CFD simulation of aerosol flow and hydrocarbon fouling on a circular disk

Coking is one of the key technologies used in upgrading of oil sands bitumen. In coking units, the bitumen is thermally cracked in the presence of steam to produce valuable lighter species and by-product solid coke. Hot vapours which contain these valuable species from the fluid coker pass through cyclones before entering the scrubber section of the coker, so that coke and heavy droplets are removed. However, some micron-sized heavy hydrocarbon droplets are not removed in the cyclones and enter the scrubber grid packing. These droplets can deposit on the scrubber grid and react over time to form coke as a result of high temperatures. A model is developed for calculation of deposition from a droplet-gas mixture at similar conditions. A simple geometry of a circular disk was used to be able to evaluate the validity of model at different conditions. The model combined Computational Fluid Dynamics (CFD) for calculating the flow hydrodynamics and droplet transport to the surface, and HYSYS simulation for prediction of mixture phase equilibrium at different temperatures. Effects of parameters such as droplet size and gas velocity were studied. Based on modeling results, Stokes number seemed to be a very important parameter on deposition of droplets. At low Stokes number, the main mechanism for deposition was molecular and eddy diffusion, and deposition did not change very much with change in droplet size and velocity. At higher Stokes number impaction was the main mechanism, and the deposition rates increased with increases in droplet size and gas velocity. The effect of surface properties on deposition was also studied. For the applied conditions and surfaces the perfect sticking assumption was considered satisfactory. Calculations suggested that application of hydrophobic material might help to decrease deposition by increasing the possibility of rebounding for droplets. Model was tested against room-temperature data for air-droplet systems and hot-unit experiments with heavy hydrocarbons carried out in parallel with the modeling work. For the latter, increases in the temperature decreased the deposition rates both by decreasing the droplet concentration and by the evaporation of volatiles formed in coking reaction. Finally, the model showed good ability in the prediction of deposition rates at different conditions.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat

OPTIMIZATION OF DISSOLVED AIR FLOTATION FOR DRINKING WATER TREATMENT THROUGH CFD MODELING

The dissolved air flotation (DAF) process is known for its efficiency in the removal of low-density particles from water. The performance of the system depends, in part, on the hydrodynamics of the flow. Whereas experimental flow measurement methods for DAF can be very challenging due to the presence of bubbles and particles, computational fluid dynamics (CFD) can be applied as an alternative approach for improving the understanding of the hydrodynamics, but would still require validation. In this study, two-phase and three-phase analytical and CFD models of DAF were developed to evaluate the formation of stratified flow (back and forth horizontal flow layers in the separation zone) and its impact on bubble and particle removal. By including the effects of bubble aggregation and bubble-particle aggregation, the models were able to predict the formation of stratified flow under different air fractions, bubble sizes, and loading rates. The CFD model showed that stratified flow improved bubble removal as well as particle removal, demonstrating that up to 130% higher loading rates can be achieved in the presence of stratified flow. An increase in air fraction and bubble size was shown to improve bubble removal, but particle removal began to decrease when air fractions and bubble sizes increased beyond optimum levels. The CFD model was then validated with a pilot-scale DAF system by comparing measurements of residence time distribution (RTD), bubble layer position and bubble-particle contact efficiency. In general, the CFD model was able to represent the pilot-scale DAF flow at different loading rates with very good accuracy (R2 values higher than 0.75). Finally, the validated model was applied to evaluate the effect of the addition of different configurations of baffles in the separation zone. The results suggested that baffles in the separation zone can enhance stratification of the flow and allow up to 86% higher loading rates.Ph.D.2019-04-15 00:00:0

Proton Density Fat Fraction Spine MRI for Differentiation of Erosive Vertebral Endplate Degeneration and Infectious Spondylitis

Vertebral Modic type 1 (MT1) degeneration may mimic infectious disease on conventional spine magnetic resonance imaging (MRI), potentially leading to additional costly and invasive investigations. This study evaluated the diagnostic performance of the proton density fat fraction (PDFF) for distinguishing MT1 degenerative endplate changes from infectious spondylitis. A total of 31 and 22 patients with equivocal diagnosis of MT1 degeneration and infectious spondylitis, respectively, were retrospectively enrolled in this IRB-approved retrospective study and examined with a chemical-shift encoding (CSE)-based water-fat 3D six-echo modified Dixon sequence in addition to routine clinical spine MRI. Diagnostic reference standard was established according to histopathology or clinical and imaging follow-up. Intravertebral PDFF [%] and PDFFratio (i.e., vertebral endplate PDFF/normal vertebrae PDFF) were calculated voxel-wise within the single most prominent edematous bone marrow lesion per patient and examined for differences between MT1 degeneration and infectious spondylitis. Mean PDFF and PDFFratio of infectious spondylitis were significantly lower compared to MT1 degenerative changes (mean PDFF, 4.28 ± 3.12% vs. 35.29 ± 17.15% [p p p p < 0.001) and 98.1% (cut-off at 0.27) for PDFFratio. Our data suggest that quantitative evaluation of vertebral PDFF can provide a high diagnostic accuracy for differentiating erosive MT1 endplate changes from infectious spondylitis

Correlation between Blood Type 0 and Risk of Chronic Subdural Hematoma Recurrence: A Single Center Retrospective Cohort Study

Chronic subdural hematoma (cSDH) is a common disease in the neurological and neurosurgical world. The recommended treatment for cSDH patients with moderate or severe neurological symptoms is surgical evacuation, but cSDH frequently recurs. The patient’s ABO blood type may influence the outcome. This study aims to evaluate the correlation between cSDH recurrence and blood type O. We performed a retrospective analysis of the data of patients with cSDH who were surgically treated. Recurrence was defined as the need for re-operation within the first 12 weeks after the initial surgery. We analyzed standard demographic data, duration and type of surgery, ABO blood types, and the re-operation rate. Univariate and multivariate analyses were conducted. A total of 229 patients were included. The recurrence of hematoma was identified in 20.5% of patients. Blood type O was found to be significantly associated with cSDH recurrence leading to re-operation within 12 weeks (p = 0.02, OR 1.9, 95% CI 1.1–3.5). Thrombocyte aggregation inhibition and oral anticoagulants were not predictors of cSDH recurrence. Patients with blood type O in our cohort were identified to be at higher risk of cSDH recurrence and may, therefore, be a more vulnerable patient group. This finding needs further evaluation in larger cohorts