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

Abstract

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 on laboratory measurements. The main goal of the study was to determine the direct light transmittance versus 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 RT21HC as a PCM. The unit was installed in a special holder and exposed to the radiation from an artificial sun. The vertical illuminance was measured by luxmeters and compared with a reference case to determine the direct light transmittance. The transmittance was determined for the whole period of measurements when some specific artefacts were identified and theoretically explained based on values of refractive indexes for paraffins in the solid and liquid state, and for a glass. The melting process of a PCM in a glass unit was identified as a complex one, with interreflections and refraction of light on semi layers characterized by a different physical states (solid, liquid or mushy). These optical phenomena caused nonuniformity in light transmittance, especially when the PCM is in a mushy state. It was revealed that light transmittance versus temperature cannot be treated as a linear function.

Heat Transfer with Phase Change in a Multilayer Construction: Simulation versus Experiment

“…One of the specific examples of PCM containers is PCM-glazing [32,33], which is characterized by transparent or semi-transparent (translucent) properties. The optical characteristics [34,35], as well as the dynamics of the melting process [36,37], have been investigated in the past. Studies have confirmed that the PCM transmittance changes significantly due to the change of phase.…”

“…Moreover, the thermal processes during the change of phase have been defined in a simplified way when the PCM layer is treated as a body of uniform. Heim et al [36] made an experiment for a triple glazed PCM window irradiated by an artificial sun. It was confirmed that the transmittance of PCM does not change linearly and the melting process in a PCM cavity is more complex, with regions of solid, mushy and melted layers.…”

Assessment of the Effect of Phase Change Material (PCM) Glazing on the Energy Consumption and Indoor Comfort of an Office in a Semiarid Climate

“…Liu, et al [9] studied the impact of the refractive index and extinction coefficients for a glazed roof filled with PCM in liquid and solid states. Heim, et al [10] determined the direct light transmittance of a triple glazed unit with one cavity filled with PCM under constant solar radiation intensity and stable air temperature. They found that the interreflections inside the PCM glazing during the phase change cause nonuniformity in the light transmission.…”