This work presents a compact, data-driven model to characterize the moisture-dependent dielectric behaviour of oil paper insulation under varying environmental and operational stresses. The model integrates dielectric response parameters loss tangent (tan δ), transfer function zeros, and polarization current to Predict Moisture content (%pm) through a nonlinear relationship. It captures the effects of thermal aging, trapped charge, temperature variation, and moisture diffusion across a wide frequency range. Experimental validation using both mineral and ester-based fluids demonstrates improved accuracy over conventional Polarization and Depolarization Current (PDC) and Cole-Cole Distribution Model (CDM) methods, especially in low-moisture conditions typical of in-service transformers. Compensation techniques address residual polarization and ambient noise, enhancing real-world diagnostic reliability. The framework offers a scalable, cost-effective tool for moisture estimation and predictive maintenance. While Frequency Domain Spectroscopy (FDS) provides noise immunity and easier shielding than PDC, field application faces challenges. Accurate FDS requires charge-free, thermally stable insulation conditions often unmet in practice due to residual dipole energy and temperature fluctuations. Reliable interpretation thus demands correction for non-idealities like thermal gradients and trapped charges to ensure accurate insulation assessment. Major Findings: This research establishes the study proposes of a compact model for accurate moisture estimation in oil-paper insulation, capturing effects of thermal aging and trapped charges. It achieves superior accuracy, especially in low-moisture scenarios. The model provides a scalable solution for insulation condition monitoring.

Improvement of as-solidified material properties requires control and understanding of parameters governing the solidification process; in particular, capturing the full-field evolution of local solidification time, composition, and transport phenomena across the solidifying domain is critical to establish a direct link between the local solidification characteristics and the final microstructure and material properties. In this article, we modelled the alloy solidification process from the integrated computational materials engineering perspective. The full-field evolution of key solidification parameters, namely the local solidification time, cooling rate, and resulting composition, microstructure and material properties, is investigated across the domain. For this, a transient numerical solver is developed in OpenFOAM (R) that integrates the alloy solidification model with the empirical microstructure and material properties models. Empirical models for microstructure (Primary dendritic arm spacing, Secondary dendritic arm spacing) and material properties (Yield strength, Ultimate tensile strength, Shear strength, Fatigue strength, Hardness) require input data such as the local solidification time, cooling rate and compositions. The evolution of thermal, flow, solid fraction and solute segregation fields, along with the final as-solidified composition predicted by the validated transient numerical solver, provides these key inputs. The results reveal strong spatial variations in the solidification parameters, the solidified composition and the derived properties across the casting domain. The cooling rate is maximum near the chill and decreases with increasing distance before rising again toward the end. Consequently, Primary dendritic arm spacing and Secondary dendritic arm spacing exhibit the inverse trend, with finer dendritic spacings near the chill and coarser structures toward the center, which directly translate into mechanical heterogeneities consistent with experimentally reported ranges. The formation of channel segregates introduces sharp mesoscale heterogeneities in solute composition, dendritic arm spacing and properties. Overall, the developed full-field framework enables quantitative prediction of local and global variations in as-solidified microstructure and mechanical properties, thereby establishing a direct process-structure-property link that forms a basis for horizontal integrated computational materials engineering with downstream manufacturing processes such as forging, rolling, and homogenization.

The defects such as freckles formed during the directional solidification of binary alloys severely affect the performance of cast products. The phenomenon of freckle formation is strongly influenced by the convective flows generated during solidification. The rejection of solute during the solidification at the solid/liquid interface induces the concentration gradients in the liquid. These concentration gradients in combination with existing temperature gradients, may induce buoyancy-driven convection in the mushy zone (plumes) and the parent liquid region (fingers). As the mushy zone evolves, small chimneys are formed, which leads to the formation of discrete plumes of interdendritic liquid. These plumes have a very complex flow structure which leads to the structural and compositional heterogeneities in the final cast product. The current study is an effort to investigate the morphological characteristics of plumes and chimneys formed during the directional alloy solidification. For this, controlled solidification experiments in a bottom-cooled rectangular cavity with an analogue transparent aqua ammonia system (NH4Cl + 74 wt% H2O) are performed. Particle Image Velocimetry (PIV), High Speed (HS) imaging and thermocouples temperature measurement techniques are used for real-time measurement of flow field, solidified and mushy zone dynamics and local temperature during the course of solidification. The dynamical nature of plumes is captured and the morphology of chimneys (shape, size, spacings, etc.) and plumes (velocity magnitude, shape, size, etc.) are quantified. The phase-locking with 180° phase difference due to the coupling between nearby plumes is observed. Also, the evolution of double-diffusive layers (DDLs) is captured and the critical value of thermal Rayleigh number for the onset of DDLs is estimated.

The present research aims to examine the energy, exergy and sustainability analysis of a traditional four-pan jaggery unit based on the consumption and resource transformations involved in the sugarcane-based jaggery production process. The exergy analysis has been conducted based on an experimental study with the help of thermodynamic relations including the component-wise specific exergy for jaggery production. The energy and exergy of the jaggery unit are compared during the winter and the summer. The obtained average thermal energy efficiency of the jaggery unit shows an increment of 8.1% as compared to the winter season. In addition, when accounting for the combustion performance of bagasse, the exergy efficiency of jaggery plant in the summer is higher than the winter. Furthermore, negative environmental impacts are indicated by a poor exergy sustainability score during both seasons. In summer, the jaggery facility operates more sustainably than in the winter, as shown by the higher value of environmental benign index. Energy analysis alone conceals the fact that the primary factor in resource use is exergy destruction due to irreversibilities in combustion and heat transfer. By assessing the process fluxes in terms of exergy, this study enhances the transparency of resource consumption and losses in the production of jaggery.

A numerical study is performed to investigate the role of heterogeneous distribution of nanoparticles in discharging behavior of nanoparticle-enhanced phase change materials (NEPCM). The numerical model considers solidification, multiphase convection, nanoparticles segregation, sedimentation, drags on nanoparticles and Brownian and thermophoresis diffusion phenomena. The discharging behavior of NEPCM is analyzed for the solidification of n-octadecane (PCM)-Cu-nanoparticles in a rectangular cavity. The discharging stage of NEPCM is also being investigated experimentally. The experiments were equipped with Particle Image Velocimetry (PIV), high-resolution imaging and thermocouples to measure real-time flow field, solidified layer thickness and local temperature. The numerically predicted results are compared with these experimental results to validate the model. Using the numerical model, the transient evolution of solidification interface morphology, nanoparticles concentration, fluid flow, temperature field, and thermophysical properties during solidification of NEPCM is described. Subsequently, the effect of process parameters such as initial nanoparticles concentration and Stefan number on system's thermal performance is delineated. It is noticed that adding nanoparticles up to a certain limit increases the discharging rate. The discharging time for 0 wt%, 2.5 wt%, 4.5 wt% and 6.5 wt% Cu-nanoparticles concentration are found to be 1115, 895, 980 and 1075 min, respectively. Thus, NEPCM with 2.5 wt% Cu-nanoparticles discharges 19.7 % faster than pure PCM. Furthermore, it is found that the heterogeneous distribution of the rejected nanoparticles significantly affects the solid-liquid interface morphology, solidification rate and alters the thermophysical properties locally as well as globally. The effective density and thermal conductivity increase with an increase in the local concentration of nanoparticles, whereas the effective specific heat capacity decreases with the increase in the local concentration of nanoparticles.

Recently, Polarization Depolarization current (PDC) measurement is widely accepted time domain spectroscopy-based method for assessing the insulation condition. Various performance parameters like Dissipation factor (%tan $\delta $ ), Paper Moisture (%pm), Dielectric Adsorption Ratio (DAR), Polarization index (PI) etc. can be estimated by analyzing the PDC data. During field measurement various factors influences the recorded PDC data. As per existing literature, presence of low frequency noise, effect of temperature variation and influence of residual charge are common during field measurement. These factors significantly affect recorded polarization current and hence estimated performance parameters. Hence, analysis using recorded polarization current data may provide misleading information regarding insulation condition. Under such practical situation where polarization current is affected by above mentioned factors that generally observed during field measurement, depolarization current should be used for analysis of insulation condition. The depolarization current does not influence by such external factors. The present work shows the importance of depolarization current where polarization current is influenced by external low frequency noise and residual charge. The analysis firstly applied on sample prepared in the laboratory and then on data collected from real life in-situ transformers. The results obtained from the analysis shows that the data obtained from depolarization current is more reliable.

A comparative study concerning dynamic, local, and zero inertia variants of volume-averaged depth-integrated porous shallow water equations has been presented. The first two hyperbolic models are resolved through an explicit augmented approximate Riemann solver, and the diffusive parabolic model employs an implicit formulation. Three benchmark tests are simulated and compared through all three counterparts. The diffusive wave model offers a wide range of time-step choices and, subsequently, lesser computational cost when the temporal variation of flow depth/velocity is relatively small. However, explicit hyperbolic models outperform in the case of rapidly varied flow interaction with granular media.

In the past, most of the numerical studies on the prediction of macrosegregation and mesosegregation (e.g. channel type segregation) were performed using in-house codes and commercial software, both of which have limitations such as huge license costs, non-availability for general public research etc. In this study, a dedicated CFD solver is developed in an open-source platform - OpenFOAM (R) for the prediction and characterization of channel segregates in castings. The solver accounts for the fluid flow, heat transfer, species transport, multiscale segregation, solidification and mushy zone drag phenomena that occur during alloy solidification. The developed solver is extensively validated with the reported benchmarked experimental and numerical results for the sn-Pb alloy solidification. Direct numerical simulations (DNS) are performed to resolve the flow field in and around the channels (which are of mesoscopic length scale) for the first time. It is observed that mesh size <= 2d2 (secondary dendritic arm spacing) is required to resolve the flow in channels and accurately predict their morphology and locations. Further, the effect of different microsegregation and mushy zone drag models on the segregation and morphology of channel segregates is thoroughly investigated. The predicted extent of negative and positive segregation is found to be more (negative segregation -7.7 wt%Pb and positive segregation -18.7 wt%Pb) in Scheil's microsegregation model compared to Lever rule. Furthermore, the inertial drag in the mushy zone significantly affects the convective transport of solute and thereby the morphology and the number of channel segregates.

We measure the upward force acting on a single, unconstrained, large particle in a granular medium of small particles flowing over inclined plane using discrete element method (DEM) simulation. Based on the computed force, we obtain an expression for the flux of large particles in a binary mixture of large and small particles and predict the equilibrium concentration profile and the velocity profile of the flowing layer. The theoretical predictions are in very good agreement with the DEM simulation results for a wide range of concentrations of large particles and inclination angles.

Flows driven by double-diffusive convection during alloy solidification strongly influence the macroscopic solute redistribution, localized remelting and solidification rates which play a dominant role in determining the mechanical, electrical and thermal properties of the final product. This experimental study is carried out to investigate the effect of initial concentration and initial cavity height on the development of double-diffusive convection and on the real-time solidification interface growth during solidification of aqueous sodium chloride solution in a top-cooled rectangular cavity. Aqueous sodium chloride solution is widely used as an analogues model system for most of the alloys to study their solidification behaviour because of its transparency that enables the flow visualization using optical techniques. In the present work, particle image velocimetry (PIV) method is used for the velocity measurement during solidification. PIV measurements show that on increasing the initial concentration and the initial cavity height, the strength of the convection flow increases. The evolution of solidification is also captured using a high-speed (HS) camera. The images captured during solidification indicates that the wavy interface formed due to remelting phenomena caused by double-diffusive convection. Further, we also noticed that the solidification rate decreases by increasing the initial concentration and decreasing the initial cavity height.

Mesh refinement is crucial for capturing the complex phenomena that governs the formation of channel segregates during binary alloy solidification. In this article, the influence of mesh size on the formation of channel segregates during the solidification of Sn-5wt%Pb alloy is numerically investigated. A solver is developed in OpenFOAM for solving the coupled transport equations of mass, momentum, energy and species. Subsequently, the simulations are performed for different mesh sizes to predict the flow field, temperature, species and solid fraction distribution including the morphology of channel segregates. From this study, it is observed that the mesh size significantly affects the morphology and the strength of channel segregates. For very fine mesh size, having sufficient number of grid point along their width, the formed channels are more continuous and the flow inside channels is resolved.

This study reports the investigative conclusions of parametric studies conducted to understand the effect of operating parameters on absorption and desorption characteristics of LaNi4.7Al0.3 metal hydride system for thermal management applications. Reactor with improved design containing 55 embedded cooling tubes is fabricated and filled with 4 kg of metal hydride alloy. Using water as heat transfer fluid (HTF), effects of supply pressure, HTF temperature and HTF flow rate on absorption and desorption characteristics of the reactor are analyzed. Increasing supply pressure leads to prominent improvement in absorption capacity while the increase in HTF temperature enhanced desorption performance. At 20 bar and 20 °C, 46.2877 g of hydrogen (1.16 wt%) was absorbed resulting in total energy output of 707.3 kJ for 300 s. During desorption at 80 °C with water flow rate of 8 lpm, heat input of 608.1 kJ for 300 s resulted in 28.5259 g of hydrogen desorption.

Implementations of conventional river training structures such as spurs, marginal embankments or levees, revetments, and longitudinal dikes are exclusively costlier and comparatively less efficient than the recently developed river training structures. In addition to the effectiveness of the structures adopted, river experts are also interested in several aspects like the cost involved, navigation development, including enhancement of ecological and morphological diversity. Different head shapes of dike behave differently as compared to the conventional straight spurs and produce more satisfactory results to ascertain the objectives of river training in many critical situations. Permeable structures like reinforced cement concrete (RCC) jack-jetties, porcupines, and timber pile dikes can be used either as a separate system or in conjunction with impermeable structures to overcome the cost-related issues and also to create a better sustainable living environment for aquatic habitats. This chapter focuses on review for the field performances of the application of different permeable and impermeable-type structures in several river basins to emphasize the effectiveness and non-effectiveness of these structures. The outcomes may be helpful for potential river engineers in utilizing the information to select a better alternative as per their field requirement.

A model of mushy zone instability is developed for characterization and prediction of channel segregation in castings. The model highlights the connection of the mushy zone instability with the mush permeability. A new criterion for amplification of the mush instability is derived, which depends on the interdendritic velocity, the isotherm velocity, the temperature gradient, and explicitly on the mush permeability. The capability of the instability criterion in the characterization of channel segregates is illustrated by comparing the estimated possible channel locations with that of numerically simulated channel segregations in a benchmark test case of solidification of Sn-Pb alloy. An Opensource CFD software OpenFOAM is used to simulate the solidification of Sn-Pb alloy in a side-cooled rectangular cavity. The new instability criterion very well characterizes the channel segregates shown in the numerical simulations. The near-liquidus part of the mushy region is more prone to the initiation of instability, which can initiate the formation of channel segregates in castings. Permeability and its derivative with respect to the liquid fraction in the outer part of mushy zone (liquid fraction more than 0.9) plays a key role in the amplification of this instability that can be responsible for the development and the formation of channel segregates. The locations of channel segregates estimated by the new instability model are also compared with those with a remelting criterion, and it has been noticed that the remelting criterion severely under characterizes these defects (e.g., their number and length). We noticed that local remelting might not be necessary for the initiation of a channel; some destabilization of the mushy zone due to local instability could be sufficient. (C) 2020 Elsevier Ltd. All rights reserved.

This paper numerically investigates air entrapment behavior when a water droplet impacts on a solid substrate in the presence of ambient air. The dynamics of air entrapment is specifically described, in particular, retraction, contraction and toroid formation have been discussed. Volume-of-fluid method has been used in order to track the liquid-gas interface. The effect of surface wettability on the air entrapment and its evolution is studied. In line with experimental findings, we have observed a dimple formation on droplet surface at the impact point in the present study which has not been reported using a numerical study so far. It has been demonstrated using numerical study that the formation of dimple leads to the air entrapment. The surface wettability is demonstrated to have significant influence on the evolution of the air film into bubble. The processes during the evolution, such as inertial retraction, contraction and pinch-off are delayed on increasing the contact angle. Air bubble formed on the substrate gets detached from the substrate for low contact angle of 35° (hydrophilic surface) however, it remains attached to the substrate for higher contact angles: 90° and 120° (hydrophobic surface). Further, the influence of air entrapment on the heat transfer characteristics is studied. The deformation of the droplet as it approaches the substrate, influences the boundary layer on the substrate which eventually affects the wall heat flux. Post impact, the wall heat flux is primarily influenced by the liquid fraction and the air entrapped. In the region of only air, the wall heat flux is very low compared with that in the region of water or mixture of water and air. The present numerical results have been validated employing experimental results available in the literature.

A biocompatible and biodegradable scaffold with load-bearing ability is required to enhance the repair of bone defects by facilitating the attachment, and proliferation of cells, and vascularization during new bone formation. However, it is challenging to maintain the porosity and biodegradability, as well as mechanical properties (especially compressive strength), at the same time. Therefore, in the present work, a biodegradable composite structure of poly(caprolactone) (PCL) was designed using compression molding with varying amounts of poly(glycolic acid) (PGA) (25, 50, 75 wt%) and fixed amount (20 wt%) of beta tricalcium phosphate (beta TCP). It was hypothesized that the fabricated composite structure will develop porosity during the degradation of the PGA and that the corresponding decrease in mechanical properties will be compensated by new bone formation and ingrowth, in vivo. Accordingly, we have systematically studied the effects of sample composition on time-dependent dissolution and mechanical properties of the PGA/beta TCP scaffolds. The compressive strength increased up to ~92 MPa at 50% compression of the designed PCL-PGA samples. Furthermore, the dissolution rate, as well as weight loss, was observed to increase with an increase in the PGA amount in PCL. Based on the mechanical properties and dissolution data, it is concluded that the PCL-PGA scaffolds with beta TCP can be suitable candidates for bone tissue engineering applications, specifically for the reconstruction of bone defects, where strength and biodegradation are both important characteristics.

The present article reports the activation and testing of large scale metal hydride based hydrogen storage system (MHHSS) for industrial application. The metal hydride reactor is fabricated using 55316 material with 99 embedded cooling tube and filled with 40 kg of LaNi4.7Al0.3. The activation was carried out by successive absorption and desorption processes. In the third absorption cycle, MHHSS had absorbed 552.356 g of hydrogen to reach a maximum storage capacity of 1.4 wt% at 40 bar pressure and 30 degrees C temperature. The testing of MHHSS was carried out by varying H-2 supply pressure, absorption and desorption temperatures and heat transfer fluid (HTF) flow rate. It was observed that the supply pressure has significant effect on absorption rate, and the optimum supply pressure was observed in the range of 10-15 bar. Similarly, during the desorption cycle, optimum desorption temperature was found in the range of 80-90 degrees C. The optimum flow velocity for HTF was observed in the range of 20-30 lpm. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Ice slurry generation is an important stage in ice slurry-based cold thermal energy storage systems. Predictive modelling and simulation of ice slurry generation requires consideration of solidification of an aqueous solution along with multiphase convection. Towards enhancing the generation, this work numerically and experimentally investigates ice slurry generation in an inclined cavity. The inclined cavity provides a driving shear force for ice slurry generation from the mushy zone. A model considering solidification, multiphase convection, interfacial drag and sedimentation is used to simulate the flow field, temperature, species and solid fraction distribution. Solidification experiments of ice slurry generation are performed. The experiments are equipped with Particle Image Velocimetry, high resolution imaging and thermocouples to measure real-time flow field, solidified and mushy zone thickness and local temperature. Experimental and predicted solid fraction distribution, velocity field, solidified and mushy zone thickness, mass of ice slurry and temperature variation have been compared. After validations, the effect of process parameters, such as cavity inclination angle, solute initial concentration and Stefan number on performance of ice slurry generation is delineated. The performance is determined by various indicators, such as mass of ice slurry produced, cold energy stored by the ice slurry and system's effectiveness.

A biodegradable scaffold with tissue ingrowth and load-bearing capabilities is required to accelerate the healing of bone defects. However, it is difficult to maintain the mechanical properties as well as biodegradability and porosity (necessary for bone ingrowth) at the same time. Therefore, in the present study, polycaprolactone (PCL) and poly(lactic-co-glycolic acid) (PLGA5050) were mixed in varying ratio and incorporated with 20 wt.% βTCP. The mixture was shaped under pressure into originally non-porous cylindrical constructs. It is envisioned that the fabricated constructs will develop porosity with the time-dependent biodegradation of the polymer blend. The mechanical properties will be sustained since the decrease in mechanical properties associated with the dissolution of the PLGA and the formation of the porous structure will be compensated with the new bone formation and ingrowth. To prove the hypothesis, we have systematically studied the effects of samples composition on the time-dependent dissolution behavior, pore formation, and mechanical properties of the engineered samples, in vitro. The highest initial (of as-prepared samples) values of the yield strength (0.021±0.002 GPa) and the Young's modulus (0.829±0.096 GPa) were exhibited by the samples containing 75 wt.% of PLGA. Increase of the PLGA concentration from 25 wt.% to 75 wt.% increased the rate of biodegradation by a factor of 3 upon 2 weeks in phosphate buffered saline (1× PBS). The overall porosity and the pore sizes increased with the dissolution time indicating that the formation of in-situ pores can indeed enable the migration of cells followed by vascularization and bone growth.