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This study investigates decompression and ejection conditions on tablet characteristics by comparing compact densities and tensile strengths made using regular rigid dies and ...custom-built die systems that enable triaxial decompression. Die-wall pressure evolution during decompression and ejection stresses did not meaningfully impact the density and tensile strength of the materials tested: microcrystalline cellulose, crystalline lactose monohydrate, and mannitol. Furthermore, the apparent differences in tensile strength between rectangular cuboids and cylindrical compacts are unrelated to decompression and ejection conditions, but rather a consequence of their shapes and of the test configurations. This suggests that elastic and plastic deformations that may occur during decompression and ejection are not significantly influenced by die-wall pressure evolution. We thus conclude that while triaxial decompression and constraint-free ejection may allow the production of defect-free compacts for materials that otherwise are defect prone using a rigid die, they seem to pose no benefits when the materials already produce defect-free compacts using a rigid die.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•The GPU-based DEM approach is used to study the lab-scale die filling system.•The numerical model is calibrated and validated well with experimental data.•The stirrer occupying a ...specific space and reducing the effective discharge area.•Flow patterns of the free-flowing powder during die filling process is analyzed.
Understanding die filling behaviour of powders is critical in developing optimal formulation and processes in various industries, such as pharmaceuticals and fine chemicals. In this paper, forced die filling is analysed using a graphics processing unit (GPU) based discrete element method (DEM), for which a powder feeder equipped with a wired stirrer is considered. The influences of operating parameters, such as the initial powder bed height, the filling speed, and the stirrer speed, on the die filling performance are systematically explored. It is shown that a larger initial powder bed height leads to a higher filling ratio, which can be attributed to a higher filling intensity; while the deposited particle mass in the die is almost independent of the powder bed height, when the initial fill level is larger than a critical bed height. Additionally, the filling ratio slightly increases with the increase of stirrer speed for cases with a stirrer, while the filling ratios are lower than that without a stirrer, which is attributed to the stirrer occupying some space above the die and reducing the effective discharge area. The obtained results can provide useful information for optimising the feeder system design and the operating condition.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Coupled CFD-DEM model built to predict the performance of common capsule DPIs.•Model predicts particle dynamics that affect powder aerosol characteristics.•Formulation and DPI design interplay ...affecting fine aerosol generation identified.•Model results correlate with experimental cascade impactor data.•Design modifications to optimize capsule DPI performance are proposed.
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Capsule-based, single-dose dry powder inhalers (DPIs) are commonly-used devices to deliver medications to the lungs. This work evaluates the effect of the drug/excipient adhesive bonding and the DPI resistances on the aerosol performance using a combination of empirical multi-stage impactor data and a fully-coupled computational fluid dynamics (CFD) and discrete element method (DEM) model. Model-predicted quantities show that the primary modes of powder dispersion are a function of the device resistance. Lowering the device resistance increases its capacity to transport a wider range of particle size classes toward the outlet and generate more intense turbulence upstream therein. On the other hand, a higher device resistance increases the velocity of the tangential airflow along the device walls, which in turn increases the intensity of particle/device impaction. Correlating model data and experimental results shows that these differing powder dispersion mechanisms affect different formulations differently, with finer aerosols tending to result when pairing a lower resistance device with formulations that exhibit low API/excipient adhesion, or when pairing a high resistance device with more cohesive formulations.
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The purpose of the study is to build a “virtual roller compactor” as a predictive tool to assess the roll force (RF)-maximum pressure (Pmax) and RF-ribbon density relationship for ...pharmaceutical roller compaction. We provided a theoretical basis to demonstrate that, there exists a critical nip angle for a pharmaceutical powder, beyond which the RF-Pmax relationship is insensitive to wall friction angle or effective angle of internal friction. We showed that for most pharmaceutical roller compaction, the critical nip angle is lower than 17 degree, and can be exceeded via wall friction elevation, using rolls with non-smooth surface. Under this condition, the original Johanson model can be substantially simplified to a single equation requiring only one material property (compressibility). By performing manufacturing-scale roller compaction using materials with diverse compressibility, we showed that the simplified, friction angle-free model performed similar to the original Johanson model. It can predict the RF-Pmax and RF-ribbon density relationship well after applying a correction factor. The predictive tool, in the form of a user-friendly graphical user interface, was created based on the simplified model. The tool was adopted for in-house, bench-scale formulation development and scale-up because of its ease-of-use, good predicting capability, and very low material demand.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study compares the density results from three-dimensional FEM simulations of a roll compaction process to those measured experimentally. Unlike previous studies, the experiments were performed ...with an air-powered piston feeder configuration that applied a known, uniform stress on the powder. All model boundary conditions were based on experimentally-measured values. To further improve model accuracy, the simulations also utilized density-dependent stress–strain constitutive parameters to describe the powder mechanical behaviors. Results show that the FEM model results agree well with the corresponding experimental data. Important experimental trends are successfully captured by the simulations, including the ribbon width-wise density distribution and the observation that the average ribbon density was independent of the inlet stress when the system was operated at conditions that allowed the roll gap to ‘float’. Further, as a result of cantilevered roll shaft supports, the experimental rolls were not perfectly parallel so the ribbon width-wise density distribution was slightly asymmetrical against the roll half-width. Incorporating non-parallel roll configurations in the FEM simulations resulted in an asymmetrical ribbon density distribution similar to the experimental observations.
Finite element method (FEM) simulations of a roll compaction process were performed using experimentally measured data as model inputs. The FEM-predicted density distribution results are compared to those measured experimentally at conditions that closely match the simulation boundary conditions. Excellent agreement between FEM and experimental data is observed. Display omitted
► Density results from FEM simulations are validated against experimental measurements. ► An air-powered piston that applies a known, uniform stress on the powder is used. ► All model boundary conditions were based on experimentally-measured values. ► The simulations also utilized density-dependent stress–strain constitutive parameters. ► FEM model density results agree well with the corresponding experimental data.
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This study compares the nip angle, normal stress at the roll gap, and the maximum material relative density computed from 2-D finite element method (FEM) simulations and the 1-D Johanson's model for ...roll compaction of powders. In general, the nip angles predicted from the Johanson model follow the same trends as those from the FEM model. Both predictions agree to within 25% using typical pharmaceutical material properties. However, the compact densities predicted by the Johanson model are greater than one regardless of the operating conditions or material parameters. As shown in the FEM model, this unrealistic result is due to a two-dimensional velocity gradient that is not accounted for in the Johanson model. Finally, the normal stresses in the roll gap predicted by the Johanson model are generally larger than those found using the FEM model. The two approaches agree better when the material is more compressible, has a lower effective internal friction angle, a larger roll-powder friction angle, and when the streamwise inlet normal stress decreases.
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► We compare the Johanson roll compaction model to a 2-D finite element model. ► The Johanson model-predicted relative densities are greater than one. ► The Johanson model overestimates roll normal stress magnitudes. ► Discrepancies are from 1-D, continuity-based derivations in Johanson's analysis. ► Nip angle results from the two approaches agree to within 25%.
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Statistical pattern imaging velocimetry (SPIV) is a new technique for the estimation of the planar velocity field from the high-speed videos. SPIV utilizes an ensemble of either backlit or side lit ...videos to obtain full planar velocities in sprays and flames. Unlike conventional particle imaging velocimetry, statistical pattern imaging velocimetry does not require well-resolved images of particles within turbulent flows. Instead, the technique relies of patterns formed by coherent structures in the flow. Therefore, SPIV is well suited for the estimating planar velocities in sprays and turbulent flames, both of which have well-defined patterns embedded in the flow videos. The implementation of the SPIV technique is relatively quite straightforward since high-speed videos can be readily obtained either in a laboratory or production floor setting. The biggest challenge for the SPIV techniques is that the procedure is computationally expensive even with an ordinary mega-pixel camera. To improve the computation speed, a successive partitioning scheme was employed. In addition, to improve spatial resolution to subpixel dimensions, a weighted central averaging scheme was used. With these two enhancements, the SPIV method was used to obtain planar radial and axial velocities in a spray emanating from a GDI injector. Sprays from GDI injectors are very dense (with obscuration levels close to the injector being greater than 99%), and velocity measurements are difficult. However, further away from the nozzle, a Phase Doppler Anemometer can be used to obtain velocity measurements. The velocities obtained using these two methods showed reasonable agreement.
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NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
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10.
Spray mechanism in paper spray ionization Espy, Ryan D.; Muliadi, Ariel R.; Ouyang, Zheng ...
International journal of mass spectrometry,
07/2012, Volume:
325-327
Journal Article
Peer reviewed
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► We describe the spray modes during paper spray ionization. ► When solvent-rich, paper spray produces multimodal droplet distributions. ► Solvent-deficient paper spray produces ...monodisperse drops and a corona discharge. ► Microfiber structures enhance the electric field near the Taylor cone(s).
Images and droplet size measurements show that paper spray operates in two distinct spray modes. Mode 1 occurs in solvent-rich systems in which multiple Taylor conejets are created producing droplets of a range of sizes. Mode 2 occurs at low solvent flow rates and the higher currents (∼1uA) suggest a contribution from corona discharge. The latter experiment produces monodispersed droplet sizes. A distinguishing feature of paper spray in both modes is a fixed droplet velocity independent of droplet size.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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