arXiv subjects

Johnson Dhanasekaran

Publications and source records attributed to Johnson Dhanasekaran.

3 recordsLinked to original sources

arXiv2025

The effect of turbulence, gravity, and non-continuum hydrodynamic interactions on the drop size distribution in clouds

The evolution of micron-sized droplets in clouds is studied with focus on the 'size-gap' regime of 15-40 $μm$ radius, where condensation and differential sedimentation are least effective in promoting growth. This bottleneck leads to inaccurate growth models and turbulence can potentially rectify disagreement with in-situ cloud measurements. The role of turbulent collisions, mixing of droplets, and water vapour fluctuations in crossing the 'size-gap' has been analysed in detail. Collisions driven by the coupled effects of turbulent shear and differential sedimentation are shown to grow drizzle sized droplets. Growth is also promoted by turbulence-induced water vapour fluctuations, which maintain polydispersity during the initial condensation driven growth and facilitate subsequent growth by differential sedimentation driven coalescence. The collision rate of droplets is strongly influenced by non-continuum hydrodynamics and so the size evolution beyond the condensation regime is found to be very sensitive to the mean free path of air. Turbulence-induced inertial clustering leads to a moderate enhancement in the growth rate but the intermittency of the turbulent shear rate does not change the coalescence rate significantly. The coupled influence of all these phenomena is evaluated by evolving a large number of droplets within an adiabatically rising parcel of air using a Monte Carlo scheme that captures turbulent intermittency and mixing.

physics.flu-dyn↗

arXiv2022

Current rectification by nanoparticles in bipolar nanopores

Bipolar nanochannels comprising two domains of positively and negatively charged walls along the pore axis are known to rectify current when exposed to an electric potential bias. We find that addition of charged nanoparticles can increase rectification considerably, by approximately one order of magnitude. Two bipolar channel geometries are considered here; their behavior is examined at rest and under the influence of a negative bias and a positive bias, respectively. We do so by relying on a molecular-level model of the electrolyte solution in the channels. The large increase in current rectification can be explained by the inherent electric field that charged nanoparticles generate within the channel. This effect is found to be largely dependent on the pore's geometry, its charge distribution, and the sign of the nanoparticles' charge, thereby offering new opportunities for design of engineered nanopore membrane-nanoparticle systems for energy storage.

physics.chem-ph↗

arXiv2022

Ionic transport in electrostatic Janus Membranes. An explicit solvent molecular dynamic simulation

Janus --or two-sided, charged membranes offer promise as ionic current rectifiers. In such systems, pores consisting of two regions of opposite charge can be used to generate a current from a gradient in salinity. The efficiency of \textcolor{black}{nanoscale} Janus pores increases dramatically as their diameter becomes smaller. However, little is known about the underlying transport processes\textcolor{black}{, particularly under experimentally accessible conditions}. In this work, we examine the molecular basis for rectification in Janus nanopores using an applied electric field. Molecular simulations with explicit water and ions are used to examine the structure and dynamics of all molecular species in aqueous electrolyte solutions. \textcolor{black}{For several macroscopic observables, the results of such simulations are consistent with experimental observations on asymmetric membranes. Our analysis reveals a number of previously unknown features, including a pronounced local re-orientation of water molecules in the pores, and a segregation of ionic species that has not been anticipated by previously reported continuum analyses of Janus pores. Using these insights, a model is proposed for ionic current rectification in which electric leakage at pore entrance controls net transport.

physics.chem-ph↗