Experimental and CFD study of the deposition of inhalable particles in the induction port of a cascade impactor

DE CHARRAS YL; BERTÍN D; RAMIREZ RIGO MV

Buenos Aires

Congreso; 11th World Congress of Chemical Engineering; 2023

Asociación Argentina de Ingenieros Químicos

The testing of pharmaceutical aerosols includes measuring the aerodynamic particle size distribution, which is usually performed on cascade impactors. In particular, in the Next Generation Pharmaceutical Impactor (NGI), the aerosol dose is introduced to the NGI through an induction port (IP), being separated into different aerodynamic diameter ranges by seven stages and a micro-orifice collector. The IP play an important role to estimate the oropharyngeal deposition fraction. While IP retains large particles, it also tends to retain particles in the respirable range.In this work, the deposition of particles in the IP of an NGI is studied, both experimentally and through CFD simulations. Experimental assays are performed for a pressurized metered-dose inhalers (pMDI) alone and with 2 commercial valved holding chambers (VHCs). For each case, the total mass deposition that occurs in the IP is measured, as well as the MMAD of the aerosol leaving the IP.Simulations for 3D meshes were performed and the procedure of Celik et al. [1] to calculate the convergence index of the mesh by comparing the air velocity profiles. Finally, a mesh with 300,000 cells was adopted. The spherical drag law was selected, and the discrete random walk model with three tries and Time Scale Constant of 0.35 was considered. The pseudo-transient coupled solver was used to solve the equations. Simulations were carried out for monodisperse particles for particle size values ranging from 1 to 15 μm. For each case, an efficiency (i.e., the quotient between the flow of particles that leaves and enters the IP) was calculated. Then, an efficiency curve as a function of particle size was generated. The "Trap" boundary condition was used in the DPM model for the contact of the particles with the walls of the IP.Experimental results indicate that when pMDI is used without VHC, the IP retains approximately 56% of the particulate material. However, this deposited fraction is reduced to less than 10% when pMDI is used in conjunction with VHC. Regarding the MMAD of the aerosol released by the IP, it is found that the shape of the size distribution is similar in all cases. Therefore, it is observed that the ability of IP to separate particles of different sizes is similar to that of the VHCs studied.The CFD model, used to study the deposition of particles of different sizes in the IP, was validated with the experimental values obtained. The results indicate that the IP effectively retains a fraction of particles corresponding to the breathable range, although the greatest retention occurs for larger particles. A particle separation efficiency curve is obtained from the CFD results of the IP, which is used to predict the MMAD of the aerosol emitted by the pMDI.