This thesis aims to investigate the thermal performance of a refrigerator equipped with a functional duct unit (FDU). The FDU designed and implemented as part of this study is a cold air duct bridging between freezer and fridge compartments just like an EPS (Expandable Polystyrene) duct unit installed in a conventional refrigerator. At the same time, it is a specially designed vessel which can contain PCM as an auxiliary thermal source. Therefore, thermal performance improvements in the refrigerator equipped with the FDU (relative to one with the EPS duct unit) are largely dependent upon thermal properties of PCM. From this standpoint, the thermal properties of PCM was first investigated to systematically justify the thermal functionality of the FDU.
PCMs were manufactured by diluting eutectic salt compounds with water. A thickener, super absorbent polymer (SAP) was also added to prevent the phase separation and supercooling of PCM that commonly takes place during phase change. The concentration of eutectic salt compounds was adjusted to range from 1 wt% to 5 wt%. The thermal properties of PCM were experimentally measured using differential scanning calorimetry (DSC) and T-history method. Measurements of thermal properties of PCM includes latent heat, specific heat, phase change temperature, supercooling temperature, and cold holding time. The most suitable PCM for the FDU was found to be eutectic salt compounds of 1 wt%.
The FDU charged with the selected PCM (1 wt%) was then installed in the 200L top mount freezer. To qualitatively investigate the thermal performance of the FDU implemented, temperature distributions inside the refrigerator equipped with the FDU were measured and compared to those measured in the refrigerator solely with the EPS duct unit. The experimental results clearly indicate that temperature deviations measured in the refrigerator were much smaller when replacing the EPS duct with the FDU. Moreover, it was found that the FDU prevents the temperature inside the refrigerator from rising rapidly during black out.