parcel
 

I am working on two-phase flow (particle tracking based on Eulerian-Lagrangian method). I have a question.

In many papers, the concept of parcel as a representative of a number of particles is used.

What is the exact procedure of defining this? Is there any limitation?which similarity needed for defining this concept?:confused:

When we used the concept of parcel, we put the total mass of included particles in parcel for mass balancing. We set the diameter of parcel k times of particle diameter. But the size of particle affect on drag force and other related forces.

Then, I completely confused that what happen for dynamics of flow? What is the strategy for determining mass, size, position and velocity of parcel. If it is necessary to change the continuous or dispersed phases physical properties for similarity?