Showing papers by "Anirban Bhattacharya published in 2022"

A Novel PCM and TCE based Thermal Management of Battery Module

Abstract: • A novel PCM-Fin arrangement is proposed for thermal management of battery module. • Phase change within PCM is modelled using source based implicit enthalpy method. • Three different discharge rates are studied with 1C charging for multiple cycles. • FS-3 is found to be the best configuration for the present study. This paper presents a novel combination of Phase Change Material (PCM) and fins as Thermal Conductivity Enhancer (TCE) for effective thermal management of battery module. A numerical study of the battery module thermal management system using PCM and internal fins for maintaining the battery temperature below the safe limit of 60 °C for more than one cycle is carried out. Both joule and entropic heat generation is considered for more generality in line with the actual case. An implicit finite volume based numerical methodology is used to solve the governing energy transport equation. Phase change in PCM is modelled using the implicit source based enthalpy method. A two-dimensional model is developed to study the thermal performance of battery module with 4S4P cell structure (16 cells) with PCM filled in between the cells. To improve the heat dissipation more effectively from PCM, metal fins as TCE are inserted in the space filled with PCM. Five fin structures with fin arrangement parallel to the boundary and tilted at an angle of 45 ° to the boundary are developed and studied to find the best configuration for effective transport of heat from the system to the boundaries and subsequent convection away to the ambient. Results shows more uniformity in temperature distribution within the battery module for better thermal performance for longer period of operation. Using fins embedded in PCM, the battery module temperature is maintained below 60 °C even after two and half discharge–charge cycle of 2C and 3C discharge rates where FS-3 structure is proved to be most efficient.

A 3D resolved-geometry model for unstructured and structured packed bed encapsulated phase change material system

Abstract: A 3D numerical model is developed to simulate melting in packed bed encapsulated phase change material (PCM) energy storage systems. The main novelty of the model is that it resolves the arrangement of capsules inside the system for both structured and unstructured packing and thus accurately captures the fluid flow, heat transfer and phase change in the capsules. To create the unstructured arrangement of capsules in the domain a novel dropping and rolling algorithm is implemented. The flow of heat transfer fluid (HTF) outside the capsules as well as the natural convection in the PCM within the capsules is also simulated. Initially, a single capsule study is performed, which shows that both natural convection inside the liquid PCM and forced convection outside the capsule affect the melting characteristics. Subsequently, the model is extended to simulate phase change in multiple capsules in a cubical domain arranged with structured and unstructured packing. The analysis of the effect of capsule arrangement on the melting and energy storage characteristics for both structured and unstructured packing of capsules is performed. Additionally, parametric studies are performed to analyze the effects of capsule size, fluid temperature, and fluid velocity for both types of systems. Simulation results show that the total melting time for unstructured packing is reduced on an average by 23.56% for the 2.5 mm capsules and by 10.14% for the 5 mm capsules as compared to structured packing. The effect of HTF temperature change is more prominent for structured cases, with an increase of 65.8% melting time as compared to 58.4% for the unstructured cases when the HTF temperature is reduced by 20 K. In contrast, the effect of velocity is less significant for the structured cases with a reduction of HTF velocity from 0.1 cm/s to 0.05 cm/s causing an increase of 27.3% melting time for the structured cases and 42.6% for the unstructured cases. The developed model can be used to capture the effect of different arrangements of capsules in encapsulated PCM energy storage systems and thus obtain effective designs for such systems.

A critical review of parameters governing the boiling characteristics of tube bundle on shell side of two-phase shell and tube heat exchangers

Abstract: Heat transfer by the process of boiling is advantageous due to the high heat transfer coefficient associated with the process. In many heat transfer applications, boiling on tubes and tube bundles are encountered. Tube bundle studies are important as these are an integral part of shell and tube heat exchangers, reboilers, evaporators used commercially both in industrial and non-industrial applications. Similarly, tube bundles with vertical configuration are integral part of nuclear reactors. In this review, the effects of different parameters affecting heat transfer in tube bundles on the shell side of two-phase shell and tube heat exchangers are analysed based on available literature. The studies included are subdivided into effect of performance parameters for flow boiling and for pool boiling. The pool boiling heat transfer devices do not require any active flow equipment, whereas in case of flow boiling active flow equipment is essential for continuously supplying the working fluid. In order to design an effective heat exchanging device having tube bundles the combined effect of parameters such as heat flux, mass flux, quality, tube geometry, spacing etc. need to be considered. This article highlights various critical parameters, considered by studies available in the open literature, which affect the heat transfer in two-phase flow heat exchanging devices.

Thermal performance assessment of PCM incorporated cool concrete pavements using numerical analysis

Abstract: Incorporating Phase Change Materials (PCM) through encapsulation is an effective method to regulate the pavement surface temperature. The present study investigates the effect of the thermal properties of concrete and encapsulating material on the cooling potential of PCM incorporated concrete pavements. An enthalpy-porosity based pore-scale heat transfer model was developed that simulates the melting of PCM in concrete pavements subjected to solar radiation. Two types of PCMs, i.e. Organic Mixture 35 (OM 35) and Organic Mixture 42 (OM 42) were incorporated into concrete slabs with the help of expanded clay aggregates (ECA) as PCM carrier. In the top 0.1 m layer of concrete, a total of 98 numbers of ECA-PCM balls of 1 cm diameter were distributed uniformly. The cooling potential of pavements with OM 35 and OM 42 improved by 82.67 % and 81.70 %, respectively with increase in the porosity of ECA from 0.1 to 0.9. Further, as the thermal conductivity of concrete increased from 1.2 to 2.4 W/mK, the cooling potential of OM 35 and OM 42 incorporated pavements increased by 36.48 % and 38.29 %, respectively. However, the thermal conductivity of the encapsulating material showed marginal influence on the cooling potential and therefore may be neglected.

Structured variational inference in Bayesian state-space models

Abstract: Variational inference is routinely deployed in Bayesian state-space models as an efficient computational technique. Motivated by the inconsistency issue observed by Wang and Titterington (Wang & Titterington, 2004) for the mean-field approximation in linear state-space models, we consider a more expressive variational family for approximating the joint posterior of the latent variables to retain their dependence, while maintaining the mean-field (i.e. independence) structure between latent variables and parameters. In state-space models, such a latent structure adapted mean-field approximation can be efficiently computed using the belief propagation algorithm. Theoretically, we show that this adapted mean-field approximation leads to consistent variational estimates. Further-more, we derive a non-asymptotic risk bound for an averaged α -divergence from the true data generating model, suggesting that the posterior mean of the best variational approximation for the static parameters shows optimal concentration. From a broader per-spective, we add to the growing literature on statistical accuracy of variational approxima-tions by allowing dependence between the latent variables, and the techniques developed here should be useful in related contexts.

Electrochemical corrosion of AA6061-AA7075 double sided FSW joints prepared with and without secondary heating

Abstract: The present study aims to evaluate corrosion behavior of different zones in the double-sided dissimilar friction stir weld between precipitation hardening aluminum alloys AA6061-T6 and AA7075-T651 of 12.7 mm thickness obtained without and with employing secondary/additional heating. Each specific zone of the welds is tested for corrosion potential, corrosion current and impedance spectroscopy. The stir zone formed is more corrosion resistive than AA7075 but less in comparison to AA6061. The corrosion resistivity of AA7075 dominated region increases significantly on the application of secondary heating. The increase is attributed to the disintegration of large corrosion susceptible precipitates due to intense mixing and stirring facilitated at elevated temperature with the application of additional heating. Although, AA6061 experienced trivial decrease in corrosion resistance as high working temperature resulted in increased grain boundary along with high misorientation angle. The scanning electron microscopic images and elemental line scan at corroded stir zone identified AA7075 as the sacrificed alloy due to galvanic coupling with AA6061 at macroscopic scale and dissolution of Mg/Si at microscopic scale. The regions with higher percentage of high angle grain boundaries observed to undergo faster corrosion rates. The heat produced in second pass left annealing effect on prior welded region wherein lower microhardness is noted.

Unveiling Liquation and Segregation Induced Failure Mechanism in Thick Dissimilar Aluminum Alloy Electron-Beam Welds

Abstract: This study presents new findings on the underlying failure mechanism of thick dissimilar electron-beam (EB) welds through a study on the AA 2219-AA 5083 pair. Contrary to the prior studies on EB welding of thin Al alloys, where liquation in the grain boundaries (GBs) in the partially melted zone (PMZ) was not observed, the present investigation for thick EB welds reports both liquation and increased segregation of Cu in the PMZ. The work is thus directed towards understanding the unusual observation in the PMZ of thick EB weld through investigation of the microstructural variation across the various regions of the produced weld. The microstructural results are correlated with the mechanical properties of the weld, i.e., hardness variation and tensile response. Results of this investigation suggest that unlike the convention that EB welding produces sound dissimilar Al welds, the weld performance for thick EB Al welds is affected by the heat input, the associated cooling rates, and most importantly by the base material thickness. Extensive liquation and Cu segregation induced failure in the PMZ on the AA 2219 side of the dissimilar weld. The underlying failure mechanism is explained through a heat-transfer analysis. Beyond a certain plate thickness, the heat transfer changes from two to three-dimensional. As a result, retarded cooling promotes liquation and Cu segregation in thick EB welds.

Effect of microstructural variation on strain localization in double‐sided friction stir welded AA6061‐AA7075 joints

Abstract: In friction stir welding (FSW), the inhomogeneous microstructure significantly affects the mechanical performance of the joints. The present study investigates the influence of microstructural asymmetry along the thickness on strain localization during tensile test using the digital image correlation technique and fracture morphology for double‐sided FSW (DS‐FSW) AA6061‐AA7075 joints. In top and bottom slices of the transverse tensile sample, nonhomogenous strain localization is noted in heat affected zone (HAZ) of the advancing side (AS), that is, AA6061‐T6, and also presents higher tensile strength. However, in the middle slice of the transverse sample, larger region including thermo‐mechanically affected zone and HAZ undergoes strain localization and exhibits higher elongation at failure. In longitudinal specimens, the strain distribution is homogeneous up to uniform elongation followed by strain concentration at a localised region and fracture. Electron backscatter diffraction revealed that the extent of dynamic recrystallization on the retreating side (AA7075‐T61) is higher than that observed on the AS of the weld. The grain orientation spread map showed a high fraction of recrystallized grains at the weld centre. Presence of major shear textures components B/B¯ and C both below the tool shoulder and weld centre regions are observed from pole figures. The recrystallized texture components P ({011}<112>), Goss ({110}<001>), Rotated Goss ({110}<110>), Cube ({001}<100>) and shear texture ({001}<110>) components is also noted at the weld centre. Middle slice both for longitudinal and transverse sample showed the finest dimple size on the fracture surfaces. The strain localization behaviour and tensile performance assessed for transverse and longitudinal samples can be helpful to find the load orientation dependency and safe design of DS‐FSW joints.

Structured Optimal Variational Inference for Dynamic Latent Space Models

Abstract: We consider a latent space model for dynamic networks, where our objective is to estimate the pairwise inner products of the latent positions. To balance posterior inference and computational scalability, we present a structured mean-field variational inference framework, where the time-dependent properties of the dynamic networks are exploited to facilitate computation and inference. Additionally, an easy-to-implement block coordinate ascent algorithm is developed with message-passing type updates in each block, whereas the complexity per iteration is linear with the number of nodes and time points. To facilitate learning of the pairwise latent distances, we adopt a Gamma prior for the transition variance different from the literature. To certify the optimality, we demonstrate that the variational risk of the proposed variational inference approach attains the minimax optimal rate under certain conditions. En route, we derive the minimax lower bound, which might be of independent interest. To best of our knowledge, this is the first such exercise for dynamic latent space models. Simulations and real data analysis demonstrate the efficacy of our methodology and the efficiency of our algorithm. Finally, our proposed methodology can be readily extended to the case where the scales of the latent nodes are learned in a nodewise manner.

Factorized Fusion Shrinkage for Dynamic Relational Data

Abstract: Modern data science applications often involve complex relational data with dynamic structures. An abrupt change in such dynamic relational data is typically observed in systems that undergo regime changes due to interventions. In such a case, we consider a factorized fusion shrinkage model in which all decomposed factors are dynamically shrunk towards group-wise fusion structures, where the shrinkage is obtained by applying global-local shrinkage priors to the successive differences of the row vectors of the factorized matrices. The proposed priors enjoy many favorable properties in comparison and clustering of the estimated dynamic latent factors. Comparing estimated latent factors involves both adjacent and long-term comparisons, with the time range of comparison considered as a variable. Under certain conditions, we demonstrate that the posterior distribution attains the minimax optimal rate up to logarithmic factors. In terms of computation, we present a structured mean-field variational inference framework that balances optimal posterior inference with computational scalability, exploiting both the dependence among components and across time. The framework can accommodate a wide variety of models, including dynamic matrix factorization, latent space models for networks and low-rank tensors. The effectiveness of our methodology is demonstrated through extensive simulations and real-world data analysis.

Laboratory reports as a learning tool – Early clinical exposure in 1st-year MBBS physiology (Hematology)

Abstract: Background: Early clinical exposure (ECE) aims to bridge the gap between pre-clinical and clinical subjects. ECE exposes students to the health-care system at an early stage of professional life, follows patient-centered approach, and increases motivation for classroom learning. Most of the studies have reported a positive attitude of students toward ECE. However, very few studies have reported the difficulties that may be faced by the students during implementation of ECE. Aim and Objectives: The aim of this was to explore the attitude of students and difficulties faced if any during implementation of ECE in 1st MBBS Physiology (Hematology) with the help of laboratory reports and clinical scenarios. Materials and Methods: One hundred and ten students participated after completion of theory and practical classes of hematology. Clinical scenarios and laboratory forms were prepared based on actual laboratory reports of patients from pathology department. Group discussions and discussion with faculty was done. Attitude of the students was noted. Results: Most of the students found this method to be interesting and better than routine methods, helped in better understanding of theory and practical concepts, and helped in better preparation for examinations and better clinical correlations. However, about half of the students agreed or were not sure about the difficulty of ECE. Conclusion: The positive attitude of the students shows that ECE provides a successful integration of basic science and clinical subjects. It also helps in understanding the relevance of a basic science subject. Concepts of the subjects are made easier and interesting by ECE. However, the difficulties faced by the students should be kept in mind and more practice sessions may be done.