Mechanical Engineering

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Shiv Nadar University

In the present investigation, various efficiencies and productivity of N identical partially covered PVT flat plate collectors integrated single slope solar distiller unit have been computed at different water depth under optimized condition to see the effect of variation of water depth on hourly and daily efficiencies and productivity. The meteorological data of 2 months: one belonging to winter season say January and the other belonging to summer season say June have been considered for New Delhi climatic condition. The hourly and daily thermal efficiencies, hourly and daily exergy efficiencies, hourly and daily electrical efficiencies, hourly and daily overall exergy efficiencies and hourly and daily productivities have been evaluated under optimized condition. It has been concluded that the increase in values of average daily efficiencies and productivity is significant till 1.4 m water depth. © 2019 Desalination Publications. All rights reserved.

World University root node

(SoE) School of Engineering

Desalination and Water Treatment

Effect of depth of water on various efficiencies and productivity of N identical partially covered PVT collectors incorporated single slope solar distiller unit

Interaction of fluid forces with flexible structures is often prone to dynamical instabilities, such as aeroelastic flutter. The onset of this instability is marked by sustained large amplitude oscillations and is detrimental to the structure's integrity. Therefore, investigating the possible physical mechanisms behind the onset of flutter instability has attracted considerable attention within the aeroelastic community. Recent studies have shown that in the presence of oncoming fluctuating flows, the onset of flutter instability is presaged by an intermediate regime of oscillations called intermittency. Further, based on the intensity of flow fluctuations and the relative time scales present in the flow, qualitatively different types of intermittency at different flow regimes have been reported hitherto. However, the coupled interaction between the pitch (torsion) and plunge (bending) modes during the transition to aeroelastic flutter has not been explored. With this, we demonstrate with a mathematical model that the onset of flutter instability under randomly fluctuating flows occurs via a mutual phase synchronization between the pitch and the plunge modes. We show that at very low values of mean flow speeds, the response is by and large noisy and, consequently, a phase asynchrony between the modes is present. Interestingly, during the regime of intermittency, we observe the coexistence of patches of synchronized periodic bursts interspersed amidst a state of desynchrony between the pitch and the plunge modes. On the other hand, at the onset of flutter, we observe a complete phase synchronization between the pitch and plunge modes. This study concludes by utilizing phase locking value as a quantitative measure to demarcate different states of synchronization in the aeroelastic response. © 2019 Author(s).

Fulltext

Chaos

Synchronization of pitch and plunge motions during intermittency route to aeroelastic flutter

Superhydrophobic textured surfaces are known to maintain a nonwetted state unless external stimuli are applied since they can withstand high wetting pressure. Herein, we report a new category of tunable, one-dimensional (1D) Cassie-to-Wenzel wetting transitions during evaporation, even on superhydrophobic surfaces. The transition initiates at the periphery of the evaporating drop, and the wetting transition propagates toward the center of the drop. The transitions are observed for surfaces with wetting pressures as high as ~ 7,568 Pa, which is much higher than the Laplace pressure, i.e., ~200 Pa. In situ high-contrast fluorescence microscopy images of the evaporating drop show that the transition is induced by preferential depinning of the air-water interface and subsequent formation of air bubbles in the cavities near the three-phase contact line. The evaporation-induced internal flow enhances the pressure within the water droplet and subsequently causes a Cassie-to-Wenzel wetting transition. © 2019, © 2019 Taylor & Francis.

Nanoscale and Microscale Thermophysical Engineering

Internal-Flow-Mediated, Tunable One-dimensional Cassie-to-Wenzel Wetting Transition on Superhydrophobic Microcavity Surfaces during Evaporation

Thermal spray coatings are widely used for addressing erosion problems in fluid machineries. However, the presence of splat boundaries, non-homogeneous microstructure and element segregation limits their performance. In this study, we developed Ni-Cr-40Al2O3 coatings on stainless steel (SS316L) substrate using high-velocity flame spray followed by post-processing using friction stir processing. The performance of as-sprayed and processed coatings was evaluated in slurry erosion, erosion–corrosion and pure corrosion in 3.5\% NaCl solution. As-sprayed coating showed lower erosion and erosion–corrosion resistance compared to stainless steel. Friction stir processing resulted in significant microstructure refinement concurrent with enhanced hardness and fracture toughness of the developed coating. At oblique impingement angle, the processed coating showed nearly 30\% to twofold higher erosion and erosion–corrosion resistance compared to stainless steel substrate. During pure erosion at normal impingement, both as-sprayed and processed coating showed higher volume loss. However, during erosion–corrosion at normal impingement, the processed coating was able to demonstrate similar volume loss as that of the substrate. In addition, the processed coating showed significant improvement in the corrosion performance as well. The study showed that friction stir processing could be a promising pathway to unravel the deleterious effects of inherent non-homogeneities in thermal spray coatings. © 2019, ASM International.

Journal of Thermal Spray Technology

Post-processing of Ni-Cr-Al2O3 Thermal Spray Coatings Through Friction Stir Processing for Enhanced Erosion–Corrosion Performance

Amorphous metals, also known as bulk metallic glasses, are promising materials for advanced healthcare applications. This is attributed to their exceptional properties, unseen in crystalline materials. Their unique ability to undergo relaxation during low temperature annealing provides opportunity to develop tailored properties. Here, we show a new pathway to significantly accelerate the relaxation kinetics in a zirconium based metallic glass through severe surface deformation using thermo-mechanical processing. The combined strain and thermal field during thermo-mechanical processing significantly reduced the relaxation time compared to vacuum annealing concurrent with remarkable enhancement in its bio-corrosion resistance. The corrosion resistance was found to have a direct correlation with the wetting behavior and oxide layer composition. The surface of relaxed glass was found to be rich in zirconium oxide compared to its as-cast state with higher fraction of aluminum oxide. The difference in oxide layer composition was attributed to annihilation of free volume in relaxed glass resulting in limited atomic transport. Relaxed metallic glass exhibited more hydrophobic nature likely due to its lower surface energy state as a consequence of structural densification. In addition, the relaxed glass showed better cell proliferation, thereby, enhancing its appeal as a next-generation biomaterial. © 2019 Elsevier B.V.

Applied Surface Science

Enhancement in bio-corrosion resistance of metallic glass by severe surface deformation

In this communication, the performance evaluation has been discussed for various kinds of photovoltaic (PV) technologies which has integrated to solar air collector with drying system. Mathematical modelling has been carried out for photovoltaic thermal air collector (PVTAC) with dryer. On the basis of mathematical model, energy analysis has been carried out for different types of partially covered PV technologies (namely, c-Si, p-Si, a-Si, CdTe and CIGS) air collector. CIGS has been found to be the best PV technology for large systems in terms of minimum embodied energy and payback period. © 2019 Elsevier Ltd. All rights reserved.

Materials Today: Proceedings

Performance evaluation of different types PV materials for PVTAC with solar drying system

Airships are fast gaining popularity as one of the most prominent modes of surveillance, reconnaissance and providing connectivity in remote areas. These airships work on the Archimedes' principle, and employ gases which are lighter than air to stay afloat in the atmosphere. These gases are the most critical and costly support element for the usage of such airships as the permeation of these gases through the envelope material limits the flight duration of the airship and further increases the cost associated with transporting and refilling of the airship, thereby limiting its utility. Engineering the material of the envelope, so as to be able to minimize the leakage of gas, becomes the most important challenge for engineers designing the airships. The traditional experimental techniques used to analyse the permeation through the laminate are known to be extremely sensitive to minor variations in temperature and pressure and involve specialized equipment, time and money. This paper proposes and discusses alternate Computational Fluid Dynamics based 2D and 3D approaches to analyse the permeation of the gas through the envelope material, particularly for high altitude airship applications. In addition to this, this paper proposes a method to determine the best suited material for the airship envelope through a qualitative and quantitative permeation analysis of different combinations of material options. © 2019 Author(s).

AIP Conference Proceedings

Analysis and retardation of helium permeation for high altitude airship envelope material

India is an agriculture prominent country. Scientist and researchers are continuously working for betterment of agriculture processes. From the research, it was found that there is a loss of power and resources in irrigation process. Present manuscript consist of proposed model which utilizes renewable energy (solar energy) to operate irrigation process which results in better handling within limited resources. Proposed system consist of moisture sensing device in the field that provide convenience to farmer by supporting them in automation at very minute energy. This proposed design uses polycrystalline photovoltaic solar panel to charge the battery and this battery provide power supply to operate the model. © Published under licence by IOP Publishing Ltd.

IOP Conference Series: Materials Science and Engineering

Investigation of Automatic Solar Irrigation Model

The combination of high strength and good ductility are very desirable for advanced structural and functional applications. However, measures to enhance strength typically lead to ductility reduction due to their inverse correlation, nano-grained structures for an instance. Bi-modal grain structure is promising in this regard, but its realization is limited by multiple complex processing steps. Here, we demonstrate a facile single-step processing route for the development of bimodal grain structure in austenitic stainless steel, SS316L. The bimodal structure comprised of fine martensite grains (<500 nm) sandwiched between coarse austenite grains (~10 µm). The dual-phase bimodal structure demonstrated higher yield strength (~620 MPa) compared to ultra-fine grain structure (~450 MPa) concurrent with high uniform tensile ductility (~35\%). These exceptional properties are attributed to unique dual-phase, bimodal grain structure which delayed the onset of plastic instability resulting in higher strength as well as larger uniform elongation and work-hardening rate. Our approach may be easily extended to a wide range of material systems to engineer superior performance. © 2019, The Author(s).

Scientific Reports

High Tensile Ductility and Strength in Dual-phase Bimodal Steel through Stationary Friction Stir Processing

Bimodal microstructures in metals are attractive because they help in achieving high strength and good ductility simultaneously thereby circumventing the strength-ductility paradox. However, there are few reports and limited understanding of the surface degradation behavior of bimodal alloys. Here, the authors report on the exceptional corrosion resistance of bimodal stainless steel developed using a simple single-step processing route. The microstructure of bimodal steel comprises of fine martensite (≈200–400 nm) in a matrix of coarse austenitic grains (≈10 μm). The bimodal steel shows significantly lower corrosion rate of 0.001 mm/year in 3.5 wt\% NaCl solution compared to 0.088 mm/year for commercially available SS316L stainless steel. The exceptional corrosion behavior of bimodal steel is attributed to favorable electronic properties of its passive layer. Formation of a depletion zone in the passive layer and higher chromium fraction limits the charge transport across metal-oxide-solution interface. The current microstructural design strategy is potentially transformative for developing high-performance structural materials with superior corrosion resistance. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim