Department of Mechanical Engineering

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Experiments are performed to study the influence of an oblique jet on convective heat transfer to a vertical heated plate. The local heat transfer coefficient is investigated parametrically for Reynolds numbers ranging from 10000 to 75000 and jet to plate spacing of 3–20 d for different inclinations of a jet in the range of 15°–75°. The experiments are carried out on a flat rectangular surface of 600 × 300 × 0.1 mm3, hit by a jet of 11.5 mm diameter, with air as the working fluid. The infrared technique is used to examine the temperature contours over the entire section of the test plate. The present investigation deals with the effect of inclination on cooling at different locations over the plate locally in all directions from the point of impingement. The effect of Reynolds number and jet to plate spacing due to inclined jet at different orientations on the longitudinal, lateral, and intercardinal axial location is studied. The study also focuses on the heat transfer phenomenon happening on the far side of the test plate. The correlation analysis is performed on the current experimental data. The local Nusselt number correlations for the inclined jet are suggested that predict the present experimental results as a function of the geometrical and flow parameters. © 2022 Elsevier Masson SAS

World University root node

International Journal of Thermal Sciences

Investigation of local heat transfer from a flat plate impinged by an inclined circular jet

The present work investigated the microstructural feature, mechanical properties, and residual stress variation for the dissimilar welded joints (DWJs) of P92 and AISI 304L steel. The multi-pass DWJs were attempted for narrow gap geometry using the tungsten inert gas (TIG) welding process employing the ERNiCrMo-3 filler metal. The martensitic microstructure produced in the P92 HAZ region after welding is brittle due to quenched martensite and the dissolution of precipitates. Thus, the post-weld heat treatment (PWHT) known as tempering was carried out at 760 °C for a period of 2 h to get tempered martensitic microstructure and re-precipitation of dissolved precipitates. The radiographic examination and macrostructure analysis showed defect-free P92/304L SS DWJs. The weld metal showed the complete austenitic microstructure with a Ni weight percentage of 36%. However, segregation of the alloying elements along with the inter-dendritic areas and variation in grain growth during solidification was observed. There is columnar grain morphology at interface, cellular, and equiaxed in the center. The major segregation along the inter-dendritic areas was observed for Nb, Mo, Ti, and Cr that led to the formation of the carbides of type Mo6C, TiC, and NbC, which was confirmed from the energy dispersive spectroscopy (EDS) analysis. From the tensile test result, 304L SS base metal (BM) was inferred as the weakest region in P92/304L SS DWJs. The ultimate tensile strength (UTS) of the as-weld joint was about 626 MPa, along with fracture location in 304L SS base metal. The Charpy impact test results showed that the region with relatively poor impact toughness was austenitic ERNiCrMo-3 filler weld (57 J) which might be due to the segregation of the Nb and Mo along the inter-dendritic areas. However, the impact toughness of the ERNiCrMo-3 filler weld met the minimum requirement of 47J (EN ISO 3580:2017). The micro-hardness result showed that in the as-welded condition, the coarse grain heat affected zone (CGHAZ) has the highest micro-hardness value (340 HV) due to the high weight percentage of Cr and N resulting from the dissolution of M23C6 precipitates followed by the fine grain heat affected zone (FGHAZ, 270 HV), and the inter-critical heat affected zone (ICHAZ, 205 HV). After PWHT, the hardness value was decreased below the maximum allowable value of 265 HV due to the tempering of the martensite. The residual stresses developed in the case of the narrow groove design were less due to the less quantity of weld metal available for volumetric contraction in the case of the narrow groove geometry. The tensile stress was dominant in the weld fusion zone due to the volumetric contraction of the weld metal, while compressive stress was dominant in P92 HAZ because of the martensitic phase transformation. © 2022, Wroclaw University of Science and Technology.

Archives of Civil and Mechanical Engineering

Study on narrow gap welding of martensitic grade P92 and austenitic grade AISI 304L SS steel for ultra-supercritical power plant application

Combining high sensitivity with fast response and high resolution remains a critical challenge for flexible temperature sensors. The present study leverages the intrinsically high surface-to-volume ratio of nanocomposite fibers as well as the high mechanical properties of nanomaterials for achieving conformable temperature sensors with accurate and fast detection of temperature. To achieve this, nanocomposite films of electrospun polyvinylidene fluoride (PVDF) with embedded silver (Ag) nanoparticles were layered with multiwall carbon nanotubes (MWCNT). The sensor showed a negative temperature coefficient (NTC) with excellent sensitivity of −0.18%/°C and a quick response rate of 11 s. The sensor also exhibited low self-heating errors for an activation current of 1&nbsp;mA and excellent anti-interference ability when tested for bending forces and wet environments. The nanocomposite fiber-based sensor can be used for real-time monitoring of human body temperature as confirmed by successful experiments. The present work lays the foundation for integrating the sensor further with a user interface to create a wearable temperature monitoring system for mobile healthcare.

Polymer Composites

High-performance flexible temperature sensor from hybrid nanocomposite for continuous human body temperature monitoring

This work represents the in-house chemical synthesis of silver (Ag) nanoparticles, electrospinning of the synthesized Ag nanoparticles and polyvinylidene fluoride (PVDF) by using optimized parameters and then air spraying different amounts of multiwall carbon nanotubes (MWCNTs) on top of the prepared electrospun Ag-PVDF films, to check the electrical conductivity of the films. The morphology of the prepared sample films were examined by standard characterization techniques such as scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) to carry out the elemental analysis or chemical characteristics of the films. The temperature vs resistance behavior of the prepared films depicted linear variation in temperature with temperature coefficient of resistance (TCR) α = − 0.43&nbsp;%/°C and − 0.63&nbsp;%/°C, for the Ag-PVDF films having 0.16&nbsp;mg and 0.8&nbsp;mg MWCNTs sprayed, respectively, which are comparable to TCR values of reported temperature sensors. The mechanical properties of the films were also determined using tensile tests, which showed great improvement in the tensile strength and Young’s modulus for the MWCNTs sprayed films. These results justify the potential of these hybrid nanocomposite films for energy, environment and sensing (especially temperature sensing) related applications.

Materials Today: Proceedings

Influence of experimental conditions on conductivity of electrospun nanocomposite fibers

Formation of a stable Taylor cone is an important phenomenon during electrospinning of nanofibers for controlling nanofiber properties. Optimizing electrospinning process parameters such as solution feed rate, applied electric voltage and tip to mandrel distance, a stable Taylor cone can be achieved and by maneuvering the parameters within a certain range, the height of the cone can be controlled. Here, we study the influence of the process parameters on the height of the Taylor cone and the corresponding nanofibers produced for polyvinylidene fluoride (PVDF) using dimethylformamide (DMF) as solvent. Characterization of the produced fibers and image analysis confirmed the optimal values as 1&nbsp;mL/h, 10.8&nbsp;kV and 10&nbsp;cm for feed rate, applied voltage and spinning distance, respectively. Observations from the study reveal that contrary to proportional variation of Taylor cone height with nanofiber diameter in case of changing feed rate and applied voltage, the relationship gets inversely proportional when tip to mandrel distance is varied.

Journal of Electrostatics

Taylor cone height as a tool to understand properties of electrospun PVDF nanofiber

A robust understanding of structure–property relations of <a href="https://www.sciencedirect.com/topics/engineering/electrospun">electrospun</a> fibers is vital for device design. However, these relationships are inherently complex and hard to model using data from limited trial and error experiments. Machine learning has emerged as an efficient approach to model multidimensional relationships but fundamentally require diverse data to learn these relationships from. In this study, we present a novel Electrospun Fiber Experimental Attributes Dataset (FEAD) by collating experimental data from literature, developing new features, and complementing with our own experiments. Fiber diameter, a key parameter for controlling electrical and thermal properties of electrospun polyvinylidene fluoride (PVDF) polymer, is modeled using a large number of solution and electrospinning process experimental parameters using a multi-model machine learning approach. This is complemented with a model-agnostic interpretable game-theoretic approach to identify the relative and absolute relationships between the variables. Experimental attributes such as feed, <a href="https://www.sciencedirect.com/topics/engineering/polymer-concentration">polymer concentration</a>, Flory-Huggins Chi parameter, and relative energy difference were found to be most impactful for modeling <a href="https://www.sciencedirect.com/topics/engineering/fiber-diameter">fiber diameter</a>. This study overcomes several limitations in existing literature such as non-availability of meta datasets, application of latest machine learning techniques, and state-of-the-art approaches for interpreting these “black box” models, thus bridging the gap between experimental and computational studies. This improved ability to generalize structure–property relationships across any PVDF-polymer solvent system presents a promising ability to reduce expensive lab testing required for developing <a href="https://www.sciencedirect.com/topics/engineering/polyvinylidene-fluoride">PVDF</a> fibers of desired mechanical and electrical properties.

Computational Materials Science

Towards an Interpretable Machine Learning model for electrospun polyvinylidene fluoride (PVDF) fiber properties

International Journal of Non-Linear Mechanics

Static and dynamic instability modeling of electro-magneto-active polymers with various entanglements and crosslinks

Free and forced vibration analysis of a geometrically rotating shaft supported on ball bearings has been studied using the numerical method and compared with the results obtained experimentally. This study is concerned with vibration analysis of geometrically nonlinear rotating model with a rigid disk. The shaft has been designed under the frame of Euler-Bernoulli beam theory with additional effects such as rotary inertia, gyroscopic effect, higher-order large deformations, and rotor mass unbalance in order to replicate an equivalent practical model of rotor-bearing system. The mathematical expressions have been derived to demonstrate the nonlinear free and forced vibrations of the rotating shaft coupled with rigid disk in two transverse planes. Solutions of the nonlinear equation are being obtained using method of multiple scales as well as numerical methods. Effects of rotor parameters such as bearing stiffness and damping coefficient are examined with help of this nonlinear mathematical model. The obtained results are portrayed for a better understanding free and forced vibration analysis with time response, FFT, phase portrait, and Poincare's map. The present outcomes enable an understanding on how the system dynamics influenced with the variations in the values of different parameters.

Lecture Notes in Mechanical Engineering

Effect of Unbalance with Bearing Flexibility on Vibration Phenomenon of Geometrically Nonlinear Rotating Shaft with Ball Bearing

Shaft misalignment, rotor unbalance, rubbing, bearing faults and cracks are the commonly observed faults in the rotor-bearing systems. Vibration signature has been considered to be one of the best ways to detect and diagnosis subsequent condition monitoring of rotor-bearing faults. A flexible shaft with a rigid disc supported by flexible bearings at both the ends has been considered for the present critical observations. The bearing is considered as a spring with linear stiffness and damping. Further, Timoshenko beam theory is considered to describe mathematically the model of rotor element. We used finite element analysis to obtain the critical whirling speeds of rotor-bearing system for different modes at various system parameters with the illustration of Campbell diagram and Fourier spectrum. Vibration spectrums in the transverse direction are illustrated for different modes of vibration using successive approaches of Hamilton principle, Galerkin's method and Newmark's integral method. Condition monitoring of vibration spectrums considering rotor unbalance and shaft misalignment as well as their identification has been analysed with FFT, time responses, phase portrait and Poincare's map, numerically and experimentally.

Condition Monitoring and Identification of Misalignment with Initial Unbalance of Flexible Rotor-Bearing System

The dissimilar combination of 2.25Cr-1Mo (P22) and modified 9Cr-1Mo (P91) obtained using Gas Tungsten Arc Welding (GTAW) process employing the Ni-based superalloy filler ERNiCr-3 (IN82) and ERNiCrMo-3 (IN625) have been investigated for microstructure evolution and mechanical properties. The butt weld joint was produced using single bevel groove geometry. The structural integrity of the welded joint was measured in respect of tensile strength, impact toughness and hardness. The alloying elements’ segregation at the inter-dendritic areas of the weld metal was witnessed while using the IN82 and IN625 filler. The impact test trials showed the mixed mode of fracture with an impact toughness of 82 ± 6 J and 70 ± 5 J for IN82 and IN625 filler, respectively, ensuring that the welded joint was safe for the end boiler application. The tensile test coupons were fractured from the P22 base metal in all the trials and for both the fillers which confirmed the negligible effect of the filler composition on the tensile properties. The hardness plots showed the inhomogeneity in hardness value, which was also supported by the microstructure evolution along the weldments. The average hardness of the IN82 filler was measured lower than the IN625 filler. © 2022 by the authors.