Comparative Assessment of In Vitro and In Silico Methods for Aerodynamic Characterization of Powders for Inhalation

In vitro assessment of dry powders for inhalation (DPIs) aerodynamic performance is an inevitable test in DPI development. However, contemporary trends in drug development also implicate the use of in silico methods, e.g., computational fluid dynamics (CFD) coupled with discrete phase modeling (DPM). The aim of this study was to compare the designed CFD-DPM outcomes with the results of three in vitro methods for aerodynamic assessment of solid lipid microparticle DPIs. The model was able to simulate particle-to-wall sticking and estimate fractions of particles that stick or bounce off the inhaler’s wall; however, we observed notable differences between the in silico and in vitro results. The predicted emitted fractions (EFs) were comparable to the in vitro determined EFs, whereas the predicted fine particle fractions (FPFs) were generally lower than the corresponding in vitro values. In addition, CFD-DPM predicted higher mass median aerodynamic diameter (MMAD) in comparison to the in vitro values. The outcomes of different in vitro methods also diverged, implying that these methods are not interchangeable. Overall, our results support the utility of CFD-DPM in the DPI development, but highlight the need for additional improvements in these models to capture all the key processes influencing aerodynamic performance of specific DPIs.

Simulation and Design Optimization of a Tall-Form Spray Dryer

Airflow stability plays a vital role in optimizing the spray dryer operation; wherein the airflow patterns present inside the drying chamber are considered as the primary factors that influences the histories of the product particle. In this paper, the optimum drying parameters that would produce a higher yield of powdered egg while retaining its quality parameter such as moisture content and water activity were determined by means of Euler-Lagrange Discrete Phase Modeling (DPM) numerical method present in the ANSYS-Fluent ver. 14.5 CFD solver. During the computational simulation, the flow pattern of the air was first identified using the Eulerian method then the results were coupled using the Lagrangian-Discrete Phase Modeling to track the particle histories of the disperse phase inside the tall-form spray drying chamber. Results showed that the optimum inlet air velocity and temperature are 8.87 m/s and 444 K respectively. At these conditions, the particle trajectories simulated exhibited that the calculated final moisture content and water activity for the dried egg powder are 1.09 % and 0.012, respectively.

Multiscale Modeling of Carbon Nanotube Bundle Agglomeration inside a Gas Phase Pyrolysis Reactor

ABSTRACTCarbon nanotube (CNT) sock formation is required for the continuous synthesis of CNT thread or sheet using the gas phase pyrolysis method. Nanometer diameter CNTs form and are carried along the reactor tube by gas flow. During the flow, the CNT stick to each other and form bundles of about 10-100 nm diameter. Coupling of the CNT bundles in the flow leads to the formation of a centimeter diameter CNT sock with a wall that is hundreds of nanometers thick. Understanding the multiscale phenomena of sock formation is vital for optimizing the CNT synthesis and manufacturing process. In this work, we present a multiscale model for the CNT bundle agglomeration inside a horizontal gas phase pyrolysis reactor. The interaction between CNT bundles was analyzed by representing the attraction forces between CNTs using a discrete phase modeling method. Flow in the synthesis reactor was studied using a computational fluid dynamics (CFD) technique with multiphase flow analysis. A model was proposed to represent the coupling between CNT bundles and the gas flow. The effect of different CNT bundles on the agglomeration phenomenon was analyzed. The modeling results were also compared with experimental observations.

A Preliminary Study of the Blade Erosion for a Wind Turbine Operating in a Dusty Environment

The process of surface erosion due to particle collision has been the focus of a number of investigations with regards to gas turbine engines, aircraft, reentry missiles, pipelines carrying coal slurry, etc. Recently, increased interest in wind energy by countries in the Saharan regions of the Middle East and North Africa (MENA) brings about some concern about leading edge erosion of wind turbines operating under such dusty conditions. Leading edge erosion can have a detrimental impact on the extracted energy as it changes the blade surface roughness causing premature/unpredictable separation. Though erosion may not be easily avoided; it may be mitigated via using airfoil families characterized by low roughness sensitivity. In this paper, a model of an airfoil erosion subjected to sand blasting is developed using the discrete phase modeling capability in ANSYS-FLUENT along with the DNV erosion model. The effect of various flow parameters, such as angle of attack, and particle size, on the extent of erosion is investigated for a number of airfoil designs. The developed model is used as a predictive tool to assess the power deterioration of eroded wind blades.

Aerodynamic Characteristics of NACA 23015 Landing Configuration with 20o Flap in Simulated Rain

In our numerical simulation the heavy rain effects have been studied on the aerodynamic performance of 2D cambered NACA 23015 airfoil landing configuration with 20o. We have used preprocessing software gridgen for creation of the landing configuration of the airfoil and then creating mesh around it. Fluent is used to solve the conservation equations. We have used discrete phase modeling (DPM) in Fluent to simulate the rain phenomenon in continuous phase flow by using two phase flow approach. In our study the coupling between the discrete and the continuous phase has been activated. In discrete phase model (DPM), we used the wall film model for the interaction of the continuous and discrete phase. The airfoil landing configuration exhibited significant decrease in lift and increase in drag for a given lift conditions in simulated rain. Post processing software like MATLAB, Tec plot and Origin are used to see the effects of the heavy rain and then results obtained are compared with the experimental results. Our numerical results in most of cases show similar trends with the experiments.

Behavior of Micron-Sized Air Bubble in Operating FDBs by Using the Discrete Phase Modeling Method

Fluid dynamic bearings (FDBs) have been applied to the spindle motor of a computer hard disk drive (HDD) because FDBs provide better dynamical characteristics of lower vibration and noise than ball bearings. However, one of the weaknesses of FBDs is the instability arising from the air bubble in oil lubricant of FDBs. Air bubbles are formed and trapped in oil lubricant by the inappropriate process of oil injection or the external shock. Trapped air bubbles decrease the rotational accuracy and the stability of a rotor-bearing system in such a way to generate non-repeatable run-out (NRRO) and to decrease the stiffness and damping coefficients of FDBs. It is important to predict the path of air bubbles in oil lubricant and to design FDBs in such a way to easily expel air bubbles out of operating FDBs.