A CFD Study of a pMDI Plume Spray

Abstract

Asthma is an inflammatory chronic disease characterized by airway obstructions disorders. The treatment is usually done by inhalation therapy, in which pressurized metered-dose inhalers (pMDIs) are a preferred device. The objective of this paper is to characterize and simulate a pMDI spray plume by introducing realistic factors through a computational fluid dynamics (CFD) study. Numerical simulations were performed with Fluent® software, by using a three-dimensional "testbox" for room environment representation. An HFA-134a with salbutamol formulation was used for characterization, whose were taken as input for the CFD simulations. Spray droplets were considered to be composed by ethanol, salbutamol and HFA-134a. Propellant evaporation was taken into consideration, as well as, drag coefficient correction. Results showed an air temperature drop of 3.3 °C near the nozzle. Also, an increase in air velocity of 3.27 m/s was noticed. The CFD results seem to be in good agreement with Dunbar (1997) data on particle average velocity along the axial distance from the nozzle.

In Silico Methods for Development of Generic Drug–Device Combination Orally Inhaled Drug Products

“…Spray characterization of MDIs using CFD is challenging because of the several physical processes that include droplet formation, the large temperature gradient at the device orifice, high initial velocity values, and rapid evaporation of the propellant . Several studies have considered MDI delivery to the lungs using CFD, with varying physical treatments . Proper characterization of an MDI spray requires the careful selection of orifice boundary conditions because this process is crucial to understanding device differences.…”

“…used several downstream experimental spray velocity measurements to extrapolate to the orifice. Most groups have used theoretical formulations to estimate spray velocity . Where reported, spray angle is either taken from experimental measurements or varied to capture its influence on particle deposition .…”

“…However, for studies that model solution‐based MDI delivery it is unclear whether this assumption is appropriate considering that ethanol, a common cosolvent in solution‐based MDIs, evaporates more slowly than the propellant . A few studies did consider evaporation, but details on model implementation were few.…”

“…24 Several studies have considered MDI delivery to the lungs using CFD, with varying physical treatments. [27][28][29][30][31][32][33][34][35][36][37] Proper characterization of an MDI spray requires the careful selection of orifice boundary conditions because this process is crucial to understanding device differences. There are no known studies that directly simulate the fluid behavior inside the MDI canister through atomization.…”

“…Most CFD studies that model MDI behavior have applied experimentally measured values to some or all of the orifice boundary conditions, which include spray velocity, spray angle, and APSD. [29][30][31][32][33][34][35][36] However, experimental spray velocity measurements are not available directly at the orifice but ~20-50 mm downstream of the orifice, where some assumptions need to be made to specify orifice boundary conditions. For example, Farkas et al 29 used several downstream experimental spray velocity measurements to extrapolate to the orifice.…”