The hydrodynamics of an agitated tank have been studied byphase-Doppler anemometry. The focus is on the impeller anddischarge region of a 45o pitched blade turbine (PBT). Thestudy includes agitation of pure water as well as of a dilutesuspension of process particles. A three-dimensionalphase-Doppler anemometer is used to measure local,instantaneous, three-dimensional velocities of the fluid and ofthe suspended particles. A shaft encoding technique is used toresolve the turbulent fluctuations from the periodic velocityfluctuation due to the impeller blades, and to provide moredetailed information about the variations relative to theimpeller blade. Velocity bias is corrected for by the total3-dimensional velocity. The mean flow field, the fluctuating velocities, and thecomplete Reynolds stress tensor, are reported for the liquidphase flow. The periodic fluctuations in the flow that aregenerated by the impeller blades are eliminated in theexamination of the turbulence. The anisotropy of the turbulenceis assessed by the invariants of the anisotropy tensor. Thetrailing vortex structure is demonstrated to be associated withhigh kinetic energy and strong anisotropy of the turbulence.The vortex is still observable 130-140 degrees behind theblade. It gradually moves down from the impeller blade but thelocation in radial direction remains essentially unchanged. Theinfluence of the periodic fluctuations is examined and it isshown that the turbulence appears more isotropic when theperiodic fluctuations are not eliminated. The solid particle concentration is low below the impellerand is high above the impeller tip. The particles diverge fromthe liquid flow mean direction, especially below the agitatorclose to the tip where the strongest turbulence is found.Periodic fluctuations in the particle concentration relate tothe variations found in the angle-resolved mean velocity andfluctuating velocity. The ratio of the maximum to the minimumconcentration is about 2.0 in the present study. The baffles influence on the conditions in the impellerregion, and this influence can be observed on the fluid meanvelocity field, the angle-resolved velocities, the kineticenergy, and on the behavior of larger process particles. In theimpeller region the highest kinetic energies are about 15%higher upstream of the baffle than at the middle plane betweenthe baffles. The highest energy level in the middle plane isactually the lowest value and is therefore not representativewhen rotation symmetry is assumed. Local energy dissipation rates have been investigated, andthe integration of the local energy dissipation rates overdifferent control volumes has been compared with macroscopicenergy balance calculations. The discrepancy is significant.Different reasons have been analyzed and recommendations forfurther investigation are given. I n the outflow region there is a significant variation alsoin the direction of the instantaneous velocity, which may leadto direction bias in the case of non-spherical measurementvolume. In order to account for this direction bias, amathematical model is developed to estimate the projected areaof the measurement volume in LDA or PDA. It is shown that theprojected area variation can lead to a significant directionbias in determination of time averaged values and localparticle concentration in a highly turbulent stirred tank flow.This bias is however negligible for an orthogonal optical setup, as is used in the present study. <b>Keywords:</b>Hydrodynamics, phase-Doppler anemometer,suspension, pitched-blade turbine, anisotropy, turbulence,Reynolds stresses, trailing vortex, kinetic energy, stirredtank

<p>The hydrodynamics of an agitated tank have been studied byphase-Doppler anemometry. The focus is on the impeller anddischarge region of a 45o pitched blade turbine (PBT). Thestudy includes agitation of pure water as well as of a dilutesuspension of process particles. A three-dimensionalphase-Doppler anemometer is used to measure local,instantaneous, three-dimensional velocities of the fluid and ofthe suspended particles. A shaft encoding technique is used toresolve the turbulent fluctuations from the periodic velocityfluctuation due to the impeller blades, and to provide moredetailed information about the variations relative to theimpeller blade. Velocity bias is corrected for by the total3-dimensional velocity.</p><p>The mean flow field, the fluctuating velocities, and thecomplete Reynolds stress tensor, are reported for the liquidphase flow. The periodic fluctuations in the flow that aregenerated by the impeller blades are eliminated in theexamination of the turbulence. The anisotropy of the turbulenceis assessed by the invariants of the anisotropy tensor. Thetrailing vortex structure is demonstrated to be associated withhigh kinetic energy and strong anisotropy of the turbulence.The vortex is still observable 130-140 degrees behind theblade. It gradually moves down from the impeller blade but thelocation in radial direction remains essentially unchanged. Theinfluence of the periodic fluctuations is examined and it isshown that the turbulence appears more isotropic when theperiodic fluctuations are not eliminated.</p><p>The solid particle concentration is low below the impellerand is high above the impeller tip. The particles diverge fromthe liquid flow mean direction, especially below the agitatorclose to the tip where the strongest turbulence is found.Periodic fluctuations in the particle concentration relate tothe variations found in the angle-resolved mean velocity andfluctuating velocity. The ratio of the maximum to the minimumconcentration is about 2.0 in the present study.</p><p>The baffles influence on the conditions in the impellerregion, and this influence can be observed on the fluid meanvelocity field, the angle-resolved velocities, the kineticenergy, and on the behavior of larger process particles. In theimpeller region the highest kinetic energies are about 15%higher upstream of the baffle than at the middle plane betweenthe baffles. The highest energy level in the middle plane isactually the lowest value and is therefore not representativewhen rotation symmetry is assumed.</p><p>Local energy dissipation rates have been investigated, andthe integration of the local energy dissipation rates overdifferent control volumes has been compared with macroscopicenergy balance calculations. The discrepancy is significant.Different reasons have been analyzed and recommendations forfurther investigation are given. I</p><p>n the outflow region there is a significant variation alsoin the direction of the instantaneous velocity, which may leadto direction bias in the case of non-spherical measurementvolume. In order to account for this direction bias, amathematical model is developed to estimate the projected areaof the measurement volume in LDA or PDA. It is shown that theprojected area variation can lead to a significant directionbias in determination of time averaged values and localparticle concentration in a highly turbulent stirred tank flow.This bias is however negligible for an orthogonal optical setup, as is used in the present study.</p><p><b>Keywords:</b>Hydrodynamics, phase-Doppler anemometer,suspension, pitched-blade turbine, anisotropy, turbulence,Reynolds stresses, trailing vortex, kinetic energy, stirredtank</p>

Electrostatic properties of formulation component materials and blends play an important role in dry powder inhalation (DPI) products, and that valid measurement of charge distribution will lead to more precise control of powder behavior in DPI manufacturing processes. Ultra-fine powders are known to be bipolarly charged, have non-spherical shapes and tend to be highly cohesive. Real time, non-invasive techniques need to be developed to obtain a precise and accurate time-history characteristic of electrically charged powders as they aerosolize from a DPI product, and how this measure relates to materials behavior throughout the various steps of a manufacturing process i.e. from drug micronisation, blending with lactose, through to filling dose units. A novel non-invasive technique for simultaneous measurement of size and charge of pharmaceutical powders is considered which employs the Phase Doppler Anemometry (PDA) system. Previous research demonstrated the advantages of this technique in measuring the bipolar charge distribution on a population of particles. These findings led to significant improvements in understanding performance of dry powder formulations, manufacturing processes and development of new platforms for inhaled drug delivery. The main aim of this research is to perform an investigation of electrostatic propertiesof pharmaceutical dry aerosols using the PDA system. The PDA technique was used to track the motion of charged particles in the presence of an electric field. The magnitude as well as the polarity of the particle charge can be obtained by solving the equation of particle motion in DC and AC fields combined with the simultaneous measurement of its size and velocity. The results show the capability of the technique to allow real-time size and charge distribution in the control of dry powder attributes that are critical to fully understanding manufacturing design space. The data obtained from initial investigations of electrical properties of pharmaceutical powders and bipolar charge measurements was used to perform an in-depth study of electrostatic properties of pharmaceutical aerosols dispensed by dry powder inhaler (DPI) devices. The delivery of a drug to the lungs can only be achieved by a combination of inhaler device and drug formulation which is capable of producing an aerosol of an aerodynamic diameter smaller than 5 μm and of appropriate charge. The aerosols generated by these devices are often bipolarly charged and can influence specific site deposition in human lung. By controlling the electrostatic charge generated by tribielectrification, it may be possible to achieve the desired drug deposition in the airways. Bipolary charged dispensed ultrafine particles are inhaled through the extrathoracic and tracheobronchial airways down into the alveolar region. Anatomically realistic respiratory airways and computation fluid dynamics (CFD) models have been created to study airflow structures and predict aerosol deposition within the human respiratory system using visible human data sets, human casts and morphometric data. Many theoretical studies of charged aerosol deposition in human respiratory systems have been developed, however getting real time, non-intrusive data of bipolar charge levels on aerosols dispensed from DPI’s within the human respiratory system represents a challenging issue. This research project presents a simplified human upper airway model which combined with the modified Phase Doppler Anemometry (PDA) system is able to provide real time bipolar charge distributions of aerosols delivered from several commercially available DPI devices. A three dimensional (3D) reconstruction of the upper respiratory system was performed from two dimensional (2D) images obtained from computerized tomography (CT), magnetic resonance imaging (MRI) and cryosectioned images available from Visible Human Server data set (Ecole Polytechnique Fédérale de Lausanne). The resulting dimensions of the model were consistent with morphometric data from the literature from which the simplified upper airway model consisting of two connected segments, i.e., the oral airways from the mouth to trachea (Generation G0), was created. The findings of this study provided a better understanding of the interaction between specific active ingredients and DPI devices. These results may be used in designing future generation DPI devices and a better understanding of aerosol transport and deposition efficiency within the human airways.