The growing applications of heat transport in engineering and hydrogeology, including ground source heat pump systems and the assessment of water flow and sediment thermal properties, necessitate precise thermal dispersion modeling. Despite various factors like particle size, shape, and distribution impacting dispersion in porous media, a lack of experimental data and analysis has limited our grasp of the relationship between flow velocity and thermal dispersion. To address this gap, we conducted solute and heat tracer experiments using sands of different grain sizes, employing analytical models based on a universal power law relationship for dispersion. Additionally, we systematically compiled dispersion data from the scientific literature to assist in interpreting of the effects of particle size, shape, and pore-scale heterogeneity on dispersion. Our findings reveal that solute and thermal longitudinal dispersion align for high flow velocities in the dispersion-dominated flow regime ( > 5), where the velocity-dispersion relationship is linear. However, in the transition regime (advection approx. equal to diffusion, 0.1–0.3 < < 5), the observed deviation from linearity () is linked to increased pore-scale heterogeneity, particularly in smaller particle sizes. This study underscores the pivotal role of thermal dispersion and underscores the need for caution when estimating thermal dispersion based on solute dispersion, given the intricate nature of real-world conditions and the potential influence of factors such as grain size distribution and pore-scale heterogeneity in natural porous materials.

中文翻译：

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实验揭示了多孔介质热传输过程中颗粒和孔隙尺度的不均匀性对热分散的影响


热传输在工程和水文地质学中的应用不断增长，包括地源热泵系统以及水流和沉积物热特性的评估，需要精确的热扩散建模。尽管颗粒尺寸、形状和分布等多种因素影响多孔介质中的分散，但实验数据和分析的缺乏限制了我们对流速与热分散之间关系的掌握。为了解决这一差距，我们使用不同粒度的沙子进行了溶质和热示踪实验，并采用基于分散的通用幂律关系的分析模型。此外，我们系统地收集了科学文献中的分散数据，以帮助解释颗粒尺寸、形状和孔隙尺度不均匀性对分散的影响。我们的研究结果表明，溶质和热纵向色散在色散主导的流态 (> 5) 中与高流速一致，其中速度-色散关系是线性的。然而，在过渡状态（平流约等于扩散，0.1–0.3 < < 5）中，观察到的线性偏差 () 与孔隙尺度不均匀性增加有关，特别是在较小的粒径下。这项研究强调了热分散的关键作用，并强调在基于溶质分散估计热分散时需要谨慎，考虑到现实条件的复杂性以及颗粒尺寸分布和孔隙尺度不均匀性等因素的潜在影响。天然多孔材料。