A Model To Predict The Residual Layer Thickness In The Injection Molding Process

Paper presented at 2018 Canadian Society of Mechanical Engineers International Congress, 27-30 May 2018.The effects of the wall temperature on the residual layer thickness of the polymers are studied numerically in the filling process in the injection molding process. A lubrication approximation model is developed to furnish a semi-analytical solution. The shear viscous heating terms are neglected to simplify the governing equations. The Cross-WLF viscosity model is used to capture the residual layer. There is a good agreement between the results of the developed model and experiments

The flow properties of bitumen in the presence of carbon dioxide

The present dissertation discusses the flow behaviour of bitumens in the presence of CO₂. Firstly, the viscoelastic behaviour of bitumen is studied and an appropriate constitutive equation is identified to describe its rheological behavior. The K-BKZ constitutive equation has been shown to represent accurately the rheological properties of bitumen. Analysis of experimental results revealed that either the Papanastasiou or the Marucci form of the damping function can be used in the K-BKZ constitutive equation. Moreover, the damping function was found to be independent of temperature (0°C-50°C). Secondly, the effects of temperature, pressure, dissolved carbon dioxide and shear rate on the rheological response of bitumen are investigated by using the reduced variable method at the temperature range of –10°C to 180°C and pressures up to 15 MPa. The double–log model is found to be the most accurate equation in describing the effect of temperature on the viscosity of bitumen over a wide range of temperature while the Barus model with the temperature–dependent parameter is found to be the most appropriate correlation to represent the effect of pressure. The Fujita–Kishimato equation, resulting from the free volume concept modelling, is employed to account for the effect of dissolved CO₂ on the viscosity of the bitumen–CO₂ mixture. The results show that the viscosity is influenced by the temperature and saturation pressure. Thirdly, the combined pressure-decay technique with rheometry is developed to measure the diffusivity of CO₂ in bitumen at the temperatures of 30˚C, 50˚C, 70˚C, 90˚C and 110˚C and saturation pressures of 2, 4 and 10 MPa. The impact of temperature on the diffusivity of CO₂-bitumen systems can be described by the Arrhenius equation. The diffusivity increases with pressure at gaseous CO₂ state. The increase is more dominant at lower temperatures while the diffusivity increase is 53% at 30˚C compared to 25% at 70˚C. It is shown that changing the state of CO₂ impacts the diffusivity values of in bitumen while the diffusivity is higher for the liquid CO₂ compared to supercritical CO₂. Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat

Analysis of Local Shear Rate Distribution in a Double Coaxial Bioreactor Containing Biopolymer Solutions Using Computational Fluid Dynamics

Uniform gas dispersion and shear distribution in highly viscous non-Newtonian fluids are challenging due to the complex rheological behavior exhibited by this type of medium. In addition, most large-scale bioreactors used in biochemical processes such as wastewater treatment and fermentation demand higher aspect ratios (i.e., fluid height to tank diameter ratio) than laboratory-scale bioreactors. This, in turn, underlines uneven gas and shear distribution throughout the bioreactor, especially those comprising yield-pseudoplastic fluids. For this type of fluid, there are two distinct zones within the bioreactor: a higher-shear zone with a lower apparent viscosity around the impeller and a lower-shear area with a higher apparent viscosity away from the impeller. Due to the viscosity gradient, homogeneous gas dispersion within a single impeller aerated bioreactor with an aspect ratio of more than one is hard to attain. It has been reported that a well-designed mixing configuration contributes to maintaining a consistent fluid viscosity, resulting in improved mixing performance and consistent final product quality. Recent studies have demonstrated the superior performance of double coaxial bioreactors furnished with two central impellers and one anchor for uniform shear distribution and gas dispersion in pseudoplastic fluids. Despite the widespread use of yield-pseudoplastic fluids in various industries, a knowledge gap was identified for analyzing the shear distribution within the double coaxial mixers containing pseudoplastic fluids possessing yield stress. This study examined the effect of four coaxial mixing configurations, including down-pumping and co-rotating, up-pumping and co-rotating modes, down-pumping and counter-rotating, and up-pumping and up-pumping and up-pumping and counter-rotating modes, on the local shear rate distribution. In this regard, computational fluid dynamics (CFD) was employed for the evaluation of the local shear distribution within the coaxial bioreactor

Predicting the Volumetric Mass Transfer Coefficient in a Double Coaxial Mixer: An Artificial Neural Network Approach

In recent years, there has been a significant emphasis on predicting the mixing effectiveness of mechanically agitated tanks, particularly those employing coaxial mixers [...

Analyzing Local Shear Rate Distribution in a Dual Coaxial Mixing Bioreactor Handling Herschel–Bulkley Biopolymer Solutions through Computational Fluid Dynamics

For the aeration of highly viscous non-Newtonian fluids, prior studies have demonstrated the improved efficacy of dual coaxial mixing bioreactors fitted with two central impellers and a close clearance anchor. Evaluating the effectiveness of these bioreactors involves considering various mixing characteristics, with a specific emphasis on shear rate distribution. The study of shear rate distribution is critical due to its significant impact on the mixing performance, gas dispersion, and homogeneity in aerated mixing systems comprising shear-thinning fluids. Although yield-pseudoplastic fluids are commonly employed in various industries, there is a research gap when it comes to evaluating shear rate distribution in aerated mixing bioreactors that utilize this fluid type. This study aims to investigate shear rate distribution in an aerated double coaxial bioreactor that handles a 1 wt% xanthan gum solution, known as a Herschel–Bulkley fluid. To achieve this goal, we employed an experimentally validated computational fluid dynamics (CFD) model to assess the effect of different mixing configurations, including down-pumping and co-rotating (Down-Co), up-pumping and co-rotating (Up-Co), down-pumping and counter-rotating (Down-Counter), and up-pumping and counter-rotating (Up-Counter) modes, on the shear rate distribution within the coaxial mixing bioreactor. Our findings revealed that the Up-Co system led to a more uniform local shear distribution and improved mixing performance

A CFD Investigation on the Aerosol Drug Delivery in the Mouth–Throat Airway Using a Pressurized Metered-Dose Inhaler Device

Inhalation therapy involving a pressurized metered-dose inhaler (pMDI) is one of the most commonly used and effective treatment methods for patients with asthma. The purpose of this study was to develop a computational fluid dynamics (CFD) model to characterize aerosol flow issued from a pMDI into a simulated mouth–throat geometry. The effects of air flow rate and cone angle were analyzed in detail. The behaviour of the multiphase flow initiated at the inhaler actuation nozzle and extended through the mouth–throat airway was simulated based on the Eulerian-Lagrangian discrete phase model, with the k-ω model applied for turbulency. We validated our model against published experimental measurements and cover the hydrodynamic aspect of the study. The recirculation we observed at the 90° bend inside the mouth–throat airway resulted in the selective retention of larger diameter particles, and the fluid flow patterns were correlated with drug deposition behaviour. Enhancing air flow rates up to three times reduced the aerodynamic particle diameters to 20%. We also observed that, as cone angle increased, mouth deposition increased; an 8° cone angle was the best angle for the lowest mouth–throat deposition.</jats:p