Research Highlights

Here, we present some highlights of our department’s research soon after they are published. An effort is made to write about the specific research in an easy-to-understand language to make it accessible to those who are not specialists on that particular topic. Specialists and those want to know more can click on the link to the publication to gain an in-depth knowledge about that work.

Simultaneous Imaging of Multiple Species in Flames using FRAME (Ravikrishna and team)

R. V. Ravikrishna

During the combustion of hydrocarbon fuels, multiple intermediate products are formed such as hydroxyl (OH), formaldehyde (CH2O), Polycyclic Aromatic Hydrocarbons (PAHs), CH, CO, etc., which depend on the stoichiometry of the flame. Intermediate products such as OH, CH2O, CH and CO control the heat release rate of a flame. Furthermore, soot is produced under fuel-rich conditions, depending on the concentration of PAH. Therefore, the “footprint” of these chemical species can be used to track the combustion and post-combustion processes. Due to the stricter emission norms, much attention has been given to further understanding of the combustion chemistry and especially, the soot formation.

Quantitative measurements in flames are challenging, as simultaneous multi-species measurements are required. A variety of optical measurement techniques are used to measure single and multi-species in flames, e.g. light scattering, absorption and fluorescence spectroscopy. The most common ones are Laser-induced fluorescence (LIF) and Laser-induced incandescence (LII).

For simultaneously imaging of multiple species in flames, a combination of multiple lasers and several cameras (which are time-gated and/or equipped with different spectral filters) are required – making the optical setup complex and resource-intensive. Furthermore, despite their ability of mapping multiple species in a plane, all the “conventional” measurements are often perturbed by issues such as stray light and background radiation.

a) Single-shot FRAME (Frequency Recognition Algorithm for Multiple Exposures) image of the flame along with cross-patterned unprocessed sub-image and its FFT consisting of modulated signals of OH-LIF and soot-LII. (b) Processed OH-LIF image (c) soot-LII image of the flame – extracted by applying the FRAME algorithm to (a).

 

A collaborative effort by Prof. Ravikrishna’s group and researchers from Friedrich‐Alexander University, Germany, reported simultaneous qualitative imaging of two species in a flame on a single camera without the use of an image doubler or additional cameras. The planar multispecies imaging technique FRAME based on structured illumination imaging was used where the intensity of the laser sheet is spatially modulated.

The link to the paper: https://www.mdpi.com/1424-8220/20/19/5534/pdf

Citation: Sensors 2020, 20, 5534; doi:10.3390/s20195534

Posted on October 10, 2020

Bubble-induced rupture of droplets on tailored surfaces (Susmita Dash and Team)

Susmita Dash

Bursting of bubbles is ubiquitous with numerous applications ranging from spraying of pesticides, drug delivery, and inkjet printing to forming emulsions. Understanding the parameters that influence the dynamics of bubble rupture is crucial to design systems with improved performance. Here, we experimentally investigate the main morphological parameters of a droplet deforming on a lubricant-impregnated surface (LIS) and hydrophobic surfaces due to continuous air inlet. We show that the extent of bubble growth upon air injection into a sessile droplet is dependent on contact angle hysteresis and viscosity of oil in the case of LIS. The location of the nucleation of hole resulting in bubble-induced rupture is explained in terms of the preferential thinning of the water and water−oil bilayer thin film near the contact line or the apex of the droplet.

The link to the paper is: https://doi.org/10.1021/acs.langmuir.0c01187

Citation: Langmuir 2020, 36, 30, 8858–8864

Posted on September 25, 2020

Mechanics of Elastic Ribbons (Ramsharan Rangarajan and Team)

Ramsharan Rangarajan

Ribbons are slender structures characterized by three disparate geometric dimensions— length 𝓁, width 𝑤 and thickness h. The pair of large aspect ratios 𝓁∕𝑤 and 𝑤∕dictate their rich buckling-dominated mechanical behavior. In many ways, a growing field of research on the mechanics of ribbons is exemplary of an evolving paradigm in engineering that considers buckling and related geometric nonlinearities as features to be exploited, rather than as modes of failure. Understanding the feature-rich behavior of thin elastic ribbons is in fact ripe with opportunities for fundamental studies exploring the nexus between geometry and mechanics, and for conceiving of engineering applications that exploit geometric nonlinearity as a functioning principle.

In a recent study, the research group of Dr Ramsharan Rangarajan critically examine modeling approaches for elastic ribbons using detailed measurements of complex three-dimensional deformations realized in experiments. Rather surprisingly, they find that simple and practically realizable ribbon deformations contradict assumptions underlying the most commonly used models. They go on to identify and validate a geometrically nonlinear theory over a useful range of loading conditions.

Through the study, the researchers demonstrate annular ribbons to be prototypical systems for studying the mechanics of elastic ribbons. Their experiments reveal that annular ribbons exhibit a tunable degree of nonlinearity, possess multiple stable equilibria, show bifurcation phenomena correlated with the number of zero crossings in the mean curvature, and provide evidence for the localization of energy, thus making annular ribbons interesting mechanical systems to study in their own right.

Reference:

A Kumar, P Handral, D Bhandari, A Karmakar, R Rangarajan
Journal of the Mechanics and Physics of Solids, 104070, 2020.

Posted on August 31, 2020