Dynamics of Melting Process in Phase Change Material Windows Determined Based on Direct Light Transmission

DELLICOMPAGNI, PABLO ROBERTO; FRANCO, JUDITH; HEIM, DARIUSZ; KNERA, DOMINIKA; KREMPSKI-SMEJDA, MICHA?; WIEPRZKOWICZ, ANNA

Energies

MDPI

Lugar: Basel; Año: 2021 vol. 14 p. 1 - 13

Detailed analyses of melting processes in phase change material (PCM) glazing units,changes of direct transmittance as well as investigation of refraction index were provided based onlaboratory measurements. The main goal of the study was to determine the direct light transmittanceversus time under constant solar radiation intensity and stable temperature of the surrounding air.The experiment was conducted on a triple glazed unit with one cavity filled with a paraffin RT21HCas a PCM. The unit was installed in a special holder and exposed to the radiation from an artificialsun. The vertical illuminance was measured by luxmeters and compared with a reference case todetermine the direct light transmittance. The transmittance was determined for the whole period ofmeasurements when some specific artefacts were identified and theoretically explained based onvalues of refractive indexes for paraffins in the solid and liquid state, and for a glass. The meltingprocess of a PCM in a glass unit was identified as a complex one, with interreflections and refractionof light on semi layers characterized by a different physical states (solid, liquid or mushy). Theseoptical phenomena caused nonuniformity in light transmittance, especially when the PCM is ina mushy state. It was revealed that light transmittance versus temperature cannot be treated as alinear function.