Linear expansion coefficient

Expansion coefficients, encompassing both linear and volume expansion, are intrinsic material characteristics determined through experimental methods and are expressed in units of measure divided by Kelvin [1/K]. Kelvin serves as the unit of absolute temperature and for Celsius scale temperature differences.

Linear Coefficient of Expansion:

The linear expansion coefficient signifies the change in length of a solid body concerning its total length L with a one Kelvin temperature variation.

Let L0 be the sample length, and ΔLk represent the length change at temperature Tk.

Precise measurement of linear expansion is conducted through dilatometry. Samples are subjected to controlled heating in an oven, following a predetermined program ensuring the required heating rate, specified temperature holding times, and defined cooling processes. Throughout this procedure, the sample dimensions are continuously monitored. Linseis offers specialized dilatometers equipped with extensive evaluation routines for various tasks.

Coefficient of Volume Expansion:

The volume-specific coefficient of expansion denotes the alteration in a body’s volume relative to its total volume when the temperature shifts by one Kelvin.

Thermal expansion in daily life

Temperature variations induce volume changes in substances, impacting various technological domains. In construction, expansion joints are designed to accommodate longitudinal expansion of building materials. In pipelines, expansion compensators, such as integrated pipe bends, are incorporated. Power supply overhead lines are engineered to prevent wire breakage in winter and maintain sufficient distance to the ground in summer. Calculations for these constructions rely on the thermal coefficient of linear expansion.

Liquid storage involves adhering to a specified maximum filling level, leaving a space above the liquid level to absorb volume fluctuations. The volume expansion coefficient is integral in such calculations.

The terminology stems from the general tendency of substances to expand when heated, with exceptions where substances contract when heated, resulting in negative values. For isotropic substances, exhibiting properties independent of the considered direction, the volume expansion coefficient is three times the coefficient of linear expansion.

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