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Karanjkar, 2003; Kukura et al., 2003). Some interesting examples of
CFD applications in pharmaceutical technology will be presented in the
following sections.
7.3.1 Inhaler development
Inhalers have been used for a long time for drug delivery to the lower
respiratory tract, in order to achieve local or systemic effects. Pressurized
metered-dose inhalers (MDIs) have been extensively used in the treatment
of respiratory diseases, such as asthma, cystic fi brosis, emphysema, etc.
However, MDIs have certain disadvantages, such as the need for
coordination of MDI actuation and patient inhalation, high oropharyngeal
drug deposition, the absence of a dose counter, etc. These disadvantages,
together with environmental concerns regarding the use of
chlorofl uorocarbon (CFC) as propellants, have led to increased research
efforts directed towards development of alternative devices, such as dry
powder inhalers (DPIs). These inhalers release a metered quantity of
powder in the airfl ow, which is drawn through the device by the patient's
inspiration. Besides the optimization of formulation and selection of an
appropriate metering system design, an important factor that determines
the performance and effi ciency of DPIs is fl ow path design. Namely, the
main limitation being attributed to these inhalers is pronounced
dependence of the dose being delivered on the inspiratory fl ow rate
(Prime et al., 1997).
CFD has been used to study the performance of MDIs and nebulizers
of various designs. However, DPI performance seems to be most
dependent on the airfl ow through the device, such as on the patient's
inspiration, in order to achieve suffi cient turbulence to fl uidize the powder
bed. Therefore, DPIs represent interesting candidates for application of
CFD in the development process (Wong et al., 2012).
Coates et al. have extensively investigated the infl uence of various
design features on DPI performance by using CFD (Coates et al., 2004,
2005, 2006, 2007). An interesting study conducted by this research
group is related to the infl uence of grid structure and mouthpiece length
on device performance (Coates et al., 2004). A fl ow rate of 60 L/min,
which is the fl ow rate that can be easily achieved by the patient, was
applied in this study, and laser Doppler velocimetry techniques were used
for validation of computational results. Changes were made in the
structure of the complete grid, and two additional modifi ed grids were
obtained (Figure 7.5). It was shown that grid structure signifi cantly
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