Fundamentals of Particle Dynamics - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 137

Chapter 6
Fundamentals of Particle Dynamics

6.1 Introduction

The previous chapters have described the dynamics of fluid motion through the so-
lution of the Navier-Stokes and continuity equations, as well as different turbulence
models for turbulent flows. This chapter describes the fundamentals of particle dy-
namics in order to understand how particles move through the respiratory airway.
Particulate pollutant penetration into the respiratory passages and deposition are se-
rious health concerns, particularly for children and elderly people. It has been well
established that particulate pollutants are linked to a variety of symptoms includ-
ing decrease in lung function, aggravated asthma, chronic bronchitis, heart attacks
and premature death for people with heart disease history. Thus, understanding the
transport and deposition of inhalable particles in the respiratory airways has attracted
considerable attention in recent years.
Before discussing the particle dynamics, the terminology for particles needs to
be defined in the context of this topic and to distinguish it from other fields that
study particles (i.e. quantum, nuclear physics). A particle can be defined as a discrete
object or quantity of matter that is separated from the surrounding environment by an
interface. Suspension of solid or liquid particles in a gas is referred to it as an aerosol
particle or simply aerosol . Dust, smoke, mists, fog, haze, and smog are various
forms of common aerosols/particles. If the particle is made up of solid material, then
we can refer to it as a solid particle or particulate matter ( PM ) whereby the solid
particle does not deform. If the particle is made up of a liquid material then we refer
to it as a droplet where deformation, breakup and coalescence of the droplets may
occur. Dust, smoke, mist, fog, haze, and smog are various forms of common aerosols
in the atmosphere. As a generalisation, we shall refer to all the forms described above
simply as particles.
In this chapter the fundamentals of aerosol particle dynamics, its motion, transport
and deposition are described, which include expressions for hydrodynamic forces
including drag and lift, particle relaxation time, gravitational sedimentation velocity,
and stopping distance. Special considerations need to be made to model nanoparticle
transport including the Brownian motion and the Cunningham slip correction to
the drag. The particle transport and deposition can be analysed by the Eulerian or