ABSTRACT
Three classes of phase change material (PCM) are available: organics, salt hydrates, and fused salts. Organic PCMs suffer by comparison with inorganic salt hydrates or fused salts by having poorer heat transfer properties, lower density, greater fire hazard, and more nuisance potential. Paraffin wax materials are available from a variety of commercial sources, including all the major refiners, and companies which specialize in oils and waxes. Cross-linked polymers are promising for heat storage, since they can be form stable, that is, they undergo a melting transition without liquefying. Congruent-melting salt hydrates can be regarded as unary systems, melting and freezing reversibly to the liquid and solid stoichiometric hydrate compound. This type of phase equilibrium behavior is the most desirable in applications as PCMs. The polyethylene glycols have also been proposed for PCM use. They are available as mixtures of different chain lengths of polymerized ethylene oxide.
