Multi-scale investigation of heat and momentum transfer in packed-bed TES systems up to 800 K
Résumé
With the rising cost of energy and the advancement of corporate social responsibility, there is a growing interest
in addressing the challenge of recovering and storing high-temperature waste heat. Sensible heat storage in
packed beds stands out as a cost-effective and seemingly straightforward solution for high-temperature Thermal
Energy Storage (TES). Engineering models developed to design low-temperature TES systems were tentatively
used to design this new generation of high-temperature systems. Delving into the physics of coupled heat
and mass transfer reveals a lack of validation of this approach. This study seeks to establish a comprehensive
bottom-up methodology - from the particle scale up to the system level - to provide informed and validated
engineering models for the design of high-temperature TES systems. To achieve this goal, we developed
a multi-scale numerical model to explore the physics of heat and momentum transfer in packed-bed TES
systems. At the microscopic scale (pore/particle), we consider the flow of a compressible high-temperature gas
between the particles, coupled to transient heat conduction within the particles, with particular attention given
to incorporating accurate temperature-dependent viscosity for the gas phase and thermal conductivity and
density for both solid and gas phases. At the macroscopic scale (engineering), we propose a high-temperature
extension of state-of-the-art two-equation TES models. The governing equations considered are the volume-
average conservation laws for gas-mass, gas-momentum and energy of both phases. The multi-scale strategy
is applied to a randomly packed bed of spherical particles generated with the discrete element method (DEM)
software LIGGGHTS. Numerical models for both scales were implemented in the Porous material Analysis
Toolbox based on OpenFoam (PATO), which is made available in Open Source by NASA. Microscopic scale
simulations were used to infer the effective parameters needed to inform the macroscopic model, namely,
permeability, Forchheimer coefficient, effective thermal conductivities, and the heat transfer coefficient. The
informed macroscopic model reproduces with excellent accuracy the average temperature fields of the physics-
based microscopic model. Pore-scale analysis shows highly three-dimensional flow characterized by reverse
flow and strong cross-flow in the packed bed system. Moreover, it indicates the coupling between temperature
and velocity fields, where a nonuniform velocity field results in uneven temperature distributions across
the fluid and the solid spheres within the packed bed, subsequently affecting the macroscopic heat transfer
coefficient. The overall strategy is validated by comparison to available experimental data. This bottom-up
methodology contributes to the understanding and opens new perspectives for a more precise design and
monitoring of high-temperature TES systems.
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licence : CC BY NC ND - Paternité - Pas d'utilisation commerciale - Pas de modification