Department of Applied Mechanics

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

For millimetre to micron sized bubbles, floating at the free surface of different low viscosity fluids with different surface tensions, and then collapsing, we study the ensuing expansion of the outer radius of the hole (ro) at the free surface, as well as its velocity of expansion (uo). Since the thin film cap of the bubble disintegrates before the hole in it reaches the static rim, the hole expansion at intermediate times occurs as if it initiates at the bubble's static rim of radius Rr; the evolution of ro then results to be a strong function of gravity, since Rr depends strongly on the bubble radius R. A scaling analysis, which includes the increase in the tip radius due to mass accumulation and the resulting change in the retraction force, along with the gravity effects by considering the hole radius in excess of its initial static radius, re = ro-Rr, results in a novel scaling law re/R∼(t/tc)4/7, where tc=ρR3/σ is the capillary time scale; this scaling law is shown to capture the evolution of the hole radii in the present study. The dimensionless velocities of hole expansion, namely, the Weber numbers of hole expansion, Weo=ρuo2R/σ, scale as Weo∼(t/tc)-6/7, independent of gravity effects, matching the observations. We also show that these Weber numbers, which reduce with time, begin with a constant initial Weber number of 64, while the viscous limit of the present phenomena occurs when the bubble Ohnesorge number Oh=μ/σρRâ‰ 0.24. © 2020 Author(s).

Department Of Chemistry

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Physics of Fluids

Hole expansion from a bubble at a liquid surface

We study concentration-driven natural convection boundary layers on horizontal surfaces, subjected to a weak, surface normal, uniform blowing velocity Vi for three orders of range of the dimensionless blowing parameter 10-8 ≥ J = Re3x/Grx ≥ 10-5, where Rex and Grx are the local Reynolds and Grashof numbers at the horizontal location x, based respectively on Vi and ΔC, the concentration difference across the boundary layer. We formulate the integral boundary layer equations, with the assumption of no concentration drop within the species boundary layer, which is valid for weak blowing into the thin species boundary layers that occur at the high Schmidt number (Sc - 600) of concentration-driven convection. The equations are then numerically solved to show that the species boundary layer thickness δd = 1.6 x(Rex/Grx )1/4, the velocity boundary layer thickness δv = δdSc1/5, the horizontal velocity u = Vi(Grx/Rex )1/4f (n), where n = y/δv, and the drag coefficient based on Vi, CD = 2.32/vJ.We find that the vertical profile of the horizontally averaged dimensionless concentration across the boundary layer becomes, surprisingly, independent of the blowing and the species diffusion effects to follow aGr2/3y scaling, where Gry is the Grashof number based on the vertical location y within the boundary layer.We then show that the above profile matches the experimentally observed mean concentration profile within the boundary layers that form on the top surface of a membrane, when a weak flow is forced gravitationally from below the horizontal membrane that has brine above it and water below it. A similar match between the theoretical scaling of the species boundary layer thickness and its experimentally observed variation is also shown to occur. © The Author(s), 2020.

Journal of Fluid Mechanics

Scaling in concentration-driven convection boundary layers with transpiration

Heat transfer across fluid–solid interfaces in nanoconfinement has received significant attention due to its relevance in nanoscale systems. In this study, we investigate the Kapitza resistance at the water–graphene interface with the help of classical molecular dynamics simulation techniques in conjunction with our recently proposed equilibrium molecular dynamics (EMD) method [S. Alosious et al., J. Chem. Phys. 151, 194502 (2019)]. The size effect of the Kapitza resistance on different factors such as the number of graphene layers, the cross-sectional area, and the width of the water block was studied. The Kapitza resistance decreases slightly with an increase in the number of layers, while the influence of the cross-sectional area and the width of the water block is negligible. The variation in the Kapitza resistance as a function of the number of graphene layers is attributed to the large phonon mean free path along the graphene cross-plane. An optimum water–graphene system, which is independent of size effects, was selected, and the same was used to determine the Kapitza resistance using the predicted EMD method. The values obtained from both the EMD and the non-equilibrium molecular dynamics (NEMD) methods were compared for different potentials and water models, and the results are shown to be in good agreement. Our method allows us to compute the Kapitza resistance using EMD simulations, which obviates the need to create a large temperature gradient required for the NEMD method.<h4>ACKNOWLEDGMENTS</h4>

Department Of Chemical Engineering

Kapitza resistance at water–graphene interfaces

Electrokinetic flows are generally analyzed, assuming isothermal conditions even though such situations are hard to be achieved in practice. In this paper, the flow of a symmetric electrolyte in a charged nanochannel subjected to an axial temperature gradient is investigated using molecular dynamics simulations. We analyze the relative contribution of the Soret effect, the thermoelectric effect, and the double layer potential in the electrical double layer for various surface charges and temperature gradients. We find the flow driven by thermal gradient is analogous to electroosmotic flow. The thermophoretic motion of the electrolyte is significant for negative surface charge than the positive surface charge. The vibrational spectrum of graphene is calculated to delineate the effect of the surface charge polarity on the observed thermophoretic motion of the electrolyte. A unique structure of interfacial water layer is observed for the positive and negative surface charges. We attribute the presence of these structures to the differences in water-carbon interactions existing for various surface charge polarity. For an applied thermal gradient in the range 2.6 K nm-1 to 8 K nm-1, we observe a continuous net flow with average velocities reaching up to 9.4 m s-1 inside the channel for a negative surface charge of -0.101 C m-2. The results indicate that in a charged graphene-based nanochannel, temperature gradients can be employed to induce streaming current, depending on the relative influence of the Soret effect and the double layer potential. © 2020 IOP Publishing Ltd.

Department Of Civil Engineering

Nanotechnology

Non-isothermal flow of an electrolyte in a charged nanochannel

A heat pump unit using CO2 as working fluid is designed to meet not only a part of the heating demand in the centralised kitchen at The Akshaya Patra Foundation, Bengaluru, India, but also the entire cooling demand to replace the existing HCFC units for AC. The proposed heat pump system generates hot water at  90oC which is stored in hot water storage tanks for use in the cooking cauldrons. Moreover, the existing space cooling systems are replaced by a centralised cooling system which circulates chilled water. In order to handle the fluctuation in cold and hot water demand, thermal storage systems are proposed. This concept offers substantial reductions in GHG emissions from the cooling system (approximately 60%). Furthermore, for the overall system (cooking process and space cooling) the reduction in energy demand, energy cost and GHG emissions are all above 30%. © 2020 International Institute of Refrigeration. All rights reserved.

Refrigeration Science and Technology

Heat pump/chiller system for centralized kitchens in India

Tuberculosis (TB) is a resurgent infectious disease affecting a large number of people in the developing countries. An on-site, affordable diagnostic screening at an early-stage for an immediate anti-TB treatment is known to tremendously minimize the high mortality rates. Lipoarabinomannan (LAM), a surface glycolipid, has been identified as a potential TB biomarker present in urine at ultra-low concentrations of a few fg/mL. Here, we report a plasmonic fiber optic absorbance biosensor (P-FAB) strategy for mannosylated LAM (Man-LAM or Mtb LAM) detection down to attomolar concentrations. It involves a plasmonic sandwich immunoassay on a U-bent fiber optic probe with gold plasmonic (AuNP) labels functionalized with anti-Mtb LAM immunoglobulin M (IgM) and anti-Mtb LAM IgG respectively. The Mtb LAM is quantified in terms of absorption of light passing through the fiber probe using a green LED and a photodetector. The choice of fiber optic probes (fused silica versus polymer), the optimum size (20, 40, 60 and 80&nbsp;nm) and concentration (2&nbsp;×&nbsp;, 10&nbsp;×&nbsp;, and 20&nbsp;×&nbsp;) of AuNP labels were investigated to obtain high sensitivity and lower limits of analyte detection (LoD). P-FAB with a simple LED-photodetector pair, 200&nbsp;μm fused silica U-bent fiber probe and 60&nbsp;nm (20&nbsp;×&nbsp;) AuNP labels gave LoDs down to 1&nbsp;fg/mL and 10&nbsp;fg/mL in the buffer and synthetic urine respectively. Moreover, the anti-Mtb LAM IgM bound sensor probes and the AuNP reagent stored at 4&nbsp;°C were stable up to 45 days. P-FAB based Mtb LAM sensor demonstrates its potential for an on-site TB diagnosis.

Department Of Biotechnology

Biosensors and Bioelectronics

A plasmonic fiberoptic absorbance biosensor for mannose-capped lipoarabinomannan based tuberculosis diagnosis

This study demonstrates a rapid, wash-free, dip-type plasmonic fiberoptic absorbance biosensor (P-FAB) capable of zeptomole analyte detection and 6-orders of wide dynamic range. It involves a sandwich immunoassay on a compact U-bent fiber optic probe surface that works by dipping an antibody-functionalized probe into a mixture of sample and gold nanoparticle (AuNP) label suspension. The U-bent fiberoptic probes with a high evanescent wave absorbance sensitivity allow detection of the high extinction AuNP labels measured in terms of light intensity change using a pair of LED and photodetector (PD). This simple and low-cost P-FAB gives an unprecedented detection limit of 0.17 zeptomole for human immunoglobulin G (HIgG) in 25 μL buffer in just 25 min. Further silver enhancement of AuNP labels for 5 min results in a limit of quantitation (LoQ) down to 0.17 zeptomole (∼100−150 molecules in 25 μL), making P-FAB a highly sensitive and low-cost technology for point-of-care diagnostics. © 2020 Elsevier B.V.

Sensors and Actuators, B: Chemical

U-bent fiber optic plasmonic biosensor platform for ultrasensitive analyte detection

In this paper, the development of weighted nonlinear beamformer, called as Filtered Delay Weighted Multiply and Sum (F-DwMAS) is reported. This method was investigated on Synthetic Transmit Aperture (STA) technique. The performance of the developed F-DwMAS method was compared with Delay and Sum (DAS) and recently introduced F-DMAS beamforming methods. Importantly, in the method proposed, an extra window stage is added after the delay stage in the F-DMAS method. The different methods of DAS, F-DMAS and F-DwMAS were compared in terms of the resulting image quality metrics, Lateral Resolution (LR), Axial Resolution (AR), Contrast Ratio (CR) and contrast-to-noise ratio (CNR), in experiments on tissue-mimicking phantoms. Experimental results show that, for STA technique, F-DwMAS resulted in improvements of AR by 46.91% and 30.19%, LR by 61.35% and 52.48%, CR by 84.68% and 27.51%, and CNR by 5.45% and 34.4% compared to those obtained using DAS and F-DMAS, respectively. Hence, it can be concluded that the image quality is improved by F-DwMAS compared to DAS and F-DMAS. © 2020 IEEE.

IEEE International Ultrasonics Symposium, IUS

A weighted non-linear beamformer for synthetic aperture ultrasound imaging

Currently, portal pressure is measured by the standard method known as hepatic venous pressure gradient (HVPG). But it is an invasive procedure; therefore, an alternative noninvasive technique to estimate portal pressure is required to monitor portal hypertension. In this work, a 3D portal vein model is developed to study the acoustic interaction with microbubbles in the portal vein. Ultrasound scattering by ultrasound contrast agent (UCA) is modelled and analyzed using finite element analysis in order to estimate portal pressure. It was found from the analysis that the subharmonic component dropped by 1.5 dB as the portal pressure raised from 0 mmHg to 10 mmHg. Over the same pressure range, the fundamental component reduced by only 0.2 dB. The results suggest that the subharmonic component from the nonlinear response of microbubble is strongly affected by the ambient pressure, and the proposed model may be used to estimate portal pressure noninvasively. Copyright © 2020 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved

Department of Engineering Design

BIODEVICES 2020 - 13th International Conference on Biomedical Electronics and Devices, Proceedings; Part of 13th International Joint Conference on Biomedical Engineering Systems and Technologies, BIOSTEC 2020

Noninvasive portal pressure estimation model using finite element analysis

Understanding the breakup morphology of an expelled respiratory liquid is an emerging interest in diverse fields to enhance the efficacious strategies to attenuate disease transmission. In this paper, we present the possible hydrodynamic instabilities associated with expelling the respiratory liquid by a human. For this purpose, we have performed experiments with a cylindrical soap film and air. The sequence of the chain of events was captured with high-speed imaging. We have identified three mechanisms, namely, Kelvin-Helmholtz (K-H) instability, Rayleigh-Taylor (R-T) instability, and Plateau-Rayleigh (P-R) instability, which are likely to occur in sequence. Furthermore, we discuss the multiple processes responsible for drop fragmentation. The processes such as breakup length, rupture, ligament, and drop formation are documented with a scaling factor. The breakup length scales with We-0.17, and the number of ligaments scales as Bo. In addition, the thickness of the ligaments scales as We-0.5. Here, We and Bo represent the Weber and Bond numbers, respectively. It was also demonstrated that the flapping of the liquid sheet is the result of the K-H mechanism, and the ligaments formed on the edge of the rim appear due to the R-T mechanism, and finally, the hanging drop fragmentation is the result of the P-R instability. Our study highlights that the multiple instabilities play a significant role in determining the size of the droplets while expelling a respiratory liquid. This understanding is crucial to combat disease transmission through droplets. © 2020 Author(s).