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

Biofuels, including biodiesel have the potential to partially replace the conventional diesel fuels for low-temperature combustion engine applications to reduce the CO2 emission. Due to the long chain lengths and high molecular weights of the biodiesel components, it is quite challenging to study the biodiesel combustion experimentally and computationally. Methyl crotonate, a short unsaturated fatty acid methyl ester was chosen for the chemical kinetic study as a model biodiesel fuel. Auto-ignition experiments were carried out in a rapid compression machine at pressures of 20 and 40 bar under diluted conditions over a temperature range between 900 K and 1074 K, and at different equivalence ratios (φ = 0.25, 0.5 and 1.0). The updated mechanism showed satisfactory agreement with the ex- perimental data with significant improvements in low-temperature ignition behavior. The key reactions at various combustion conditions and the improved reactivity of the modified mechanism were analyzed by performing sensitivity and path flux analysis. The importance of low-temperature pathways in predicting the ignition behavior of methyl crotonate at intermediate and low temperatures was demonstrated.

World University root node

Proceedings of the Combustion Institute

Experimental and kinetic modeling studies on the auto-ignition of methyl crotonate at high pressures and intermediate temperatures

This paper reports the simultaneous generation of multiple fundamental ultrasonic guided wave modes L(0,1), T(0,1), and F(1,1) on a thin wire-like waveguide (SS-308L) and its interactions with liquid loading in different attenuation dispersion regimes. An application towards liquid level measurements using these dispersion effects was also demonstrated. The finite element method (FEM) was used to understand the mode behavior and their dispersion effects at different operating frequencies and subsequently validated with experiments. In addition, the ideal configuration for the simultaneous generation of at least two modes (L(0,1), T(0,1), or F(1,1)) is reported. These modes were transmitted/received simultaneously on the waveguide by an ultrasonic shear wave transducer aligned at 0◦/45◦/90◦ to the waveguide axis. Level measurement experiments were performed in deionized water and the flexural mode F(1,1) was observed to have distinct dispersion effects at various frequency ranges (i.e., &gt;250 kHz, &gt;500 kHz, and &gt;1000 kHz). The shift in time of flight (TOF) and the central frequency of F(1,1) was continuously measured/monitored and their attenuation dispersion effects were correlated to the liquid level measurements at these three operating regimes. The behavior of ultrasonic guided wave mode F(1,1) when embedded with fluid at three distinct frequency ranges (i.e., &gt;250 kHz, &gt;500 kHz, and &gt;1000 kHz) were studied and the use of low frequency Regime-I (250 kHz) for high range of liquid level measurements and the Regime-II (500 kHz) for low range of liquid level measurements using the F(1,1) mode with high sensitivity is reported. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Department of Electrical Engineering

Fulltext

Sensors (Switzerland)

Experimental study on dispersion effects of f (1,1) wave mode on thin waveguide when embedded with fluid

An extensive analysis of radiative flux biases in the Climate Forecast System Model Version 2 (CFSv2) is done. Annual mean and seasonal variations of biases at the surface and top of the atmosphere (TOA) are reported in the global domain. Large regional biases in shortwave (SW) and longwave (LW) radiation are observed over convectively active zones in the tropics. The relative contribution of various processes responsible for the reported biases is quantified. The poor simulation of clouds and inadequate representation of surface properties seem to be major contributors. Over certain regions, errors due to different processes add up, whereas, over other regions, errors tend to nullify each other. Surface and atmospheric variables taken as input parameters in the radiative transfer modules are compared with satellite-based observations. The maximum biases in SW and LW radiation are observed over the regions of persistent low clouds. The magnitude of the SW and LW biases at the TOA is in phase with the biases in cloud fraction by and large. However, the error in the radiative fluxes due to errors in surface radiative properties is of equal importance. The cold bias in near-surface air temperature reported in other studies may partly be attributed to an underestimation in the net SW radiation at the surface. In the present study, a plausible prescription is also provided to correct the source of the biases. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.

Department of Metallurgical and Materials Engineering

Climate Dynamics

An assessment of radiative flux biases in the climate forecast system model CFSv2

The poor machining characteristics of super duplex stainless steels (SDSS) affect the surface integrity as it induces tensile residual stress in the parts. When this machined part is exposed to hostile chloride conditions, it results in the stress corrosion crack (SCC) formation, thereby impacting their service life. To understand the cracking phenomenon involved, it is important to study the distinct characteristics of cracks formed in compliance with the machining (turning) process. This study focusses on studying the effects of machined surface integrity on the stress corrosion cracking of SDSS. Following machining, the specimens were subjected to SCC examination in the chloride condition at different immersion time of 1 h, 2 h, and 5 h. The testing was done in pursuant with ASTM G36 standard. The result indicated that major cracks generated along both parallel as well as the perpendicular direction of machining marks due to the high magnitude of biaxial tensile residual stress. With the increase in immersion time (5 h), new forms of crack and localized corrosion were noticed on the surface. At 1 h and 2 h, only the major cracks were evident, along with minor pit formation on the surface. But at 5 h, selective attack/selective leaching occurred on the turned surface along with the formation of network of cracks. Analysis of the transition pit/crack behaviour of revealed that different pits merge to form a detrimental crack with more intensity than the major cracks. The crack density continue to grow with immersion time of 5 h and also there is no evidence was observed on reduction of crack density. However, the quantification of crack density was not possible at 5 h due to the complex network of high density crack formation. The microstructure analysis revealed that the ferrite phase was more vulnerable to SCC than the austenite phase in chloride environment. © 2021 Elsevier Ltd

Engineering Failure Analysis

Effect of machined surface integrity on the stress corrosion cracking behaviour of super duplex stainless steel

In many structural applications like bridges, arches, etc., frames are used, and it is important to study their dynamic behavior. Finite element method (FEM) is usually used for computational simulation of vibration for such frame structures. However, FEM simulations for high frequency are computationally intensive and lack accuracy. This paper proposes a wave propagation-based approach for the vibration analysis of a frame having angular and curved joints. The reflection and transmission matrices for the joints are derived using the kinematic compatibility and equilibrium conditions. Reflection, transmission, and propagation matrices are assembled leading to matrix equation terms of the wave amplitudes. Modal analysis and harmonic analysis of frames having curved and angular joints are performed using the present formulation. The frequency response function for point harmonic forcing acting on such structures is also presented. The formulation and the results are non-dimensionalized for wider applicability. The results obtained using the present formulation are compared with those obtained through FEM simulation in a commercial package. It is found that the results obtained using the two methods are in excellent correlation. The computational efficiency of the present method over FEM simulation is also reported. © 2021 American Society of Civil Engineers (ASCE). All rights reserved.

Journal of Vibration and Acoustics, Transactions of the ASME

Wave analysis for in-plane vibration of angular and curved frames

The present study investigates the effect of inclination on the buoyancy driven systems. There are extensive studies on the cavity systems which exhibit a heat transfer coefficient jump upon the change in the inclination as the system moves from one steady state to another. The present numerical study makes use of 2-D and 3-D CFD simulations to investigate if a similar behaviour occurs in natural circulation systems such as a Natural Circulation Loop and a Coupled Natural Circulation Loop. The study identifies a combination of flow pattern rearrangement and flow direction reversal as the phenomena responsible for the heat transfer coefficient jump. The study also examines carefully as to why the same was not reported previously. The CFD study is validated thoroughly with the numerical and experimental data available in the literature. A parametric study is also conducted to examine the effects of the aspect ratio, the Rayleigh number, the Prandtl number and the inclination with the plane of the Natural Circulation Loop. © 2020 Elsevier Ltd

International Communications in Heat and Mass Transfer

Numerical investigation on the heat transfer coefficient jump in tilted single-phase natural circulation loop and coupled natural circulation loop

Filtering of the sub-band spectral radiation is an attractive technique to overcome the lower efficiencies of direct conversion thermophotovoltaic technology. The poor performance of these systems is due to the relatively small portion of the incident energy being above the bandgap of photovoltaic cell. To effectively filter the majority of the sub-bandgap radiation and re-employ it as regenerative heat, a viable solution is to design an efficient spectrally selective filter ideally matched to the photovoltaic cell's bandgap. Here, we have explored a high contrast amorphous silicon grating on a quartz substrate. Quartz due to its inherent nature inhibits transmission of sub-band gap radiation in the infrared (IR) region (>4.75 μm), whereas gratings further filter radiation above 1.8 μm suitable for GaSb photovoltaic cell. The optimized filter is fabricated using direct write laser lithography, and optical characterization result shows that 72% of incident radiation in unconvertible region (>1.80 μm) is filtered and recycled. Further, the thermal characterization results of IR filter carried out using a ceramic heater has shown the drop in effective temperature from 1074.9 to 813.2 K in above bandgap region. This suppressed radiation has contributed to an absolute increase in source body temperature by 16.0 K resulting in increase in the above bandgap radiation available for thermophotovoltaic conversion. The proposed spectral filtering design can be tailored to solar cells of any bandgap and is scalable for employment in various thermophotovoltaic applications. © 2021 Society of Photo-Optical Instrumentation Engineers (SPIE).

Department Of Civil Engineering

Journal of Photonics for Energy

Spectral filtering of sub-bandgap radiation using all-dielectric gratings for thermophotovoltaic applications

Machining of complex features and holes on superalloys is a topic of both industrial and academic interest. Though the demand for high aspect ratio holes on Ti-6Al-4V is high in aerospace, biomedical and chemical industries, machining the same is very challenging due to the low thermal conductivity and debris accumulation in the machining zone. The present-day methods of hole drilling by unconventional methods like Electric Discharge Machining (EDM) make use of electrodes with poor flushing capabilities. Hence the motivation of the present work is to develop a method to modify the geometry of Electric Discharge Drilling (EDD) tools in order to enhance debris removal. For the first time an attempt has been made to machine micro double-helical grooves on EDD tools in a single pass. Solid, single-helical and double-helical electrodes are developed and through-holes are drilled on a Ti-6Al-4V workpiece. A comparative analysis of the performance of these three types of tools with respect to the machining time, electrode wear rate and hole quality is carried out. From Computational Fluid Dynamics (CFD) simulations it is seen that the double-helical grooved tool is superior in debris removal. The best values of the machining time of 183.33 s, overcut of 2.19 mm, hole taper angle of 7.93° and area of recast layer of 6.66 mm2 are obtained on the holes machined using double-helical electrodes. The mentioned tool has the potential to overcome the problem of debris removal in high aspect ratio hole drilling and surpass the present-day electric discharge drilling tools. © IMechE 2021.

Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture

Effect of micro double helical grooved tools on performance of electric discharge drilling of Ti-6Al-4V

In process industries, the study of granular mixing can substantially optimize energy costs and the quality of final products. In this work, we study the mixing of binary granular systems assisted by fluid flow through the assembly. The granular system is exposed to continuous fluid flow from the bottom to the top. Particle mixing is simulated by the coupling of Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). Parameters like particle stacking order, density ratio, and size ratio show a significant influence on mixing. The presence of tilted plates as a geometric intervention with different configurations plays a critical role in mixing efficiency. A new mixing index which captures the nature of contact creation, and the degree of mixing is proposed. The present work helps develop efficient strategies for particle mixing in fluidized beds. © 2021 Elsevier B.V.

Powder Technology

Fluid flow assisted mixing of binary granular beds using CFD-DEM

Numerical modeling of the thermo-elastic fracture using a hybrid phase-field method is presented. The model’s capability to simulate complex thermo-elastic crack propagation paths under the temperature and mechanical loads’ influence is demonstrated through a few example problems. The evolution of complex crack patterns in a ceramic plate subjected to quenching are simulated. Further, the behavior of functionally graded specimens with a spatial variation of material properties when subjected to thermal shock is investigated. A staggered solution scheme is used to solve the coupled system of multi-field partial differential equations using an open-source finite element software FEniCS. © 2021 Taylor & Francis Group, LLC.