Heat Transfer Q&A: Sun, Metal Heat Sinks, & Conductivity

[RobA]

Hi, I'm working on a project and would like some help regarding heat transfer and heat conductivity. Any help would be appreciated, I'm more or less a layman.

If I wanted to use heat from the sun to heat water via a metal conductor, does the size of the heat sink have proportional heating capacity?

For example, would a copper square measuring one square meter get significantly hotter then a copper square measuring one square foot, due to the increased surface area, and thus more heat radiation collects in the metal? IF so, would that increase proportionally? Would a copper square measuring one square mile increase in temperature in proportion to it's size (I assume at least until it reached the melting point of copper)?

second part, I understand heat conductivity, but what is heating capacity, as it relates to heat transfer? Copper is more conductive then aluminum, but aluminum has a higher heating capacity. Which would be the best metal to choose if I wanted to transfer heat from the sun, to a liquid? And would the thickness of the metal heat sink make a difference? I.e. would a copper square measuring one square meter and 1/4" thick transfer more heat then a copper square measuring one square meter and 1" thick?Any help would be greatly appreciated.

 

[nasu]

The equilibrium temperature depends on both heat absorbed and heat lost to the environment.
The heat lost to the environment is also proportional to the area of the metal plate.
So the answer should be no. Think that you have two separate plates of equal area, heated by the sun in the same conditions.The fact that you put them in contact along one of the edges to make a plate of twice the area won't double the temperature.
Or consider the surface of the Earth (the hemisphere facing the Sun). How much hotter do you think it gets, compared with the temperature of 1 square meter of ground in the back yard?

 

[Tom.G]

Just to get things started, I'll tackle the easy one.
Regarding the different sizes, the temperature is related to the amount of energy gained minus the amount of energy lost. A larger plate will gain more energy than a smaller one but will also lose more energy, both due to the larger surface area. The end result is they will be at the same temperature.

As an additionally bit of info, as the temperature difference between a plate (or anything else) and the ambient increases, the rate of energy transferred from the high-temperature item to the low-temperature item increases.

Oh, I see nasu got in here as I was typing... with a more intuitive comment at that!