Department of Chemical Engineering

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Silver-polymer core-shell nanoparticles show interesting optical properties, making them widely applicable in the field of plasmonics. The uniformity, thickness and homogeneity of the polymer shell will affect the properties of the system which makes a thorough structural characterization of these core-shell silver-polymer nanoparticles of great importance. However, visualizing the shell and the particle simultaneously is far from straightforward due to the sensitivity of the polymer shell towards the electron beam. In this study, we use different 2D and 3D electron microscopy techniques to investigate different structural aspects of the polymer coating. © 2018 The Royal Society of Chemistry.

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Nanoscale

Characterization of silver-polymer core-shell nanoparticles using electron microscopy

Steady two-dimensional solutions and their stability analysis are presented for thin film of a thermoviscous liquid flowing inside a cylinder rotating about its horizontal axis. The inner surface of the cylinder is either uniformly hotter or colder than the enveloping air. The mass, momentum, and energy equations are simplified using thin-film approximation. The analytically obtained film thickness evolution equation consists of various dimensionless parameters such as gravitational number, Bond number, Biot number, thermoviscosity number, and Marangoni number. The viscosity of the liquid is considered as an exponential function of temperature. The viscosity increases (decreases) within the film thickness away from the inner surface of the cylinder when the surface is uniformly hotter (colder) than the atmosphere. For hotter (colder) surface, the film thickness on the rising side decreases (increases) when convective heat transfer at the free surface is increased. The surface tension gradient at the free surface generates Marangoni stress that has a destabilizing (stabilizing) effect on the thin film flow in the case of a hotter (colder) cylinder. The thermoviscosity number stabilizes (destabilizes) the flow on a heating (cooling) surface and this effect increases with an increase in the heat transfer at the free surface. For a hotter surface and in the presence of Marangoni stress, the convective heat transfer at the interface has the destabilizing effect for small values of the Biot number and assumes a stabilizing role for larger values. Non-linear simulations show consistency with the linear stability analysis. © 2018 Author(s).

Physics of Fluids

Hydrodynamic stability of thermoviscous liquid film inside a rotating horizontal cylinder: Heating and cooling effects

APS March Meeting Abstracts 2018, E17.

Effect of Thermocapillary stress on the Stability of a Non-isothermal Thin Liquid Film Flowing Inside a Heated Rotating Horizontal Cylinder

This paper reports on the determination of the flame height of a flare system using theoretical approach based on the laws of conservation of mass, momentum and energy. The set of ordinary differential equations at steady state conditions are solved numerically by fourth order Runge-Kutta method. The extent of reaction between the fuel and the entrained air has been studied by introducing the reaction mixing efficiency parameter, as the reaction rate is fixed by local entrainment rate. The reaction mixing efficiency parameter is a key measure to determine the height of the flame and its variation with the source velocity is limited by the flame width and the maximum vertical flame velocity at the tip of the flaming region. The variation of different parameters as vertical flame velocity, flame geometry and flame temperature with flame height are shown in plots. It is found that the flame geometry undergoes an initial necking up to a certain height, followed by an increase in its spread thereafter. The flame geometry and the flame dynamics depend exclusively on the burner design and the stack exit velocity. The flame height to burner diameter ratio of the jet diffusion flame is found to vary linearly with Froude number with a constant slope in the logarithmic plot. © 2018 Universidad Nacional Autonoma de Mexico. All rights reserved.

Journal of Applied Research and Technology

One dimensional modeling of jet diffusion flame

In this paper, topology identification of dynamic systems in the continuous time (CT) framework is considered. The main objective is to identify the direction of information flow and to estimate the transfer function of each node simultaneously. The output of each node is affected by the outputs of the other nodes along with transportation delay and noise. In contrast to the existing works which are in discrete setting, the current paper uses continuous orthonormal basis to represent the transfer functions. As the network is sparsely connected, the topology identification problem is defined as an estimation of a block-sparse signal from the measurements and a standard l0 minimization algorithm known as the block orthogonal matching pursuit (BOMP) is used to identify the topology. The accuracy of the proposed method is demonstrated using data obtained from a system of interconnected tanks. A comparison with discrete time topology identification methods shows that the CT method is more robust and provides the exact topology with higher probability. © 2018 IEEE.

2018 Indian Control Conference, ICC 2018 - Proceedings

Topology identification of sparse networks of continuous time systems

Ni3(VO4)2 nanosheet arrays are grown on aminated r-GO sheets through a facile hydrothermal route. The growth of Ni3(VO4)2 nanosheet arrays on aminated r-GO sheets (NiV@r-GO nanocomposites) is confirmed by XRD, FESEM, TEM, XPS, and Raman spectroscopy. The length, height and thickness of the Ni3(VO4)2 nanosheet arrays are ∼100, ∼20 and ∼10 nm, respectively. The density of the Ni3(VO4)2 nanosheet arrays on the r-GO sheets is directly related to the concentration of precursor used. The generation of mesoporosity during synthesis originates from the high surface area in the NiV@r-GO nanocomposites. The high surface area causes the mesoporous NiV@r-GO nanocomposite based electrode to exhibit a specific capacity of 170 C g-1 at 0.5 A g-1, which is approximately three times higher than that of aminated r-GO sheets. The capacity retention of the NiV@r-GO nanocomposite is 97.2% at 0.5 A g-1 current density after 1400 cycles. Other than the faradic redox reaction, the superior electrochemical performance of NiV@r-GO nanocomposites over the aminated r-GO sheet based electrode is related to the three-dimensional (3D) morphology as an effect of the Ni3(VO4)2 nanosheet array, which results in a higher surface area, more active sites and greater electrolyte penetration in the electrode. © 2018 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

New Journal of Chemistry

Free-standing Ni3(VO4)2 nanosheet arrays on aminated r-GO sheets for supercapacitor applications

In this work, we have presented the numerical results for 2D, steady, laminar and incompressible flow in a square, two-sided, lid-driven cavity with a decentered heated triangular block (maintained at the isothermal thermal condition, TH) for non- Newtonian power-law fluids. The range of flow governing parameters considered for the numerical experimentations are Reynolds number (100 ≤ Re ≤ 1000), Richardson Number (Ri = 0.01, 1, 10) power law index; (0.2 ≤ n ≤ 1.8), blockage (10% and 30% of the height of cavity) and Prandtl number of Pr = 1. The upper and lower walls of the square cavity are kept moving in the opposite directions along –x axis (u−ux) and are thermally insulated. The left and right stationary walls are exposed to ambient condition (Tc). The governing flow equations are solved by using the finite volume approach and SIMPLE algorithm. Heat transfer characteristics and flow kinematics are revealed by systematic variation of streamlines and temperature contours. The effect of mixed convection parameter, i.e., Ri, found to have a negligible impact on fluid and thermal structure inside the cavity for fluids with n = 0.2.Heat transfer rate found to be lower for Ri = 0.01 for both blockages. © 2018 Elsevier Ltd

International Journal of Mechanical Sciences

Mixed convection in a two-sided lid-driven cavity containing heated triangular block for non-Newtonian power-law fluids

The efficacy of electrocoalescence is critically dependent upon the interfacial tension of the crude–water interface. This study demonstrates the effect of interfacial tension on the electrocoalescence efficiency in crudes with high acidity. The interfacial tension is estimated using spinning drop tensiometer (SDT) and electrocoalescence experiments are performed at an electric field = 1.15 kVrms/cm at a frequency of 50 Hz. It is observed that separation of water from the crude is hindered at high pH for two very different reasons depending upon the source of alkalinity. Calcium hydroxide induced alkalinity leads to more rigid interface, resulting in delayed electrocoalescence. On the other hand, sodium hydroxide based alkalinity leads to ultra-low tension of crude–water interface, thereby causing oil-in-water emulsion. Increase in the pH also leads to poor quality of brine resolution, in case of sodium hydroxide based alkalinity (pH = 10) we get unresolved turbid emulsion. © 2018 Elsevier B.V.

Colloids and Surfaces A: Physicochemical and Engineering Aspects

Interrelationship between electrocoalescence and interfacial tension in a high acidity crude: Effect of pH and nature of alkalinity

Transition metal oxides are the primary choice for cathode materials in lithium ion batteries. These oxides occur as different polymorphs that have varied structures, stabilities, and affinities for Li+, and consequently, it is desirable to develop heuristics for the choice of the optimal polymorph. MnO2 is the most extensively used cathode material for lithium ion battery, and it exists in more than ten polymorphic forms. Among them, γ-MnO2, the most electrochemically active polymorph, is a mixture of pyrolusite and ramsdellite polymorphs. Here we have focused on the less explored ramsdellite MnO2 (R-MnO2). Highly crystalline R-MnO2 has been synthesized, and the experimentally obtained discharge features are compared with the calculations based on density functional theory followed by cluster expansion to obtain molecular insights into the intercalation process. R-MnO2 shows voltage fading beyond x = 0.5 (in LixMnO2). Computational results suggest that change in Li environment from tetrahedral to octahedral beyond x = 0.5 (in LixMnO2) causes the voltage fading. This change in Li environment is also correlated with experimentally obtained Mn 2p, O 1s, and valence band XPS spectra. The shift in the d-band center, plotted for valence band spectra at different lithium concentrations, is adduced for the migration of lithium ion from the tetrahedral site to the less favorable octahedral site beyond x = 0.5. Volume expansion of about 20% at full lithiation is accompanied by Jahn-Teller distortion of MnO6. Further, computations reveal the diffusional energy barrier to be 200 meV in the limit of dilute Li concentration (x = 0.125) and 481 meV in the limit of dilute vacancy concentration (x = 0.875). A structural rationale for the energy barrier is developed. The experimental and computational studies provide insight into the lithiation mechanism in R-MnO2 and are relevant to rationalize the high performance of the intergrowth structure of γ-MnO2. We discuss a wider implication of the study by correlating the voltage profile with structural changes in MnO2 polymorphs, which gives general design principles to make better cathodes through polymorphic engineering. © 2018 American Chemical Society.

Journal of Physical Chemistry C

Correlating Voltage Profile to Molecular Transformations in Ramsdellite MnO2 and Its Implication for Polymorph Engineering of Lithium Ion Battery Cathodes

Disinfectants are typically used in water distribution networks (WDNs) to maintain the microbiological quality of potable water throughout the network. Disinfectant residual levels in such large distribution networks need to be maintained within the prescribed bounds to address two major problems: (1) preventing microbial regrowth, and (2) minimizing harmful disinfection by-product (DBP) formation resulting from high levels of the disinfectant itself. These requirements pose a two-point constrained control problem of disinfectant residual levels. Another important aspect of consideration is that such WDNs exhibit spatial and temporal variations in water quality at different points in the network. Therefore, conventional systems engineering tools such as modeling, optimization, and control need to be adapted to accommodate these variations for water quality management in distribution networks. In this paper, we propose a novel zone control based approach to address the two-point quality control problem. Further, to combat the spatial complexity, we combine the zone control approach with a decentralized optimization strategy, namely, the model coordination method, which has been widely proposed to solve large-scale optimization problems. The resulting novel formulation is proposed here to address the aforementioned problems in operational optimization of booster chlorination water distribution systems by using a realistic multispecies model developed from a previous study. We demonstrate the efficacy of this approach on a real-scale distribution network of Cherry Hill Brushy Plains (CH/BP) (EPANET Example network 2). © 2018 American Society of Civil Engineers.