The role of particle-flow interactions in cloud microphysics
by
Pijush Patra
→
Europe/Stockholm
Albano Building 3
Albano Building 3
Description
zoom link : https://stockholmuniversity.zoom.us/j/622224375
The collision of particles sedimenting in a flow field is relevant to many environmental and industrial processes, such as droplet growth in warm clouds and the aggregation of aerosol particles in industrial settings. The evolution of the drop size distribution in clouds depends on the collision rate between the drops, where the combined effects of background flow, gravity, and interparticle interactions drive the collision dynamics. A study of this problem may explain the condensation-coalescence bottleneck (or the ‘size gap’ of 15 - 40 microns droplets) in warm rain formation, where neither condensation nor gravitational collision alone is the dominant growth mechanism. We have focused on studying the collision dynamics of particle pairs subject to a background flow (simple shear flow, turbulent flow) and gravity, incorporating hydrodynamic and interparticle interactions.
In the first problem, we have studied the role of Brownian motion in the coagulation of bidisperse like-charged spherical particles interacting via non-continuum hydrodynamics, van der Waals, and electrostatic interactions. We have found that electrostatic interactions can enhance the collision rate between like-charged Brownian particles while interacting through non-continuum hydrodynamics, and their charge ratio is high. To consider the effect of a background flow, we have studied the collision of hydrodynamically interacting particle pairs settling in a laminar simple shear flow. By incorporating non-continuum hydrodynamics, van der Waals interactions, and the coupled driving forces of sedimentation and simple shear, our work provides collision efficiency results relevant to flows of suspensions through vertical pipes and channels, sampling of aerosols, and the transport of particulate matter in riser reactors. Finally, we have also investigated collision dynamics of sub-Kolmogorov interacting spheres rapidly settling in a homogeneous isotropic turbulent flow. This work relied on formulating an equation for the pair probability PDF and solving it semi-analytically.
