aerosol-particle-transport-modeling-explanationGDE

CONVECTION (Free or Natural Convection)
- For the Free or Natural Convection: Use Bousinessq Parameters (Bousinessq Model) to consider Bouyancy effect.
- The default operating temperature is under Boussinesq Parameters.
This temperature will be the temperature of the wall, . (lower hot).
- It is tempting to specify an operating density here too, but the help panels say that it is not necessary to specify operating density when using the Boussinesq approximation.
- The air movement is normally promoted by temperature difference between warm zone and cold zone under natural convection situations, and/or by pressure difference due to wind or mechanical ventilation. It is known that the airflow pattern plays a fundamental role in the deposition, migration and distribution of aerosol particles in the multi-zone area.

EXTERNAL FORCES
* Gravity force or Body force
Here are the influences of Gravity force or Body force for particles:
- particles size dp > 4 micron will deposit on internal surfaces quickly under the influence of gravity,
- particles size less than 2 micron may become aerosol particles and remain suspended in the air and the occupied spaces in which particle molecular diffusion and air movement dominate the particles’ movement and the gravitational force becomes less important.
- particles which are between 2 and 4 micron may settle down on the interior surfaces or remain suspended in the air, which is mainly influenced by both the airflow pattern and gravity.

*Thermophoresis
- Thermophoresis refers to the behavior in which aerosol particles suspended in a gas acquire a velocity in the direction of decreasing temperature due to collisions with the surrounding gas molecules. In a non-isothermal system with relatively cool walls, thermophoresis causes aerosol particles to move toward and deposit on the walls.

*Initial force

*Stochastic Brownian force
- the translational and rotational motion of rigid aggregates of aerosol particles has been developed, taking into account the stochastic Brownian force, gravity, and the hydrodynamic drag as functions of the size, overall shape and internal structure of the aggregate.

*Drag force (hydrodynamic drag)
- in parallel side : use Stoke’s drag equation with Faxen’s correction
- The steady state drag is the drag force which acts on the particle in a uniform pressure field when there is no acceleration or deceleration of the relative motion between the particle and the conveying fluid.
- The drag force at various Reynolds numbers is based on the introduction of the drag coefficient CD. (Further in El-Batsh theory, p.32, 38).

*coulombic force

*image force

*Rarefaction effect
- Rarefaction effect becomes important when the particles are very small. In such a situation, the gas flow around the particle can not be regarded as a continuum. Instead, the particle motion is induced by collisions of gas molecules with the particle surface. This results in a reduction of the drag coefficient. (Further in El-Batsh theory, p.33, 39).

*Pressure Gradient Force and Unsteady Forces
- The local pressure gradient in the flow gives an additional force in the direction of the pressure gradient.
- In addition, the acceleration or deceleration of the relative velocity between the particle and the fluid produces forces which can be divided into two parts: the virtual mass effect and the Basset force.
- The virtual mass effect relates to the force required to accelerate or decelerate the surrounding fluid. The Basset term describes the force due to the lag of boundary layer development with changing relative velocity.

DIFFUSION
- the process whereby particles of liquids, gases, or solids intermingle as the result of their spontaneous movement caused by thermal agitation and in dissolved substances move from a region of higher to one of lower concentration.
- The diffusion coefficient is shown to be a strong function of the number of particles forming the aggregate (N), as well as of the detailed structure of the aggregate (Moska and Pavatakes, 2006).

COAGULATION
*Particle-particle interaction

*Summation over the entire particle size distribution

PARTICLEGROWTH

INTERNALSOURCES

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