Effect of Biot number on the thermocline evolution of a packed bed TES system Articles uri icon

publication date

  • February 2025

start page

  • 1

end page

  • 12

volume

  • 110

International Standard Serial Number (ISSN)

  • 2352-152X

Electronic International Standard Serial Number (EISSN)

  • 2352-1538

abstract

  • Thermal Energy Storage systems are becoming of paramount importance in the context of an efficient and sustainable energy use utilization. These systems are particularly attractive for Concentrated Solar Power plants where the energy surplus is stored as heat and dispatched when solar radiation is insufficient to drive the power block. Among the different storage alternatives, sensible heat storage in granular media is widely used but strongly affected by the behaviour of the thermocline, which directly depends on the particle Biot number. The effect of the Biot number on the thermocline performance of a packed bed Thermal Energy Storage system of sensible heat based on granular material is analysed through particle resolved simulations and an analytical model of a bed of particles. The models used for analysing this kind of systems usually neglect intraparticle conduction. This simplifies the solution of the numerical models and it is a reasonable assumption provided a small enough Biot number. Nonetheless, certain combinations of particle properties and operating conditions might promote non-negligible intraparticle conduction (viz. a sufficiently high Biot number) being required to be considered. Particle Resolved Simulations are required to analyse the coupled problem of the fluid percolating through the particle voids and the heat transfer both inside the particles and from its surface to the fluid. The main novelty of the work is the coupled analysis using two different modelling approaches of packed bed Thermal Energy Storage systems and, more particularly, the successful modelling of the Particle Resolved Simulations. The results indicate a great variation of the thermocline thickness when the Biot number changes, penalizing its performance when the thickness grows. This increase is observed not only when the Biot number augments but also when the Biot number approaches 0, showing an optimum behaviour in a range of Biot numbers, roughly, from 0.1 to 1.5.

subjects

  • Chemistry
  • Renewable Energies