CFD modeling of ice formation and melting in horizontally cooled and heated plates

Abstract

This paper investigates the ice formation and melting processes in a novel CTES unit using the commercial CFD software ANSYS Fluent 19. The storage unit is designed to operate as a peak shaving device integrated into the R744 circuit of a R717/R744 cascade refrigeration system in a food-processing plant. The CTES unit consists of a stack of pillow plates heat exchanger (PPHEX) immersed in a steel tank filled with water as the phase change material (PCM) for ice storage. A PP-HEX consists of two spot-welded and inflated steel plates creating a path for the CO2 to circulate and exchange heat with the PCM. The refrigerant evaporates and condenses within the plates during the cold charging and discharging processes, respectively. In order to investigate the characteristics of this novel CTES unit, a 2D CFD model was created in ANSYS Fluent. The main CFD parameters affecting both charging and discharging times were identified. The effect of the mushy zone constant (Amush) and the phase change temperature range (ΔTpc) on the results were investigated. The results show that increasing the Amush and ΔTpc both increased the charging time of the unit. Changing Amush had the most significant effect on charging time (35% increase), while the effect of ΔTpc was less important (6.5% increase). The results from the melting cycle showed that Amush has a considerable effect on the melting time of the system. Higher values of Amush increased the time for melting significantly (70 to 165 min), whereas the melting process was accelerated by increasing ΔTpc from 0.5 K to 1.0 K. The CTES storage capacity was about 108 kWh after 10 hours of charging, while 51 % could be reached after only 1 hour of charging.