·
A
typical metered dose inhaler (as shown in fig. 3) consists of propellants, drug
formulation, metering valve, and actuator. Propellants in inhalers are liquefied compressed gases that
are in the gaseous phase at atmospheric pressure, but form liquids when
compressed. While drugs in M.D.I.s take the form of either particulate
suspensions or solutions. For the scope of analysis, we have assumed the
formulation to be in form of a particulate suspension while propellants to be
in gaseous states. Hence our fluid is a mixture of gas and solid particulate.
·
Propellants
normally used in DPIs have with molecular
mass of approx. 137 gm/mol & density of 41.49 g/cm3 are generally
used, while we assume properties of Salbutamol (i.e. approx. molecular mass: 239.31
g/mol & density 0.1 g/cm3) for the formulation particulate.
·
Formulation
particulates have diameters spanning from 1-12µm, hence we have selected 10µm
as the R.M.S. value for analysis.
·
Assumed
that there is no slip condition of the fluid inside the airways.
·
There
is a one way coupling between fluid and solid.