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We just covered in the previous blog post what thermal conductivity and heat capacity were. Well, now it’s important to consider how those two thermal parameters are connected to each other. They are connected through a term called thermal diffusivity.

So…what is it?

Let’s look at the mathematical equation for it:

κ=k/ρC

Where k= thermal conductivity, ρ=density of the object, and C= the heat capacity of the object. What it’s telling us is that is the amount of heat that can be transferred relative to the object’s density and how much heat it can store. Remember that each object has a set thermal conductivity and heat capacity. Therefore two different objects that have the same density will have different diffusivities.

A object with the higher diffusivity indicates that heat transfer can occur very rapidly due to the object either having high conductiveness or not requiring much energy to raise it’s temperature. Objects that have a low diffusivity mean that they are better insulators because heat is not easily transferred through the object. This is why when scientists and engineers do a thermal analysis for choosing a good insulator material, they will most likely look at an diffusivity values of various materials to determine which one has the lowest value.

Rule of thumb, always remember the diffusivity equation when thinking of thermal analysis, that is if you find yourself in a situation where you have to.