Characteristics of Turbulent Particle Transport in Human Airways under Steady and Cyclic Flows

Abstract

Motion of monodispersed micron-sized particles suspended in air flow was studied on transparent model of human airways using Phase-Doppler Particle Analyser (P/DPA). Time-resolved velocity data for particles in size range 1 to 8 um were processed using Fuzzy Slotting Technique embedded in Kern software (Nobach, 2002) to estimate power spectral density (PSD) of velocity fluctuations. Optimum setup of the software for these data was found and recommendations for improvements of future experiments were given. Typical PSD plots are documented and mainly differences among (1) steady-flow regimes and analogous cyclic breathing regimes, (2) inspiration and expiration breathing phase and (3) behaviour of particles with different size are described for several different positions in the airway model. Systematically higher content of velocity fluctuations in the upper part of frequency range (30 to 500 Hz) was found for cyclic flows in comparison with corresponding steady flows. Expiratory flows in both the (steady and cyclic) cases produce more high-frequency fluctuations compared to inspiratory flows. Negligible differences were found for flow of particles in the inspected size range 1 to 8 um at frequencies up to 500 Hz. This finding was explained by Stokes number analysis. Implied match of the air and particle flows thereby confirms a possibility to use the P/DPA data as air flow velocity estimate.Motion of monodispersed micron-sized particles suspended in air flow was studied on transparent model of human airways using Phase-Doppler Particle Analyser (P/DPA). Time-resolved velocity data for particles in size range 1 to 8 um were processed using Fuzzy Slotting Technique embedded in Kern software (Nobach, 2002) to estimate power spectral density (PSD) of velocity fluctuations. Optimum setup of the software for these data was found and recommendations for improvements of future experiments were given. Typical PSD plots are documented and mainly differences among (1) steady-flow regimes and analogous cyclic breathing regimes, (2) inspiration and expiration breathing phase and (3) behaviour of particles with different size are described for several different positions in the airway model. Systematically higher content of velocity fluctuations in the upper part of frequency range (30 to 500 Hz) was found for cyclic flows in comparison with corresponding steady flows. Expiratory flows in both the (steady and cyclic) cases produce more high-frequency fluctuations compared to inspiratory flows. Negligible differences were found for flow of particles in the inspected size range 1 to 8 um at frequencies up to 500 Hz. This finding was explained by Stokes number analysis. Implied match of the air and particle flows thereby confirms a possibility to use the P/DPA data as air flow velocity estimate.