Thermophysical characterization of a by-product from the non-metallic industry as inorganic PCM

Abstract

Physical characterization and thermal properties of bischofite, a by-product from the non-metallic industry, were determined and compared with those to MgCl2 6H2O with the idea of using it as phase change material in thermal energy storage applications. The melting point and heat of fusion were measured in the temperature range from 30 1C to 150 1C, where Tfus and ΔHfus were 100 1C and 115 kJ/kg for bischofite, and 114.5 1C and 135 kJ/kg for MgCl2 6H2O. The solid heat capacity was determined from 25 1C to 60 1C, being 2.1 kJ/(kg K) at 60 1C for both samples. The measurements of the liquid heat capacity of bischofite were done from 115 1C to 125 1C and the Cp showed linear increase from 1.71 kJ/(kg K) to 3.01 kJ/(kg K). The thermal stability test (30 heating/cooling cycles) of bischofite and MgCl2 6H2O shows subcooling of about 37 K and 29 K, respectively. The solid and liquid densities were determined using the pycnometrically method; for bischofite, ρsolid decrease from 1686 (at 30 1C) to 1513 kg/m3 (at 50 1C) and ρliq was 1481 kg/m3 (at 115 1C). Based on the thermophysical properties evaluated, the energy storage density was evaluated for both materials, being 170 J/cm3 for bischofite and 192 J/cm3 for MgCl2 6H2O. This study established that bishofite is a promissory PCM with similar thermophysical characteristics to magnesium chloride hydrate, but with a lower cost. Nevertheless, further work is needed to overcome the two main problems found, subcooling and segregation of the material.

The authors would like to acknowledge the collaboration of the company SALMAG. The authors acknowledge to FONDECYT (grant no 1120422), CONICYT/FONDAP no 15110019, and the Education Ministry of Chile Grant PMI ANT 1201 for the financial support. This work was partially funded by the Spanish project ENE2011-22722. Dr. Luisa F. Cabeza would like to acknowledge the Generalitat de Catalunya for the quality recognition 2014-SGR-123. Andrea Gutierrez would like to acknowledge to the Education Ministry of Chile her doctorate scholarship ANT 1106 and CONICYT/PAI no 7813110010