170 research outputs found
Three-Dimensional Modeling of Electrostatic Precipitator Using Hybrid Finite Element - Flux Corrected Transport Technique
This thesis presents the results of a three-dimensional simulation of the entire precipitation process inside a single-electrode one-stage electrostatic precipitator (ESP). The model was designed to predict the motion of ions, gas and solid particles. The precipitator consists of two parallel grounded collecting plates with a corona electrode mounted at the center, parallel to the plates and excited with a high dc voltage. The complex mutual interaction between the three coexisting phenomena of electrostatic field, fluid dynamics and the particulate transport, which affect the ESP process, were taken into account in all the simulations. The electrostatic field and ionic space charge density due to corona discharge were computed by numerically solving Poisson and current continuity equations, using a hybrid Finite Element (FEM) - Flux Corrected Transport (FCT) method. The detailed numerical approach and simulation procedure is discussed and applied throughout the thesis. Calculations of the gas flow were carried out by solving the Reynolds-averaged Navier-Stokes equations using the commercial FLUENT 6.2 software, which is based on the Finite Volume Method (FVM). The turbulence effect was included by using the k-ε model included in FLUENT. An additional source term was added to the gas flow equation to include the effect of the electric field, obtained by solving a coupled system of the electric field and charge transport equations, using the User-Defined-Function (UDF) feature of FLUENT. The particle phase was simulated using a Lagrangian-type Discrete Random Walk (DRW) model, where a large number of particles charged by combined field and diffusion charging mechanisms was traced with their motion affected by electrostatic and aerodynamic forces in turbulent flow using the Discrete Phase Model (DPM) and programming UDFs in FLUENT. The airflow patterns under the influence of electrohydrodynamic (EHD) secondary flow and external flows, particle charging and deposition along the channel, and ESP performance in removal of submicron particulates were compared for smooth and spiked discharge electrode configurations in the parallel plate precipitator assuming various particle concentrations at the inlet. Finally, a laboratory scale wire-cylinder ESP to collect conductive submicron diesel particles was modeled. The influence of different inlet gas velocities and excitation voltages on the particle migration velocity and precipitation performance were investigated. In some cases, the simulation results were compared with the existing experimental data published in literature
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Investigation of bipolar charge distribution of pharmaceutical dry powder aerosols using the phase doppler anemometry system
This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London.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.Engineering and Physical Sciences Research Council. Pfizer team, U
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