Abstract
Interest in low-temperature refrigeration (at temperatures below -50 °C) has grown in recent years,
especially due to the COVID-19 pandemic. Consequently, this high demand is exerting stress on the electrical
grid. Generally, latent heat storage in phase change materials (PCMs) can be used to relieve the stress.
Nevertheless, there is a shortage of suitable/reliable PCMs for such temperatures. Due to its desirable
properties, carbon dioxide has the potential to be used as the PCM for temperatures around -55 °C. To this
end, the heat exchanger should withstand high pressures. Pillow plate heat exchangers (PPHXs) meet this
criterion and have recently gained research attention. Therefore, in this study, the solid-liquid transition of
carbon dioxide in PPHXs was numerically studied to analyse the impact of storage orientation as well as plate
distance. The commercial software ANSYS Fluent was used for simulating a periodic segment of the storage.
It was found that the orientation did not have a meaningful impact on the solidification, whereas higher plate
distance caused a weak natural convection. According to the results, to achieve a more uniform solidification,
it is recommended that the neighbouring plates have an offset of half pitch distance in both transversal and
longitudinal directions. The results of this study lay the foundation for further progress in this field especially
for developing an experimental prototype followed by real life implementation of the system.
Keywords: Phase Change Material, Carbon Dioxide, Pillow Plate Heat Exchanger, Numerical Simulation
especially due to the COVID-19 pandemic. Consequently, this high demand is exerting stress on the electrical
grid. Generally, latent heat storage in phase change materials (PCMs) can be used to relieve the stress.
Nevertheless, there is a shortage of suitable/reliable PCMs for such temperatures. Due to its desirable
properties, carbon dioxide has the potential to be used as the PCM for temperatures around -55 °C. To this
end, the heat exchanger should withstand high pressures. Pillow plate heat exchangers (PPHXs) meet this
criterion and have recently gained research attention. Therefore, in this study, the solid-liquid transition of
carbon dioxide in PPHXs was numerically studied to analyse the impact of storage orientation as well as plate
distance. The commercial software ANSYS Fluent was used for simulating a periodic segment of the storage.
It was found that the orientation did not have a meaningful impact on the solidification, whereas higher plate
distance caused a weak natural convection. According to the results, to achieve a more uniform solidification,
it is recommended that the neighbouring plates have an offset of half pitch distance in both transversal and
longitudinal directions. The results of this study lay the foundation for further progress in this field especially
for developing an experimental prototype followed by real life implementation of the system.
Keywords: Phase Change Material, Carbon Dioxide, Pillow Plate Heat Exchanger, Numerical Simulation
