A New Mesh-Independent Model for Droplet/Particle Collision

Abstract

The droplet collision algorithm of O’Rourke has been considered as the standard approach of droplet collision calculations. This model is based on the assumption that those droplets within a parcel are distributed uniformly in a single computational cell and also other parcels are considered to be collision partners only if they are located in the same cell. Hence, it has a problem of mesh dependency for the calculation of collision rate resulting obviously from the block of collision by cell boundaries and droplet density distortion when the average parcel number per cell, ψ, is small. This can cause an unacceptable computational expense for engineering applications. To overcome the above problem, the present study establishes a new mesh-independent collision model based on the adaptation of the volume in which droplets within a parcel are uniformly distributed and the corresponding space for search of the collision partners. The new model is found valid over a wide range of ψ. The collision rate calculated from it agrees well with O’Rourke's model for large ψ and remains virtually invariable with ψ. This allows an appropriate calculation to use significantly less parcels and thus less time. Such an advantage of the new model is confirmed in its application to a three-dimensional (3D) case. The 3D calculation also suggests that fine particles tend to agglomerate where the fluid flow direction changes rapidly and in between two eddies where they interact with each other.

Copyright 2012 American Association for Aerosol Research

Acknowledgments

This work was supported by the Natural Science Foundation of China (grant no. 50876001, 50706001) and also by the Ministry of Science and Technology of China through an 863 project (grant no. 2007AA05Z300).

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