PhD Theses (Energy Science and Engineering)
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Item Process Development for Microalgal Cultivation System Towards Enhancement of CO2 Fixation and Biochemical Production Efficiency(2024) Chauhan, Deepesh SinghMicroalgae present a promising avenue for CO₂ sequestration and biofuel production due to their rapid growth and high lipid content. However, their commercial viability faces challenges, such as low CO₂ capture efficiency, sensitivity to environmental stresses, and high water and nutrient demands. This thesis aims to overcome these challenges by focusing on strain selection, optimizing cultivation conditions, ensuring CO₂ utilization stability, achieving high biomass productivity, cost-effective harvesting, and water reuse strategies.Item Design, Optimization, and Intensification of a Biological Gas to Liquid (BioGTL) Process for Methane Conversion to Methanol(2024) Priyadarshini, AradhanaThis study investigates the methane bioconversion to methanol using biological gas-to-liquid (BioGTL) technique and especially addresses the United nation’s SDG 7 (Affordable and clean energy) and SDG 13 (Climate action). The principal aim of the present thesis is to design, optimize and intensify a bio-process for conversion of methane into methanol. Chapter 1 introduces and discusses impact of methane in climate change and why methane bioconversion to methanol is essential. The critical bioconversion of methane to methanol is made possible by soluble methane monooxygenases (sMMO) and particulate methane monooxygenase (pMMO). Chapter 2 studies and reports the potential of methanotrophic consortium enriched from rice field soil in methanol production. The consortium achieved a high methanol production titre of 130 mM (4.16 g/L). The maximum methanol titre of 160 mM was obtained using the Methylomicrobium buryatense 5G. Further, Methylotuvimicrobium buryatense 5GB1C was studied for their methanol accumulation capability in Chapter 3. This study attempted to maximize the methanol production using statistical optimization of the crucial fermentation parameters (phosphate buffer concentration, pH and temperature) resulting in a methanol titre of 8.54 mM in 24 h. Further investigation employed a methanol dehydrogenase inhibitor to prevent methanol breakdown, leading to an increased accumulation of 10.37 mM. The process was scaled up to a 3.7 L bioreactor, and significantly improved both methanol concentration (23.7 mM) and methane conversion efficiency (47.8%).Item Applications of Passion Fruit Extracts as Bioactive Pharmaceuticals, Biodiesel Additive for Oxidation Stability and Corrosion Resistance(2023) Purohit, SukumarFruits and vegetables are frequently consumed because of their contents - minerals, dietary fibers, vitamins, and antioxidants which are beneficial for the health. In developing countries there are very limited to negligible waste management policies. As a result, most of the waste materials are directly exposed to the open environment causing severe environmental pollution. Agro-waste materials are having enormous potential for valorization as they contain abundant bioactive phytochemicals, including polyphenols, anthocyanins, tannins, glycosides, vitamins, alkaloids, and many more. These compounds have also profound therapeutic values as antidiabetic, antimicrobial, anticancer, and so on. Moreover, the natural antioxidant extracted from this waste can also be utilized as natural additives to second-generation biofuels (biodiesel) for their quality improvement as oxidative stabilizers and corrosion inhibitors. Northeast India is bestowed with two biodiversity hotspots with variety of flora and fauna. Passion fruit is a less popular plant cultivated in these regions. The main edible part of this fruit is its flavourful and nutritious juice. The rest of the parts i.e. rind and seed make upto 60% of the total weight of fruit and are disposed directly without any treatment.Thus, the present work aims to explore the antioxidant potential of these two varieties of passion fruit (yellow and purple passion fruit) from Northeast India for various applications. The entire thesis work has been divided into four major parts. The first part of the thesis presents the collection, morphological and physico-chemical characterization of the rind and seed of yellow passion fruit and purple passion fruit collected from Northeast India. The second part of the thesis discusses the phytochemical profile of the rind and seed extracts from yellow and purple passion fruit and their role as antioxidant and antibacterial agents. In this context, the samples were extracted using four different solvents such as ethyl acetate, acetone, methanol and water. Phytochemical mining study revealed presence of many phytochemicals from the passion fruit sample. Further, in the subsequent part of the thesis, role of the antioxidant rich passion fruit extracts for increasing oxidation stability of different biodiesel was elaborated. Biodiesel is prone to oxidation because of high moisture content and unsaturated fatty acid composition.Item Aerodynamic Design and Wind Tunnel Testing of Small Horizontal-axis Wind Turbine for Multirotor Configurations(2023) Siram, OjingThe present investigation explores the applicability of small horizontal-axis wind turbines (SHAWTs) to be employed as a power-generating source in places where Energy Science and Engineering demand isminimal or as a potential off-grid power source. The design and testing of SHAWT have been carried out at low λ (0.5 < λ < 6) and low Re (0.3×105 ≤ Re ≤ 3×105) conditions. The rotor blades were designed using the blade element momentum theory and fabricated using the 3D printer. The rotors’ performance was tested in the wind tunnel using the rotary torque sensor (RTS). Based on the literature review, airfoil E216 (M1), SG6043 (M2), NACA63415(M3), and NACA0012 (M0) have been chosen for developing the model rotors. From BEMT analysis and experimental investigation, the M1 rotor shows maximum power coefficient of 0.37 and 0.34, respectively. The complexity of the BEMT rotor necessitates the development of a non-BEMT rotor, which in the present study are straight and linear tapered (SLT rotors). The SLT rotors with the root-to-tip chord (Cr/Ct) of 1:1 show favourable results. Furthermore, an in-depth investigation of wake propagation using particle image velocity (PIV) has been carried out. The near wake (x/R < 6) study shows the formation of a W-shape. The time-resolve and timeaveraged stream wise PIV assessment reveal Gaussian-like (skew) distribution and the presence of two opposite crests, marking the flow movement. The high-fidelity PIV data were then used to develop an ANN-based wake model. It is observed that experimental and ANN-based models can produce much better and more reliable results than their analytical counterparts.Item Study of Algal Biofilm to Enhance Biomass and Lipid Accumulation(2023) Devi, Nongmaithem DebeniMicroalgal biomass for the production of biodiesel is emerging at the forefront in the relevant research realm. They are considered the most versatile biomass due to certain characteristics such as (1) the ability to convert carbondioxide (CO2) into biomass through transesterification, (2) short life-cycle, (3) high growth rate, and (4) microalgae cultivation that does not compete for fertile fields with food crops. Biodiesel production can be improved by increasing biomass and lipid yield (LY), as well as optimizing downstream processing. Studies have shown various approaches to increase microalgae biomass and lipid production. High biomass productivity (BP) and LY depends on the potential of strains and cultivation strategy. The goal of this thesis is to investigate the potential of microalgae species that are native to North-Eastern, India for biodiesel production and to assess their ability to treat wastewater and produce biomass that can be used for animal feed. The freshwater microalga, Scenedesmus sp. DDVG I was selected as a potential strain for biomass production. The freshwater cyanobacterium, Limnothhrix sp. DDVG II was used as an auto-flocculating strain. The BioEnergy Science and Engineering Lab isolated both strains from a swampy region of the Indian Institute of Technology Guwahati (IITG), Indai. DDVG I and DDVG II microalgal isolates were molecularly characterized using 18S and 16S rRNA gene sequence analysis. The sequences were submitted to NCBI GenBank as MN630585 and MN630310, respectively. DDDVG I and DDVG II strains grew the fastest in a normal BG11 medium at pH 7 and 27 °C, with specific growth rates of 0.12±0.005 d-1 and 0.11±0.00 d-1, respectively. Further supplementation of the medium with 1.05 g/L urea, 0.04 g/L K2HPO4, and 6 g/L glucose resulted in increased biomass and LY of up to 8.5 g/L & 39.5% for DDDVG I and 3.3 g/L & 19.9% for DDVG II, respectively.Item Studies on Spirulina Species NCIM 5143 for Microbial Fuel Cell Applications(2023) Quadir, Mohd Golam AbdulThis study utilizes Spirulina species NCIM 5143 procured from National Collection of Industrial Microorganisms, Pune, India. The phylogenetic analysis from 16S rRNA revealed its identity closer to Spirulina subsalsa BGLR6. The species was cultured in inorganic Zarrouk medium supplemented with trace elements in white light of 2500 lux at temperature of 32°C at 180 revolutions per minute. The specific growth rate and doubling time were found to be 0.0771 day-1 and 8.98 days respectively. The species was found to be a helical filament in structure with a diameter of 3 μm and pitch length of 1 μm. It exhibited gliding motility and moved towards light exhibiting phenomenon of positive phototaxis. This property influences the pattern of biofilm formation by the cyanobacteria and the configuration of filamentous cells within it, depending on the direction of illumination. The static culture always formed a network of filaments on walls that developed into biofilms over time and stuck to the walls. This natural biofilm formation capacity was utilized and the wet weight was inoculated into an H- type biofuel cell setup, leading to the formation of a biofilm over the electrodes. Interestingly, a subpopulation of bacteria was detected in the vicinity of the Spirulina filaments, and a few cells were directly attached to the filament structures. This close physical association indicates that crucial metabolite and nutrient exchange might occur between the host and bacterial cells. Four distinct heterotrophic colonies were isolated and identified through 16S rRNA sequencing as Halomonas saliphila, Halomonas campaniensis, Alcanivorax pacificus, and Pelagibacterium lentulum. We inferred, that these pure culture strains were the dominant members of the Spirulina-associated bacterial community as they could form colonies on the zarrouk medium plate devoid of any organic carbon source, thriving on residual extracellular organic carbon and metabolites exuded by the phototrophic host (Spirulina). These associations indicate a copiotrophic habitat typical of a phytoplankton bloom or matured phototrophic biofilm. We believe that this combination of predominant bacterial species isolated by us might be involved in efficient carbon and nitrogen cycling assisting the sustained growth of the host cyanobacterium (Spirulina subsalsa).Item Development and Performance Assessment of Gaseous fuel based Porous Radiant Burners(2023) Kumar, M ArunThis thesis presents the development and performance testing of Porous Radiant Burners (PRBs) using different fuels, including LPG, natural gas, and biogas, for cooking and industrial applications. These PRBs show promise in enhancing thermal efficiency and reducing emissions compared to conventional burners. In addition, an analytical model was developed to determine the factors influencing the primary air entrainment in a PRB. And experimental investigations were performed to check the validity of the developed analytical expression. Further, performances of the developed PRBs were assessed in terms of thermal efficiency and emissions. Through experimental investigations, it was found that the developed LPG-PRB and NG-PRB, exhibit improved thermal efficiency and fuel savings. Furthermore, a BG-PRB cookstove for domestic use was developed and demonstrated substantial gains in thermal efficiency and reduced emissions compared to conventional biogas burners. Environmental and economic assessments of the developed PRBs were conducted, highlighting the environmental benefits and cost savings associated with the use of these innovative PRBs. This research work contributes to the sustainable Energy Science and Engineering transition and offers practical solutions for cleaner and more efficient Energy Science and Engineering utilization in cooking and Industrial applications.Item Distributed Microgrid System Design and Control Algorithms for Oil and Gas fields(2023) Bishnoi, DeepikaGas flaring is an issue of serious environmental concern worldwide. Globally approximately 100 BCM (Billion Cubic Metres) of natural gas is flared every year, which leads to 400 million tons of CO2 (Carbon Dioxide) emissions and wastage of nearly 20 million dollars annually. The burning of expensive natural gas is not just an economical loss, it also poses a severe environmental threat to the flora and fauna and a risk of health abnormalities for human settlements around oil and gas fields, petroleum refineries, and petrochemical plants. Almost all the gas flaring sites are situated at remote locations because of which unreliable electricity is another major issue faced in the region.Item Design And Fabrication Of Solid State TiO2|Ag Structure For Developing Efficient Plasmonic Photo-Electric Conversion Device(2024) Devi, Kshetrimayum PriyalakshmiThe 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.Item Development and Performance Evaluation of Methanol and Ethanol Operated Cookstoves(2023) Maurya, PratibhaThe 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.Item Design and Development of Hybrid Nanomaterials for Efficient Photocatalysis(2024) Devi, Thongam DebikaWater 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.Item Optimal Operating Parameters for Performance Improvement of a Biogas Fueled Spark Ignition Engine(2023) Hotta, Santosh KumarThe 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.Item Exploring potential genetic routes for enhancing lipid accumulation in microalgae for biofuel application(2022) Sharma, Prabin KumarTo 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.Item Surface Heat Flux Recovery during Short Duration Experiments–Conceptual Demonstration from Probe Design to Soft computing Analysis(2022) Rout, Anil KumarRecovery 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 ANFISItem Studies on Metal Hydride Based Hydrogen Storage and Purification Systems(2022) Kumar, AlokThe 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.Item Development and Characterization of Advanced FO Membranes using Exfoliated 2D Nanomaterials for Energy Generation and Separation Processes(2023) Deka, PriyamjeetWater 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 demeritsItem Development and Performance Evaluation of a Medium Scale Clustered LPG Stove with Porous Radiant Burner(2022) Deb, SunitaThis 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.Item Waste peels as low-cost substrate for microalgal cultivation under a biorefinery approach(2023) Malakar, BarasaThe 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.Item Prospects of Energy Production from Lignocellulosic Biomass, Solar Photovoltaic and Hybrid Systems(2023) Buragohain, SachankarFossil 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.Item Performance Investigation and Optimization Studies on a Solar-Assisted Liquid Desiccant Air Conditioning System(2021) Bhowmik, MrinalLiquid 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.