A CFD analysis for the performance assessment of a novel design of plates-in-tank latent storage unit for freezing applications

Abstract

In this paper, the charging and discharging processes of a recently developed cold thermal energy storage (CTES) unit integrated into a poultry processing plant is investigated. A mathematical model of the CTES was created based on the two-dimensional transient Navier-Stokes equations using the ANSYS Fluent commercial software package. Thermal storage is commonly designed either for full storage (to meet the entire needs during peak hours) or for partial storage (to meet a fraction of the needs when there is a time shift between the energy supply and demand). In this study, the storage unit is designed to operate in a full storage operational mode integrated in the R744 circuit of a R717/R744 cascade refrigeration system. The CTES unit consists of a stack of heat exchanger (HEX) plates immersed in a steel tank filled with a phase change material (PCM). The selection of the appropriate PCM is based on the operational temperature range required in the system. Water is chosen as the PCM for this study. It is characterised by a high energy storage density and well-defined thermal properties. The HEX plates are called pillow plates (PP-HEX), and consists of two spot-welded and inflated steel plates that allows the CO2 to circulate in a specific pattern and enhance the heat transfer. The CO2 circulates within the plates to freeze and melt the PCM during the charging and discharging processes, respectively. The pressure-based model was selected to model the phase change based on the enthalpy-porosity formulation. This study aims to evaluate the relevance of detailed modelling of the PP-HEX structure compared to flat walls for the melting/solidification process. Results show that the flat wall model have comparable melting/solidification time and heat transfer rate to the PP-HEX geometry.