Modelling for air pollution control

Period: 2017.03~2017.08

Purpose of this project: Calculate the dynamic motion of particles and develop air control model

class: Engineering and design for Air Pollution control

1. What is aerosol

A system of colloidal particles dispersed in a gas;smoke or fog.

Particle size: 0.002μm~100μm

Most of liquid phase aerosol is spherical and solid phase aerosol is non-spherical

Particle distribution can be divided into 3 modes;

Nuclei mode(0.001~0.1μm), Accumulation mode(0.1~2.5μm), Coarse particle mode(2.5~100μm)

2. Aerosol theory

2.1. Reynolds number

The Reynolds number is the ratio of inertial forces to viscous forces

within a fluid which is subjected to relative internal movement due to different fluid velocities.

Re = ρuL/μ

ρ is the density of the fluid (SI units: kg/m3)

u is the velocity of the fluid with respect to the object (m/s)

L is a characteristic linear dimension (m)

μ is the dynamic viscosity of the fluid (Pa·s or N·s/m2 or kg/m·s)

2.2. Stokes law (when Re<1)

3. Particles removal mechanisms

1. Cyclone

Polluted air from plants enters to cyclone. Then it is swirled by the mechanically generated wind.

Large particles: have too much inertia to follow the tight curve of the stream, and strike the outside wall, then fall to the bottom of the cyclone.

Lapple's model

The first developed cyclone medel.

It is based on plug flow. (+Simple structure)

μ: viscosity of air

b: inlet width

Ne: number of turns the flow makes from the entrance to the midpoint of the core section

Vi: inlet velocity

p: particle density

Collection efficiency

1/(1+(dp50%/total inlet)^2)

->With this equation I made simple cyclone model.

If I can get the information of inlet flow, particle density, viscosity of air and Inlet particles, I can calculate optimal inlet width of Cyclone. (and for Ne, I need to caculate this value with another concerned equations based on several assumption.)

2. Filter dust collector

Powder plants have filter dust collector.

Influent temperature: 25 Celsius

Pressure: 1atm flow: 9000Nm^3/hr

Velocity: 1m/min,

D(of filter bag):156mm

Length of filter bag: 3m,

distance btw bags:10cm ->design this filter dust collector into 1/10 size