Mechanistic Factors Affecting The Deposition Of Aerosols

Factors affecting the deposition of aerosols can be divided into two groups: those that are determined primarily by the patient and those that are due essentially to the properties of the aerosol themselves.

Mechanisms

There are five basic physical mechanisms that cause the deposition of aerosols. Inertial Impaction

Inertial impaction is caused by the tendency of particles and droplets to move in a straight direction instead of following the gas streamlines. Hence, impaction may occur on the obstacle downstream in the trajectory of the particle.

If a particle with mass m is moving with initial velocity v0, through still air, then it can be shown [22] that, as a result of fictional forces, the particle will stop after traveling the stopping distance, S:

where B is the mechanical mobility of the particle (i.e., the velocity per unit of force). The stopping distance in an extreme impaction situation is the distance the particle would travel in the original direction of motion from the point where the gas stream, which carries it, turns at a right angle. Clearly, the greater the particle mobility, mass, and initial velocity, the longer it will persist flying in the original direction, and, therefore, its chances of hitting the obstacle placed in front of it are increased.

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