Alternating Current Electroosmotic Flow of Maxwell Fluid in a Parallel Plate Microchannel with Sinusoidal Roughness

The EOF of a viscoelastic Maxwell fluid driven by an alternating pressure gradient and electric field in a parallel plate microchannel with sinusoidal roughness has been investigated within the Debye-Hückel approximation based on boundary perturbation expansion and separation of variables. Perturbation solutions were obtained for the potential distribution, the velocity and the mean velocity, and the relation between the mean velocity and the roughness. There are significant differences in the velocity amplitudes of the Newtonian and Maxwell fluids. It is shown here that the velocity distribution of the viscoelastic fluid is significantly affected by the roughness of the walls, which leads to the appearance of fluctuations in the fluid. Also, the velocity is strongly dependent on the phase difference θ of the roughness of the upper and lower plates. As the oscillation Reynolds number ReΩ increases, the velocity profile and the average velocity um(t) of AC EOF oscillate rapidly but the velocity amplitude decreases. The Deborah number De plays a similar role to ReΩ, which makes the AC EOF velocity profile more likely to oscillate. Meanwhile, phase lag χ (representing the phase difference between the electric field and the mean velocity) decreases when G and θ are increased. However, for larger λ (e.g., λ > 3), it almost has no phase lag χ.

Effects of Surface Smoothness on Inertial Particle Deposition in Human Nasal Models

Computational fluid dynamics (CFD) predictions of inertial particle deposition have not compared well with data from nasal replicas due to effects of surface texture and the resolution of tomographic images. To study effects of geometric differences between CFD models and nasal replicas, nasal CFD models with different levels of surface smoothness were reconstructed from the same MRI data used to construct the nasal replica used by Kelly et al. (2004) [Aerosol Sci. Technol. 38:1063-1071]. One CFD model in particular was reconstructed without any surface smoothing to preserve the detailed topology present in the nasal replica. Steady-state inspiratory airflow and Lagrangian particle tracking were simulated using Fluent software. Particle deposition estimates from the smoother models under-predicted nasal deposition from replica casts, which was consistent with previous findings. These discrepancies were overcome by including surface artifacts that were not present in the reduced models and by plotting deposition efficiency versus the Stokes number, where the characteristic diameter was defined in terms of the pressure-flow relationship to account for changes in airflow resistance due to wall roughness. These results indicate that even slight geometric differences have significant effects on nasal deposition and that this information should be taken into account when comparing particle deposition data from CFD models with experimental data from nasal replica casts.