What is thermal conductivity and how is it measured?
Definition of thermal conductivity
Thermal conductivity (symbol λ or k) describes the ability of a material to transport thermal energy by heat conduction. It indicates how quickly and efficiently heat is transferred through a material.
GOBA processes thermally defined insulation materials for motors, transformers and power electronics.
Unit of thermal conductivity
The unit is watts per metre and kelvin (W/(m·K)). It indicates how much thermal energy is transported through a one-metre-thick material layer at a temperature difference of one kelvin.
Measurement methods for thermal conductivity
- Laser flash method: a laser pulse heats the surface, and the temperature rise on the back is measured
- Hot wire method: a wire embedded in the material is heated by electric current
- Plate methods: measurement of the amount of heat conducted through a material sample
Which factors influence the thermal conductivity of metals?
Properties of metals and their effects
Metals consist of a crystal structure with freely movable electrons. These free electrons are responsible for the high thermal conductivity of metals, as they transport heat efficiently.
Temperature dependence of thermal conductivity
With rising temperature the thermal conductivity of most metals decreases, since the increased lattice vibration of the atoms hinders the transport of heat by electrons.
Influence of alloys on thermal conductivity
Alloys reduce the thermal conductivity compared to pure metals, because foreign atoms restrict the mobility of the electrons.
How does the thermal conductivity of various metals differ?
Metals with particularly high thermal conductivity
- Silver: highest thermal conductivity of all metals (429 W/(m·K))
- Copper: 401 W/(m·K), used in heat sinks, electrical cables and heat exchangers
- Aluminium: 237 W/(m·K), lightweight cooling systems and heat exchangers
Metals with low thermal conductivity and their applications
- Lead: insulating material in radiation shielding
- Stainless steel: relatively low thermal conductivity, ideal for cookware and industrial machinery
What role does thermal conductivity play in construction?
Significance for thermal protection in buildings
Materials with low thermal conductivity such as mineral wool or polystyrene foam serve as thermal insulation and reduce the energy consumption of buildings.
Applications of metals with high thermal conductivity
Metals with high thermal conductivity are used for heat distribution, for example in underfloor heating and radiators.
Use of metals with low thermal conductivity
Low-conductivity metals serve as protective layers in fire protection structures and as thermal barriers.
How is thermal conductivity calculated in practice?
Formula for calculating thermal conductivity
Thermal conductivity λ is calculated by: q = λ × (ΔT / Δx), where q is the heat flow in watts, ΔT is the temperature difference in kelvin and Δx is the material thickness in metres.
Relationship with other thermal properties
- Heat capacity: storage capacity for thermal energy
- Density: higher density often correlates with better heat conduction
- Thermal diffusivity: speed of heat propagation in the material
Which applications use the thermal conductivity of metals?
Use in electronics and electrical engineering
In computer processors, heat sinks and LEDs, high thermal conductivity is decisive for heat dissipation and reliable operation.
Applications in heat engineering and energy efficiency
Heat exchangers, solar systems and heating systems use materials with high thermal conductivity for efficient heat transport.
Use in industry and production
In the automotive industry and in mechanical engineering, materials with specific thermal conductivity are used to minimise thermal stresses.
GOBA Takeaway
Thermal conductivity is a fundamental physical property that plays a role in nearly every technical field. From thermal insulation in construction through the cooling of electronic components to efficient energy transfer: understanding and deliberate use of thermal conductivity are decisive for the development of high-performance and energy-efficient systems.