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Glossary of terms

Term Definition
Heat capacity Heat capacity, also called thermal mass, is the ability of a material to store heat. It can be differentiated by sensible and latent heat storage. Heat capacity is measured in J/K.
Most commonly, heat is stored as sensible heat: An increase in heat transferred to the storage medium results in a temperature increase of (= heat storage) in the storage medium. Heat capacity is expressed as ratio of stored heat to temperature rise.
Phase change materials can not only store sensible but also latent heat. The latent heat is stored during the phase change = melting process and equals the melting enthalpy.
Specific heat capacity Specific heat capacity measures the heat capacity by unit degree of unit mass of a substance. It is typically measured in J/kgK.
Heat storage capacity See heat capacity
Thermal mass Thermal mass simply the amount of material present times the specific heat capacity of that material.
Thermal conductivity Material’s ability to transmit heat.
Heat conductivity See Thermal conductivity.
Volume change Phase Change Materials change their density, consequently their volume during the phase change process. The volume change depends on the material type, for solid-liquid phase change materials it is typically less than 10%.
Stability In the PCM terminology, stability refers to how reliable the phase change reproducibility is over the life-time of the PCM.
Latent heat Name for heat stored by a PCM during the melting process. It equals the melting enthalpy.
Sensible heat Name for heat storage if an increase in heat transferred to the storage medium results in a temperature increase of the storage medium.

Source: DuPont, ZAE Bayern Germany, Fraunhofer Institut Germany