Abstract
In this study, a thermal energy storage tank filled with commercial phase change material flat slabs is investigated. The tank provides heat at around 15 °C to the evaporator of a seasonal thermal energy storage system developed under the EU-funded project SWS-Heating. A 2D numerical model of the phase changed material storage tank based on the finite control volume approach was developed and validated with experimental data. Based on the validated model, an optimization was performed to identify the number, type and configuration of slabs. The final goal of the phase change material tank model is to be implemented into the whole generic heating system model. A trade-off between results’ accuracy and computational time of the phase change material model is needed. Therefore, a comparison between a 2D implicit and 2D explicit scheme of the model was performed. The results showed that using an explicit scheme instead of an implicit scheme with a reasonable number of nodes (15 to 25) in the heat transfer fluid direction allowed a considerable decrease in the computational time (7 times for the best case) with only a slight reduction in the accuracy in terms on mean average percentage error (0.44%).
Highlights
Thermal energy storage (TES) allows the supply of thermal demand to be independent of the heat source, especially when the heat source is discontinuous, such as solar energy
The presented model can be used to analyze the thermal performance of phase change materials (PCM) storage units with flat slabs, since it showed good accuracy
The PCM tank presented in this study was intended to provide heat to the evaporator of a seasonal sorption TES system based on selective water-sorbent materials
Summary
Thermal energy storage (TES) allows the supply of thermal demand to be independent of the heat source, especially when the heat source is discontinuous, such as solar energy. The use of PCM as storage material is usually complicated due to certain limitations, such as low thermal conductivity, subcooling, phase segregation, non-uniform distribution of the PCM inside the slabs or capsules, or the non-uniform composition of the PCM Some of these effects are very difficult to be considered in a theoretical model, a numerical simulation model can be very useful to analyze its performance before designing or experimentally testing a PCM storage unit, especially when it is coupled to another system. The model was based on the finite differences method, solved using an implicit scheme, and considering two dimensions for the PCM nodes and one dimension for the heat transfer fluid (HTF) and wall nodes They identified the following input variables that had more influence on the deviation of the results: HTF inlet temperature profile and some PCM properties, such as melting temperature, density, and specific heat capacity
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