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Notes:
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In general, PCM are classified in organic and inorganic groups or families. First group mainly encloses paraffin,
fatty acids, and sugar alcohols. Inorganic are mostly represented by salt hydrates, salt solutions, and metals.
Eutectics and mixtures are also being formulated to obtain a desired phase change temperature. One of the most
important PCM requirements is being stable after a number of repeated melting/freezing cycles, which is known
as cycling stability. A PCM should present the same or almost the same thermal, chemical and physical properties
after a repeated number of freezing and melting cycles. Thermal cycling tests results and detailed tests
procedures are classified by PCM type in this review. Moreover, the parameters that must be considered in order
to perform cycling stability tests are highlighted depending on the importance they have on the following four
issues: the choice of the equipment to perform the cycling tests; the selection of the techniques to characterize
the PCM before and after thermal cycling test and to follow the PCM thermal degradation; the definition of the
number of cycles to perform; and finally, the choice of the heating rate and thermal cycling method (pyramid, or
dynamic, or others) to perform the tests. It is mandatory to conclude that, based on the literature reviewed, no
common standard for thermal cycling stability tests is available at the moment.
The research leading to these results has received funding from the European Commission Seventh Framework Programme (FP/ 2007-2013) under grant agreement No. PIRSES-GA-2013-610692 (INNOSTORAGE). Furthermore, the work is partially funded by the Spanish government (ENE2011-28269-C03-02 and ENE2011- 22722). The authors would like to thank the Catalan Government for the quality accreditation given to their research groups GREA (2014 SGR 123) and DIOPMA (2014 SGR 1543). Aran Solé would like to thank the Departament d'Universitats, Recerca i Societat de la Informació de la Generalitat de Catalunya for her research fellowship. |
