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 what happened. Stuart
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 regulation.
Feel free to take all of that out of context in any way you see fit.
Parametric studies on automotive radiators Applied Thermal Engineering, Volume 27, Issues 11-12, August 2007, Pages
2033-2043 C. Oliet, A. Oliva, J. Castro and C.D. Pérez-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.
An old all-copper car radiator might not corrode, but it might not have an electric fan, and it might be hard to find one, and a replacement if needed.
Aha. Thanks. Now where did I put the August issue...
I'd like to get 800 Btu/h-F, like a MagicAire 2347.
I'm wondering how it will do without wind, just its own fan.
At idle, it might have to dissipate 25% of 1 gph, about 30.5K Btu/h...
One quick google suggests at least 25% ethylene glycol...
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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 with EG.
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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.
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 volume coolant systems where one wouldn't change many gallons of antifreeze just because the protection package is depleted. Stationary diesels, locomotive engines, things like that.
Additionally, the aluminum can be completely protected from corrosion by fresh water using cathodic protection. There are many thousands of RV water heaters out there with aluminum tanks that handle all sorts of tap water without corrosion. The reason is the magnesium anode screwed into the tank. I would think that an RV replacement anode could easily be fitted to an aluminum radiator.
John
-- John De Armond See my website for my current email address
We can do that, but mechanics say an electrically-isolated alum>Coolant anti-corrosion/passivation chemical packages are available separate
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.
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and Stop-Rust #200 oxygen scavenger which is the very last item on the page.
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 re-wetted).
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.
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.
After talking with Modine and Farwest and Galvotec
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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 dwellings says
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...)]
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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 leaking.
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.
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'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.
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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