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oldcorollas
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January 2003

Re: Radiators: alloy vs Brass

Fri, 07 October 2005 16:28

wilbo666 wrote on Fri, 07 October 2005 10:53

Material / Thermal conductivity (298K) W·m-1·K-1
Copper: 401
Aluminum: 237
Brass: 120

Cheers
Wilbo

bingo...

i dunno if i'm going to add anything here but... Razz

heat transfer can be remarkably affected by even the thinnest of layers. for jet turbine blades, we use about 0.1mm to reduce the temperature (from one side of the layer to the other.. ie in 0.1mm thickness) by 100-200degC. this material is usually 8%PSZ (partially stabilised zirconia), but similar in properties to alumina...

anyway... liquid to metal direct heat transfer is usually very fast, and transfer of heat within a liquid, especially when it is agitated is also very fast, so for a radiator, you can assume a very small thermal gradient in the water at the water/metal interface. as long as the inside of the radiator is perfectly clean, it will transfer heat well.. once you start getting scale and sludge, you can reduce the heat transfer remarkably..

heat transfer through the materials, i think, is not as important as you think.... see.. both materials transfer heat well, but if they are both transferring heat fast enough, then the outside of the core/tube will be at almost the same temperature as the inside of the core/tub, and so the relative conuctivity is of little concern... if they conductivity was low, and there was a significant (maybe.. 5-10deg) temperature gradient across the thickness of the metal (0.5mm??) then you chould be worried.. but i don't think there is such a big gradient there...

umm... weight reduction?? minimal, especialyl considering the thing is filled with water, and you are likely to put larger end tanks on it anyway.. AND the alloy is likely to be thicker than the copper/brass...

bras is copper and zinc. copper is more expensive than aluminium in a mass production sense, and aluminium is easy to attach to plastic tanks (thicker material, bend it over and it seals.. no way you are going to have 1mm thick brass/copper for the ends of the core in a production vehicle!!!)

aluminium is MORE reactive than copper. aluminium OXIDE (ie anodised/corroded) is LESS reactive than copper, and self healing Wink

BUT, aluminium oxide (alumina) has good insulating properties.. so the maybe.. 5-10 micron thick (at a guess) layer of alumina should be good enough to decrease the heat transfer by a little bit... then again, how insulating is the paint used on conventional radiators?

as for the ARE site, there is a fair bit of fact, mixed in with some snake oil and good old fashioned salesmanship....

hmm, copper tin (solder) thermal conductivity
well.. lead = 35
tin = 66 ?? something like that.. and the change is linear between them. or close enough http://www.interfluxusa.com/images/thermalconducti vity.jpg
solder aint a great conductor of heat...

by contrast.. thermal conductivity of air is....

0.026.. compared to aluminium of about 240, and...
WATER of 0.60

hmm, thermal capacities
aluminum 0.896 kJ/kgK.
Copper 0.383 kJ/kgK.

how are the alloy fins connected? spot/resistance welded??

methinks it is the interface with the fins, as well as the thermal transfer rate from the surface (be it bare metal, painted, or oxidised) that determines the effectiveness...

i'd start by measuring the temperature of the water in the radiator at inlet and outlet... the surface temperature of the tank or a tube if you can, near inlet or outlet.. and go from there..

you do have a thermostat? the water is not flowing too fast?

regardless of water temp in.. if the radiator is doing it's job (and the water is slow enough) you should have a large decrease between inlet and outlet temperature... or at least you should remove the same amount of heat as will be put back in as it passes thru the engine...

you could even try restricting the water flow, and see how that affects both heat transfer to and fron the water...

i'd be trouble shooting the current system before splashing out of a bling radiator Wink

(regardless if it is more effective)

Cya, Stewart

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