Radiators

Cooling

 

Aluminum versus Copper:

 The debate rages on but really there is no debate. Copper out performs Aluminum in every aspect except weight. The weight is not as open and closed as it may seem at first glance.

 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...

 If your alloy radiator has plastic tanks and you have a leak involving a tank you will have to buy a new radiator. If you have a leak only in the alloy portion of the radiator it may be repairable. The only way to repair the alloy is with a Tig welder and first you have to get it good and clean. Most of the really good cleaners are not alloy friendly and few people are good enough with a Tig to repair your radiator to start with. Even if you do manage to repair your radiator loosing a couple of cooling tubes and some fin area in an alloy radiator is exponentially much worse than loosing the same number in a copper radiator.

In conclusion;

 Radiators of the exact same configuration, number of tubes - rows - fin design - tank design and overall volume, the aluminum alloy radiator will always weigh less than the copper radiator and have a much lower thermal conductivity. In most cases the aluminum alloy radiator will cost less than the copper.

Periodic Table of the Elements
Thermal Conductivity

Group
Period123456789101112131415161718
1H
0.1815
He
0.152
2Li
84.7
Be
200
B
27
C
155
N
0.02598
O
0.2674
F
0.0279
Ne
0.0493
3Na
141
Mg
156
Al
237
Si
148
P
0.235
S
0.269
Cl
0.0089
Ar
0.0177
4K
102.5
Ca
200
Sc
15.8
Ti
21.9
V
30.7
Cr
93.7
Mn
7.82
Fe
80.2
Co
100
Ni
90.7
Cu
401
Zn
116
Ga
40.6
Ge
59.9
As
50
Se
2.04
Br
0.122
Kr
0.00949
5Rb
58.2
Sr
35.3
Y
17.2
Zr
22.7
Nb
53.7
Mo
138
Tc
50.6
Ru
117
Rh
150
Pd
71.8
Ag
429
Cd
96.8
In
81.6
Sn
66.6
Sb
24.3
Te
2.35
I
0.449
Xe
0.00569
6Cs
35.9
Ba
18.4
La
13.5
Hf
23
Ta
57.5
W
174
Re
47.9
Os
87.6
Ir
147
Pt
71.6
Au
317
Hg
8.34
Tl
46.1
Pb
35.3
Bi
7.87
Po
20
At
1.7
Rn
0.00364
7Fr
15
Ra
18.6
Ac
12
Rf
Db
Sg
Bh
Hs
Mt
Uun
Uuu
Uub
LanthanidesCe
11.4
Pr
12.5
Nd
16.5
Pm
17.9
Sm
13.3
Eu
13.9
Gd
10.6
Tb
11.1
Dy
10.7
Ho
16.2
Er
14.3
Tm
16.8
Yb
34.9
Lu
16.4
ActinidesTh
54
Pa
47
U
27.6
Np
6.3
Pu
6.74
Am
10
Cm
10
Bk
10
Cf
10
Es
10
Fm
10
Md
10
No
10
Lr
10

Key: Thermal Conductivity

0-33
 
33-66
 
66-100
 
100-133
 
133-166
 
166-200
 
200-233
 
233-

 

 

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