Old radiator shot, thinking about Jeg's Universal Aluminum, any one done this?

[Psycho71]

I would like to add another question to this debate. Alum. radiators are left unfinished (no paint). Copper Radiators are painted. I think that the paint on a copper unit would diminish it's transfer capabitlities. While the alum. is left unfinished, it would transfer heat at a faster rate.

I would imagine that all of this is cost related. But with a Be Cool costing upwards of $500, Construction cost does look to be an issue. For that kind of money performance should be the only concern. If copper worked better, I would think copper is what they would use.

Aluminum is used on all kinds of heat sinks, not copper. Heck, if I want to thaw meat out quickly I put it on an alum cookie sheet and place it where air can move around it. Meat will thaw up to 3-4 times the rate vs just setting it out on the counter. Of course we have no copper cookie sheet so I can't test the alternative.

I do know this. Copper will scale up faster than alum. inside, thus decreasing it's transfer rate. Alum. will not scale like copper, and would transfer better over the life of the unit. This is probably one of the biggest factor in the material used, aside from cost. I also question wether copper will TRANSFER heat to air, any faster than aluminum? I know coppper CONDUCTS better, but TRANSFER to air is another matter. Then the paint comes into play as well. The paint is an insulator. It's not meant to be that, but IS none the less.

When mine goes, it will get replaced w/aluminum.


Jay

[Old Yeller 1970]

Digging deeper into the differences between Cu and Al here is what I have found.
First, The conductivity of a metal is given in the units W/m-c. The higher the W/m-c the better it conducts heat from metal to metal or water to metal or metal to air.

The conductivity of pure Cu is 386 W/m-c.
However the core of a Copper radiator is Brass (70% Cu and 30% Zn) and the conductivity is 111 W/m-c.
The conductivity of pure Al is 220 W/m-c. But the Al in a radiator is almost certainly tempered which drops it's conductivity to somewhere between between 128-180 W/m-c.
Since the core of a copper radiator is brass, it appears that an Al radiator regardless of which Al temper is used will conduct heat away from the water better. By taking an average of Tempered Al (128+180/2) we get 154 W/m-c. Comparing this to the Brass core of a Cu radiator (154/111=1.38) we see that Al is approximately 38% better at conducting heat than Brass.

Next we consider the fins. If the fins are made of pure Cu this is where the Copper radiator really shines over Al. Comparing pure Cu to pure Al, the Cu has a 75% advantage over Al (386/220=1.75). I doubt if pure Cu is really used and if that is the case it's thermal conductivity will be drastically lowered. For instance household copper wire has a thermal conductivity of only 287 W/m-c. Likewise tempered Al is probably used for the fins. By taking the average conductivity of tempered Al used above (154W/m-c) and comparing that with houshold copper (287/154=1.86) we see that Cu fins would have an 86% advantage over Al. If the best tempered AL is used (287/180=1.59) copper's advantage drops to 59%.

It looks like an Al core probably conducts heat 38% better than brass but Cu fins are probably 59%-86% better than Al at conducting heat.
The last part of this whole equation is the number of fins per inch. The OEM Cu radiators used in our trucks have 10 fins/inch. The aftermarket Al radiators have 16 fins/inch.
10 - 1"x1" Cu fins with a conductivity of of 287 W/m-c will conduct 2870 W inch sq/m-c. (10x287=2870)
16 -1"x1" Al fins with a conductivity of 154 W/m-c will conduct 2464 W inch sq/m-c. (16x154=2464)
That still gives Cu fins a 16% advantage over Al. (2870/2464=1.16)
Since the Al core conducts heat better than a Brass core, that probably sways the advantage back towards Al.

If the core and fins of a radiator are 50/50 in their ability to remove heat then the difference between the Al core at 38% (over the Brass) and the Cu fins at 16% (over Al) favors the Al radiator by 22%. My gut feeling tells me the fins are more important at removing heat than the core (say 40/60) which lessens the advantage of the Al radiator down to about 6%.

To be honest there are simply too many unknowns about the purity of the materials used making it impossible to know their true conductivities. It is also quite likely I've made any number of incorrect assumptions or miscalculations. That being said, the numbers I have generated are hardly definitive and anyone can make them come out anyway they want to to prove a point. My hope is this will be of some help in trying to understand the differences between Al and Cu radiators.

http://www.arrowheadradiator.com/14_...utomobiles.htm
http://episteme.arstechnica.com/6/ub...85&m=106091502
http://www.engineersedge.com/properties_of_metals.htm

[Psycho71]

Great info, and alot of math on your part. Thanks for the info. Do any of the recources you gained info from address adding paint or scale? I know this would insulate the metal. How much? I do not know. But add some scale inside, and some paint outside, and we might have the reason aluminum is better (over the long run). I know the scale comes w/age, but the paint comes from the factory.


Jay

[Old Yeller 1970]

Regarding paint, in the second reference there was a mention by two guys who discussed college experiments with painting radiators. According to them paint is not a good thing because it changes the radiator's abiltity to conduct heat to the air.

However, they also mentioned that over time Al will oxidize effecting it's abiltiy to conduct heat which is why, in the world of computer heat sinks, anodizing is popular. I think the reason Cu radiators are painted is because they will also oxidize and turn green (think Statue of Liberty) reducing it's ability to conduct heat also. Considering how badly Cu oxidizes (including scaling in the core) compared to Al, I would say Al is probably not effected as much as Cu over the long term by oxidation. And since Al doesn't have to be painted that definitely gives it an advantage over a painted Cu radiator with regard to conducting heat.

Like I said at the beginning, pound for pound Cu is a better conductor of heat than Al. But a lot of compromises have to be made with Cu that helps make an Al radiator as good as or better than a Cu radiator.