Neelarun Mukherjee

Neelarun Mukherjee

Ph.D. Candidate @UT Austin

Publications

Three-dimensional Simulations of Two-phase Plug Flow in a Microfluidic Channel

Published in Physics of Fluids, 2024

Abstract: A fundamental understanding of two-phase flow behavior in microfluidics is crucial for various technological applications across different disciplines, including energy, chemical, and material engineering, as well as biomedical, environmental, and pharmaceutical sciences. In this work, we elucidate the flow fields of low Capillary number [Ca] segmented Taylor flows of immiscible CO2 emulsions/bubbles transported by water in a low aspect ratio microchannel. We conducted high-resolution two- and three-dimensional (2D and 3D) numerical simulations using an improved volume-of-fluid two-phase flow solver and validated their accuracy against experimental data. Our results show that 3D simulations are necessary to accurately capture the dynamics of liquid and supercritical CO2 emulsions produced at relatively higher Ca. The 3D simulation results also reveal diverse patterns of spanwise vortices, which are overlooked in 2D simulations. Calculating the Q-criterion in 3D revealed that vortices with relatively higher vorticity magnitudes are adjacent to the sidewalls, with the strongest ones emerging across the microchannel in the third dimension. More specifically, gaseous CO2 bubbles display relatively intense vortex patterns near the interfacial region of the bubble body and the cap due to the influence of the surrounding thin liquid film and slug flow. At higher Ca, liquid and supercritical CO2 emulsions exhibit similar flow dynamics, however, with prominent vortex patterns occurring in the upstream cap region. These findings pinpoint specific areas within the emulsions/bubbles that require attention to enhance stabilization or exchanging mechanisms for low-Ca Taylor flow of emulsions/bubbles.

Recommended citation: https://doi.org/10.1063/5.0220101

Groundwater Dominates Fluxes of Water and Organic Carbon in a Permafrost Watershed Across Hydrologic States

Published in Journal of Hydrogeology (under review), 2024

Abstract: Supra-permafrost aquifers within the active layer are present in the Arctic during summer. Permafrost thawing due to Arctic warming can liberate previously frozen particulate organic matter (POM) in soils to leach into groundwater as dissolved organic carbon (DOC). DOC transport from groundwater to surface water is poorly understood because of the unquantified variability in subsurface properties and hydrological environments. These dynamics must be better characterized because DOC transport to surface waters is critical to predicting the long-term fate of recently thawed carbon in permafrost environments. Here, we quantified groundwater and DOC fluxes based on Darcy’s Law into Imnavait Creek, Alaska, a representative headwater stream of a continuous permafrost watershed. We developed a statistical ensemble approach to model steady-state groundwater flow. We quantified the model prediction uncertainty using statistical sampling of in situ active layer soil hydro-stratigraphy, high-resolution topography data, and DOC data. The predicted groundwater discharge values representing all possible hydrologic conditions towards the end of the thawing season are similar to and span the observed range of Imnavait Creek streamflow. As the Arctic warms and the supra-permafrost aquifer deepens, groundwater flow is expected to increase. This increase is expected to impact river and lake biogeochemical processes by dissolving and mobilizing more soil constituents in continuous permafrost regions. This study highlights how quantifying the uncertainty of hydro-stratigraphical input parameters helps understand and predict supra-permafrost aquifer dynamics and connectivity to aquatic systems using a simple, but scalable, modeling approach.

Recommended citation: (Under Review) Mukherjee, Neelarun and Chen, Jingyi and Neilson, Bethany T. and Kling, George W. and Cardenas, M. Bayani, Groundwater Dominates Fluxes of Water and Organic Carbon in a Permafrost Watershed Across Hydrologic States. Available at SSRN: https://ssrn.com/abstract=4783339 or http://dx.doi.org/10.2139/ssrn.4783339 --