Just found this and the one on effusivity. Thank you so much. It's often difficult to explain to people what you intend the end result to be without using the human senses as examples and you've helped me do that
The m in the units of W/m·K refers to the thickness but surely the area of transmission is a component too. Is it to be assumed that we are measuring the heat flow in a unit area. If this were so, shouldn't the units be W/m·K/sq.m
This is a very interesting and very clear explanation, we know that Ti and Al are metal but TiO2 and Al2O3 are oxide-based materials, what is the microstructure looks like and how these two materials transfer the heat? Thanks, Dr. Jack
Can someone help me out here. I don't major in physics. However, does this mean that the thermal conductivity of a material (poor or good conductors) is also dependent on their structural formation?
Yes, that's also what dr. Is trying to convey in the video. It greatly depends on molecular arrangement. Diamond for example, is an excellent conductor of heat because of its highly orderly arrangement of molecules.
I do have one question. There are a few materials now that have a high thermal conductivity along (example) their x,y axis but it is a huge difference along the z axis. How can you explain that to people.
Great question Paul. Anisotropy in thermal conductivity can have a number of different causes: It can be an inherent property of the crystal structure of a pure crystalline material (such as in graphite, sapphire, or boron nitride sheets). Sometimes, it can be a result of the manufacturing of an amorphous or semi-crystalline material (many polymers, for example, exhibit anisotropy in thermal conductivity when they have been extruded due to the extrusion’s orientation of the polymer chains). And sometimes it has to do with the orientation of high-conductivity components of a mixture or composite system (for example, often filled polymer composites have high-conductivity fillers with large aspect ratios - such as carbon nanotubes - which conduct heat very efficiency along their length but can’t pass heat as well through the polymer matrix). In the case of crystalline materials, the difference is due to the difference in phonon transmission efficiency along the different axes of the material. In the case of non-crystalline long-chain materials, like polymers, it’s to do with chain organization: heat transmits more efficiently along a chain than between chains - and therefore if the polymer chains exhibit some degree of organization, the thermal conductivity will be higher in the direction that the chains tend to be oriented towards. In the case of composites, it is due to more efficient heat-transfer along the filler materials than through the matrix. Hope that helps!
This video talks the difference between crystalline solids and plastics. However, the case of metal is different with other solids because of free electrons, which also plays an important role in thermal transport, in particular at high temperature. That is why thermal conductivity of metal is higher than other solids, such as diamond?
