This paper presents a comprehensive computational model capable of simulating fouling layer thickness evolution using dynamic mesh model. This computational methodology has been developed to reproduce the deposit generation during fouling process with an innovated work method. Dynamic mesh model, from Ansys Fluent software, and external routines have been used to implement this advanced numerical model which allows to move the boundaries of a region relative to other boundaries of the zone. The displacement of the nodes of the mesh is the mechanism that this model uses to adjust the geometry according to the fouling layer evolution. During the simulation process, the geometry under investigation is modified to reproduce the emergence and gradual change of the fouling layer. Different rules of deposition and removal of the fouling process can be implemented in the proposed algorithm. The direct interaction between fouling expressions and governing equations of the main flow is used to predict deposits formation and growth. In this paper, numerical simulations of soot fouling layer formation have been presented. Deposits evolution has been calculated inside different heat exchanger technologies used in exhaust gas recirculation systems to analyse fouling process and to verify the advantages of this new computational strategy.

In this study, a cough cycle is reproduced using a computational methodology. The Eulerian wall film approach is proposed to simulate airway mucus flow during a cough. The reproduced airway domain is based on realistic geometry from the literature and captures the deformation of flexible tissue. To quantify the overall performance of this complex phenomenon, cough efficiency (CE) was calculated, which provided an easily reproducible measurement parameter for the cough clearance process. Moreover, the effect of mucus layer thickness was examined. The relationship between the CE and the mucus viscosity was quantified using reductions from 20 to 80%. Finally, predictions of CE values based on healthy person inputs were compared with values obtained from patients with different respiratory diseases, including chronic obstructive pulmonary disease (COPD) and respiratory muscle weakness (RMW). It was observed that CE was reduced by 50% in patients with COPD compared with that of a healthy person. On average, CE was reduced in patients with RMW to 10% of the average value of a healthy person.

The clearance of mucus through coughing is a complex, multiphase process, which is affected principally by mucus viscosity and airflow velocity; however, it is also critically affected by the thickness of the two layers of mucus—the serous and gel layers—and oscillation level. The present study examines the effects of the latter parameters more closely. To do so, the mucus clearance process is simulated with a transient 3D volume of fluid (VOF) multiphase model in ANSYS Fluent. The model includes mucus’ bilayer properties and a wide range of boundary conditions were tested. The model was analysed in both a straight tube and a realistic trachea. Ultimately, the model was able to both capture air-mucus interface wave evolution and predict the overall behaviour of the clearance process. The results were consistent with experimental clearance data and numerical airflow simulations, which indicates our methodology is appropriate for future studies. Ultimately, the mere presence of the serous layer was found to increase mucus clearance by more than 15 percent. An oscillating flow enhanced clearance by up to 5 percent. Interestingly, interface wave steepness was found to be inversely correlated with mucus thickness, but directly with mucus velocity, which suggests it will be an interesting parameter for further study.

In this study, we have reproduced the cough clearance process with an Eulerian wall film model. The simulated domain is based on realistic geometry from the literature, which has been improved by adding the glottis and epiglottis. The vocal fold movement has been included due to the dynamic mesh method, considering different abduction and adduction angles and velocities. The proposed methodology captures the deformation of the flexible tissue, considers non-Newtonian properties for the mucus, and enables us to reproduce a single cough or a cough epoch. The cough efficiency (CE) has been used to quantify the overall performance of the cough, considering many different boundary conditions, for the analysis of the glottis effect. It was observed that a viscous shear force is the main mechanism in the cough clearance process, while the glottis closure time and the epiglottis position do not have a significant effect on the CE. The cough assistance devices improve the CE, and the enhancement rate grows logarithmically with the operating pressure. The cough can achieve an effective mucus clearance process, even with a fixed glottis. Nevertheless, the glottis closure substantially improves the CE results.