lämmönjohtuvuuden

Lämmönjohtuvuus, or thermal conductivity, is a material property that describes its ability to conduct heat. It is defined as the quantity of heat that passes in unit time through a plate of the material of unit area and unit thickness, in a temperature gradient of unit magnitude. The SI unit for thermal conductivity is watts per meter-kelvin (W/(m·K)).

Thermal conductivity is influenced by several factors, including the material's structure, temperature, and the presence of impurities or defects. Metals generally have high thermal conductivity due to their free electrons, while non-metals typically have lower values. For example, copper has a thermal conductivity of about 401 W/(m·K), while air has a value of approximately 0.026 W/(m·K).

Thermal conductivity is crucial in various applications, such as heat exchangers, insulation materials, and electronic devices. In heat exchangers, materials with high thermal conductivity are used to efficiently transfer heat between fluids. Conversely, in insulation, materials with low thermal conductivity are employed to minimize heat transfer and maintain temperature differences.

The thermal conductivity of a material can be measured using various techniques, including the guarded hot plate method and the transient plane source method. These measurements are essential for selecting appropriate materials in engineering and industrial applications.