Department of Mechanical 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 evaporation of colloidal dispersions is an elegant and straightforward route to controlled self-assembly of particles on a solid surface. In particular, the evaporation of particle laden drops placed on solid substrates has received considerable attention for more than two decades. Such particle filled drops upon complete evaporation of the solvent leave behind a residue, commonly called particulate deposit pattern. In these patterns, typically, more particles accumulate at the edge compared to the interior, a feature observed when coffee drops evaporate. Consequently, such evaporative patterns are called coffee stains. In this article, the focus is on the evaporation of highly dilute suspension drops containing particles of larger diameters ranging from 3 to 10 μm drying on solid substrates. This helps us to investigate the combined role of gravity-driven settling of particles and capillary flow-driven particle transport on pattern formation in drying drops. In the highly dilute concentration limit, the evaporative patterns are found to show a transition, from a monolayer deposit that consists of a single layer of particles, to a multilayer deposit as a function of particle diameter and initial concentration of particles in the drying drop. Moreover, the spatial distribution of particles as well as the ordering of particles in the deposit patterns are found to be particle size dependent. It is also seen that the order-disorder transition, a feature associated with the organization of particles at the edge of the deposit, observed typically at moderate particle concentrations, disappears at the highly dilute concentrations considered here. The evaporation of drops containing particles of 10 μm diameter, where the effect of gravity on the particle becomes significant, leads to uniform deposition of particles, i.e, suppression of the coffee-stain effect and to the formation of two-dimensional percolating networks. © 2021 American Chemical Society.

World University root node

Department Of Chemical Engineering

Langmuir

Further Insights into Patterns from Drying Particle Laden Sessile Drops

This paper presents a market study indicating that Patch Repair without galvanic anodes (PR strategy) can lead to continued corrosion (due to the halo effect and residual chloride effect) and another major repair in about five years. Repeated patch repairs can lead to continued corrosion and eventual replacement of structures and huge life cycle cost (LCC). On the other hand, the strategy of cathodic protection using galvanic anodes (CP strategy) can enhance the service life and reduce LCC. The data on long-term depolarized potential of steel, output current from the anodes and/or visual observations indicated that the galvanic anodes were successful in controlling the chloride-induced corrosion for up to 14 and 10 years, in a jetty and industrial building, respectively. It was also found that the additional cost of galvanic anodes is only about 4% of the repair cost for the jetty structure – breaking the myth of high capital cost of CP strategy. Then, a framework to estimate the LCC of PR and CP repair strategies is developed and it is found that CP and cathodic prevention (CPrev) strategies are highly economical than the PR strategy. Also, the LCC of 30 repair projects confirmed that the use of CP strategy can lead to LCC saving of up to about 90% in about 30 years after the first repair. More importantly, the CP and CPrev strategies can enhance the service life to as long as needed by the replacement of anodes at regular intervals and at minimal cost. Also, a way forward to promote CP strategy in concrete repair industry is provided. © 2021

Department Of Civil Engineering

Journal of Building Engineering

Long-term performance and life-cycle-cost benefits of cathodic protection of concrete structures using galvanic anodes

In this study, researchers have explored real-world driving conditions and developed emission factors for 58 passenger cars using on-board emission measurement technique while driving on five different routes in Delhi. The measured average emission factors of CO, HC, and NO were 3.99, 0.34, and 0.54 g/km for diesel vehicles, 7.26, 0.17, and 0.62 for petrol vehicles respectively. Road, traffic, vehicle type, and driving characteristics affect the quantity of emissions released. However, speed and acceleration significantly impact emission rates increasing with the increase in speed and acceleration. Also, emissions were minimal at 40–60 kmph and −0.5–0.5 m/s2. The estimated city-wide CO, HC, and NO emissions were 60.8, 4.8, and 9.72tonnes/day. These results demonstrate the importance of monitoring the real-world exhaust emissions given the substantial difference between test cycle measurements used for compliance testing of new vehicles. © 2021 Elsevier Ltd

Transportation Research Part D: Transport and Environment

Characteristics of real-world gaseous exhaust emissions from cars in heterogeneous traffic conditions

Propane, n-butane, and their mixtures are commonly used as fuels for various applications. Reliable numerical simulations of flames involving these fuels are most essential to study their efficient use in domestic and industrial burners. Such simulations require a suitable reaction mechanism containing the necessary kinetics to predict key combustion characteristics in flames accurately. However, the use of detailed kinetic mechanisms for these computations is formidable in multidimensional simulations, owing to their large sizes. To address this, in this work, a compact mechanism (45 species, 392 reactions) for propane, n-butane, and their mixtures, suitable for multidimensional simulations is derived and comprehensively validated against available experimental data in flames. The main oxidation pathways retained in this compact model are showcased. One-dimensional (1D) computations of premixed and nonpremixed flames are carried out using FlameMaster and Chemkin-Pro. Two-dimensional (2D) calculations are performed within ANSYS-FLUENT. Here, multicomponent diffusion, thermal diffusion, and radiation submodels are used. Laminar flame speeds, extinction strain rates, and amounts of major species in premixed flat flames are validated using 1D computations. Temperature and major species in propane and n-butane jet diffusion flames are verified in 2D simulations. Further, 2D computations using the compact mechanism also predict the laminar burning velocity of premixed flames of n-butane and propane mixtures established over a Bunsen burner. The ability of the compact mechanism to predict desired targets in premixed and nonpremixed flames is analyzed from a kinetic basis. Validation using 2D simulations demonstrates the usability of the compact mechanism in multidimensional computations. © 2021 Wiley Periodicals LLC

International Journal of Chemical Kinetics

Reduced mechanism for flames of propane, n-butane, and their mixtures for application to burners: Development and validation

Centrifugal Pendulum Vibration Absorbers (CPVAs) reduce the torsional fluctuations of rotating shafts at fixed vibration order by changing the natural frequency in accordance with the excitation frequency. Attenuation of multiple orders is necessary in the case of the rear wheel drive vehicle and cylinder deactivation applications for achieving refined vehicle performance. Single pendulum vibration absorbers attenuate only one vibration order at a time and the pendulum length must be reduced for higher orders in the order of (1/n2) times the distance between the center of rotation and pivot point to attenuate nth order vibration. Use of single pendulum absorbers for reducing higher orders has limitations due to manufacturing inaccuracies and occurrence of wear of joints over prolonged usage which reduces the effectiveness of absorber in reducing the torsional vibration. In this study, a centrifugal double pendulum vibration absorber (CDPVA) is proposed to make the design easy for higher orders by deploying two pendulums in series. The CDPVA is designed to attenuate the fundamental excitation order (n) and its second harmonic (2n) without significant reduction in the pendulum length hence making the design robust for prolonged usage. The mass and length values of the double pendulum are tuned to match the two natural frequencies correspond to the fundamental and second harmonic order of the torsional vibration excitation. Torsional springs are used at the pivot joints of the double pendulum to counteract the gravitational effects at low speeds and the influence of spring stiffness on the natural frequencies is analyzed. The nonlinear second order equations of motion of pendulum masses and rotor are solved analytically using method of multiple time scales and the stability characteristics of pendulum motion are analyzed at the excitation frequencies with different torque levels. Numerical simulation of complete nonlinear equations is carried out and the analytical results are compared with the simulation results. The designed CDPVA for 2nd and 4th order is tested on a 4-cylinder the rear wheel drive vehicle and considerable reduction is achieved in the torsional vibration of the drive shaft and also in the vibration levels at seating locations. The proposed methodology helps in designing the CDPVAs for attenuating the torsional vibration of multiple higher orders yet avoiding impacts in low speed operation. © 2020 Elsevier Ltd

Applied Acoustics

Torsional vibration reduction of rotating shafts for multiple orders using centrifugal double pendulum vibration absorber

The unsteady wake of a rotating and translating sphere is experimentally investigated at Reynolds numbers (Re) ranging from 115 to 550 for two rotational speeds. Non-dimensional rotational speed, Ω∗, is defined as the ratio of the maximum azimuthal speed of the sphere and the speed of translation. Motion of the sphere is generated using a specially designed mechanism in a channel, and its wake has been visualized using fluorescent dye. Unlike the steady flow past a stationary sphere where the limiting Reynolds number is 270, the flow becomes unsteady when sufficient rotation rate is introduced at much lower Reynolds number (Re = 115 , Ω∗= 0.375). The transition from one-sided to double-sided hairpin vortex occurs at one critical Re for a given rotational speed, and it switches back to one-sided hairpin vortex shedding at another critical Re. Particle image velocimetry results demonstrate the vorticity distribution in the wake and the variation of the wake width with axial distance. At very low Re, velocity profiles in the wake are nearly self-similar. The strength of the vortex rings weakens in the far wake. The decay of centerline velocity in axial direction confirms the dissipation of the vorticity in the far wake. In this unsteady flow, the time-averaged value of the separation angle is higher than that of the steady flow on the advancing side due to enhanced adverse pressure gradient. The Strouhal number calculated from the dye visualization in this range of Ω∗ and Re varies from 0.175 to 0.25, a clear increasing trend both with increasing Re and Ω∗. The coefficient of drag evaluated at the center plane remains constant at 0.94 for the present investigation up to Re = 550. The wavelength of the unstable hairpin vortices is found to scale inversely with the translational velocity of the sphere. © 2021, Springer-Verlag GmbH Austria, part of Springer Nature.

Acta Mechanica

Wake of transversely rotating and translating sphere in quiescent water at low Reynolds number

This study is focused on investigating the dual performance of Rh/CeO2/γ-Al2O3 catalyst for steam reforming of ethanol (SRE) and thermochemical water splitting (TCWS) using a packed bed reactor. The catalyst is designed to be thermally stable containing an active phase of Rh and the redox component of CeO2 for oxygen exchange, supported on γ-Al2O3. The catalyst has been characterised by SEM, XRD, BET, TPR, TPD, XPS and TGA before testing in the reactor. The optimal temperature for SRE reaction over this catalyst is between 700 °C and 800 °C to produce high concentrations of hydrogen ( 60%), and low CO and CH4. The selectivity towards CO and CH4 is higher at low temperatures and drops with rise in reaction temperature. Further, Rh/CeO2/γ-Al2O3 is found to be active for TCWS at relatively low temperatures (≤1200 °C). At temperatures as low as 800 °C, this catalyst is especially found suitable for multiple redox cycles, producing a total of 48.9 mmol/gcat in four redox cycles. The catalyst can be employed for large number of redox cycles when the reactor is operated at lower temperatures. Finally, the reaction pathways have been proposed for both SRE and TCWS on Rh/CeO2/γ-Al2O3 catalyst. © 2021 Hydrogen Energy Publications LLC

Department Of Chemistry

International Journal of Hydrogen Energy

Thermochemical hydrogen production using Rh/CeO2/γ-Al2O3 catalyst by steam reforming of ethanol and water splitting in a packed bed reactor

Electromagnetic acoustic transducers (EMATs) can efficiently generate the shear horizontal (SH) guided wave modes. In this article, the Halbach magnet array pattern is explored as an alternate to the conventional periodic permanent magnet (PPM) structure. The magnetic field strength of a Halbach array is significantly higher on one side of the structure while it is weak on the opposite side of the array. This magnetic field distribution enables Halbach EMATs to generate ultrasonic waves with relatively large amplitude. To observe this phenomenon, this study compares the amplitude generated from multiple single-row Halbach EMATs with single-row PPM EMAT configurations using finite-element-based simulation models for SH0 ultrasonic wave generation. This article then presents the ultrasonic wave fields generated by various double-row Halbach EMAT configurations using finite-element-based simulation models and experimentally validated for guided fundamental SH0 mode generated in an aluminum plate specimen. It is observed that distinct ultrasonic guided wave beam patterns be associated and predicted for different double-row Halbach EMAT configurations. © 1986-2012 IEEE.

Department of Metallurgical and Materials Engineering

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control

Characterizing Halbach EMAT Configurations for SH0 Ultrasonic Waves

A 1-D numerical modelling of the dynamics of inclined closed loop buoyancy driven heat exchangers with inclusion of the wall conduction effect at the heat exchanger is presented in the current study. A Coupled Natural Circulation Loop (CNCL) is an ideal system for studying the closed loop buoyancy driven heat exchanger. The modelling utilises a Fourier series based approach to develop a 1-D model of the Conjugate CNCL system, which is then verified with the 3-D CFD studies of the respective cases. A good agreement is observed with the 3-D CFD data, which demonstrates the suitability of the 1-D model for transient behaviour prediction. The non-dimensional numbers and thermal coupling sensitivity coefficients which govern the dynamics of the Conjugate CNCL are identified and an appropriate parametric study is conducted. Results show that the wall conduction and inclination have a significant effect on the transient behaviour of the Conjugate CNCL system. A jump in the heat transfer coefficient with variation in the inclination of the Conjugate CNCL system is observed. The 1-D model is also able to capture the flow direction reversal with change in the inclination of the Conjugate CNCL system for zero flow field initial conditions. © 2021 Elsevier Masson SAS

International Journal of Thermal Sciences

Fourier series based 1-D numerical modelling of the dynamics of inclined closed loop buoyancy driven heat exchangers with conjugate effect

The microstructure attributes are responsible for the deformation mechanism of material, which induces shear instability primarily in difficult-To-machine material like Ti-6Al-4V. Consequently, the dynamic cutting force yields serrations in the chip morphology. Therefore, microstructure induced shear instability has been investigated in the present work using an analytical tool to unveiled the deformation behavior in correlation with microstructural characteristics (grain sizes, phase fractions, and microhardness) and process parameters: Temperature, strain, and strain rate. The combined effect of feed rate and high cutting speed was found to enhance the strain localization phenomena, which leads to a more pronounced cracking, inducing dynamic cutting force. Segmentation frequency and force-frequency correlation imply a significant transition exhibit from the static to dynamic nature of cutting force. The segmentation frequency of the equiaxed microstructure is lowest among the rest at lower cutting speed, revealing the shear instability dependency on the microstructure. The grain size effect restricts the dislocation movement at the higher cutting speed, which led to a larger strain in as-received microstructure followed by equiaxed and fully lamellar microstructure. © 2021 Georg Thieme Verlag. All rights reserved.