PhD Theses (Energy Science and Engineering)


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    Design And Fabrication Of Solid State TiO2|Ag Structure For Developing Efficient Plasmonic Photo-Electric Conversion Device
    (2024) Devi, Kshetrimayum Priyalakshmi
    The global shift towards renewable energy sources, propelled by environmental concerns, has ignited a surge in research aimed at developing efficient solar energy technologies. This thesis is dedicated to the creation of a solid-state plasmonic energy harvesting device using low cost methodologies. Initial simulations compare various noble metal nanoparticles for their plasmonic resonance properties, with silver identified as particularly advantageous due to its sensitivity and electronic characteristics. Semiconductor substrates are synthesized through a simplified Sol-Gel technique, resulting in the production of TiO2 thin films tailored for solar applications. Subsequently, a solid-state energy harvesting device is fabricated, leveraging metal/semiconductor heterojunctions to achieve promising cell performances. Furthermore, the thesis delves into an environmentally friendly approach to synthesizing silver-graphene nanocomposites, which holds significant potential for enhancing device efficiency. These findings represent a significant stride forward in the design and implementation of efficient plasmonic energy harvesting devices, paving the way for sustainable advancements in solar power generation.
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    Development and Performance Evaluation of Methanol and Ethanol Operated Cookstoves
    (2023) Maurya, Pratibha
    The present thesis emphasizes on the need for clean cooking fuel sources in developing countries where 2.8 billion people rely on solid fuels, posing health hazards due to indoor air pollution. Although liquefied petroleum gas (LPG) and biogas are cleaner alternatives, they face adoption barriers, including cost and availability. Methanol and ethanol have gained traction as a cleaner cooking source, and several countries have launched programs promoting their use. However, conventional methanol and ethanol cookstoves have drawbacks, such as low firepower and soot formation. In this regard, the thesis aims to evaluate the performance, safety, and sustainability of Free Flame Combustion based (FFC) methanol cookstoves, develop a Porous Media Combustion (PMC) based methanol cookstove, assess the feasibility of ethanol as a cooking fuel in FFC and PMC based cookstove, analyse indoor air quality due to use of PMC based cookstoves and compare it with the existing FFC based cookstove, and develop an Indian standard for the use of methanol and ethanol cookstoves.
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    Design and Development of Hybrid Nanomaterials for Efficient Photocatalysis
    (2024) Devi, Thongam Debika
    Water is our life and its quality degradation has imposed a major threat to the health and environment with the emerging contaminants. Photocatalytic advanced oxidation processes (AOP) using reactive oxygen species (OH¯, •OH, H2O2, HO2•, O2•¯, O22¯) provide complete degradation of these persistent pollutants by using nanomaterials triggered by light absorption. However, its real-time application is limited by the use of high-power light sources to trigger the reaction and its limited performance. Thus, this thesis focuses on understanding and addressing these bottlenecks by― (a) designing and developing a sunlight-responsive photocatalyst to harvest natural sunlight, (b) developing heterostructure photocatalysts for enhanced efficiency by developing interfacial charge transfer, and (c) studying and discovering ways to enhance charge transfer by manipulating heterostructure photocatalyst responsive to natural sunlight. To achieve efficient photocatalysis, different sunlight-responsive photocatalysts were synthesized by varying― synthesis mediums and methods introducing surface defects and producing different nanoparticle morphologies. The dependence of the charge transfer, charge carrier lifetimes, surface structures, induced defects, and morphologies on the photocatalytic efficiencies were discussed elaborately. Variable ZnO samples were synthesized using DMF or DEG solvents using solvothermal and chemical synthesis methods showing different properties― morphologies, surface, and chemical properties. The influence of the charge transfer pathways in the photocatalytic efficiencies is discussed and explored with different charge transfer methods― self-assembled ZnO nanoparticles on three electronically different SWCNTs (metallic-SWCNT/ZnO, semiconducting-SWCNT/ZnO, and pristine-SWCNT/ZnO); Type I ZnO/Fe3O4 and Type II ZnO/TiO2 composite heterostructures; g-C3N4 & Z-scheme g-C3N4/ZnO composites, and other composites― g-C3N4/SWCNT, and g-C3N4/ZnO/SWCNT. By taking RhB as a model pollutant, these nanoparticles were used as the floating photocatalyst by coating on the face-mask fabric showing variable efficiencies up to 99% of 10 ppm RhB degradation within the 100 min natural sunlight exposure.
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    Optimal Operating Parameters for Performance Improvement of a Biogas Fueled Spark Ignition Engine
    (2023) Hotta, Santosh Kumar
    The environmental concerns and the uncertainties associated with the future availability of fossil fuel are driving the interest of utilizing renewable biofuels in the internal combustion (IC) engines. Among the renewable gaseous fuels, biogas is an attractive source of energy in rural areas and is mainly composed of CH4 (50-70%), CO2 (25-50%), H2 (1-5%), N2 (0.3-3%) with traces of H2S. Direct use of biogas as a standalone fuel in CI engine is almost impossible due its properties such as higher self-ignition temperature, higher resistance to auto ignition and knock. But, the physical and chemical characteristics of biogas have a great resemblance on the octane fuels in higher compression ratio (CR) SI engines. Although SI engines are best suitable for renewable or non-renewable high-octane fuels, they need special attention to accommodate biogas. The combustion process in a SI engine is greatly influenced by the operating parameters. Various techniques such as alteration in CR and IT, preheating, pre-chamber ignition, etc. were proposed to enhance the performance, combustion and emission characteristics of the biogas fueled SI engine. Thus, one of such techniques, with proper optimization of operational parameters, can be employed to develop an efficient biogas-based SI engine. The current research is mainly focused to determine the optimal operating parameters (optimum compression ratio, maximum brake torque timing, throttle position and optimum air-fuel ratio) of a biogas fueled SI engine through a multi fuel, variable compression ratio (VCR), spark ignited research engine setup for effective implementation in a commercial SI engine.
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    Exploring potential genetic routes for enhancing lipid accumulation in microalgae for biofuel application
    (2022) Sharma, Prabin Kumar
    To harness the benefit of microalgal biotechnology for biofuel application, genetic manipulation of metabolic pathways is essential, requiring an efficient genetic transformation method. Besides, an efficient gene transfer system in microalgae would allow a way to understand cellular metabolism regulation by characterizing the genes involved through a reverse genetics approach. A. tumefaciens-mediated genetic transformation is a method of choice for ease in transformation and its ability to precisely integrate low copy number transgene into transcriptionally active genomic regions. However, in C. sorokiniana, the lack of a reliable and efficient Agrobacterium-mediated gene transfer method limits its potential uses in commercial scale utilization. We described an efficient A. tumefaciens-mediated genetic transformation in C. sorokiniana. For the first time in C. sorokiniana, it highlighted the reliable detection of stable transgene integration and expression in C. sorokiniana, which opens up limitless possibilities in biofuel production and other commercially valuable commodities. Further, as higher lipid biosynthesis and accumulation are essential to achieve sustainable production of biofuel in microalgae. The green microalgae Chlorella sorokiniana was genetically engineered with a rate-limiting enzyme of neutral lipid biosynthesis, diacylglycerol acyltransferase 1 from Jatropha curcas (JcDGAT1) and a transcription factor WRINKLED 1 from Arabidopsis thaliana known to involve in lipid biosynthesis in higher plants, to enhance the lipid content. The results offer a valuable strategy for enhancing oil production and might facilitate a platform strain with industrial potential. Our results suggest genetic means to increase neutral lipids and unsaturated fatty acids in C. sorokiniana for biofuel production. In conclusion, this research provides proof of concepts to make microalgae an economically viable source for biodiesel production. A similar technique may be helpful for the biosynthesis of certain high-value compounds in microalgae.
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    Surface Heat Flux Recovery during Short Duration Experiments–Conceptual Demonstration from Probe Design to Soft computing Analysis
    (2022) Rout, Anil Kumar
    Recovery of surface heat flux in short duration experiments is a challenging task due to the dominance of unsteadiness in the temperature signal. Therefore, the heat flux estimation is carried out using the transient temperatures through suitable sensor modeling. In most of the cases (e.g., in thin-film gauges and coaxial probes), the sensor is assumed as a semi-infinite body with one-dimensional heat conduction through the sensing surface and substrate. In some cases, the surface heat flux is computed through numerical simulation. Nevertheless, all these processes involve various assumptions, simplifications and mathematical complications. In recent years, the advanced data science and soft computing methods are considered as important techniques in various applications. Therefore, the theme of the thesis is to introduce soft computing approach as a benchmark tool for recovery of surface heat flux in short duration experiments. The foremost intention of the present study is to implement a soft computing technique; Adaptive neuro-fuzzy inference system (ANFIS), to recover heat flux from the temperature signal in case of short duration experiments. The ANFIS technique needs a training process through known data sets (temperature signals and their corresponding heat flux). Therefore, the training data sets (transient temperature and surface heat flux) have been generated through various heat transfer experiments involving step and impulsive loads, convective and radiative heat loads. Side by side, numerical modelling of sensors (with similar experimental environment) is also considered as training data generation for ANFIS methods. Subsequently, inverse approach is followed to recover unknown (surface heat flux) parameters through trained data sets of ANFIS
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    Studies on Metal Hydride Based Hydrogen Storage and Purification Systems
    (2022) Kumar, Alok
    The world is witnessing an inevitable shift of energy dependency from fossil fuels to cleaner energy sources like wind, solar, hydrogen, etc. The governments from all over the world have realized that for limiting the global rise in temperature to 1.5 °C, hydrogen has to be given a reasonable/sizable share in meeting global energy demand by mid of 20th century. Hydrogen can be produced through several means using renewable energy sources and can be stored either in solid, liquid or gaseous state. Though, compressed and liquefied hydrogen storages are well-established technologies in the commercial sector, however, due to the leakage risk, boil-off losses and explosive nature, world is exploring a safer way of hydrogen storage i.e. absorption/adsorption based solid-state hydrogen storage technology. Although hydrogen can be produced from various extraction processes, such as through decomposition of fossil fuels, electrolysis of water, thermolysis of water, biomass conversion, etc., it is not always in the pure form. Metal hydride (MH)- hydrogen system can be a suitable solution for safe hydrogen storage and easy purification technology. Considering these issues, in the present study, thermodynamic screening of MH alloys was studied to filter suitable alloys for efficient working of metal hydride based hydrogen purification system MHHPS. From alloy screening, LaNi4.7Al0.3, LaNi5 and La0.9Ce0.1Ni5 alloys were considered for MHHPS. In order to check feasibility of metal hydride (MH) for hydrogen storage and purification application, parametric investigation of LaNi4.7Al0.3, LaNi5 and La0.9Ce0.1Ni5 alloys have been performed by varying different set of experimental parameters like hydrogen supply pressure, absorption temperature, and desorption temperature at fixed flow rate of ‘heat transfer fluid (HTF)’ at 4 lpm. The experiments have been carried out using 6 ECT reactor configuration. The rector was designed using numerical simulations performed using COMSOL Multiphysics, and further the numerical results were validated using experimental data. The results show that, all the selected alloys were suitable for hydrogen storage and purification application. Parametric studies for optimizing the operational parameters of the coupled reactor in multi-stage MHHPS were performed. For efficient system operation, the suggested absorption temperature is in the range of 20 °C to 30 °C with supply pressure 5 bar to 20 bar, while the flushing and desorption are suggested in the ranges of 15 °C to 20 °C and 70 °C to 90 °C, respectively.
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    Development and Characterization of Advanced FO Membranes using Exfoliated 2D Nanomaterials for Energy Generation and Separation Processes
    (2023) Deka, Priyamjeet
    Water shortage has become a global problem due to the high human consumption, rapid industrialization and low availability of freshwater resources. Extensive efforts have been put forward by researchers to overcome the freshwater crisis by exploring new desalination techniques, and wastewater reuse without damaging the natural freshwater ecosystems. One such pivotal technology for purifying water was the membrane technology. Membrane technology is an emerging and advanced process that can provide a sustainable solution to desalination and wastewater treatment. Although pressure-driven membrane separation processes were used for producing freshwater, its high energy consumption prevent them from further employment. Hence, modification of existing membrane-based separation technology is required to overcome its demerits
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    Development and Performance Evaluation of a Medium Scale Clustered LPG Stove with Porous Radiant Burner
    (2022) Deb, Sunita
    This thesis presents a detailed investigation on improving the performance of a Porous Radiant Burner (PRB) by the means of clustering small sized burner against a large size burner. Experimental results suggested that clustering smaller sized PRBs yield higher thermal efficiency and reduced CO and NOx emissions. The Clustered Porous Radiant Burner (CPRB) was evaluated for its performance investigation over the stable range of power inputs and subsequently an improved CPRB was developed by changing the burner diameter. The performance investigations revealed that the CPRB with individual burner diameter 80 mm (CPRB8) was found to yield maximum thermal efficiency of 59.2% while individual burner diameter 90 mm (CPRB9) produced the lowest emissions. Subsequently a selfaspirated CPRB was developed to eliminate the requirement of compressed air. The development was carried out by design optimization of the geometrical components. Maximum therm+F40al efficiency was obtained as 58.2% at a power input of 8 kW. Minimum CO emissions of 5 ppm were obtained at 8 kW, while the emissions of NOx were untraceable. The self-aspirated CPRB was found to be energy saving and more environment friendly when compared to a conventional burner. Numerical investigations were carried out to study the effect of air entrainment on the combustion stability of a self-aspirated PRB. Observations revealed that at certain combinations of the orifice and the mixing tube, optimized primary aeration was obtained that resulted in stable combustion. The PRB was observed to operate under stable partially submerged combustion for orifice diameter 0.3 mm when positioned at 30 mm from the bottom of the mixing tube of diameter 29 mm.
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    Waste peels as low-cost substrate for microalgal cultivation under a biorefinery approach
    (2023) Malakar, Barasa
    The potent utilization of cheap and renewable biomass for the production of fuels and value-added bio products is important for addressing the problems related to fossil fuel depletion. Microalgae has emerged as an excellent resource in this regard but the excessive cost of nutrients is a vital restriction for producing economically viable algal fuels. Substitution of the chemical growth medium of microalgae with low cost organic biomass such as food or agricultural waste substrate could help in dealing the cost related problems associated with cultivation of microalgae and also in dealing with heaps of agricultural and food waste generated daily. The suitability of potato, banana and sweet lime peel hydrolysate were evaluated for microalgae cultivation. Different pre-treatment processes were carried out for all the three peels and the best conditions yielding higher amount of glucose concentration were further hydrolyzed by enzyme. Response surface methodology (RSM) was used to optimize the hydrolysis conditions to attain high glucose concentration. The three parameters chosen for the study were; time (h), temperature (oC) and the rotation frequency or agitation speed of the incubator (revolutions per minute i.e. RPM). 46.17 ±0.77 g L-1, 29.84 ± 0.57 g L-1 and 35.90 ±0.43 g L-1 of glucose yield were obtained for potato, banana and sweet lime peels respectively under optimum conditions. The waste peels were further characterized through proximate and ultimate analysis, compositional analysis, FESEM, EDX, FTIR and pH study. Two indigenous microalgae strains Chlorella sorokiniana KMBM_I (Strain “I”) and Chlorella sorokiniana KMBM_K (Strain “K”) were tested for their growth and adaptability in the peel wastes. Growth kinetic parameters of the strains were analyzed in varying culture conditions. A new insight can be obtained with this study as it integrates the concept of lipid extracted microalgal biomass residue utilization (LEMBR) approach along with waste disposal thereby serving in the management of these wastes. Biorefineries follows the concept of zero waste production and are very energy efficient. The spent biomass after extraction of lipids were reused and recycled for sustainable biofuel synthesis. For microalgal based bioethanol production, the defatted biomass after lipid extraction was hydrolyzed and the obtained hydrolysate was fermented to generate bioethanol. This is a significant step in the production of sustainable biofuels through reuse and recycling of spent microalgal biomass. The isolates demonstrated a remarkable amount of lipid, protein and carbohydrate. The strains also exhibited notable amount of pigments like chlorophyll-a, chlorophyll-b and carotenoids. Experimental results indicated that a waste-based refinery could lead to efficient production of value-added products from microalgae utilizing the organic wastes, in turn contributing to the establishment of a “green society”. The highest biomass yield of 2.56±0.09 g L-1 and lipid content of 26.34±0.24 % was observed when the microalgal strain “K” was cultivated in the mixed peel extract of potato, banana and sweet lime. This lipid can be further processed to produce biodiesel while the spent defatted LEMBR were utilized to produce bioethanol of 7.16±0.43 g L-1. This study demonstrates the potential of indigenous native species of microalgae, for a biorefinery that generates lipids, bioethanol and various value-added products. The study demonstrated sustainable bioenergy production with simultaneous value added bioproducts generation from microalgae through waste peel valorization. This bioconversion facilitates the way for emergence and creation of algae based biorefinery through the production of biofuels and bioproducts. Further, this waste peels based microalgal biorefinery concept could aid in the establishment of “zero waste” strategies with proper scale up techniques.
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    Prospects of Energy Production from Lignocellulosic Biomass, Solar Photovoltaic and Hybrid Systems
    (2023) Buragohain, Sachankar
    Fossil fuel energy sources have been the primary source of energy and has a major share in meeting the energy demands of the day-to-day activities. However due to constant depletion of fossil fuel sources and low replenishment rate, it has forced mankind to shift its approach towards more renewable and sustainable energy sources. In recent years, all nations have shifted their approach from a fossil reliant nation to a more sustainable and greener approach nations. India being an agriculturally rich country with abundant biomass resources and ample solar radiation for maximum time of the year has invested majorly in biomass and solar. Anaerobic digestion of organic and lignocellulosic biomass has been a major area of research in many parts of this region. Though large-scale anaerobic digestion of organic biomass has already been implemented in some cities, use of lignocellulosic biomass has not been extensively done. The lignocellulosic biomass resources are either dumped in fields or are burned down releasing more carbon dioxide in the atmosphere. Keeping in view the constant depletion of fossil fuel sources and ever rising energy demand, it is essential that application and feasibility of renewable energy sources at community level is emphasized. The study was thus sub divided into three parts focusing on energy generation from anaerobic digestion, solar photovoltaic and hybrid systems. The anaerobic mono- and co-digestion of three lignocellulosic biomasses viz. duckweed, switchgrass and rice straw were performed in 1 litre laboratory-scale batch reactors. The initial biochemical methane potential test was performed at three different total solids concentrations (10%, 15%, 20%) and cattle dung to feedstock ratios (1:1, 1:1.5, 1:2) under mesophilic conditions (28–32 °C) for 36 days. Co-digestion of feedstocks at 1:1 ratio yielded better results than other cattle dung to feedstock ratios. Optimized physical parameters were further implemented for a scale-up co-digestion study of biogas potential from 4 m3 community-size biogas digesters. The investigation was performed for 60 days maintaining a hydraulic retention time of 40 days, and a comparative analysis with mono digestion of cattle dung was also analyzed. Average daily biogas production for digester containing rice straw and cattle dung was 0.36 m3/kg-VS, whereas it was 0.34 m3/kg-VS and 0.32 m3/kg-VS for switchgrass and duckweed, respectively. An overall comparative analysis of the biogas production and its composition for both biochemical methane potential tests and continuous processes are discussed in this work.
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    Performance Investigation and Optimization Studies on a Solar-Assisted Liquid Desiccant Air Conditioning System
    (2021) Bhowmik, Mrinal
    Liquid desiccant dehumidification is a promising energy-extensive process for air dehumidification, which can easily be driven by any waste or renewable heat sources. In the current thesis, efforts are devoted to explore the thermo-kinetic properties of pure LiBr, CaCl2 as well as their mixtures through numerous material characterization techniques. Further, a thermal model for assessing the heat and mass transfer characteristics of the liquid desiccant dehumidifier/regenerator is developed based on the finite difference method. In order to assess the performance of the overall liquid desiccant system using a novel desiccant mixture, an experimental setup of solar-assisted liquid desiccant dehumidification has been fabricated, where solar evacuated tube collectors were used as a regeneration source to drive the liquid desiccant system in a close-loop. The overall energy balance between the ambient air and the liquid desiccant was estimated. Effects of independent parameters such as the solution to air flow rate, solution concentration and temperature on the dehumidifier-regenerator performance parameters such as latent heat ratio, condensation rate, desiccant mass fraction index, evaporation rate and latent and enthalpy effectiveness were analyzed. The results obtained from the present investigation showed that high solution to airflow (L/G) ratio enhanced the dehumidification and low L/G ratio enhanced the liquid desiccant regeneration rate. For tested liquid desiccant dehumidifier, condensation rate and latent effectiveness lie in the range of 2.2 to 5.6 g/m2-s and 36 to 68%, respectively. The evaporation rate, sensible and the latent effectiveness of the regenerator lies in the range of 0.1 – 11.2 g/m2-s, 25.9 – 63% and 10 – 92% depending on the operating conditions. The maximum latent heat ratio for the dehumidifier at the design condition was 0.62, and the thermal coefficient of performance of the system was found as 1.1. Further, the relationships between the performance parameters and control variables is developed through the application of various well-known artificial intelligence (AI) based methods such as artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS), and gene expression program (GEP). Subsequently, best AI model (GEP) based fuzzy logic is developed for optimizing dehumidifier/regenerator inlet process parameters in terms of multi-responsive performance characteristics using genetic algorithm. At a near-optimum point, the experimental results condensation rate (CR) of 5.584 g/m2-s, moisture effectiveness (ɛm) of 42% and latent heat ratio (LHR) of 0.83, respectively, were obtained. Lastly, an effort has been made to develop a novel liquid desiccant doped sodium carboxymethyl cellulose (NaCMC) films using citric acid as a crosslinker to explore the air dehumidification and regeneration capability of films.
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    Experimental Investigations for the Enrichment of Biogas Employing Biomass-Based Scrubbing Agents and Bio-Electrochemical Approaches
    (2022) Bora, Deep
    Biogas produced from anaerobic digestion of organic waste is one of the potential alternative biofuels and is economically feasible, which might benefit the future energy supply demands as well as contribute to a reduction of greenhouse gas emissions. Biogas is primarily composed of methane (CH4) and carbon dioxide (CO2) as the major constituents, with trace amounts of other components like water vapour, hydrogen sulphide (H2S), hydrogen (H2), and nitrogen (N2). The presence of H2S in biogas needs special attention for cooking, power generation, as well as upgrading to bio-methane due to its foul-smelling odor, corrosion, health issues, and environmental problems. Scrubbing of CO2 is also essential for the upgradation of biogas, which increases the calorific value of the treated gas and enhances its efficiency for being used as vehicular fuel and power generation. Among various purification technologies, the absorption and adsorption methods are found to be simple, cost-effective, and easy to operate for the removal of CO2 and H2S from decentralized biogas plants installed in rural areas. Generally, the use of different alkaline chemicals in the chemical absorption and adsorption processes is a common technique for the removal of CO2 and H2S from biogas. But, the problem arises in the disposal of the used chemicals due to their toxic and environmentally unfriendly nature.
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    Functional Nanomaterials for Electrochemical Energy Storage in Supercapacitors
    (2022) Choudhury, Bhaskar Jyoti
    Energy storage systems are essential for the practical implementation of renewable energy systems because the majority of renewable energy sources are intermittent in nature. Supercapacitors (SCs) are one of the most promising energy storage devices owing to their performance characteristics, viz. high power density, rapid charge–discharge, and ultra-long cycle life. However, their usage is significantly limited by the drawbacks of low energy density. The main aim of this work is to develop advanced electrode materials for supercapacitors with improved energy density while maintaining high power density and long cycle life. This thesis reports investigations on the synthesis of four electrode materials for supercapacitors, including nanocomposites (Fe3O4/rGO and MWCNT/MnO2/rGO), and carbon materials (rGO and PC–x). The two nanocomposites were synthesized by facile ultrasound–assisted synthesis methods. The reduced graphene oxide (rGO) was synthesized via chemical reduction of highly oxidized graphene oxide. Lastly, oxygen-enriched porous carbon (PC–x) was prepared by co–pyrolysis and KOH activation process from a ternary blend of biomass. These materials have been extensively characterized using standard techniques and the electrochemical performances were investigated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectrometry (EIS) techniques. The fabricated supercapacitors have been demonstrated to possess excellent electrochemical properties as follows: (1) The Fe3O4/rGO based all–solid–state supercapacitor with PVA/KOH polymer–gel electrolyte exhibited an energy density of 8.46 W h kg–1 at a power density of 338 W kg–1. Ternary MWCNT/MnO2/rGO nanocomposite based supercapacitor with commercial–level mass loading (~12 mg cm–2) demonstrated high specific capacitance (314.6 F g−1 at 5 mV s−1), energy density (21.2 W h kg−1 at 150 W kg−1) and excellent cycle stability at a wide cell voltage of 1.5 V in 1 M Na2SO4 electrolyte. (2) The rGO based aqueous supercapacitors (rGO–SCs) with commercial–level electrode mass loadings achieved energy densities of 15.39 W h kg–1 (at 180 W kg–1, 1.8 V), 21.42 W h kg–1 (at 180 W kg–1, 1.8 V), and 22.87 W h kg–1 (at 210 W kg–1, 2.1 V) in 1 M Li2SO4, redox–additive electrolyte (0.1 M Na2MoO4 + 1 M Li2SO4), and water–in–salt (11 M NaNO3) electrolyte, respectively. (3) Oxygen–enriched porous carbon (PC–x) based aqueous supercapacitors with commercial–level mass loadings exhibited an energy density of 22.75 W h kg–1 (at 200 W kg–1, 2 V) and 96.8% capacitance retention over 10000 cycles in 1 M Li2SO4. The energy density of the device was enhanced to 37.24 W h kg–1 (at 200 W kg–1, 2 V) in a redox–additive electrolyte (0.1 M Na2MoO4 + 1 M Li2SO4). On a whole, the results of this thesis have demonstrated the efficacy of the fabricated supercapacitors with concurrent high energy and power densities. Therefore, these materials have tremendous potential for the development of high-performance supercapacitors for commercial applications.
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    Sequential separation and characterization of cellulose, xylan and lignin from alkali pretreated sugarcane tops and utilization of cellulose for higher scale bioethanol production by recombinant enzyme saccharification and fermentation
    (2022) Khaire, Kaustubh Chandrakant
    The increasing use of non-renewable resources and their continuous depletion have become a major concern nowadays. The production of renewable fuels from agricultural lignocellulose waste is sustainable and economically feasible. Sugarcane top is one of the most abundant lignocellulosic biomasses in India. In the first methodology, the separation of cellulose (40 g) and xylan (25 g) was successfully carried out and characterized from 100 g of raw sugarcane tops (SCT) after delignification by following the alkaline pretreatment method and proven its commercial grade by analyzing using analytical methods such as FESEM, XRD, LCMS, HPSEC, DLS, TGA and enzymatic activity assay. In the second methodology, the sequential extraction of xylan (26.5 g) and lignin (8.5 g) was carried out by precipitation from the alkali-pretreated sugarcane tops (apSCT) hydrolysate after alkaline pretreatment of water-soluble extractives free SCT (100 g) without the delignification. The characterization of apSCTx and apSCTal was performed using various analytical methods such as HPSEC, LCMS, TGA, CHNS, FESEM and FTIR to prove their commercial grade. The alkali-pretreated SCT solids were optimized for its saccharification using recombinant and commercial cellulolytic enzymes which yielded about 265 mg (7.95 g/L) and 672 mg (18.6 g/L) of TRS per g of apSCT, respectively. The higher scale saccharification using commercial cellulases at optimized conditions at (3.6 L) resulted in 687 mg/g (18.8 g/L) TRS yield. The produced reducing sugars were further optimized for fermentation using hydrolysate containing 15 g/L TRS supplemented with 3 g/L yeast extract and 5% (v/v) consortium of fermenting microbes (Saccharomyces cerevisiae, Pichia stipitis and Pachysolen tannophilus, 1:1:1 from 107 CFU/mL) in 20 mL was carried out at initial pH 5, 100 rpm and 35°C for 48 h which resulted in 7.5 g/L of bioethanol. Under the same fermentation conditions, the higher scale bioethanol production in a 5 L bioreactor at 3 L working volume gave 7.43 g/L of bioethanol within 24 h with 96.9% fermentation efficiency. The biorefinery approach of sequential extraction of apSCTx and apSCTal from alkali-pretreated SCT hydrolysate waste can enhance the economics of the extraction process.
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    Development and Performance Investigation of Parabolic Trough Solar Collector and Latent Heat Storage Units for Indoor Cooking Application
    (2021) Abreha, Berihu Gebreyohannes
    The main objective of the present study is to design, develop and investigate the thermal performance of a suitable indoor solar hybrid cooking system using thermal energy storage materials. For this reason, a parabolic trough solar collector (PTSC) and latent heat storage (LHS) units are designed and fabricated. The thermal performances of both systems are investigated experimentally and numerically. Furthermore, a hybrid PTSC and LHS system is proposed for solar cooking application and lab-scale experimental setup are coupled to test the performance of the hybrid system. The performance of the fabricated PTSC system is investigated experimentally, analytically and numerically. The important parameters for all the methods are inlet temperature, beam radiation, mass flow rate. The result indicates that the efficiency and useful heat decrease while inlet temperature increases keeping other parameters constant. On the other hand, the thermal efficiency is increased along with mass flow rate and solar radiations. Besides, the effect of the nanofluids on the thermal performance of PTSC is investigated numerically. However, addition of nano-particles into the base fluid brought insignificant difference. The experimental results indicate that the thermal performances of PTSC are better in the month of June as compare to October in the north east region of India. The maximum HTF outlet temperature recorded are 110.7 0C and 108 0C on June 15 and 22, respectively. Similarly, the maximum HTF outlet temperature recorded on October 13 and 18 are 89.9 0C and 86.8 0C, respectively. It is to mention that the analytical, numerical and experimental results are found in the good agreement. Similarly, an experimental and numerical study of the lab-scale LHS unit is conducted. Erythritol (C4H10O4) and cooking waste oil are employed as PCM and HTF, respectively. The performance of the LHS unit is tested experimentally during the charging process, whereas, both charging and discharging characteristics of the storage unit are studied during the numerical study. The performance of LHS is investigated with the help of charging time, liquid fraction, average transient temperature and stored energy parameters. During the charging process, both numerical as well as experimental tests are conducted at HTF volume flow rate of 75 LPM at 138 0C. For the discharging process, HTF inlet temperature is chosen to be at 87 0C keeping the volume flow rate same as that of the charging process. The optimal number of tubes and fins are decided after multiple investigations of different LHS models. The effect of operating parameters on the performance of the storage unit is examined using both experimental and numerical analyses. It is observed that an increase in the flow rate of HTF and inlet temperature enhances the heat transferring rate of PCM and minimizes the charging time of the LHS unit. The experimental outcome of the storage unit is validated along with numerical results. The numerical analysis results exhibit very good similarity with the experimental data exhibiting a maximum deviation of 6.0%. The total time consumed in the complete melting and solidification of PCM inside LHS is estimated to be 175 min and 156 min, respectively. During the melting of PCM, the sensible heat, latent heat and total energy stored in LHS are found to be 9.3 MJ, 17.74 MJ and 27.03 MJ, respectively. Similarly, the sensible heat, latent heat and total energy released during the solidification process are 4 MJ 17.6MJ and 21.6 MJ, respectively. A hybrid lab-scale PTSC and auxiliary source of energy are proposed to power LHS developed for indoor cooking purposes. The experimental investigations of the coupled PTSC and LHS units, and the numerical investigation of the proposed LHS unit powered by PTSC and auxiliary energy source are evaluated. First, the performance of the LHS unit is examined using PTSC as a heat source, where the energy from the sun is generated in the receiver tube. The experimental test is conducted on a sunny day starting from 9:30 PM local time and at 14:00, the average temperature of the LHS is 88 0C. Although the experimental test is conducted for more than five hours, the PTSC does not collect enough solar radiance for the complete charging of LHS. Therefore, an auxiliary energy source is required for the complete melting of PCM.
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    Design and Implementation of Estimators and Controllers for a DFIG-based Wind Energy Conversion Systems
    (2021) Mondal, Prosenjit
    The effective operation of a typical doubly-fed induction generator (DFIG)-based wind energy conversion system (WECS) requires efficient control of the two power electronic converters connected back-to-back. Out of these two converters, one converter is tied to the grid or the stator of the DFIG and is called active front-end converter or grid side converter (GSC) or stator side converter (SSC), and another one is tied to the rotor of the DFIG and is called rotor side converter (RSC). The present thesis mainly focuses on the design of controllers and observers for the DFIG. The efficient control of the GSC depends upon the accurate information on the phase and frequency of the grid voltage, which can be estimated through a phase-lock-loop (PLL) system. Hence, a modified synchronous reference frame (SRF)-based PLL technique is proposed to estimate the phase and frequency of the grid. The estimated phase from the proposed PLL is utilized to convert the three-phase sinusoidal variables in the stationary reference frame (abc) of the grid (voltage and current) to two-phase stationary DC variables in the synchronously rotating reference frame (dq). The dynamic model of the GSC in dq-reference frame is utilized here to develop the controllers for the GSC. Two current control algorithms are proposed to control the active and reactive grid currents of the GSC, and one voltage control algorithm is proposed to control the DC-bus voltage of the GSC. One of the current controllers is based on adaptive multiple-input multiple-output (MIMO) control, and the other current controller is based on first-order sliding mode control (FOSMC). The developed voltage controller is based on an extended state observer (ESO) augmented with an adaptive control technique. Efficient control of the RSC depends upon the accurate information on the rotor speed and rotor position/angle, which can be measured directly by a rotary encoder. However, the failure-prone nature of these encoders makes the system unreliable; hence, reliable solutions in the form of rotor speed and position observers are proposed in this thesis. Two observers are developed using the dynamic model of the DFIG. The stator current and rotor flux are used as the states for both the observer models. The first observer is based on the first-order sliding mode observer (FOSMO), and the second observer is based on second-order sliding mode observer (SOSMO). The performance of these observers is also validated in real-time with close loop terminal voltage control of a standalone DFIG system.
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    Development of Small Scale Alcohol Biofuel Cells using Enzymes as Catalyst
    (2021) Das, Priyanki
    The major objective of the present study is to develop small-scale alcohol fuel-based enzymatic biofuel cells (EFCs) for power generation and alcohol biosensing applications using alcohol oxidase (AOx) as anodic catalyst. One of the key approaches we propose to develop the small-scale EFCs is to exclude external pumping system from fabricating the devices. To make the idea effective, we introduce natural cellulosic materials (cotton or papers) in the device fabrications to deliver the fuel to the bioanode through passive diffusion activity. An additional important objective of the present work is to develop a biocompatible conductive ink with high aqueous stability for fabrication of the bioelectrodes, as these are vital properties of an ink to harvest stable bioelectrocatalytic function of the redox enzymes on the electrode surfaces. We studied some biopolymers and eventually identified silk-sericin and polyethylene glycol (PEG) as suitable materials for developing a graphite-based conductive ink in a ratio of 0.03:2.0:1.0 for sericin:PEG:graphite. Interestingly, sericin facilitates transformation of amorphous graphite powder to a crystalline form in PEG environment that improved the conductivity of the ink (11.2 by 5.6-folds from the ink devoid of sericin. The viscosity and shear rate values of the ink were calculated as 0.11 Pa.s and 100s-1, respectively, thermos-stability up to 100 0C, and heat of formation (ΔHf) -4.204 KJ/g. In addition, the ink coated over paper surface retains high aqueous stability and the reason being recognized as the enhancement of β–sheets content of sericin by 2.8% upon mixing it with PEG. Then we moved towards the selection of a cathodic enzyme and used laccase for the same. The laccase enzyme, which is extracted from Tramates versicolor fungi, can oxidize phenolic compounds with concomitant reduction of molecular oxygen to water. Laccase was immobilized on a glassy carbon electrode using a nanocomposite matrix comprising of osmium tetroxide on poly 4-vinylpyridine, multiwalled carbon nanotubes, nafion and carbon black. SEM images revealed that the nanocomposite matrix provides a porous structure for easy immobilization of the enzyme. Whereas cyclic voltammetry studies explained that, the nanocomposite matrix offers a highly electroactive surface for facile diffusion-free electron transfer kinetics. The response of the bioelectrode for oxygen substrate at the determined formal potential of laccase was established. The heterogeneous electron transfer rate constant (ks) and surface concentration of the ionic species (Γ) of the bioelectrode were discerned as 0.67s-1 and 1.32×10-8, respectively. The results infer the potential application of the constructed bioelectrode as oxygen breathed biocathode for EFC application. This bioelectrode also offers a reliable electrochemical response towards pyrocatechol in a biocatalytic mode. The response of the fabricated biosensor was generated at a potential of 0.14 V from the electrocatalyzed reduction of 1, 2-benzoquinone formed from the biocatalyzed oxidation of pyrocatechol. The bioelectrode showed a linear range of output current against pyrocatechol in the concentration range of 3.98 nM-16.71 nM with a minimum detection limit of 2.82 nM and a sensitivity of 3.82 ± 0.31 nA nM-1. After working on cathodic enzyme, we focus on developing a small sized EFC utilizing paper (pEFC) as support material for methanol biosensing application. We used the as prepared Graphite-PEG-Sericin conductive ink for making support electrode for enzymes on chromatography paper surface. To this end, we immobilized AOx on anode, and bilirubin oxidase (BOx) instead of laccase on cathode. It may be mentioned that due to incompatibility of laccase in physiological pH, we later replaced this enzyme with BOx, which exhibits high activity in the pH value. The sensor showed a linear range of output current of 0.03125μΜ -0.5μΜ (R2 = 0.9988), sensitivity of 0.66245 μAμM-1 and a detection limit of 0.022 μM for methanol validating the potential of the pEFC for methanol biosensing application. Next, we report a methanol-fueled pure EFC fabricated by using AOx and BOx as anodic and cathodic catalysts, respectively with a focus on power generation. Here, we have fabricated EFC with a new design strategy comprising a passive fuel pumping facility to the anode, efficient anoxic conditions in the anodic chamber and adequate airflow to the cathode for enhancing oxygen reduction reactions, and a connected storage tank for fuel. A bio-nanocomposite paste comprising of the as prepared Graphite-PEG-Sericin ink with magnetic nanoparticle over the supporting carbon cloth electrode was used as the biocompatible enzyme immobilization matrix for harvesting electron in the EFC through direct electron transfer mechanism. The open circuit potential of the device increased to 4.3-fold (3.1V) upon stacking six units of the EFCs in series. The device also rested at a stable state under a light emitting diode as load with a half-life of 372 days (w.r.t voltage) and a coulombic efficiency of 60%. This exceptional high operational stability has been accredited to the efficient anoxic setup in the anodic chamber that supported the stability of AOx, the activity of which was intact even after 49 days of the operation. This work also validated that the prolonged interaction of molecular oxygen with AOx significantly inactivates it without affecting the structural integrity of the enzyme protein. This EFC with improved design and functions is a step forward for achieving practical application as a standalone power supply to small-scale devices.
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    Study of the Laminar Burning Velocities and Instabilities of Premixed Producer Gas-Air/O2 Mixtures at Elevated Pressures
    (2022) Tippa, Muniraja
    This thesis consists of experimental investigations and inferences mainly focused on the effects of Initial pressure and composition variation of producer gas mixtures on combustion characteristics. A detailed literature survey on producer gas composition led to the observation of high variation in the composition. The extent of variation in individual gaseous components was recorded and experiments were designed accordingly. A new test facility which was capable of conducting spherical flame experiments such as Laminar burning velocity study in both constant pressure and volume configurations were constructed. The facility was tested for integrity before commissioning. A detailed post-processing procedure was also developed for processing the recorded data such as image-time and pressure-time data. An image processing algorithm was also developed for extracting flame data from the recorded images using a high-speed shadowgraph technique. Laminar burning velocity, Burned gas Markstein length, Effective Lewis number, Critical Lewis number, thermo-diffusive instability parameters and hydrodynamic instability parameters were calculated. The consolidated results brought insights into the Laminar burning velocity and intrinsic instability characteristics of the producer gas mixtures.
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    Fabrication and Studies of MAPbI3 Perovskite Thin Films and Solar Cells
    (2022) Basumatary, Pilik
    The present thesis contains seven (07) chapters. Chapter 1 introduces metal halide perovskite (MHP) material and MHP based solar cells. Chapter 2 describes the deposition process of MAPbI3 thin films and the fabrication of solar cells. This chapter also briefly describes different characterization techniques used to study different properties of MAPbI3 thin films and the performance of fabricated solar cells. This chapter also details optimizing absorber layer parameters for MAPbI3 perovskite solar cells using the Sentaurus-TCAD simulation tool. Chapter 3 presents studies on the structural, optical, and electrical properties of the MAPbI3 perovskite thin films deposited using a one-step solution method. A detailed study of luminescence features of MAPbI3 perovskite thin films was carried out using photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy at varying excitation wavelength (λex) and emission wavelength (λem) are also discussed in this chapter. Chapter 4 contains studies on the structural, optical, and electrical properties and stability of the MAPbI3 perovskite thin films deposited using the two-step method TE&DC (thermal evaporation and dip coating) and SC&DC (spin coating and dip coating). In addition, transient photocurrent measurements were done to study the charge transport and carrier recombination process in MAPbI3 perovskite thin films at different illumination time duration (30-90 s) and temperatures (25-70 °C) at varying illumination intensity (100-1000 Wm-2). Chapter 5 presents the fabrication and studies on p-i-n planar heterojunction MAPbI3 PSC. The influence of absorber layer thickness variation on the performance of one-step deposited PSC (FTO/PEDOT:PSS/MAPbI3/PCBM/BCP/Ag) and the role of a thin ITO layer as a passivation layer in the two-step deposited PSC (ITO/PEDOT:PSS/MAPbI3/PCBM/ITO/Ag) are discussed in this chapter. Chapter 6 presents the optimization of absorber layer parameters for high-efficiency MAPbI3 solar cells with n-i-p (FTO/SnO2/MAPbI3/Spiro-OMeTAD/Ag) and p-i-n (FTO/PEDOT:PSS/MAPbI3/PCBM/Ag) structures using Sentaurus-TCAD simulation software. Chapter 7 is the final chapter of the thesis, which summarizes the contents of each chapter and gives the conclusion of the work reported in the thesis. The thesis work is concluded with the scope for future work from the present investigation.