EVALUATION OF THE LIMITING CONDITIONS OF THE LOCAL THERMAL EQUILIBRIUM ANALYSIS OF CONVECTIVE HEAT TRANSFER IN POROUS MEDIA

Despite its widespread use, there are no universally established guidelines for determining when the local thermal equilibrium (LTE) assumption is applicable, leading to inconsistencies in porous media heat transfer modeling. To address this gap, this study conducted a comprehensive numerical analysis using critical parameters such as the flow rate, permeability, and thermal diffusivity ratio of hydrodynamic and thermal characteristics. Using the Darcy-Forchheimer-Brinkman model, simulations were conducted for a wide range of Reynolds numbers (1 to 1000), Darcy numbers (10<sup>-6</sup> to 10<sup>0</sup>), and thermal diffusivity ratios (10<sup>-3</sup> to 10<sup>3</sup>) to assess thermal behavior with both the LTNE and LTE approaches. The results indicated that, at low Reynolds numbers (Re ≤ 10), significant temperature differences existed between the solid and fluid phases, implying a dominant LTNE regime. However, as the Reynolds number increased beyond Re ≈ 100, enhanced convective effects facilitated better thermal coupling, validating the LTE assumption. The Darcy number significantly influenced thermal dispersion, with low Da (≤ 10<sup>-6</sup>) enhancing mixing and promoting LTE while high Da (≥ 10<sup>0</sup>) restricted thermal interaction due to boundary layer formation. The impact of the thermal diffusivity ratio was most pronounced at low Re, where a high value (≥ 10<sup>3</sup>) led to significant thermal disequilibrium due to the solid's high conduction capability relative to the fluid. However, at high Re (≥ 1000), convection dominated, making LTE applicable across a wide range of TDR values. By systematically mapping the LTE-LTNE transition across a broad parametric space, this study provides a novel framework for assessing the applicability of the LTE assumption.