Lämmönjohtaminen

Lämmönjohtaminen, or thermal conductivity, is a fundamental property of materials that describes their ability to conduct heat. It is defined as the quantity of heat that passes through a unit area of a material in a unit time, under a unit temperature gradient. The thermal conductivity of a material is typically denoted by the symbol k and is measured in 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 the free movement of electrons, while non-metals typically have lower thermal conductivity. For example, copper has a high thermal conductivity of about 401 W/m·K, while wood has a much lower thermal conductivity of around 0.12 W/m·K.

The thermal conductivity of a material is crucial in various applications, such as heat exchangers, insulation, and electronic cooling. 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 Fourier's Law of Heat Conduction describes the relationship between heat flux, temperature gradient, and thermal conductivity. According to this law, the heat flux (q) is proportional to the negative gradient of temperature (dT/dx) and the thermal conductivity (k) of the material:

q = -k * (dT/dx)

This equation highlights the importance of thermal conductivity in determining the rate of heat transfer in a material. Understanding and controlling thermal conductivity is essential in designing and optimizing thermal systems for various engineering and scientific applications.