Phase change materials (PCMs) are substances with a high latent heat (typically of fusion) which may be used to store a large degree of heat energy by melting and crystallizing at a certain temperature. PCMs can be organic, inorganic, eutectics, and hydroscopics (where the phase change is not a change of fusion but rather of absorption and desorption of water vapor). A key performance metric of a PCM is its ability to exchange heat with its surroundings – a metric which is often referred to as “thermal inertia” or, more commonly, “thermal effusivity.” A higher thermal effusivity allows a material to be thermally activated in a more rapid manner – and therefore more thermal load can be stored during a dynamic thermal process. In short: PCMs with higher thermal effusivity can absorb or release more thermal energy, faster.
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