Abstract

The use of Phase Change Materials (PCMs) in the evaporator of conventional refrigerators/freezers has demonstrated multiple benefits in energy efficiency and food preservation quality in the last decades. However, their implementation in convective freezers, with inlet/outlet airflows, has not been analyzed using accurate solid-fluid numerical models under different scenarios and processes. In this work, we study the effect that PCMs have on the energy and thermal performance of a domestic convective freezer-cabinet and a salmon-fillet at its center through numerical simulations. The influence of two different PCM-plates internally attached to the freezer walls, 19.5 wt% NH4CL (PCM-1) and PlusIce E-10 (PCM-2), on the food's heat transfer and the energy efficiency is investigated under different scenarios during the charging, discharging, and normal operation processes. A conjugated solid-fluid model describes the convective, diffusive, and radiative heat transfer in the air and the solid elements; incorporating the k-omega SST turbulent model, the net radiative method, and the specific heat and liquid fraction phase change models. The set of equations is solved by the Finite Volume Method in an in-house code. The results indicate that the energy efficiency improved by 11.4 % with PCM-2 and by 6.2 % with PCM-1 during the normal operation process, in relation to the scenarios without PCM; the PCM-2 performed better due to its lower temperature range of phase change, which allowed to take full advantage of latent heat. In the scenario without food, the PCM-2 demonstrated to mitigate the reduction of energy efficiency from 11.5 % to 4.5 % by the addition of the thermal load. Furthermore, by increasing the inlet airflow velocity from 0.05 ms-1 to 1.2 ms-1, the energy efficiency increased by 8.2 %, but the food and PCM-plates fluctuated in a lower temperature range.