Mechanical Engineering

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In present communication, a solar dryer having semi-transparent photovoltaic thermal (SPVT) roof has been used to dry bitter gourd. Experimentation has been done and results were validated with linear regression method through mathematical modelling as well as for non-linear Artificial Neural Network (ANN) modelling has been used. The experimental data namely, ambient air temperature, moisture evaporated, bitter gourd surface temperatures, solar intensity on different surfaces of dryer, room temperature and relative humidity have been recorded for the climatic condition of Varanasi, UP, India. The numerical value of convective heat transfer coefficients for bitter gourd found to be between 0.69–14.45 W/m2 K. The results for mass transfer (moisture evaporated) during drying of bitter gourd from theoretical model (linear regression method and ANN) and experiments showed good agreement. Further, net electrical energy, thermal energy and overall thermal energy were found to be 0.62, 3.77 and 5.41 kWh/m2/day respectively. The payback period at 10\% interest rate and 4\% inflation rate with ₹ 50 ($0.77) and ₹ 100 ($1.54) saving rate per kg were found to be 1.47 and 0.72 years respectively. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.

(SoE) School of Engineering

Heat and Mass Transfer/Waerme- und Stoffuebertragung

ANN and mathematical modelling for moisture evaporation with thermal modelling of bitter gourd flakes drying in SPVT solar dryer

The vibration analysis of the geometrically imperfect functionally gradient (FGM) plate has been performed using hybrid higher order deformation theory. The present theory contains the nonlinear variation of thickness coordinate in in-plane and transverse displacement. The equation of motion for FGM plates are obtained through variational principle. The solution has been performed using a finite element method by employing C0 continuous isoparametric formulation with 72 DOF/element. The parametric study has been done to examine the influence of geometric configurations, volume fraction index and various modes of geometric imperfection on the vibration characteristics of the FGM plate. © Springer Nature Singapore Pte Ltd. 2020.

World University root node

Lecture Notes in Mechanical Engineering

Vibration response of shear deformable gradient plate with geometric imperfection

The solar power tower plant consists of thousands of heliostats, and heliostat field cost contributes nearly 40–50\% of the total plant cost. This makes the cost of heliostat an important parameter while designing solar power tower plant, and it varies considerably with its size and wind loads. Furthermore, the size and aspect ratio of heliostat have a significant influence on the wind loads impacting its load-bearing components. While the importance of optimum size of reflector area has been studied by several researchers, its aspect ratio (width/height) has not been examined in detail. In this view, the main objective of this study is to identify the appropriate aspect ratio of a heliostat’s reflector area. An analysis of heliostat cost using its reflector area and the aspect ratio as variable parameters illustrates that heliostat cost per unit area can be minimized by distributing costs into various categories having different cost dependencies on area as well as aspect ratio. Using the component-wise cost break-up of 148 m2 Advanced Thermal Systems' heliostat as a reference, optimum area and aspect ratio of heliostat are determined parametrically. Further, a hypothetical power tower plant with 50 MW capacity and 6 h of thermal energy storage is simulated with heliostat fields comprising heliostats built with various aspect ratios and corresponding optimum reflector area. The results indicate that it is not only more economical to build heliostats with aspect ratio of around 2, but also such heliostat fields deliver higher optical efficiency on an annualized basis. © 2019, King Fahd University of Petroleum & Minerals.

Arabian Journal for Science and Engineering

Effect of Aspect Ratio of Heliostat on Cost of Energy from Solar Power Tower Plants

In present communication, environ-economic analysis has been done for PVT drying system in which different types of PV module (c-Si, p-Si or m-Si, a-Si, CdTe, and CIGS) taken into consideration. Environmental feasibility has been explored in terms of CO2 emission, net CO2 mitigation and carbon credit earned based on energy and exergy output of the system on yearly basis. For yearly analysis of PVT system based on energy, input data has been taken from IMD Pune, India. The results showed that CO2 emission is maximum in the case of c-Si and minimum in CIGS manufacturing for given setup, respectively. Further, carbon credit earned has been evaluated based on energy and exergy analysis and found to be minimum and maximum in the case of CIGS and C-Si respectively. © 2020 IEEE.

International Conference on Electrical and Electronics Engineering, ICE3 2020

Environmental Feasibility of PVT Drying System

Friction stir processing of an Al0.1CoCrFeNi high entropy alloy (HEA) was performed at controlled cooling conditions (ambient and liquid submerged). Microstructural and mechanical characterization of the processed and as-cast HEAs was evaluated using electron backscat-ter diffraction, micro-hardness testing and nanoindentation. HEA under the submerged cooling condition showed elongated grains (10 µm) with fine equiaxed grains (2 µm) along the boundary compared to the coarser grain (∼2 mm) of as-cast HEA. The hardness showed remarkable improvements with four (submerged cooling condition) and three (ambient cooling condition) times that of as-cast HEA (HV ∼150). The enhanced hardness is attributed to the significant grain refinement in the processed HEAs. Cavitation erosion behavior was observed for samples using an ultrasonication method. All of the HEAs showed better cavitation erosion resistance than the stainless steel 316L. The sample processed under a submerged liquid condition showed approximately 20 and 2 times greater erosion resistance than stainless steel 316L and as-cast HEA, respectively. The enhanced erosion resistances of the processed HEAs correlate to their increased hardness, resistance to plasticity, and better yield strength than the as-cast HEA. The surface of the tested samples showed nucleation and pit growth, and plastic deformation of the material followed by fatigue-controlled disintegration as the primary material removal mechanism. © 2020, University of Science and Technology Beijing and Springer-Verlag GmbH Germany, part of Springer Nature.

International Journal of Minerals, Metallurgy and Materials

Enhanced cavitation erosion resistance of a friction stir processed high entropy alloy

Thermal spray coatings (TSCs) are widely utilized for limiting degradation of structural components. However, the performance of TSCs is significantly impaired by its inherent non-homogeneous microstructure, comprising of splat boundaries, porosities, secondary phase-formation, and elemental segregation. Herein, we report a simplistic approach for significantly enhancing the corrosion resistance of TSCs. Ni-Cr-5Al2O3 coatings were deposited on stainless steel using high-velocity oxy-fuel technique. The microstructure of as-sprayed coating showed significant inhomogeneities in the form of isolated splats and elemental segregation. The microstructure of developed coatings was modified using a novel processing technique, known as stationary friction processing (SFP). The SFP treatment resulted in complete refinement of coating microstructure with elimination of splat boundaries and pores along with elemental homogenization. The corrosion behavior of as-sprayed and SFP treated coating was evaluated in 3.5\% NaCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy. The SFP treatment reduced the corrosion rate of as-sprayed coating by an order of magnitude. Long-time immersion studies showed continuously decreasing impedance of the as-sprayed coating due to the penetration of the electrolyte along the splat boundaries. In contrast, impedance for the SFP treated coating increased with the immersion time due to the removal of all microstructural defects. Copyright © 2020 American Chemical Society.

Fulltext

ACS Omega

Facile and Green Engineering Approach for Enhanced Corrosion Resistance of Ni-Cr-Al2O3Thermal Spray Coatings

Three dimensional dynamics of rising bubbles in gradually mixing fluids due to the effect of Rayleigh-Taylor instability have been numerically investigated. The effect of various parameters such as Eotvos (Eo) number and Morton (M) number for three different cases represented as single bubble rising, inline bubbles rising and offset bubbles rising are comprehensively investigated. It is observed that, two raising bubbles either inline or offset exhibits higher terminal Reynolds number (ReT) in quiescent liquids when compared with single rising bubble. They enhances ReT by 120.22\% for Eo = 38.8 and M = 9.71 × 10−4. Moreover, in gradually mixing fluids due to the presence of Rayleigh-Taylor instability, single rising bubble also exhibits higher ReT and at earlier time. In fluids with low Eo and high M values, mixing effect is very slow because of the presence of higher value of fluids internal resistance as well as high cohesive forces. This causes a delay in the formation of bubble behind the rising pre-defined bubbles. Whereas, in the opposite case, this bubble forms much quicker. But the rising pre-defined bubble breaks up and gradually vanishes off with time. Due to significant decrement in the fluids internal resistance, it is also observed that; at same Eo = 10, by decreasing the value of M from 9.71 × 10−4 to 9.71 × 10−8, the ReT value is increased by 48.84\% for inline and offset bubbles. Furthermore, at same M = 9.71 × 10−4, by increasing the value of Eo from 10 to 38.8, 18.3\% lower time is required for single bubble to attain higher velocity. This is due to the presence of low cohesive forces and high fluids internal resistance. © 2020

International Journal of Multiphase Flow

Dynamics of rising bubbles in gradually mixing fluids due to the effect of Rayleigh–Taylor instability

This chapter focuses on investigating the phenomenon of intermittency in the dynamical behavior of aeroelastic systems. To that end, a classical two degree-of freedom pitch plunge aeroelastic system is considered as the representative aeroelastic model. Investigations are first carried out on the route to aeroelastic flutter in fluctuating flow conditions through wind tunnel experiments. The recurring nature of intermittent periodic bursts observed in the pre-flutter response are subsequently utilized to develop quantitative measures using time series based tools, that can serve as precursors to flutter instability. To gain further insights into the experimental observations, numerical investigations are carried out using a well known two degree-of-freedom pitch plunge mathematical model for the aeroelastic system. A stochastic bifurcation analysis is also carried out that provide insights into the noise induced dynamical stability characteristics. Finally, a detailed study is undertaken to investigate the physical mechanisms that lead to the appearance of intermittency. Particularly, the effect of time scales of the flow fluctuations are investigated. © 2020, Springer Nature Singapore Pte Ltd.

Energy, Environment, and Sustainability

Intermittency in a Pitch-Plunge Aeroelastic System

Structural materials are subjected to severe forms of material degradation for a prolonged life period. The most common material degradation is wear, erosion, and corrosion which severely impairs the service life of the components. State-of-art-of materials are of paramount importance to mitigate these forms of degradation phenomenon. NiTi alloy exhibits outstanding properties in terms of superelasticity, high fatigue strength, and exceptional corrosion resistance. In this work, the tribological behavior of NiTi alloy synthesized using arc melter (TIG) under different cooling conditions (ambient and water quenching) was studied via cavitation erosion, sliding wear, slurry erosion-corrosion and electrochemical corrosion. The microstructural study disclosed the formation of dendritic structures for both the samples. Hardness observed for the ambient cooled sample was around 980 HV which is 1.3 times higher than the quenched NiTi alloy. The difference in the hardness was attributed to the presence of pores for the latter. Both the NiTi alloy samples showed significant improvement in the degradation behavior compared to SS316L under pure erosion and erosion-corrosion conditions. Despite the lower hardness obtained for the quenched NiTi alloy, almost similar degradation resistance in terms of cavitation erosion and dry sliding wear was observed for both the alloyed samples. This is explained based on the work hardening ability behavior of the NiTi alloy. Slurry and sliding wear performed under 3.5\% NaCl solution portrayed greater results for quenched alloy which is attributed to its higher corrosion and passivation resistance compared to the ambient NiTi alloy and SS316L. In conclusion, the microstructural, mechanical and tribological behavioral study of NiTi alloy indicated its dominance over SS316L in dry as well as wet conditions and hereby, emphasizing its importance as an alternative material for marine applications in hydrodynamic environment. © 2019 Elsevier Ltd. All rights reserved.

Materials Today: Proceedings

Tribological behavior of NiTi alloy processed under different cooling conditions

Cavitation erosion is a huge problem in engineering structures working under hydrodynamic conditions. The synergistic effect of erosion and corrosion can aggravate the material removal by several orders of magnitude. Surface coatings are widely used to address material degradation by erosion–corrosion. However, non-homogenous microstructure and presence of defects leads to premature coating failure under erosion–corrosion conditions. Thus, it is imperative to identify plausible solutions to address cavitation-related material degradation. In this study, Ni-Cr-5Al2O3 coatings were deposited on stainless steel substrate using high-velocity-oxy-fuel technique. The as-sprayed coating showed highly non-homogeneous microstructure comprising splats, pores, intermetallic compounds and elemental segregation. A new thermo-mechanical processing technique, stationary friction processing (SFP), was utilized for achieving through-thickness microstructural refinement in as-sprayed coating. As-sprayed and SFP-treated coatings were tested in pure cavitation erosion, corrosion in 3.5\% NaCl solution and erosion–corrosion. SFP treatment resulted in 5-times enhancement in the erosion and corrosion resistance compared to as-sprayed coating. The remarkable performance of Ni-Cr-5Al2O3 coatings after SFP treatment is attributed to significant enhancement in the mechanical properties including hardness and fracture toughness which is the consequence of complete removal of splat boundaries, pores, intermetallic compounds and uniform element distribution up to the coating–substrate interface. © 2020, ASM International.