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

The dataset presented in this article are related to research articles “Effect of electrolyte convection velocity in the electrode on the performance of vanadium redox flow battery cells with serpentine flow fields” [1] and “Effect of channel dimensions of serpentine flow fields on the performance of a vanadium redox flow battery” [2]. The combined dataset on the pressure drop and electrochemical behavior of the vanadium flow battery cells with active areas of 400 cm2, 900 cm2 and 1500 cm2 were obtained using battery life cycler for the circulation of vanadium electrolyte of concentration 1.61 M VOSO4 dissolved in 5 M H2SO4. The cells were designed with various combinations of flow-channel dimensions of serpentine flow field and the electrochemical performance has been obtained at various flow rates and current densities. In addition to the experimental data, computational fluid dynamics simulations have been performed to investigate the electrolyte distribution across the cell. The shared data enables the reader of research articles to delve into the life cycle behavior at various operating conditions and emphasize the importance of flow-channel dimensions, flow rate and uniform distribution of electrolyte in combating the concentration over-potential. © 2021 The Authors

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Dataset on performance of large-scale vanadium redox flow batteries with serpentine flow fields

Liquefied natural gas (LNG) is increasingly becoming a fossil fuel of choice, especially in growing economies. The trade in LNG has traditionally been governed by long-term contracts (LTCs); however, recently, spot trade of LNG cargos is becoming popular. There is no approach reported in the literature for making LNG procurement decisions from both LTCs and spot cargos. In this work, we study this tactical procurement decision while considering factors such as price difference between the spot market and LTCs, demand at the regasification terminals, and LTC obligations. Two distinct strategies are proposed for this purpose: (1) LNG procurement heuristics (LNGPH) based on a locally optimal greedy search and (2) a mathematical programming-based LNG procurement model (LNGPM) that determines the optimal set of cargos by solving a mixed-integer linear program. We demonstrate both the methodologies using an illustrative example. To account for various uncertainties, a scenario-based comparison was also performed. In a range of 27 different scenarios, LNGPM consistently outperformed LNGPH, leading to an average annual saving of $83 million. However, LNGPH has a distinct advantage over LNGPM in computational time. Also, the solver was unable to solve one scenario even after 24 h. Therefore, LNGPH can be used as a low-cost backup when LNGPM is unable to deliver a solution in a reasonable time. &copy; 2021 American Chemical Society. © 2021 American Chemical Society. All rights reserved.

Industrial and Engineering Chemistry Research

Optimal procurement of liquefied natural gas cargos from long-term contracts and spot market through mathematical programming

Global LNG trade continues to grow owing to increasing energy demand, especially from the Asia-Pacific region. However, the trade of LNG has inherent vulnerabilities that can eventually manifest as disruptions. Typical consequences of disruptions include excess or shortfall of inventory, and plant shutdown, all of which can significantly impact profit. In this paper, we seek to develop a systematic methodology that can be used by an LNG receiving terminal to mitigate the effects of disruptions. We develop an agent-based dynamic model of the LNG supply chain and use it to systematically design operational interventions that can ameliorate the adverse consequences of disruptions. As a case study, we focus on a sudden decrease in demand. The disruption is managed through fire sales of a product. We demonstrate that a key parameter in this rectification strategy, the fire sale price, can be systematically determined using the proposed agent-based model. © 2021 Elsevier B.V.

Computer Aided Chemical Engineering

Designing a Rectification Strategy for Managing Disruptions in LNG Supply Chain

Reinforcement learning (RL) algorithms that include Monte Carlo Tree Search (MCTS) have found tremendous success in computer games such as Go, Shiga and Chess. Such learning algorithms have demonstrated super-human capabilities in navigating through an exhaustive discrete action search space. Motivated by their success in computer games, we demonstrate that RL can be applied to inverse materials design problems. We deploy RL for a representative case of the optimal atomic scale inverse design of extended defects via rearrangement of chalcogen (e.g. S) vacancies in 2D transition metal dichalcogenides (e.g. MoS2 ). These defect rearrangements and their dynamics are important from the perspective of tunable phase transition in 2D materials i.e. 2H (semi-conducting) to 1T (metallic) in MoS2. We demonstrate the ability of MCTS interfaced with a reactive molecular dynamics simulator to efficiently sample the defect phase space and perform inverse design—starting from randomly distributed S vacancies, the optimal defect rearrangement of defects corresponds a line defect of S vacancies. We compare MCTS performance with evolutionary optimization i.e. genetic algorithms and show that MCTS converges to a better optimal solution (lower objective) and in fewer evaluations compared to GA. We also comprehensively evaluate and discuss the effect of MCTS hyperparameters on the convergence to solution. Overall, our study demonstrates the effectives of using RL approaches that operate in discrete action space for inverse defect design problems. © 2021 The Author(s). Published by IOP Publishing Ltd.

Journal of Physics Communications

Reinforcement learning in discrete action space applied to inverse defect design

Recently, gas hydrates based technologies have been exploited for few novel applications such as storage and transpiration of natural gas, gas mixtures separation, CO2 capture, and seawater desalination. Most of these applications are currently facing a challenge of low rate of gas hydrate formation. Chemical additives like surfactants can play a role of a good kinetic promoter for gas hydrate formation. The present study reports the application of biosurfactant for enhancing gas hydrate formation. Biosurfactant was produced by Bacillus subtilis strain A21. These types of microbes show their presence in the real gas hydrate sites also. The surfactin was characterized using many sophisticated techniques, conforming the formation of surfactin. It was used in the presence of fixed bed media of silica gel, and it was observed that surfactin in the presence of silica gel increased the consumption of moles of methane as well as reduced the induction time also as well as the conversion was also increased up to 27.9% for 390 min for 1000 ppm surfactin hence indicating it to be a clean and novel promoter of methane hydrate formation in combination with silica gel which can replace its synthetic counterparts which have environmental concerns. © 2021 American Society of Mechanical Engineers (ASME). All rights reserved.

Department Of Physics

Journal of Energy Resources Technology, Transactions of the ASME

Combination of silica gel and surfactin promoting methane hydrate formation

Photoelectrochemical water oxidation is a challenging reaction in solar water splitting due to the parasitic recombination process, sluggish catalytic activity, and electrode stability. Oxide semiconductors are stable in an aqueous medium but show huge charge carrier recombination. Creation of a heterojunction is found to be effective for extracting the photogenerated electrons/holes before they recombine to the ground state. In this work, we created a heterojunction of BiVO4 with vacancy-ordered halide perovskite Cs2PtI6 and used it as a photoanode in PEC water oxidation. Cs2PtI6 is the only halide perovskite that is found to be extremely stable even in strong acids and bases. We utilized the stability of this material and its panchromatic visible light absorption property and made the first unprotected heterojunction dual-absorber photoanode for PEC water oxidation. At 1.23 V (vs RHE), bare BiVO4 gave 0.6 mA cm-2 photocurrent density, whereas the BiVO4/Cs2PtI6 heterojunction shows 0.92 mA cm-2. With the addition of IrOx cocatalyst, at 1.23 V (vs RHE), the heterojunction gave ∼2 mA cm-2. To obtain 2 mA cm-2 photocurrent, pure BiVO4 requires 560 mV overpotential, whereas the heterojunction requires 250 mV. The increase in the photocurrent arises from the increase in the efficiency of charge separation from BiVO4 to Cs2PtI6 and the complementary absorption offered by the latter. © 2021 American Chemical Society.

ACS Applied Materials and Interfaces

BiVO4/Cs2PtI6Vacancy-Ordered Halide Perovskite Heterojunction for Panchromatic Light Harvesting and Enhanced Charge Separation in Photoelectrochemical Water Oxidation

A recent article [Khair and Kabarowski Phys. Rev. Fluids 5, 033702 (2020)10.1103/PhysRevFluids.5.033702] has studied the cross-streamline migration of electrophoretic particles in unbounded shear flows with weak inertia or viscoelasticity. That work compares their results with those reported in two of our previous studies [Choudhary J. Fluid Mech. 874, 856 (2019)10.1017/jfm.2019.479; J. Fluid Mech. 898, A20 (2020)10.1017/jfm.2020.397] and reports a disagreement in the derived analytical expressions. In this comment, we resolve this discrepancy. For viscoelastic flows, we show that Khair and Kabarowski have not accounted for a leading order surface integral of polymeric stress in their calculation of first-order viscoelastic lift. When this integral is included, the resulting migration velocity matches exactly with that reported in our work [J. Fluid Mech. 898, A20 (2020)10.1017/jfm.2020.397]. This qualitatively changes the migration direction that is reported by Khair and Kabarowski for viscoelastic flows. For inertial flows, we clarify that Khair and Kabarowski find the coefficient of lift to be 1.75π compared to 2.35π in our previous work [J. Fluid Mech. 874, 856 (2019)10.1017/jfm.2019.479]. We show that this difference occurs because Khair and Kabarowski accurately include the effect of a rapidly decaying O(1/r4) velocity field (a correction to the stresslet field 1/r2), which was neglected in our work. © 2021 American Physical Society.

Physical Review Fluids

Comment on "migration of an electrophoretic particle in a weakly inertial or viscoelastic shear flow"

Recent experimental work has shown that polymer crystallisation can be used to “move” and organize nanoparticles (NP). As a first effort at modeling this situation, we consider the classical Stefan problem but with the modification that polymer crystallisation does not occur at a single temperature. Rather, the rate of crystallisation is proportional to its subcooling, and here we employ a form inspired by the classical Avrami model to describe this functional form. Our results for the movement of the polymer crystallisation front, as defined as the point where the crystallinity is 50%, closely track the results of the classical Stefan problem. Thus, at this level of approximation, the crystallisation kinetics of the polymer do not cause qualitative changes to the physics of this situation. Inspired by this fact we study the more interesting situation where the directional recrystallisation of a polymer melt is considered,e.g., through the application of a moving heat sink over an initially molten polymer, reminiscent of a processing technique termed zone annealing. The polymer crystallisation shows that a steady state exists for a range of sink velocities. The solid-melt interface moves slightly ahead of the sink but at the same velocity. The steady-state distance between the sink and the interface decreases with increasing sink velocity - this is a consequence of the excess cooling provided by the sink over what is required to crystallise the melt. The most interesting new result is that the temperature of the crystal-melt interface decreases with increasing sink velocity. This is in line with the ansatz of Lovinger and Gryte who suggested that larger zone annealing velocities correspond to progressively larger effective undercoolings at which polymer crystallisation occurs. © The Royal Society of Chemistry 2021.

Soft Matter

Modeling polymer crystallisation induced by a moving heat sink

We report a novel approach for the fabrication of porous polymer films and their self-folding behavior in response to water. In this approach, the poly(vinyl alcohol) (PVA) films of tunable porosity are prepared by direct casting of aqueous PVA solution into a nonsolvent, isopropyl alcohol (IPA). The method developed is simple, efficient and low-cost. The results presented provide a modular route to tune the distribution of pores across the film thickness by varying the volume of nonsolvent and the polymer solution. We show that asymmetric porous polymer films (which consist of pores across a certain thickness of the film in the plane perpendicular to its surface) as well as symmetric porous polymer films (which have pores across the entire film) can be fabricated by this versatile method. The percentage of pores in the polymer film calculated as , wheretpis the thickness of the film across which the pores exist andttotalis the total thickness of the film, can be tuned over a wide range. The emanated porous PVA films are found to show self-folding behaviour in response to water. Our results indicate that the pore architecture in the films significantly enhances the actuation speed. The self-folding originating due to the diffusion of water molecules across the film is observed to occur in a controlled and predictable manner for the films with 60% pores and above. A detailed study of the folding characteristics and actuation speed in relation to folding time is substantiated. © The Royal Society of Chemistry 2021.

Department of Applied Mechanics

Engineering polymer film porosity for solvent triggered actuation

Industrial flow battery stacks require large area cells for which flow fields are essential to ensure uniform distribution of the electrolyte. Serpentine flow fields have proven to be ideal from a flow distribution point of view but suffer from high pressure drop. In the present work, a new flip-flop directional split serpentine flow field is proposed to reduce pressure drop by splitting the flow field into segments and improving electrochemical performance by quick evacuation of reaction products. Comparative experimental studies with a single serpentine and two other split serpentine flow fields confirm the effectiveness of the new flow field. An improvement of around 12% in discharge energy and 3% in round-trip efficiency has been observed with flip-flop at current densities of 90 mA cm−2 and 120 mA cm−2 over a single serpentine flow field for a cell active area of 900 cm2. Calibrated computational fluid dynamics simulations confirm that the proposed flow field ensures good distribution and quick evacuation of product species. Scalability of the new flow field to large cell size has been demonstrated by obtaining good performance data on a cell of 2200 cm2 active area, which is among the largest reported in the literature. © 2020 Elsevier B.V.