if something has a low specific heat, does that mean it conducts heat well?
If something has a high specific heat, does that mean it insulates?
Like, copper has a specific heat of only 0.385 and it conducts heat well, yet teflon has a specific heat somewhere in the 900s and it also conducts heat well.
No. Specific heat means heat capacity (per kg or lb of material). It measures how much heat it can hold - i.e. how much energy is needed to warm it up, and how much energy you must remove to cool it down.
Heat conductance (or thermal conductivity) is how well the material transmits heat through it.
So if you want to cool down a hot object by connecting it to a radiator, you use a material with high thermal conductivity. If you want something to temporarily soak up heat, or give out heat as it cools down, you choose a material with high heat capacity.
It looks like I was wrong, and that teflon actually has a very low thermal conductivity.
Specific heat mostly just depends on molecular weight: When you look at heat per particle, instead of heat per mass, there’s very little variation between different substances. Substances with high specific heats per mass, like water, just have a very low molecular mass (you won’t find many solids or liquids with a lower molecular mass than water).
Conductivity, meanwhile, mostly just depends on whether it’s a metal or not. Nearly any metal will have a much higher conductivity than nearly any non-metal.
Right. And if you want to picture how heat moves around in an object, for example if you want to model the evolution of its temperature field, after an initial temperature gradient, you would be more interested in its volume specific heat, as opposed to its mass specific heat (which is what is usually meant by “specific heat”). For example the speed at which a temperature change propagates through an object is just a function of the conductivity divided by the volume specific heat, which fraction is also called the “thermal diffusivity”.
What’s easy about thinking in terms of volume specific heat is that practically all solids are fairly close to two million joules per cubic meter kelvin, as a volume specific heat.
And, yeah, plastics tend to run something like a thousand times less conductive than copper. Polyethylene will do a bit better better, but not the fluorocarbons.
As Chronos pointed out, I think you are looking for thermal diffusivity. Chronos gave the physics aspect of it, i’ll Try the engineering aspect :
If you see this page, it will give you the thermal diffusivity of many substances :Thermal diffusivity - Wikipedia
You can see the thermal diffusivity of many materials like water, engine oil, hydrogen and bricks. The thermal diffusivity is great tool to select solid state elements for heat transfer applications (like bricks for home insulation).
However, thermal diffusivity is not a good down selection parameter for liquids and gases. This is because momentum transfer (convection) plays a role in liquids and gases.
For liquids and gases, Prandtl number (Prandtl number - Wikipedia) is a better down selection number.
Using the above numbers, you can see why Hydrogen is used as a coolant for large (100 MW +) generators, why molten sodium was used as a working fluid in nuclear reactors and how engine oil is characterized.