###### Abstract  
Aeration is a key post-harvest grain processing operation that forces air through the pore volume of the grain bulk to establish favorable conditions to maintain grain quality and improve its storability. However, during storage, grain bulk experiences self-compaction due to its dead weight, which alters the bulk properties and impedes the uniform flow of air during aeration. Thus, this study focused on investigating the effect of self-compaction on the pressure drop \(\Delta P\) of wheat bulk (_Triticum aestivum_ L., cv. 'Pionier', \(X\) = 0.123 kg\(\cdot\)kg\({}^{-1}\) d.b.) accommodated in a laboratory-scale bin (\(V_{b}\) = 0.62 m\({}^{3}\)) at a coherent set of airflow velocities \(v_{a}\). Pressure drop \(\Delta P\) was measured at bulk depths \(H_{b}\) of 1.0, 2.0, 3.0 and 3.4 m and storage times \(t\) of 1, 65, 164 and 236 h. For the semi-empirical characterization of the relationship between \(\Delta P\) and \(v_{a}\), the model of [PERSON] was used, which was proficient in describing the experimental data with decent accuracy (\(R^{2}\) = 0.990, \(RMSE\) = 68.67 Pa, \(MAPE\) = 12.50%). A tailored product factor \(k\) was employed for the specific grain bulk conditions. Results revealed a reduction of in-situ pore volume \(\varepsilon\) from 0.413 to 0.391 at bulk depths \(H_{b}\) of 1.0 to 3.4 m after 1 h storage time \(t\) and from 0.391 to 0.370 after 236 h storage time \(t\), respectively. A disproportional increase of the pressure drop \(\Delta P\) with bulk depth \(H_{b}\) and storage time \(t\) was observed, which was ascribed to the irreversible spatio-temporal behavior of self-compaction. The variation of pore volume \(\varepsilon\) was modeled and facilitated the development of a generalized model for predicting the relationship between \(\Delta P\) and \(v_{a}\). The relative importance of modeling parameters was evaluated by a sensitivity analysis. In conclusion, self-compaction has proven to have a significant effect on airflow resistance, therefore it should be considered in the analysis and modeling of cooling, aeration and low-temperature drying of in-store grain bulks. a 2022 202 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 202 2  
reduces the bulk temperature to a safe storage level to prevent insect and mite infestation, spontaneous heating and off-odors [7]. In addition, it inhibits the development of microflora by reducing the excess moisture and intergranular air humidity in isolated grain dump nests. Intergranular air humidity refers to the relative amount of water available in the air at a particular temperature described by sorption isotherms [8]. At sufficiently high levels (above 60%), the development of bacteria, fungi and yeasts is promoted, leading to the formation of toxins that are detrimental to humans [9; 10]. Hence, ensuring adequate aeration throughout the grain bulk can be an important preservative measure to effectively control harmful substances. During aeration, as the air flows through the pore volume of the grain bulk, it loses its kinetic energy due to intergranular friction and turbulence, resulting in airflow resistance known as pressure drop [11]. The grain species and cultivars, as well as their properties such as moisture content, physical and mechanical properties, surface roughness, bulk depth, pore volume configuration and extraneous impurity quantity, have a significant impact on the aeration process and uniformity of the airflow throughout the grain bulk [12; 13; 14]. They also influence the intergranular air pathways and associated inter-speed currents as well as the exchange of temperature and moisture in bulk [15]. Therefore, assessing the prevailing airflow resistance in grain bulks is essential for the energy-efficient design of ventilation systems, aeration management and grain quality retention [16]. Physical experiments are commonly used to assess the airflow resistance of grain bulks and serve as important means for the development of mathematical models.