Thermal expansion

Increase in size — length, volume, or surface area — of a body in response to heating. For liquids, the expansivity observed directly is called the apparent expansivity, since the container holding the liquid also expands with rising temperature; absolute expansivity is the apparent expansivity plus the volume expansivity of the container. In food plants, thermal expansion matters practically: hot-filled containers need headspace to accommodate contraction on cooling, pipelines require expansion loops, and volumetric filling must be temperature-corrected. Ignoring expansion causes under-fills, burst seals, or inaccurate dosing in temperature-varying processes.