Mechanical Engineering

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In the present work, we developed eco-friendly and cost-effective nanocomposite coatings. These wax-derived coatings showed high superhydrophobicity while exhibiting mechanical and thermal robustness. The addition of nano-alumina particles in wax (Beeswax and Paraffin) significantly enhanced de-wetting (contact angle ~ 156°) with extremely low hysteresis (&lt;5°). The Paraffin-based composite coating showed better thermal (up to 50 °C) and mechanical (Δθ≈5°) (droplet impacts) stability than Beeswax counterpart, while also sustaining outdoor exposure. The superhydrophobic coatings showed self-cleaning ability with significantly low water consumption (&lt;1 μl/mm2). We showed that nanocomposite-wax coatings possess required durability and are potential candidates for developing non-fluorinated self-cleaning surfaces. © 2020 Elsevier B.V.

(SoE) School of Engineering

Materials Letters

High durability of non-fluorinated superhydrophobic nanocomposite coatings

A numerical investigation of the binary collision of two off-center unequal sized liquid droplets in the gaseous environment has been performed. The complete process of collision of droplets is dynamically simulated by solving the incompressible Navier–Stokes equations. Simulations are performed using three-dimensional, multiphase finite volume based solver in OpenFOAM platform. The gas-liquid interface is captured by using the volume of fluid (VOF) method. The solver is appropriately validated and is applied to study the effect of the droplet diameter ratio and the impact parameter on the droplet collision characteristics. The numerical study is done by fixing a moderately high Weber number and Reynolds number for unequal sized droplet collision, where stretching separation is expected as a collision outcome for equal sized droplets. The geometrical characteristics of ligament structures are presented both qualitatively and quantitatively. The satellite droplet formation is also well captured with the present simulations. Post-collision characteristics from the simulations are compared with an existing collision model. It is believed that the present study serves as a first step towards the development of a more accurate droplet collision models. © 2020

World University root node

International Journal of Multiphase Flow

Detailed numerical simulations of unequal sized off-centre binary droplet collisions

In this current study, we developed SiC (10 wt\%) reinforced AlCoCrFeNi complex concentrated alloy composite claddings with different particle sizes (micro, nano and bimodal) on stainless steel 316L substrate using microwave irradiation. Microstructural analysis showed cellular structured claddings with intermetallic phases occupying the intercellular regions along with low porosity (&lt;1\%). The claddings were mainly composed of A2 (disordered BCC) and B2 (ordered BCC) along with Cr23C6. The bimodal (mixture of nano and micro) composite cladding showed highest hardness and fracture toughness (810 HV and ~12.2 MPa√m) followed by nano and micro composite claddings. Under cavitation erosion (distilled water) condition, bimodal cladding showed highest incubation period (IP) (~13 h) with extremely low mean depth erosion rate (MDER) (~0.089 μm/h) with 16 and 27 times lower than stainless steel 316L and WC-based coating, respectively. The cavitation erosion resistance observed for the bimodal composite cladding is among the highest demonstrated by the CCAs at present. However, under erosion-corrosion conditions, non-reinforced and micro-reinforced claddings showed higher degradation resistance with lower material removal rates than that observed for bimodal cladding. Standalone electrochemical corrosion studies also showed highest corrosion and passivation resistance for non-reinforced cladding. These results were explained on the basis of formation of Cr-depleted micro-galvanic cells due to high negative enthalpy of Cr with C dissociated from SiC particle. The detailed morphological analysis of the tested samples showed presence of tearing top surface as the primary degrading mechanism along with fracture of intermetallic phases. The results show that bimodal composite CCA cladding provides a potential surface engineering solution for improvising the serviceability of the many engineering systems. © 2020 Elsevier B.V.

Surface and Coatings Technology

Complex concentrated alloy bimodal composite claddings with enhanced cavitation erosion resistance

The leaching out of toxic elements from metallic bioimplants has serious repercussions, including allergies, peripheral neuritis, cancer, and Alzheimer's disease, leading to revision or replacement surgeries. The development of advanced structural materials with excellent biocompatibility and superior corrosion resistance in the physiological environment holds great significance. High entropy alloys (HEAs) with a huge compositional design space and outstanding mechanical and functional properties can be promising for bioimplant applications. However, microstructural heterogeneity arising from elemental segregation in these multiprinciple alloy systems is the Achilles heel in the development of next-generation HEAs. Here, we demonstrate a pathway to homogenize the microstructure of a biocompatible dual-phase HEA, comprising refractory elements, namely, MoNbTaTiZr, through severe surface deformation using stationary friction processing (SFP). The strain and temperature field during processing homogenized the elemental distribution, which was otherwise unresponsive to conventional annealing treatments. Nearly 15 min of the SFP treatment resulted in a significant elemental homogenization across dendritic and interdendritic regions, similar to a week-long annealing treatment at 1275 K. The SFP processed alloy showed a nearly six times higher biocorrosion resistance compared to its as-cast counterpart. X-ray photoelectron spectroscopy was used to investigate the nature of the oxide layer formed on the specimens. Superior corrosion behavior of the processed alloy was attributed to the formation of a stable passive layer with zirconium oxide as the primary constituent and higher hydrophobicity. Biocompatibility studies performed using the human mesenchymal stem cell line, showed higher viability for the processed HEA compared to its as-cast counterpart as well as conventional metallic biomaterials including stainless steel (SS316L) and titanium alloy (Ti6Al4V). Copyright © 2020 American Chemical Society.

ACS Applied Bio Materials

Enhanced Biocorrosion Resistance and Cellular Response of a Dual-Phase High Entropy Alloy through Reduced Elemental Heterogeneity

The use of ultrasound to enhance the regeneration of zeolite 13X for efficient utilization of thermal energy was investigated as a substitute to conventional heating methods. The effects of ultrasonic power and frequency on the desorption of water from zeolite 13X were analyzed to optimize the desorption efficiency. To determine and justify the effectiveness of incorporating ultrasound from an energy-savings point of view, an approach of constant overall input power of 20 or 25 W was adopted. To measure the extent of the effectiveness of using ultrasound, the ultrasonic-power-to-total power ratios of 0.2, 0.25, 0.4 and 0.5 were investigated and the results compared with those of no-ultrasound (heat only) at the same total power. To analyze the effect of ultrasonic frequency, identical experiments were performed at three nominal ultrasonic frequencies of ~28, 40 and 80 kHz. The experimental results showed that using ultrasound enhances the regeneration of zeolite 13X at all the aforementioned power ratios and frequencies without increasing the total input power. With regard to energy consumption, the highest energy-savings power ratio (0.25) resulted in a 24\% reduction in required input energy and with an increase in ultrasonic power, i.e. an increase in acoustic-to-total power ratio, the effectiveness of applying ultrasound decreased drastically. At a power ratio of 0.2, the time required for regeneration was reduced by 23.8\% compared to the heat-only process under the same experimental conditions. In terms of ultrasonic frequency, lower frequencies resulted in higher efficiency and energy savings, and it was concluded that the effect of ultrasonic radiation becomes more significant at lower ultrasonic frequencies. The observed inverse proportionality between the frequency and ultrasound-assisted desorption enhancement suggests that acoustic dissipation is not a significant mechanism to enhance mass transfer, but rather other mechanisms must be considered. © 2020 Elsevier B.V.

Fulltext

Ultrasonics Sonochemistry

Ultrasound-assisted regeneration of zeolite/water adsorption pair

In the present work, we devised a facile, and environmental imprinting and hot-water treatments for developing a durable self-cleaning aluminum surface. The micro and nanostructured surfaces were composed of pillars and ellipsoidal flakes, respectively. The fluorination (vapor deposition) of surfaces imparted superhydrophobicity (θs &gt; 150°), with high adhesion observed for micro-patterned surface, while nano and hierarchical surfaces exhibited low hysteresis and tilting angles (θ &lt; 5°). The nanostructured (ΔE=-0.3J/m) surface has shown the prevalence of stable Cassie state compared to hierarchical (ΔE=-0.07J/m) counterpart. The nanostructured surface has also exhibited higher durability under static and dynamic conditions than the hierarchical counterpart. © 2020 Elsevier B.V.

Sustainable approach for the development of durable superhydrophobic metallic surfaces

Present communication is an attempt to explore the best PV technology suitable for PVT solar drying system through environmental and economic feasibility. Experimental setup for one of the PV technology (c-Si) has been taken for experimental validation with theoretical model. Further, the environmental feasibility and environ economic evaluation for drying system having roof with various PV namely, c-Si, p-Si or m-Si, a-Si, CdTe, and CIGS have been evaluated through energy matrices (EPBT, EPF, and LCCE), CO2 emission, net CO2 mitigation and carbon credit earned which is based on energy and exergy output of the system on yearly basis. The economic analysis has been carried out with experimental data taken on c-Si PVT drying system by considering grapes as a crop. Cogeneration efficiency has been calculated for different PV technologies and found to be highest for c-Si PV technology that is, 61.71\%, 77.98\%, and 12.25\% based on energy (electrical and thermal) gain, equivalent (overall) energy gain, and exergy gain, respectively. LCCE on energy basis reveals that for the five-year system life, c-Si and CIGS have equal efficiency but after five years, c-Si is best. Cogeneration efficiency of system on the basis of energy (electrical + thermal) gain, equivalent (overall) energy gain and overall exergy gain found to be maximum with c-Si PV technology that is, 61.71\%, 77.98\%, and 12.25\%, respectively. © 2020 American Institute of Chemical Engineers

Environmental Progress and Sustainable Energy

Environmental and economic sustainability of PVT drying system: A heat transfer approach

In this study, superhydrophobic surfaces were fabricated using 1H,1H,2H,2H-perfluorooctyltriethoxysilane monolayer deposition on thermally oxidized brass. The superhydrophobic surface showed a contact angle (CA) of 155° with a CA hysteresis of 3.5°. The corrosion behaviour of developed superhydrophobic surface was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies in 3.5\% NaCl solution. The superhydrophobic surface showed exceptional corrosion behaviour with nearly 21 times higher corrosion resistance compared to as-received (AS) brass. The EIS analysis suggests the presence of Warburg impedance in the AS brass indicating diffusion phenomena, while superhydrophobic brass surface showed a reversed loop in the low-frequency spectra, signifying significantly delayed kinetics of the electrochemical system. The study provides a facile, promising means of developing highly corrosion-resistant surfaces in engineering materials. © 2020, © 2020 Institute of Materials, Minerals and Mining Published by Taylor & Francis on behalf of the Institute.

Surface Engineering

Facile fabrication of superhydrophobic brass surface for excellent corrosion resistance

In this study, a novel processing technique for microstructural refinement of Ni-Cr-5Al2O3 composite coating developed using high velocity oxy-fuel (HVOF) technique is demonstrated. The processing technique, known as stationary friction processing (SFP) is an adaptation of the well-known friction stir processing (FSP). The as-sprayed coating showed a typical lamellar microstructure along with non-homogeneous elemental distribution. The SFP treatment resulted in significant microstructural refinement with complete elimination of splat boundaries and pores together with fully homogeneous elemental distribution. The performance of as-sprayed and processed coatings was evaluated in slurry erosion, erosion-corrosion and pure corrosion in 3.5\% NaCl solution. At oblique impingement angle, the SFP treated sample showed minimum erosion rate of nearly 0.1 mm3/h which is 3–5 times lower than the as-sprayed coating and the substrate. For normal impingement, the erosion rate of SFP specimen was nearly 30\% lower compared to the as-sprayed coating and the substrate. This is attributed to higher hardness as well as fracture toughness of the SFP treated coating as a result of microstructural refinement. In addition, the SFP treated coating was able to demonstrate superior resistance under erosion-corrosion conditions as well. Further, the processed sample showed lowest corrosion rate of 0.079 μA/cm2, 5–6 times lower than the as-sprayed coating (0.39 μA/cm2). The enhancement in the corrosion resistance of the coating after processing is attributed to complete homogenization of the coating with removal of all splats, splat boundaries, pores and regions of elemental segregation. © 2020 Elsevier B.V.

Structural rejuvenation of thermal spray coating through stationary friction processing

This study focuses on numerically investigating the response dynamics of a pitch–plunge airfoil with structural nonlinearity under dynamic stall conditions. The aeroelastic responses are investigated for both deterministic and randomly time varying flow conditions. To that end, a pitch–plunge airfoil under dynamic stall condition is considered and the nonlinear aerodynamic loads are computed using a Leishman–Beddoes formulation. It is shown that the presence of structural nonlinearities can give rise to a variety of dynamical responses in the pre-flutter regime. Next, a response analysis under the presence of a randomly fluctuating wind is carried out. It is demonstrated that the route to flutter occurs via a regime of pre-flutter oscillations called intermittency. Finally, the manifestation of these stochastic responses is characterized by invoking stochastic bifurcation concepts. The route to flutter via intermittency is presented in terms of topological changes occurring in the joint-probability density function of the state variables. © 2019 Elsevier Ltd