Thermal Conductivity Materials Determined By The Physical Properties

In aerospace applications, thermal conductivity plays an important role. Understanding Thermal Conductivity Materials defines the rate of heat transfer between two points in a material. The higher the thermal conductivity of a material, the faster it will transmit energy to a colder region in contact with the material. Conversely, materials with low thermal conductivity act as excellent insulators. Thermal conductivity is determined by the physical properties of a material and can be measured experimentally using various techniques.

A material’s thermal conductivity depends on its atomic or molecular composition, its crystal structure and the distance over which it must transmit energy (known as the path length). In addition, the chemical or physical interaction between the constituents of the material can also impact its thermal conductivity. For example, a metal with strong carbon-to-carbon bonding on its basal planes tends to have high in-plane thermal conductivity due to the close proximity of the molecules.

The speed at which energy can be transferred through a material is proportional to the temperature gradient between the points on its surface and the material’s thermal conductivity. In the case of a metallic material, this can be seen as a straight line in a plot of its temperature and conductivity.

For non-metallics, however, the relationship between temperature and thermal conductivity is more complex. As a material increases in temperature, its atoms and molecules will vibrate more vigorously, which can reduce the mean free path for free electrons by a process known as phonon scattering. This effect can be overcome, at least to some degree, by increasing the packing density of atoms and molecules in a material. This can be achieved by varying the crystal lattice structure of a material: FCC (face-centered cubic) structures like copper, for example, have a higher thermal conductivity than BCC (body-centered cubic) structures such as iron.

The thermal conductivity of a material can be measured by subjecting it to a steady-state or transient heat flow and measuring the rate at which its temperature rises. It can also be predicted by using first-principles models, Monte Carlo simulations and other computational methods. However, high-fidelity modeling of pure materials is often impractical and requires extensive data collection over a range of temperatures and pressures. This data is often used to create empirical or theoretical expressions for a material’s thermal conductivity, which are then fit to available measurement data. These reference correlations are then used by thermophysical modeling software to predict the thermal conductivity of a new or existing material at a given temperature and pressure.

In addition to its intrinsic characteristics, the thermal conductivity of a material can be influenced by its porosity and the nature of the gases that comprise it. Porous materials can exhibit poor gaseous thermal conductivity if the pore size is too large or if air is trapped within the voids. This can be avoided by using cores made of nano-structured materials that require a lower evacuation pressure to achieve the same results as conventional materials.