Thermal conductivity is a property of materials that shows that heat can flow easily through the material. It is usually represented by the symbol ‘k’, but can also be represented by ‘λ’ and ‘κ’. The reciprocal of this quantity is known as thermal resistance. Materials with high thermal conductivity are used in heat sinks, while materials with low values ​​of λ are used as thermal insulators.

In this article, we will learn about, Thermal Conductivity, Thermal Conductivity Formula, Thermal Conductivity Measurement, Examples, and others in detail.

What is Thermal Conductivity?

The ability of any material to move heat from one place to another without the material itself moving. In other words, it is a measurement of how much heat can be emitted through the weight of an object. Well-insulated heat apparatus can pass warmth very fast, on the other hand, objects having low thermal conductivity transfer the temperature slowly. They typically document the ability to transfer heat in watts per meter kelvin (W/(m·K)). In many cases, it includes building insulation of buildings cooling electronics, and material studies.

Thermal Conductivity Formula

Every material has its own capacity to move and transfer heat. The formula to calculate thermal conductivity k is given by:

k = Q × ΔT × L/A

where,

• k is Thermal Conductivity
• Q is Rate of Heat Transfer
• L is Thickness of Material
• A is Area of Material
• ΔT is Temperature Gradient

Thermal Conductivity Measurement

Thermal conductivity is determined from heat flow and temperature differential across samples by techniques such as Guarded Hot Plate method or Heat Flow Meter methods. Thus, measuring techniques need to be calibrated, samples prepared and temperature dependencies compensate for accuracy of measurements. This form of evaluation is necessary all through areas such as construction, electronics and energy where decisions on the choice of materials in production to achieve efficient heat management solutions are made.

Unit of Thermal Conductivity

A standard unit of thermal conductivity in the SI system(International System of Units) – Watts per Meter Kelvin, W/(mK).

Steady-State Techniques of Thermal Conductivity

Constant – state heat conduction methods use situations where a material’s temperature change remains the same determining uniform flow of heat. In conditions where nothing changes, a uniform discrepancy in temperature is maintained through the thickness of material. This pushes heat flow. When conditions remain constant, methods such as protected hot plate work, heat measuring tools and laser fast perception are used to determine how well materials pass on the transfer of temperature.

Steady-state methods lets us determine whether a material can handle heat equally and easily. This aids in selecting specific materials for particular uses.

Transient Techniques of Thermal Conductivity

Short-term methods observe how heat moves when things change. They note the shift in warmness over time. These methods track heat propagation through materials revealing slow heating and spreading. One common way is by the use of heat pulse in a technique referred to as laser flash analysis, whereby the rate at which hotness spreads can be seen through changes of temperature.

Few methods use sudden temperature or heat shift materials accompanied by time-temperature lines. Temporary uses time-based math problems and mathematical models that describe how heat moves during changing circumstances..

Effect of Temperature on Thermal Conductivity in Metals

Metals and the way temperature changes how heat moves in metals differ due to different atomic arrangements of atoms and molecules. Here’s an explanation in points:

• Temperature Dependence: It is usually the case that many metals become poorer in heat conduction as temperatures increase. This action takes place because high temperatures lead to more vibrations (phonons) within the structure. This reduces the ease with which heat moves well between different parts of a thing.

• Phonon and Electron Contributions: In non-metals, heat travels majorly through shaking or vibrating (phonons) rather than free electrons like in metals. Phonons can change the ways of scattering interaction and temperature causes heat flow paths. This leads to varied thermal conductivity due variations in temperature.

• Crystalline vs. Amorphous: Non-metals consist of two types crystalline and amorphous. Their heat conducting capabilities are not the same. An uneven pushing exists in some crystal structures. Structureless forms which have no set direction do not uphold this distinction either.

• Phase Transitions: Some things that are not too difficult to accomplish can transform into other states (like turning from liquid or solid) at specific temperatures and this determines how they handle heat. When substances transform their structure, factors such as molecule alignment and bonds alterations can be influenced. This could lead to some quick or peculiar changes in the rate of heat transference via thermals conductivity.

• Impurities and Defects: Bad things or additives in non-metals can significantly alter the progress of heat with temperature. This extra stuff could lead to scattered spots, alter the manner in which phonons interact or affect how molecules move. This can affect heat flow characteristics.

Effect of Temperature on Thermal Conductivity in Non-Metals

The way temperature changes how heat moves in non-metals differs from metals because of different ways that atoms and molecules are arranged. Here’s an explanation in points:

• Temperature Dependence: Unlike metals, where less heat passes through them because more bouncing occurs because it is hotter here than non-metallic body what happens can be really hard sometimes. Some non-metals may even become better conductors of heat when they get warmer because more energy from shaking and improved sound wave travel are available.

• Phase Changes: Non metals will melt like boiling or simply reshape from solid to gas at certain temperatures. These movements can relocate atoms and their bonds, which then determine how effective a material is at conducting heat. For instance, when solid is converted to a liquid or gas the differences in heat sharing can be very drastic because there are distinct changes in the way molecules talk and move.

• Anisotropic Behavior: Some not-metals, particularly crystal things may have unsymmetric heat moving. This means that the way in which they distribute heat changes along different axes of their pattern structures. This unevenness can be affected by the changes in temperature, leading to movement of heat differently.

• Intermolecular Interactions: Generally, in non-metals heat travels through phonons and how molecules interact. These linkages are affected by changes in temperature and cause variations. For instance, if it is hot more movement in tiny parts can help the heat better spread by causing sound waves to travel right.

• Material Composition: One can determine whether a non-metal is hard or soft by the material that they made of, even more extra parts are added in. Changes in temperatures can disrupt how parts function together. Phonons get scattered in a different way and it also impacts the general ability to move heat.

Factors that Affect Thermal Conductivity

Different materials have different natural abilities to conduct heat due to their atomic or molecular structures and elemental compositions. Thermal conductivity frequently varies with the temperature of an object; some materials can be less thermally conducting as a result increasing phonon scattering. Materials with crystalline structures may be anisotropic in their conductivity, which means its value depends on the direction of a crystal.

Thermal conductivity can be changed by impurities, alloying elements or defects because they introduce scattering mechanisms or cause heat transfer to actually fail. Higher densities usually lead to higher thermal conductivities for materials due to increased atomic or molecular interactions. In porous materials or soils, moisture acts as a thermal insulator, influencing the material’s overall ability to conduct heat.

Read More,

• Heat Capacity
• Latent Heat
• Convection

Thermal Conductivity: FAQs

What is Thermal conductivity?

The ability of a given material to conduct/transfer heat is called Thermal Conductivity of the material.

What is SI Unit of Thermal Conductivity?

SI unit of thermal conductivity is watt per meter per kelvin or Wm^-1K^-1.

What is Formula of Thermal Conductivity?

Formula for thermal conductivity is K = (QL)/(AΔT)

What is Effect of Temperature on Thermal Conductivity of Metals?

When temperature increases, the vibration of metal ions increases. As a result, the metal becomes more resistant, which lowers conductivity.

Is a Higher or Lower Thermal Conductivity Better?

Lower thermal conductivity is better, because the material conducts less heat energy and these material are used to make objects that do not required to conduct heat.