Deposition inertial ranges

Unlike diffusion, which is a stochastic process, particle motion in the inertial range is deterministic, except for the very important case of turbulent transport. The calculation of inertial deposition rates Is usually based either on a force balance on a particle or on a direct analysis of the equations of fluid motion in the case of colli Jing spheres. Few simple, exact solutions of the fundamental equations are available, and it is usually necessary to resort to dimensional analysis and/or numerical compulations. For a detailed review of earlier experimental and theoretical studies of the behavior of particles in the inertial range, the reader is referred to Fuchs (1964). 

Deposition efficiencies for particles in the respiratory tract are generally presented as a function of their aerodynamic diameter (e.g. [8,12]). Large particles (> 10 pm) are removed from the airstream with nearly 100% efficiency by inertial impaction, mainly in the oropharynx. But as sedimentation becomes more dominant, the deposition efficiency decreases to a minimum of approximately 20% for particles with an aerodynamic diameter of 0.5 pm. When particles are smaller than 0.1 pm, the deposition efficiency increases again as a result of dif-fusional displacement. It is believed that 100% deposition due to Brownian motion might be possible for particles in the nanometer range. 

The inertial confinement concepts utilize the idea of heating a pellet of D-T-fuel either by absorption of light from a powerful laser, a relativistic electron beam or a heavy ion beam to the ignition temperature in a time short compared to vaporization of the pellet. The reaction time must also be short compared with the confinement time to allow a sufficient burn up of the fuel for energy gain. In addition, the range of the 3.5 MeV a-particles has to be shorter than the pellet radius if their energy is to be efficiently deposited in the pellet. 

The often expressed intuitive belief that small particles are more difficult to remove From a ga.s than laige ones is usually not correct. The particles most difficult to collect are those in the size range corresponding to the transition from diffusional to inertial deposition, usually between 0.1 and 1 iim. The transition may be strongly influenced by direct interception (finite particle diameter effect) depending on the dimensions of the system. 

The fate of an orally inhaled particle is strongly dependent on its aerodynamic diameter. Generally, particles larger than ca. 5 pm will inertially impact the mouth or throat, and be swallowed. Particles in the range of ca. 3-5 pm in diameter will reach the upper or conducting airways of the lung and can deposit on the smooth muscle of these structures. Particles of approximately 1-3pm may follow the airstream all the way to the alveoli and be deposited, and particles less than about 1 pm may be exhaled. Thus, careful control of the particle size distribution of medical aerosols is essential for effective drug delivery. 

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