Modeling Collision Efficiencies for Coalescence of Small Drops and Particles

EPA Grant Number: R827115
Title: Modeling Collision Efficiencies for Coalescence of Small Drops and Particles
Investigators: Koch, Donald L.
Institution: Cornell University
EPA Project Officer: Shapiro, Paul
Project Period: October 1, 1998 through September 30, 2001
Project Amount: $305,155
RFA: Exploratory Research - Physics (1998) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Land and Waste Management , Air , Engineering and Environmental Chemistry


Coagulation of particulate pollutants and drop-drop and drop-particle coalescence play important roles in the transport of pollutants and in strategies for pollution prevention. Particle-particle collisions may be driven by Brownian motion, atmospheric turbulence, or differential sedimentation. Although one can easily make an estimate of coalescence rate based on an assumption that particles do not interact and every collision leads to coalescence, the actual coalescence rate is usually much smaller. The objective of this project is to compute the collision efficiency, the ratio of the actual coalescence rate to the hypothetical rate for non-interacting particles for particles and/or drops with diameters of 0.01 - 100 µm.


When the interfacial deformation induced by viscous forces between colliding drops is sufficiently large, the drops will bounce before the gas is forced out of the gap between them. We will solve coupled partial differential equations describing the interfacial deformation and the non-continuum lubrication flow in the gap between drops to determine the conditions for which a bounce occurs. The accuracy of these calculations will be tested by comparing with high-speed video observations of drop-interface collisions. Non-continuum gas flow plays an important role in the coagulation of small particles. We will develop a new simulation based on the direct-simulation Monte Carlo technique to solve the linearized Boltzmann equation for this rarefied gas flow. The resulting predictions of the gas' resistance to particles' motion will be incorporated into computations of the dynamics of particle collisions driven by Brownian motion, sedimentation and turbulence.

Expected Results:

The theoretical predictions of collision efficiency will clarify the dependence of coagulation rate on the size, mass and relative velocity of the particles, the pressure of the gas, and the surface tension of the air-liquid interface. These predictions will improve the accuracy of models for pollution-control technologies, the transport of particulate pollutants, and the scavenging pollutants by precipitation.

Publications and Presentations:

Publications have been submitted on this project: View all 7 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 4 journal articles for this project

Supplemental Keywords:

particulate pollution, toxicity, air pollution control, pollutant transport modelling, combustion., RFA, Scientific Discipline, Air, Waste, particulate matter, Environmental Chemistry, Physics, Atmospheric Sciences, Ecology and Ecosystems, Engineering, Chemistry, & Physics, Incineration/Combustion, collision efficiency models, pollution control technologies, air pollution modeling system, air pollution, Brownian motion, pollutant transport, differential sedimentation, emission controls, atmospheric transport, coalescence, particle surface interactions, incineration, pollution dispersion models, particle collision models, atmospheric models, particle collision, particle transport

Progress and Final Reports:

  • 1999 Progress Report
  • 2000 Progress Report
  • Final Report