## Materials and Methods
### Numerical Simulation  
The functioning of the cyclone bag filter was investigated through CFD simulation at optimal operating conditions, i.e., with clean sleeves, and at increasing clogging levels. The aim of these simulations was to evaluate the impact of the clogging on the system's functioning. The first quantity evaluated was the pressure drop. However, this information by itself is not exhaustive, as a variation in the pressure drop could be caused by several issues that could not be related to clogging, such as a variation in flow rate, the presence of broken sleeves, or a combination of both aspects. To this end, the simulations performed were exploited to determine if, and how, the gradual increase in the clogging level of the filtering sleeves would impact other physical quantities that could be measured by installing additional sensors on the device. Firstly, to perform the simulations, a 3D model of the cyclone bag filter was developed with Ansys SpaceClaim [47]. The real dimensions of the filter were reproduced, and all 31 sleeves were modeled inside the device. The thickness of the sleeve walls was not directly reproduced as a separate volume in the geometry, as it would result in a dramatic increase in the computational weight of the simulation. Instead, the physical presence of the filtering medium was accounted for in the simulation settings. The geometrical features of the system are reported in Table 1. \begin{table}
\begin{tabular}{c c c} \hline
**Dimension** & **Value** & **Units** \\ \hline Separator height & 5308 & mm \\ Separator diameter & 1300 & mm \\ Conical bottom height & 1550 & mm \\ Sleeves length & 3000 & mm \\ Sleeves diameter & 123 & mm \\ \hline \end{tabular}
\end{table} 
Table 1: Main dimensions of the system. According to the manufacturers and the end-users of these filters, as well as the results of previously performed simulations validated in [45], the clogging tends not to be uniform along the sleeve length. To this end, a division into three sectors was introduced, resulting in top, middle, and bottom sectors being defined for each of the 31 sleeves. The geometry generated is presented in Figure 3.  
The domain was then discretized in a finite number of volumes with Ansys Meshing [48], generating a tetrahedral mesh, appropriately refined to accurately reproduce the airflow even in the narrowest gaps between the sleeves. To decrease the number of volumes, and thus the computational time, the conversion of the tetrahedral mesh volumes to polyhedra was performed. This operation resulted also in an increase in both the mesh quality and the convergence properties [49; 50]. Finally, Ansys Fluent [51; 52] was used to simulate the functioning of the filter by solving the flow field and turbulence equations at each volume node. The fabric filtering sleeves were reproduced with the \"porous jump\" model, a 1D simplification that allows for the calculation of the pressure drop introduced by a porous medium without having to directly model the momentum field inside it. To this end, the thickness of the sleeves and their permeability had to be specified. A number of iterations sufficient to guarantee the convergence and the stability of the solutions were performed for each simulation. The settings and the boundary conditions considered are summarized in Table 2.