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

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

World University root node

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

Detail characterization of the liquid jet core in a model cross-stream airblast atomizer by application of the Optical Connectivity (OC) technique is the goal of the present paper. The unique ability of the technique in imaging the fluorescence signal exclusively from the jet core region facilitates simultaneous visualization of the liquid jet from the side- and the front-view with high background contrast. This allows measurement of some important primary breakup characteristics. The jet penetration and breakup length are obtained from the side-view images, while the front view images provides the jet width and the spreading angle. The above parameters are measured for a wide range of injector operating conditions. The measurement of mean jet trajectory and mean penetration/breakup length indicated large difference in comparison to the past studies based on experiments conducted in wind-tunnels. This is attributed to air flow confinement within the atomizer in the present case and also accurate measurement of breakup location in the OC technique. The range of the measured mean width of the jet and spreading angle indicated ’sheet breakup mode’ of the liquid jet for all injector operating conditions. Correlations are obtained to describe the evolution of different mean quantities with respect to relevant non-dimensional numbers. The fluctuations of jet breakup parameters are also measured. Some interesting correlations are obtained between fluctuations of different primary breakup characteristics which are discussed in the paper. © 2021 Elsevier Ltd

International Journal of Multiphase Flow

Liquid jet core characterization in a model crossflow airblast atomizer

Three-dimensional numerical computations have been carried out in flow past two inline finite-height circular cylinders using Open Source Field Operation and Manipulation. Investigations have been carried out for the varying Reynolds number (Re) ranging from 150 to 300. The diameter of the upstream cylinder is varied in such a way that the size ratio (SR, ratio of the diameter of the upstream cylinder to that of the downstream cylinder) takes values of 0.25, 0.5, and 1.0. For each size of the upstream cylinder, the downstream cylinder is placed at different locations in the streamwise direction. Effects of Re, SR, and inter-cylinder spacing (S) on three-dimensional unsteady wake characteristics behind upstream and downstream cylinders have been examined using iso-Q surfaces. Unsteady wake oscillations in both the wakes are analyzed qualitatively and quantitatively in terms of Hilbert spectra and the degree of stationarity using the transverse velocity component in the wake. Different flow regimes for upstream and downstream wakes have been identified and discussed with the change in Re, SR, and S. Transitions in the wake flow are illustrated using vorticity contours, frequency spectra, and bifurcation diagram. The level of wake synchronization in the upstream wake, downstream wake, and between both the wakes has been identified with the help of the cross correlation function. © 2021 Author(s).

Department of Computer Science and Engineering

Physics of Fluids

Effects of size ratio and inter-cylinder spacing on wake transition in flow past finite inline circular cylinders mounted on plane surface

Improving accuracy in cutting of expanded polystyrene (EPS) foam using hot wire depends on understanding and controlling the kerf width, which in turn depends on temperature distribution in the foam during cutting. We present here a comprehensive temperature-validated numerical thermal model that incorporates important factors such as convective heat transfer between the wire and molten/ablated foam and the surroundings, thermal coupling between the wire and EPS, temperature dependent EPS foam and wire properties and the latent heat of melting and ablation of EPS, to predict the three-dimensional temperature distributions in the EPS foam in the region immediately around the hot wire and across the entire width of the EPS foam being cut. Based on isothermal temperature contour at the melting point of the foam, kerf width is predicted and compared with experimental measurements. Average kerf width and kerf width variation across the width of the work are seen to be predicted reasonably by the model. The barrelling of the cut profile due to the variation of wire temperature along its length is also quantified and compared with experiments. Selectively switching off various model parameters such as temperature dependent EPS and wire properties and the thermal coupling between wire and EPS shows significant contributions of these factors towards the error in kerf width predictions. Convective heat losses are found to be important when the width of EPS being cut is less such as in thin sheets. As confirmed by experimental data, kerf width is higher near the work edges and stays constant within the bulk region of the work. The model developed comprehensively captures the thermal effects and thus can be used to improve precision while cutting EPS shapes. © 2020 The Society of Manufacturing Engineers

Journal of Manufacturing Processes

A comprehensive numerical model for kerf width prediction in hot wire cutting of expanded polystyrene

Understanding the physics of primary liquid breakup process and its correlation with the evolution of spray characteristics in a rotary slinger atomizer is the goal of the present research. Experiments were conducted in a high-speed slinger test rig that houses a static liquid delivery manifold to uniformly supply the liquid to the rotating slinger disc that contains a single row of orifices carved on its peripheral surface for liquid injection.The atomizer was operated for a wide range of conditions by varying the rotational speed and liquid feed rate. The liquid breakup structure at the exit of the slinger orifices was visualized using front light illumination technique, while the droplet size was measured at different radial stations away from the slinger surface by application of the Interferometric Laser Imaging for Droplet Sizing (ILIDS) technique. The visualization images highlighted strong influence of Coriolis force as the liquid tends to accumulate on one side of the channel (that is opposite to the rotational direction) for all cases. It was observed that while the liquid thickness is smaller for higher rotational speed, it does not vary much with liquid feed rate at the same speed and, instead, in such case the span of the liquid is wider. A theoretical analysis was developed to describe the in-channel liquid behaviour that accounts for the effect of Coriolis and surface tension forces. Interestingly, the theory could explain the above observations. The differences in the predictions in comparison to the analysis by Dahm et al. (2006a) was attributed to the assumption of annular film flow in the latter. The liquid breakup mode (stream, sheet or transition mode) could be described by Coriolis Bond number (Bo) that refers to the ratio of Coriolis to surface tension forces and proportional to the spread parameter (span to thickness ratio), while the liquid breakup regimes were identified on a Bo−q plot, where q is the liquid to air momentum flux ratio. The variation of characteristic droplet sizes with both rotational speed and feed rate were examined, and again some interesting trends are identified. The correlation between liquid breakup mode/regime with the measured droplet size was established using the above non-dimensional numbers. © 2020

Coriolis-induced liquid breakup and spray evolution in a rotary slinger atomizer: Experiments and analysis

TiAl4V is used widely in aerospace and biomedical application due to its high specific strength and good bio-compatibility. Its poor tribological performance restricts usage for hip implant articulation. Various surface characteristics such as surface roughness and wettability affect the tribological behaviour of Ti6Al4V sliding. Surface texturing is the recent technique to modify the surface features and improve the wettability. This study aims to compare the wettability and coefficient of friction (CoF) of discrete and continuous texture under bio-lubricated condition. Dimple and crosshatch textures are fabricated using laser surface texturing (LST) technique. The geometrical parameters such as depth, pitch and area density have been kept the same. Wettability associated with both the textures are analysed by measuring surface contact angles using goniometer. Further, friction behaviour is evaluated for all the textured and non-textured surfaces under biological environment using reciprocating pin-on-disc tribometer. Results show a significant reduction in contact angle for crosshatch texture compared to dimple and non-textured surface. Also, both the texture reduced the friction by 24% compared to non-textured surface. © 2021, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Lecture Notes in Mechanical Engineering

Comparing Wettability and Frictional Performance of Laser Micro-machined Discrete and Continuous Textures

FDAPT (2-formyl-5-(4′-N,N-dimethylaminophenyl)thiophene) is an efficient environment-sensitive fluorescent probe, which senses the alteration of its microenvironment with six different fluorescent parameters, namely, emission intensity, wavelength, fluorescence anisotropy, and corresponding three time-dependent parameters fluorescence lifetime, time-resolved emission spectrum, and anisotropy decay. In the present work, the nature of saccharide-induced dehydration of a F127 polymeric micelle is investigated in detail with FDAPT emission. Using a multiparametric fluorescence approach, it is observed that the saccharide molecules not only decrease the critical micellization temperature of the F127 solution but also strongly alter the physical properties inside the micellar structures. The local polarity and fluidity significantly decrease in the saccharide-induced micelle as compared to the normal F127 micelle. The probe solvation dynamics study reveals that the water content in the core as well as corona domain diminishes significantly in the saccharide-induced micelle as compared to the normal micelle. More precisely, dehydration occurs more in the core region than in the corona region. Also, the saccharide-induced dehydration alters the relative size of the core and corona regions. The extent of dehydration varies with different saccharide molecules. It is also found that the dehydration efficiency order is trisaccharide (raffinose) > disaccharide (sucrose) > monosaccharide (glucose and fructose). © 2021 American Chemical Society.

Department Of Chemistry

Langmuir

Nature of Saccharide-Induced F127 Micellar Dehydration: An Insight with FDAPT (2-Formyl-5-(4′- N, N-dimethylaminophenyl)thiophene), a Multiparametric Fluorescent Probe

Closed form expressions for the domination number of an n× m grid have attracted significant attention, and an exact expression has been obtained in 2011 [7]. In this paper, we present our results on obtaining new lower bounds on the connected domination number of an n× m grid. The problem has been solved for grids with up to 4 rows and with 6 rows and the best currently known lower bound for arbitrary m, n is [11]. Fujie [4] came up with a general construction for a connected dominating set of an n× m grid. In this paper, we investigate whether this construction is indeed optimum. We prove a new lower bound of for arbitrary m, n≥ 4. © 2021, Springer Nature Switzerland AG.

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)

The Connected Domination Number of Grids

Machining of multidirectional Hybrid Fiber Reinforced Composite (HFRC) is a challenging task because of defects like matrix cracking, fiber pullouts, delamination, burr formation, and heat affected zones. The current study is focused on machining and characterization of in-house fabricated HFRC made of carbon and silica glass fiber using Abrasive Jet Machining (AJM). Machining of holes in fabricated multidirectional HFRC has been carried out using a set of input machining parameters -air pressure, abrasive grit size, and standoff distance. The output responses selected for the experiment are material removal rate, circularity, Depth Averaged Radial Overcut (DAROC), Taper Angle (TA), and Surface Roughness (Ra.) A novel technique has been contrived for measuring DAROC by using Computerized Tomography images. At the same time, the microstructure, surface roughness, and burr height of the machined samples are carried out using High-resolution Scanning Electron Microscope (HRSEM) images and 3D-profilometer images. Subsequently, the machining parameters are optimized using multi-objective GRA to strike a balance between the output parameters. The obtained results indicated the absence of defects like delamination, burr formation, heat affected zones in the machined samples. The outcome of the experiment corroborates the application suitability of the AJM process for machining multidirectional HFRC used in industrial and commercial products. © 2020, Springer Nature B.V.