Speaker
Description
Thermal energy storage (TES) in packed beds is a promising approach for improving the efficiency and flexibility of energy systems. Its performance strongly depends on local heat transfer between gas and solid phases. A pore-scale numerical framework is developed to determine the volumetric heat transfer coefficient (hv) in randomly packed beds and to quantify the effects of gravity and flow orientation on interphase heat exchange under temperature-dependent properties. Realistic beds of uniform spheres are generated via DEM, and conjugate, transient simulations are performed in OpenFOAM with body-fitted meshes. Four representative cases are examined: downward (flow parallel to gravity), upward (flow opposite to gravity), transverse (flow perpendicular to gravity), and zero-gravity, reflecting the relative flow–gravity orientations encountered during charging and discharging. Results show that gravity shapes the vertical stratification of temperature and the local flow topology, thereby modulating hv. At high Reynolds number (505.3), hv increases in time and differs by less than 5% between with-gravity and no-gravity cases (e.g., 9800 to 13700 vs. 10200 to 14300 W m^{-3} K^{-1}). At low Reynolds number (101.0), buoyancy becomes influential: the downward (aiding) case tends to enhance hv, the upward (opposing) one reduces and stabilizes it, and transverse flow exhibits intermediate behavior; the no-gravity case yields the lowest and nearly invariant hv (e.g., 4400 W m^{-3} K^{-1}). Besides, across 300–800 K, gas thermal conductivity and density vary by about a factor of two, underscoring the need for variable-property modeling. The study delineates conditions where classical correlations remain adequate and where orientation and buoyancy must be retained for reliable hv closure.
| Country | China |
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