Cooling

 Let us look at some of the technical aspects first. Both aluminum and copper are pure elements found on the periodic chart of the elements. All elements have a specific atomic weight. The greater the atomic weight the denser the material. The denser the material the heavier per volume the material is. An example would be a pound of Hydrogen occupies a lot more space than a pound of lead. Or the old children's riddle, "which weighs more a pound of feathers or a pond of iron?". They both weigh the same but the impression is feathers since it takes up so much more room.

 Aluminum has an Atomic weight of 26.98, copper 63.546. So in any given equal volume copper will always be heavier than aluminum and if weight was the only factor in radiators the discussion would end here. Another property that the scientist have figured out for all of the elements is thermal conductivity.

Thermal
conductivity is the quantity of heat transmitted, due to unit
temperature gradient, in unit time under steady conditions in a
direction normal to a surface of unit area when heat transfer is
dependent only on the temperature gradient {w/p/k @ 300 K}

   We need to know no more than someone has figured it out and assigned the numbers. The higher the number the greater the conductivity of the element. Here are some thermal numbers of the elements we will be discussing in this article. Copper (Cu) 400, Aluminum (Al) 235, Magnesium (Mg) 160, Silicon (Si) 150, Manganese (Mn) 7.8 & Zinc (Zn) 120.

 A very important fact, thermal conductivity tends to fall with decreasing purity.

  Now as we can see pure CU has a much higher thermal number than AL  but AL is almost never in it's pure state. And it is never used in it's pure state to build radiators. The alloy that is used in your aluminum radiator contains magnesium, silicon & manganese. The tanks will either be a cast Al alloy in the most expensive models or plastic in the less. Neither the cast tanks or the plastic conduct heat as well as the alloy used in the finned section of your radiator. In a copper radiator the tanks are usually brass which is a Cu alloy made of copper and zinc and the finned section is pure copper.

 A radiator is made up of three sections; the tanks, which hold a volume of water and depending on the cooling system of a particular vehicle may be also used to allow expansion and contraction of the coolant; The fins, which conduct heat from the last part the tubes. The tubes are what actually carry the coolant through the radiator.

 Through a property called thermal conduction, the transfer of heat between two solid materials that are physically touching each other, heat is moved from your engine out to your radiator and eventually to the air surrounding the fins. In reality you do not cool your coolant but heat the air. In your cooling system the coolant in the system and the air flowing through your radiator are considered solids to a degree. The heat transfer is not as direct as if they were actually solid but for our purposes here we will just go with this one definition.

 We have just learned that pure copper conducts heat much better than pure aluminum and much, much better than an aluminum alloy. What does this mean to you and your radiator? In the real world if we build two exactly identical radiators, where their volume (size) is the same the alloy radiator will weigh less and conduct a lot less heat. You would need to greatly increase the size of the alloy radiator to equal the thermal conductivity of the copper radiator. Keep in mind that as we increase the size of the radiator we will also be increasing the volume of coolant that is used in the system and both weights would have to be calculated to decide how much of a weight savings the alloy radiator would be. That calculation is beyond most of us and very few of us will ever be able to claim we lost a race because our car weighed 5 pounds more than the winner. No, for most of us one of the deciding factors will be the cost. Alloy radiators are usually less expensive than copper. But a few thoughts on less expensive...

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