Soojuskoefitsiente

Soojuskoefitsiente is a thermophysical term used to describe a coefficient that quantifies how a property responds to temperature changes. It encompasses various specific coefficients, such as the linear thermal expansion coefficient, the volumetric expansion coefficient, the temperature coefficient of resistance, and the temperature coefficient of refractive index. Each coefficient expresses the relative change of a property per unit temperature change.

Definition and formula: For a property P that changes with temperature T, the coefficient κ is defined as κ = (ΔP / P0) / ΔT, within a defined temperature interval. For linear expansion, α = (ΔL / L0) / ΔT. Volumetric expansion β ≈ 3α for isotropic materials. For electrical resistance, the temperature coefficient of resistance (TCR) is ΔR / (R0 ΔT). These coefficients are typically determined experimentally and can depend on temperature, pressure, and material state.

Measurement and units: Coefficients are obtained by methods such as dilatometry for length changes, four-terminal resistance measurements for TCR, or interferometric techniques for refractive index. Units vary with the property: per kelvin (1/K) for many linear or volumetric measures, or dimensionless per degree if the quantity is normalized. In practice, coefficients may be specified over a temperature range, reflecting their temperature dependence.

Applications and examples: Soojuskoefitsiente is crucial in engineering design to manage thermal stresses and deformation when materials with different coefficients are joined. Typical room-temperature values (approximately): steel about 11–13×10−6 /K, aluminum about 23×10−6 /K, copper about 16–17×10−6 /K. The concept is also central in electronics, optics, and materials science, where accurate knowledge of temperature response informs reliability and performance.