@tally-ho,
You and I have the same numbers for (massic) heat capacity. See post
#468:
Metal | Density (g/cm3) [source] | Specific heat capacity (J/g °C) [source] | Thermal diffusivity (mm2/s) [source] |
---|
Aluminium | 2.70 | 0.89 | 97 |
Copper | 8.96 | 0.385 | 111 |
Iron | 7.86 | 0.450 | 23 |
Copper is dense stuff... more than iron! While it stores
less heat per
gram than iron... it has more
grams per unit volume than iron. Multiply density and specific heat capacity and iron and copper look pretty much the same. They can both store a very similar amount of heat per volume of material (iron has a very slight advantage). But look at the thermal diffusivity! Heat moves almost 5x faster through copper than iron!
While aluminium spreads heat about as fast as copper... it stores about 1.5x less heat per volume than copper/iron.
If you want 'fast' cast iron... get the thickest copper you can!
A cube of the same weight of aluminum and copper are not the same size, the aluminum piece is twice as big
If you are talking about equivalent mass; I have copper being 3.3x more
dense than aluminium. So for a cube of copper and a cube of aluminium to have the same weight, the aluminium will need to have 3.3x more
volume. The volume of a cube is... the cube of its side... (
)! So to equalise the mass, we need the aluminium cube to be 3.3^(1÷3) ~= 1.5x bigger on all sides...
I also included thermal diffusivity (conductivity)... I am going to assert that for all human intents and purposes... aluminium and copper will be perceived as having identical diffusivity. If we are talking about cubes of equivalent dimensions (
volume), copper and aluminium cubes share the same time for heat to conduct from one face to the opposite. But in this scenario the aluminium will store less heat energy. If we are talking about the same
mass of material, since the aluminium cube is 1.5x bigger on each side, the heat has to travel 1.5x further... so it will feel 'slower' than the copper cube.
A disc of aluminum and a disc of copper of the same radius and thickness seem to have the same heat capacity.
Be careful not to confuse (massic) heat capacity (J/g °C) with heat energy stored
per volume (J/cm3 °C).
If you are talking about discs with the same dimensions, they will have identical
volumes. Not
mass. Nor heat energy stored. From the table above, copper stores 3.4 J/cm3 °C whereas aluminum only stores 2.4 J/cm3 °C. Since copper stores approximately 3.4÷2.4 ~= 1.4x more heat energy per volume than aluminium, to equalise the heat energy.... same math as before.... the aluminium cube needs to be 1.4^(1÷3) ~= 1.1x bigger on all sides. In this scenario the cubes ought to store the same amount of heat but now they do not share the same volume or mass....
I think I got that right??!
I'd be happy for somebody to math/science/engineer review me