Capillary filling dynamics of water in nanopores

We portray a universal description of dynamic slip-stick behavior of water flowing through nanoscale pores. Based on fundamental molecular transport considerations, we derive a generalized constitutive model for describing resistive forces acting on the water column in a capillary that is being dynamically filled, as a combined function of the meniscus height, surface wettability, and roughness. This effectively acts like a unique signature of nanopore imbibition characteristics of water, which, when substituted in a simple one-dimensional force balance model agrees quantitatively with results from molecular dynamics simulations for a general class of problems, without necessitating the employment of any artificially tunable fitting parameters

Electrokinetic energy conversion in nanofluidic channels: addressing the loose ends in nanodevice efficiency

We bring out a nontrivial coupling of the intrinsic wettability, surface charge, and electrokinetic energy conversion characteristics of nanofluidic devices. Our analyses demonstrate that nanofluidic energy conversion efficiencies may get amplified with increase in surface charge density, not perpetually, but only over a narrow regime of low surface charges, and may get significantly arrested to reach a plateau beyond a threshold surface charging condition, as attributed to a complex interplay between fluid structuration and ionic transport within a charged interfacial layer. We explain the corresponding findings from our molecular dynamics simulations with the aid of a simple modified continuum based theory. We attribute our findings to hitherto-unexplored four-way integration of surface charge, interfacial slip, ionic transport, and the water molecule structuration. The consequent complex nonlinear nature of the energy transfer characteristics may bear far-ranging scientific and technological implications toward design, synthesis, and operation of futuristic energy conversion devices of molecular length scales

Improving water removal efficiency in a PEM fuel cell: Microstructured surfaces for controlling instability-driven pinching

Proton Exchange Membrane Fuel Cell (PEMFC) is a clean, sustainable energy generation device, and its large-scale usage is becoming popular due to green and secure energy demand worldwide. The performance, efficiency, and lifespan of PEMFC largely depend on the water removal and management within the cell. Under the influence of the cross-air flow, the generated water filaments deform, and as the filament radius lowers, the curvature and capillary pressure increase, ejecting fluid out of the neck at increasing velocities. The moment the filament radius vanishes, the governing equations reach the point of singularity, and the filament breaks. We propose an optimum micro-patterned surface design for efficient water removal from PEMFC. We perform a numerical study of water generation on the surface followed by breakup under shear flow within confinement. We further theoretically identify the breakup behavior with characterization, recognizing the influence of the microstructures toward an efficient design. The hydrophobic microstructures are observed to decrease the dominance of viscous force over inertia and capillary force. This leads to a greater propensity of end-pinching or truncation of the generated droplet at the neck, which reduces the production of undesired satellite droplets that would have otherwise caused flooding of the chamber. In this work, we show that a proper combination of substrate structure and jet velocity-induced shear can mitigate the generation of satellite droplets and reduce the breakup time, significantly increasing the water removal efficiency of the PEMFC

Nonlinear Amplification in Electrokinetic Pumping in Nanochannels in the Presence of Hydrophobic Interactions

We discover a nonlinear coupling between the hydrophobicity of a charged substrate and electrokinetic pumping in narrow fluidic confinements. Our analyses demonstrate that the effective electrokinetic transport in nanochannels may get massively amplified over a regime of bare surface potentials and may subsequently get attenuated beyond a threshold surface charging condition because of a complex interplay between reduced hydrodynamic resistance on account of the spontaneous inception of a less dense interfacial phase and ionic transport within the electrical double layer. We also show that the essential physics delineated by our mesoscopic model, when expressed in terms of a simple mathematical formula, agrees remarkably with that portrayed by molecular dynamics simulations. The nontrivial characteristics of the initial increment followed by a decrement of the effective zeta potential with a bare surface potential may open up the realm of hitherto unexplored operating regimes of electrohydrodynamically actuated nanofluidic devices

Slippery to Sticky Transition of Hydrophobic Nanochannels

Contrary to common intuition that hydrophobic surfaces trivially cause water to slip, we discover a slippery-to-sticky transition in tunable hydrophobic nanochannels. We demonstrate this remarkable phenomenon by bringing out hitherto unveiled interplay between ion inclusions in the water and the interfacial lattice configuration over molecular scales. The consequent alterations in frictional characteristics illustrate that so-called hydrophobic nanochannels can be switchable to manifest features that are otherwise typically associated with hydrophilicity, causing water to stick. Our proposition may bear immense consequences toward fluidically functionalizing a hydrophobic interface without necessitating elaborate surface treatment techniques, bringing in far-ranging implications in diverse applications ranging from nature to energy

Renewable energy potential towards attainment of net-zero energy buildings status – A critical review

Global warming, climate change, and resource depletion have forced us to reconsider energy usage and efficiencies over the last few decades. Residential and commercial buildings are both large energy consumers, so improving energy and material usage efficiency in this sector is a common research topic. According to a recent study, the Building Sector (BS) accounts for 40% of greenhouse gas emissions. The primary objective of this paper is to examine and assess the potential of Renewable Energy Systems (RES) and their combinations for enhancing energy efficiency in the BS. Specifically, the focus will be on converting low energy-efficient buildings into highly efficient ones. The potential of the RES and their combinations for the BS is evaluated based on payback durations, energy generation, and reduction of CO2 emissions. The optimization flow charts for the RES, feasibility studies, commercialization road maps of energy storage systems and the necessity of control mechanisms for enhancing RES efficiency were discussed. Additionally, the technology drawbacks are discussed, along with various innovative techniques recommended to direct future study in this area. Finally, this article assists the audience clear idea in the selection of the right combination of potential RES based on different conditions to achieve deep decarbonization in BSs