George A. Lane

Low temperature heat storage with phase change materials

SYNOPSIS A group of promising phase change heat-storage materials was selected through study of the literature, laboratory tests of freeze—melt behaviour and determination of thermophysical properties. Means were developed of encapsulating these materials in metal or plastic containers. Four of these phase-change materials, suitably encapsulated, were tested in a sub-kale thermal storage unit of about 20MJ capacity, using air as the heat-transfer fluid. In most cases, measured thermal-storage capacity exceeded 90% of the theoretical value. After considering a number of heating and cooling schemes employing phase-change heat storage, we selected a forced hot air, central storage design, using CaCl2.6H2O encapsulated in plastic pipes. A home was designed, using a two-storey conservatory for solar collection with vertical glazing and movable insulation.

Phase change materials for energy storage nucleation to prevent supercooling

Abstract Phase change materials (PCMs) are useful for storing heat as the latent of fusion. Such storage has potential in heating and cooling buildings, waste heat recovery, off-peak power utilization, heat pump systems, and many other applications. Among the PCMs that have proven useful in heat storage applications are calcium chloride hexahydrate, CaCl2·6H2O, magnesium chloride hexahydrate, MgCl2·6H2O, and magnesium nitrate hexahydrate, Mg(NO3)2·6H2O. Many salt hydrate PCMs, including those listed above, have the disadvantage that during extraction of stored heat the material supercools before freezing. This reduces the utility of the material, and if too severe can completely prevent heat recovery. Many factors determine whether a particular additive will promote nucleation, for example, crystal structure, solubility, and hydrate stability. Candidate isomorphous and isotypic nucleating additives, with crystal structures that fit well with the PCM structure, were selected from tables of crystallographic data. Epitaxial nucleators, with less obvious lattice structure features that promote nucleation, were selected mostly by intuition. Effective nucleators were discovered by both methods. Based on laboratory test results, promising materials were developed into formalations based on CaCl2·6H2O, MgCl2·6H2O, Mg(NO3)2·6H2O, Mg(NO3)2·6H2OMgCl2·6H2O eutectic, and Mg(NO3)2·6H2ONH4NO3 eutectic salt hydrate PCMs. Subsequently, attempts were made to correlate crystal structure and hydrate stability with nucleating efficacy, and to speculate about active nucleating structures.