Thermal Conductivity Materials
Understanding Thermal Conductivity Materials is the rate at which heat energy is transferred from hotter areas within it to cooler areas in contact with it. This property is determined by the type and structure of a material, as well as its state and temperature. It is a physical property that will change based on these variables, making it a very important factor in many applications, such as thermal management and aerospace insulation.
The best materials for thermal conductivity are metals, whose high thermal conductivity results from the delocalized electron movement within metallic bonding. As a result, heat moves very quickly through these materials. However, not all metals have the same thermal conductivity, and non metallic materials also tend to have good thermal conductivities. Other common materials with high thermal conductivity include carbon in the form of graphite and tungsten, copper, aluminum nitride, and polymer composites.
Unlike non metallic solids, gases have much lower thermal conductivities, as the molecules in gaseous matter are not tightly packed. Instead, the transfer of thermal energy in a gaseous material occurs through particle agitation, with less frequent collisions between particles. This leads to a lower rate of transfer, and makes gases poor thermal conductors.
A significant factor in determining a material's thermal conductivity is its thickness. Thicker materials will have a lower thermal conductivity than thinner ones. The reason for this is that thicker materials have more mass, which tends to interfere with the flow of heat through them. This is why it is very important to ensure that a material is of the correct density for its intended application.
The inverse of thermal conductivity is thermal resistance, which is the ability of a material to resist the flow of heat. While not as useful as conducting materials, insulators like glass and plastics are often used to block the flow of heat in certain applications.
Thermal conductivity is generally measured in a laboratory by measuring the difference between the temperature of a sample at one end of the specimen and the temperature at the other. The magnitude of this difference is then divided by the thermal conductivity of the material.
There are two primary ways to measure a material's thermal conductivity: steady-state and transient. Steady-state techniques measure the thermal conductivity of a material once it has achieved a steady-state temperature profile. This method is typically slower and more difficult to implement than transient techniques, which are more sensitive to small fluctuations in the temperature profile of a sample.
Thermophysical modeling software typically uses reference correlations to predict the thermal conductivity of a material over a range of temperatures and pressures. These are usually compiled from experimental data and may be proprietary or open source. Alternatively, first-principles calculations can be performed. These provide higher-fidelity results, but they are generally not feasible for fluids that exist in the gas, liquid, and supercritical phases.