Legitimacy of the local thermal equilibrium hypothesis in porous media: A comprehensive review

Local thermal equilibrium (LTE) is a frequently-employed hypothesis when analysing convection heat transfer in porous media. However, investigation of the non-equilibrium phenomenon exhibits that such hypothesis is typically not true for many circumstances such as rapid cooling or heating, and in industrial applications involving immediate transient thermal response, leading to a lack of local thermal equilibrium (LTE). Therefore, for the sake of appropriately conduct the technological process, it has become necessary to examine the validity of the LTE assumption before deciding which energy model should be used. Indeed, the legitimacy of the LTE hypothesis has been widely investigated in different applications and different modes of heat transfer, and many criteria have been developed. This paper summarises the studies that investigated this hypothesis in forced, free, and mixed convection, and presents the appropriate circumstances that can make the LTE hypothesis to be valid. For example, in forced convection, the literature shows that this hypothesis is valid for lower Darcy number, lower Reynolds number, lower Prandtl number, and/or lower solid phase thermal conductivity; however, it becomes invalid for higher effective fluid thermal conductivity and/or lower interstitial heat transfer coefficient.</p

Towards a benchmark velocity database of a Generic Cycling Mannequin

Engineering of Sport 15 - Proceedings from the 15th International Conference on the Engineering of Sport (ISEA 2024) Over the last decade, considerable effort has gone into understanding the flow around a cyclist to reduce the aerodynamic drag and, in turn, increase the rider’s speed. Recent studies typically use cyclist geometries obtained through scanning actual riders resulting in highly realistic cyclist models for numerical simulations and wind-tunnel experiments. Despite the relevance of the results, the model geometries are personal anthropometric data and, so, cannot be published. This hampers direct comparison of results and the ability to build upon the research of others. Similar to generic vehicle models, e.g., the DrivAer, that are used in the automotive aerodynamic community, a commonly used cyclist model has the potential to advance the general understanding of cycling aerodynamics. We aim to introduce open-source, realistic generic cyclist models (GCM) including a benchmark dataset of the surrounding flow. The goal of this work is to investigate the similarities and differences in the aerodynamic loads acting on the time-trial (TT) GCM and in the large-scale wake structures obtained from experiments in two different wind tunnels, using different flow measurement techniques. </p