Modeling and improvement of a packed bed latent heat storage filled with non-spherical encapsulated PCM-Elements

A thermal energy storage filled with a packed bed of macro-encapsulated latent heat storage elements is studied. Such a storage can be used in combination with, for example, a solar thermal heating system. Conventional capsule designs based on spherical shape do not allow for optimal packing density and heat transfer within the capsule. Therefore, capsule designs were introduced, which deviate from this basic geometry. These designs are built upon a super-ellipsoidal shape with multiple surface extensions, e.g. holes and grooves, in order to enhance heat transfer. To further optimize the thermal performance of the storage system, a model describing the charging and discharging processes of the heat storage was developed based on a new approach for the treatment of non-spherical capsules. The model was validated against experimental temperature data obtained from charging and discharging measurements with flow rates ranging from 216 to 1000 kg/h. The maximal observed deviation between simulation and experiment was +/- 0.82 K. Furthermore, new capsule geometries based on super-ellipsoids were evaluated with respect to their storage capacity and thermal power output. A promising capsule design was identified which has a more than 20% higher storage capacity than the other shapes and provides a reasonable thermal power output of approximately 4 kW during the phase change of the storage material. The energy density was increased from 51.5 kWh/m(3) to 64.1 kWh/m(3). (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

A study on a thermal energy storage system filled with macro-encapsulated latent heat storage elements was conducted. The introduction of capsule designs based on super-ellipsoidal shapes improved heat transfer efficiency. A new model was developed to describe the charging and discharging processes, allowing for accurate prediction of temperature changes and system performance.