Department of Chemical Engineering

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In the present work, heat transfer and fluid flow characteristics for both Newtonian and non-Newtonian fluids in tube-in-tube helical coil (TTHC) heat exchangers have been investigated numerically. The various TTHC heat exchanger configurations studied are (1) parallel and (2) counter flow, with and without baffles. The power law index (n) and Dean number (NDe) are varied from 0.5 to 1.25 and 50 to 500, respectively. Further, two different models have been proposed to predict the friction factor (f) and Nusselt number (Nu) in TTHC. It is observed that f and Nu in the TTHC heat exchanger with baffles in the annulus is higher as compared to without baffles. Furthermore, at low Prandtl number the baffles have significant influence on heat transfer, while at high Prandtl number flow configuration has high significance. Copyright © 2020 American Chemical Society.

World University root node

Industrial \& Engineering Chemistry Research

Heat transfer and fluid flow characteristics for Newtonian and non-Newtonian fluids in a tube-in-tube helical coil heat exchanger

Electrical Impedance Tomography (EIT) can be used to study the hydrodynamic characteristics in multi-phase flows such as gas holdup in bubble columns, air-core in hydrocyclone, etc. In EIT, the main objective is to estimate the electrical properties (conductivity distribution) of an object in a region of interest based on the surface voltage measurements. The main challenge in such reconstruction (estimation of conductivity distribution) is the low spatial resolution. In this paper, a sparse optimization approach for image reconstruction in EIT is presented. The main idea presented in this article is based on considering the L1 norm on the data term, which enhances the reconstruction of conductivity distributions with sharp changes near phase boundaries. Further, this method is also robust to outliers in the data. The accuracy of the proposed method is demonstrated with the help of two phantoms, and a comparison with the existing methods is also presented. Copyright © 2020 The Authors. This is an open access article under the CC BY-NC-ND license

IFAC-PapersOnLine

Sparsity constrained reconstruction for electrical impedance tomography

The present numerical work delineates the flow and heat transfer characteristics due to the combined convection (free and forced) inside semi-circular, top lid-driven cavity. The flow conditions are assumed to be laminar, steady-state, incompressible, and for non-Newtonian power-law fluids. The curved surface of the cavity is subjugated to constant heat flux (CHF) thermal condition, while the top wall is sliding with uniform velocity (Ulid) along –x-direction. The governing parameters utilized for numerical experimentation are Richardson number (Ri = 0.1–10), non-Newtonian power-law index (n = 0.5–1.5), modified Prandtl number (Pr = 1–100) and Grashof number (Gr = 104). The study is also intended to provide a comparative explanation for the use of adiabatic blockage of varying cross-sections on the flow and thermal patterns in the cavity. In particular, the influence of the shape of blockage in the cavity, viz., circular, square, and triangular investigated. Normalized Nusselt numbers have also plotted to give the idea of heat transfer enhancement/deterioration by the presence of block with that of the absence of block. Empirical correlations are also developed for summarizing the results of the study. The triangular block shows better heat transfer results as compared with the circular and square blocks in the semi-circular cavity. © 2020 Elsevier Ltd

International Communications in Heat and Mass Transfer

Mixed convection in the semi-circular lid-driven cavity with heated curved wall subjugated to constant heat flux for non-Newtonian power-law fluids

Non-native structures have more open structure with less stable bulk formation energy compared to their native structure and hence, non-native structured cathodes are expected to generate higher discharge potential and better lithium mobility. However, non-native structures are limited in stability, which can be enhanced by scaffolding with native structure. We synthesize highly crystalline non-native Ramsdellite MnO2 (r/NN1–MnO2) and gradually thermal phase transform to native Pyrolusite MnO2 (β/N–MnO2), intimately interfaced (r/NN1–MnO2)/(β/N–MnO2) intergrowth intermediate structures are realized. As the temperature increases, the ratio of r/NN1–MnO2 to β/N–MnO2 in intergrowth structure decreases, so does the discharge potential and lithium mobility. The wider discharge plateau for intergrowth structures is rationalized using density functional simulations followed by statistical averaging to account for interfacial intercalation sites with greater stability. Improved capacity retention for intergrowth structure is due to the higher structural stability and available free volume, where the presence of native structure acts as a stabilizing element. Electrochemical impedance spectroscopy correlates faster transport in the intergrowth structure with higher percentage of non-native phase with wider 2 × 1 channel compared to native phase with narrow 1 × 1 channel. The insights generated from this study have broad implications for interface engineering in multicomponent electrodes such as Li-rich-NMC oxides. © 2019 Elsevier B.V.

Journal of Power Sources

Higher voltage, wider voltage plateau, longer cycle life, and faster kinetics via thermally modulated interfaces between Ramsdellite and Pyrolusite MnO2 for lithium-ion battery cathodes

This study investigates the optimization of free chlorine-based disinfectant dosage for controlling the dissolution of lead (Pb) while limiting disinfection by-products (DBPs) formation in water distribution networks. A dynamic optimization framework is developed in this study to account for the impact of spatial and temporal variations of network hydraulics and water chemistry on dissolved lead concentrations. Accordingly, a dynamic schedule of disinfectant dosage is proposed to minimize water lead levels and two-point chlorine residual violations in the network. The results suggest that optimization of water chemistry parameters such as pH and orthophosphate dosage provide an additional degree of freedom to be explored in the problem of optimizing disinfectant dosage for compliance with conflicting mandates regulating lead levels and DBPs concentration in drinking water. © 2020, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.

Control of lead contamination in water distribution networks: A dynamic optimization framework

Physics of Fluids

Flow and stability of a gravity-driven thin film over a locally heated porous wall

In the existing literature, convergence results for particle filters are given explicitly only for the case when the underlying dynamic model is a Markov process. When output feedback control is used, the evolution of the state process is no longer Markovian due to the dependence of inputs on the outputs. In this paper, it is shown that the random probability measures produced by the particle filter converge to the true prior and posterior measures in this nonMarkovian case. Firstly, it is proved that the recursive equations relating the prior and posterior measures continue to hold for output feedback control. These recursive equations are then used to show the required convergence of the random measures. Finally, the convergence is also illustrated using simulations on a nonlinear dynamical system. © 2020 EUCA.

European Control Conference 2020, ECC 2020

Convergence of Particle Filter for Output Feedback Control

The major mechanism responsible for plasmonic enhancement of titanium dioxide photocatalysis using gold nanoparticles is still under contention. This work introduces an experimental strategy to disentangle the significance of the charge transfer and near-field mechanisms in plasmonic photocatalysis. By controlling the thickness and conductive nature of a nanoparticle shell that acts as a spacer layer separating the plasmonic metal core from the TiO2 surface, field enhancement or charge transfer effects can be selectively repressed or evoked. Layer-by-layer and in situ polymerization methods are used to synthesize gold core-polymer shell nanoparticles with shell thickness control up to the sub-nanometer level. Detailed optical and electrical characterization supported by near-field simulation models corroborate the trends in photocatalytic activity of the different systems. This approach mainly points at an important contribution of the enhanced near field. © 2019 American Chemical Society.

ACS Applied Nano Materials

Electron Transfer and Near-Field Mechanisms in Plasmonic Gold-Nanoparticle-Modified TiO2 Photocatalytic Systems

The impact of implementing an advanced water quality model for simulating the dead-end sections of drinking water distribution networks on the outcomes of booster chlorination optimization is investigated. An advection-dispersion-reaction transport model that accounts for the realistic spatial distribution of water demands along dead-end pipes is linked to a genetic algorithm to find the optimal layout and operation of booster chlorination stations. The objective function is formulated and solved to find the optimal locations and chlorine dosing schedules of the booster stations that minimize the total costs of design and operation of the booster system, while maintaining a sufficient residual throughout the distribution network. The results highlight the importance of considering dispersive solute transport, as well as the excessive residence times encountered in the dead-end branches in the water quality simulations conducted for network optimization problems. While this study addresses the optimization of booster chlorination systems, its implications extend to a wide array of network optimization applications, including pump scheduling for water quality optimization, optimal sensor placement for reactive contaminant detection, and design of real-time boost-response systems. © 2019 American Society of Civil Engineers.

Journal of Water Resources Planning and Management

Influence of Dead-End Sections of Drinking Water Distribution Networks on Optimization of Booster Chlorination Systems

The coalescence of water drops, dispersed in oil, is critical to the destabilization of a water-in-oil emulsion under an electric field. In this work, we determine the conditions for coalescence or non-coalescence of two aqueous water drops that are suspended in an insulating oil and subjected to a uniform electric field. Specifically, we investigate the effect of the conductivity of the droplet phase (σ), the type of oils (silicone oil and castor oil), the effect of waveform AC and DC and frequency, and the separation between the droplets on the electrocoalescence/non-coalescence of two suspended aqueous drops. The main highlights are, (i) we provide expressions for critical electrocapillary number (Cac) vs. σ for silicone oil (Cac = 0.010 × σ−0.20) that shows cone-cone and castor oil (Cac = 0.022 × σ−0.15) that shows cone-dimple mode of contact. (ii) Two closely spaced drops can coalesce at electrocapillary numbers much higher than the critical electrocapillary number for widely spaced drops due to a smaller cone angle at the point of contact. These results should be important in the design of industrial electrocoalescers. © 2019