end up being showstoppers or inspection-
passing obstacles; and usually don't have any time left for the
theoretical niceties. I'm not qualified to discuss the theoretical
utility of active cathodic-protection systems; I can report that I've
never seen a Chief Engineer direct an underling to pay attention to
the cathodic protection system.
Magnetic Silencing seems to fall into the same category. I guess that
will change the first time the Iranians use a torpedo against us.
Nonsense, surely you've seen a rag-hat or someone replacing 'zincs'. The
zinc anodes put into the water-box ends of sea-water cooled items is exactly
that. And along the hull near the shafting and propellers. Their
inspected/replaced as part of every drydocking. Even the insides of ballast
tanks have a few 'zincs' welded into them in key locations.
As I said before, *active* cathodic protection is something that I've only
seen used on ships in the 'mothball' fleet while tied up four abreast in
places like Mare-Island (now closed).
Funny, many's the time I dragged degaussing cables around submarines in dock
to reduce their overall magnetic signature. Minesweepers were about the
only ones I knew with active systems though. Had to learn the function of
'D', 'H' and 'T' coils just for EM3&2.
change "sailor" to "mariner", if you're referring to a SS, an M/V, a
USNS, or one of the command ships (USS Mount Whitney, USS Blue Ridge).
The Ready Reserve ("mothball") Fleet is in the custody of the
Maritime Administration. Red & white stripes on the stack. Many were
activated for the recent show in Iraq.
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