Department Of Chemical Engineering

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Self-assembly of non-ionic surfactant pentaethylene glycol n-octyl ether (C8E5) in aqueous solution containing anionic polyelectrolyte poly (acrylic acid) PAA was investigated via atomistic molecular dynamics (MD) simulations. The concentration of surfactant (Cs) varied in the range (Cs = 9.6 × 10−4–0.3 M) of dilute to concentrated systems while polymer concentration was in dilute solution condition (i.e. Cp = 0.01 M). Binary and ternary systems show formation of nearly spherical micellar aggregate at low Cs and lamellar aggregates at high Cs. Strong interaction between PAA and C8E5 is observed at low Cs, in agreement with experimental data. PAA chain adsorbs onto the micellar aggregate and wraps around the aggregate. For lamellar phase aggregates PAA chain shows polar interactions with hydrophilic moieties of surfactant, originating from interactions between COOH groups of PAA and CO groups of C8E5. The concentration at which free-micelles form in ternary (polymer, surfactant and water) solution is greater than CMC of the binary surfactant-water system, in qualitative agreement with experimental data. At low Cs the interaction between surfactants and polymer chain is weak and does not perturb chain conformations. The radius-of-gyration Rg of PAA increases with Cs. Interaction of surfactant molecules with water is more cooperative at higher values of surfactant concentration, as evident from the values of solvation enthalpy. Significant hydrogen bonds were observed to occur between polar oxygens and hydroxyl oxygen (O2HA) of PAA. The number of h-bonds between polar oxygens and O2HA of PAA increase with Cs. Hydrogen bonds of PAA with surfactant molecules increases with Cs as the polymer expands at high Cs. Formation of surfactant aggregate is enthalpically favored across the entire range of concentration in binary and ternary solution. Binding of PAA to surfactant aggregate is favorable at higher surfactant concentration. The enthalpy of formation of ternary solution exhibits a transition from unfavorable to favorable which interestingly is driven by the structural transition from spherical micellar to the lamellar phase. This signature for this transition is also seen by conformation change of PAA upon binding to surfactant aggregate. © 2020

World University root node

Computational Materials Science

Structure and dynamics of aqueous solutions containing poly-(acrylic acid) and non-ionic surfactant pentaethylene glycol n-octyl ether (C8E5): A molecular simulations study

Vanadium redox flow batteries show enormous scope in large-scale storage and load balancing of energy from intermittent renewable energy sources. Although a number of studies have been published in the last two decades on various aspects of these flow batteries, very few have reported on practical aspects such as design considerations, guidelines and operational failures. Adequate attention to engineering aspects, failure detection and diagnosis are essential for smooth operation of the flow batteries. This paper discusses a few case studies of operational failures during the design and development of kilowatt-scale flow batteries together with their diagnoses and remedial actions. Specifically, failures in the membrane, tubing network and state of electrode have been discussed and suitable recommendations and guidelines are given to avoid these. In each case, rectification of the malfunction was confirmed through results obtained using electrochemical testing protocols established in previous studies. Based on these experiences, good practice guidelines have been recommended for proper fabrication, assembly and characterization of stacks. © 2020 Elsevier Ltd

Journal of Energy Storage

Case studies of operational failures of vanadium redox flow battery stacks, diagnoses and remedial actions

The effect of Prandtl number (Pr) on the multiplicity of the steady states (flow and temperature maps) is investigated for the natural convection of Newtonian fluids within a square enclosure involving hot bottom wall, cold side walls and adiabatic top wall. The analysis is based on the steady state governing equations, which are solved by penalty Galerkin finite element method and Newton–Raphson solution scheme. A novel perturbation technique has been developed, which is applied in conjunction with an in-house continuation scheme for the initiation of various symmetric as well as asymmetric steady states. The current computation strategy involving perturbation and continuation schemes leads to a rich bifurcation diagram in the parameter space of Pr (0.01⩽Pr⩽10) for Ra (Rayleigh number) =106. It is found that the occurrence of multiple steady states depends on Pr. Only one symmetric solution is obtained in the high–Pr regime (Pr&gt;0.42), while a highly populated bifurcation diagram consisting of 6 symmetric branches, 18 asymmetric branches and 4 isolas is obtained in the low–Pr regime (especially for Pr≲0.05). The solution branches correspond to a wide spectrum of flow structures involving single cell, multiple cells, reverse-cells, corner-cells, horizontally stacked cells, vertically stacked cells etc., which are reported for the first time. These flow structures result in a wide range of Nusselt numbers (average heat transfer rates) at a given Pr, especially for the low–Pr fluids (such as liquid metals). The flow structures are critically analyzed in terms of the location of the flow intensification and its impact on the overall heat transfer rates. It has been shown that the overall heat transfer rates for the low–Pr fluids can be significantly enhanced (80 –100% in few cases) based on corner-cells or single cell driven flow. © 2021 Elsevier Ltd

Department of Metallurgical and Materials Engineering

International Journal of Heat and Mass Transfer

Critical role of Prandtl number on multiple steady states during natural convection in square enclosures: Analysis of heat transfer rates, flow and thermal maps

In this work, microcrystalline cellulose (MCC) and sawdust (SD) green fillers have been demonstrated as reactive fillers and moisture reservoirs for enhanced curing and adhesion strength of one-component moisture-curing polyurethane (PU) adhesives. The chemical reaction between the MCC or SD fillers and isocyanates present in the PU adhesives was tracked using Fourier-transform infrared spectroscopy (FTIR), while the joint strength was determined using lap-shear tests. The results showed that the addition of MCC or SD leads to an accelerated curing rate through the early consumption of isocyanates. The lap-shear strength of unreinforced PU adhesive joints was achieved in 12 hours. In turn, the curing time in MCC and SD reinforced joints was achieved in 5 hours. The addition of MCC and SD fillers also enhanced the lap-shear strength of the joints under full cure conditions. An autocatalytic growth model was used to describe the lap-shear strength variation with respect to curing time. © 2021 Elsevier Ltd

Department of Mechanical Engineering

International Journal of Adhesion and Adhesives

Effect of cellulosic fillers addition on curing and adhesion strength of moisture-curing one-component polyurethane adhesives

Hypothesis: Evaporating sessile drops containing surface active colloids is a promising route to self-assemble two-dimensional nanostructures. The standard protocol is to first self-assemble surface active nanoscale particles at the water-vapour interface and subsequently transfer it on to a solid surface. Colloidal monolayers with very few morphologies have been fabricated, exploiting this bottom-up self-assembly technique. However, the evaporation kinetics under controlled humidity conditions may dramatically alter the microstructure of self-assembled colloidal monolayers at the liquid–vapor interface and that on the solid surfaces, an aspect that has not been fully addressed in the prior studies. Experiments: To this end, we present an experimental study of evaporation driven self-assembly of soft poly(N-isopropylacrylamide) (pNIPAM) microgel particles loaded in a sessile drop. The surface-active microgel particles spontaneously populate the water-vapour interface facilitating the suppression of the coffee-ring effect and the formation of monolayer stains. The role of evaporation kinetics under controlled humidity conditions on the colloid's microstructure adsorbed to the solvent-air interface and on the morphology of the colloidal monolayer transferred onto the solid surface are studied in detail. Findings: The formation of particle-free and particle-rich regions at the water–vapor interface is observed for sessile drops evaporated under saturated humidity conditions. We show that the evaporation induced shrinkage of the interface area and the enhancement of the areal density of microgel particles adsorbed onto the interface leads to a restructuring of the particle-laden interface. The rearrangement of microgel particles along the water–vapor interface resembling the de-wetting assisted patterns is transferred to the solid substrate upon complete evaporation of the solvent. The microgel particles in the deposit assemble into domains with enhanced crystalline order. The evolution of Voronoi entropy across the monolayer deposit patterns obtained by the standard and slow evaporation routes are presented. © 2020 Elsevier Inc.

Department Of Physics

Journal of Colloid and Interface Science

Colloidal monolayers with cell-like tessellations via interface assisted evaporative assembly

Compound particles are a class of composite systems in which solid particles encapsulated in a fluid droplet are suspended in another fluid. They are encountered in various natural and biological processes, for e.g. nucleated cells, hydrogels, microcapsules etc. Generation and transportation of such multiphase structures in microfluidic devices is associated with several challenges because of the poor understanding of their structural stability in a background flow and the rheological characteristics of their dispersions. Hence, in this work, we analyse the flow in and around a concentric compound particle and investigate the deformation dynamics of the confining drop and its stability against breakup in imposed linear flows. In the inertia-less limit (Reynolds number,) and assuming that the surface tension force dominates the viscous forces (low capillary number, limit), we obtain analytical expressions for the velocity and pressure fields up to for a compound particle subjected to a linear flow using a domain perturbation technique. Simultaneously, we determine the deformed shape of the confining drop correct up to, facilitating the following. (i) Since calculations account for the rotation of the anisotropically deformed interface, the reorientation dynamics of the deformed compound particles is determined. (ii) Calculations involving the shape of the confining interface are found to be important for compound particles as calculations make qualitatively different predictions in generalised extensional flows. (iii) An constitutive equation for the volume-averaged stress for a dilute dispersion of compound particles was developed to study both shear and extensional rheology in a unified framework. Our analysis shows that the presence of an encapsulated particle always enhances all the measured rheological quantities such as the effective shear viscosity, extensional viscosity and normal stress differences. (iv) Moreover, linear viscoelastic behaviour of a dilute dispersion of compound particles is characterised in terms of complex modulus by subjecting the dilute dispersion to a small-amplitude oscillatory shear (SAOS) flow. (v) Various expressions pertaining to a suspension of particles, drops, and particles coated with a fluid film are also derived as limiting cases of compound particles. © 2021 Georg Thieme Verlag. All rights reserved.

Fulltext

Journal of Fluid Mechanics

Dilute dispersion of compound particles: Deformation dynamics and rheology

The Jews living in the state of Kerala enact their diasporic identities through a unique narrative network including songs, stories, and memoirs. Drawing on memory studies and affect theory, this article aims to examine selected Jewish folk songs as an example of entanglement of memory and culture, nostalgia and narrative. We study Oh, Lovely Parrot (2004), which is a compilation of 43 typical Kerala “parrot songs” – devotional hymns and songs for special occasions – translated from Malayalam into English by Scaria Zacharia and Barbara C. Johnson. Performances of these songs constitute cultural as well as affective phenomena that bring together Jewish identities, especially female rituals, in a collective effort to preserve their ethnic memory and its associated social identity. The music unique to this community illustrates the ancestry and tradition of the Kerala Jews which held them together even after ‘aliyah’ (a Hebrew word referring to the migration to the nation state of Israel post-1948). Using selected songs from the book, the article aims to examine the community's cultural identity markers related to experiential and discursive diasporic memory. It also draws on the memoir Ruby of Cochin: An Indian Jewish Woman Remembers (2001) by Ruby Daniel and Barbara C. Johnson to analyse the affective quality of songs which unites the community in collective imagination and in complex nostalgia narratives. © AesthetixMS 2020.

Department of Humanities and Social Sciences

Rupkatha Journal on Interdisciplinary Studies in Humanities

“An umbrella made of precious gems”: An examination of memory and diasporic identities in Kerala Jewish songs and literature

The stable operation of a turbulent combustor is not completely silent; instead, there is a background of small amplitude aperiodic acoustic fluctuations known as combustion noise. Pressure fluctuations during this state of combustion noise are multifractal due to the presence of multiple temporal scales that contribute to its dynamics. However, existing models are unable to capture the multifractality in the pressure fluctuations. We conjecture an underlying fractional dynamics for the thermoacoustic system and obtain a fractional-order model for pressure fluctuations. The data from this model has remarkable visual similarity to the experimental data and also has a wide multifractal spectrum during the state of combustion noise. Quantitative similarity with the experimental data in terms of the Hurst exponent and the multifractal spectrum is observed during the state of combustion noise. This model is also able to produce pressure fluctuations that are qualitatively similar to the experimental data acquired during intermittency and thermoacoustic instability. Furthermore, we argue that the fractional dynamics vanish as we approach the state of thermoacoustic instability. © 2021 Author(s).

Department of Aerospace Engineering

Chaos

Capturing multifractality of pressure fluctuations in thermoacoustic systems using fractional-order derivatives

Many countries are currently facing a severe water crisis. Further, in various industrial sectors, small and medium enterprises operate multistage, multiproduct batch processes that require large quantities of water. This work is motivated by the inability of such enterprises to deploy complex water-reuse strategies since their plants are neither well instrumented nor automated. The design and operational strategies of water reuse networks for multistage, multiproduct batch processes is inherently challenging due to the underlying discontinuities and other nonlinearities. In this paper, we propose an easy-to-implement water-reuse strategy that utilizes intermediate storage tanks with finite capacities. The strategy relies on a simple heuristic that maps discharge from specific stages to be stored in corresponding tanks. A fallback sequence is also provided in case the tank cannot accommodate the entire discharge volume. An analogous scheme for reusing water from the tanks in appropriate process stages is also proposed. In this paper, we demonstrate using a textile industry case study that this simple reuse strategy can result in significant water savings. For this, we develop an optimal production schedule using a genetic algorithm that simultaneously minimizes production makespan and the freshwater consumption. Our results show that for a set of 4 products with up to 14 production stages, 76% of the freshwater could be reduced if 13 tanks can be deployed. Even with 2 tanks, the proposed strategy results a 42% reduction of the freshwater requirements. © 2021 Institution of Chemical Engineers

Chemical Engineering Research and Design

A simple strategy to maximize water-reuse in multistage, multiproduct batch processes

The plant pathogen Agrobacterium tumefaciens causes crown gall disease and is a widely used tool for generating transgenic plants owing to its virulence. The pathogenic process involves a shift from an independent to a living form within a host plant. However, comprehensive analyses of metabolites, genes and reactions contributing to this complex process are lacking. To gain new insights about the pathogenicity from the viewpoints of physiology and cellular metabolism, a genome-scale metabolic model (GSMM) was reconstructed for A. tumefaciens. The model, referred to as iNX1344, contained 1,344 genes, 1,441 reactions and 1,106 metabolites. It was validated by analyses of in silico cell growth on 39 unique carbon or nitrogen sources and the flux distribution of carbon metabolism. A. tumefaciens metabolic characteristics under three ecological niches were modelled. A high capacity to access and metabolize nutrients is more important for rhizosphere colonization than in the soil and substantial metabolic changes were detected during the shift from the rhizosphere to tumour environments. Furthermore, by integrating transcriptome data for tumour conditions, significant alterations in central metabolic pathways and secondary metabolite metabolism were identified. Overall, the GSMM and constraint-based analysis could decode the physiological and metabolic features of A. tumefaciens as well as interspecific interactions with hosts, thereby improving our understanding of host adaptation and infection mechanisms.