11 research outputs found
Coproduction with Molten Carbonate Fuel Cells: Exploring the feasibility of coproducing hydrogen and electricity from internal reforming molten carbonate fuel cells
No full textThe concept of coproduction has been explored in combined heat and power applications. It is a method of improving the efficiency of the energy generating system by utilising waste heat. In the coming years hydrogen is expected to play an important role in decarbonization as it does not emit greenhouse gas at the point of application. Hydrogen today is primarily generated from fossil fuels and the processes of producing hydrogen are energy intensive, while also emitting large quantities of greenhouse gases into the atmosphere. As the amount of hydrogen generated today is limited, it has restricted the growth of industries such as the automobile industries producing fuel cell vehicles that are to use hydrogen as fuel. In this thesis report a coproduction concept using high temperature molten carbonate fuel cell has been examined. The molten carbonate fuel cells operate at very high temperature, and it is possible to utilise the waste heat for internal reforming reaction of a fuel such as natural gas to liberate hydrogen required by the fuel cell. Excess hydrogen can also be produced from such fuel cell systems when the fuel utilisation in the fuel cell is reduced. This concept has been studied with solid oxide fuel cells and a paper published in 2008 by Hemmes et al. titled "Flexible Coproduction of Hydrogen and Power Using Internal Reforming Solid Oxide Fuel Cells System" has served as the inspiration for this thesis report. Three modes of operations have been simulated in this thesis on the Cycle-Tempo software with varying fuel utilisations, similar to what has been shown with the solid oxide fuel cells in that paper. With molten carbonate fuel cells, overall efficiency of up to 80% was obtained in terms of electricity and hydrogen coproduction. By doing so it is also possible to produce overall power output of nearly three times than what can be achieved by conventional electricity production. The results obtained have also been compared with the solid oxide fuel cells in this report. While high coproduction efficiencies for flexibly coproducing hydrogen and power have been shown to be possible, other factors would also play important roles in the success of this technology. In this report some of those factors such as the status and expected growth of the hydrogen market, molten carbonate fuel cell market, role of actors, role of policy makers have also been examined. As this technology does rely on a fossil fuel that is natural gas, the benefits of using natural gas in hydrogen production has also been highlighted along with the positive effects these systems could have on the society
Exploring the Possibility of Using Molten Carbonate Fuel Cell for the Flexible Coproduction of Hydrogen and Power
No full textFuel cells are electrochemical devices that are conventionally used to convert the chemical energy of fuels into electricity while producing heat as a byproduct. High temperature fuel cells such as molten carbonate fuel cells and solid oxide fuel cells produce significant amounts of heat that can be used for internal reforming of fuels such as natural gas to produce gas mixtures which are rich in hydrogen, while also producing electricity. This opens up the possibility of using high temperature fuel cells in systems designed for flexible coproduction of hydrogen and power at very high system efficiency. In a previous study, the flowsheet software Cycle-Tempo has been used to determine the technical feasibility of a solid oxide fuel cell system for flexible coproduction of hydrogen and power by running the system at different fuel utilization factors (between 60 and 95%). Lower utilization factors correspond to higher hydrogen production while at a higher fuel utilization, standard fuel cell operation is achieved. This study uses the same basis to investigate how a system with molten carbonate fuel cells performs in identical conditions also using Cycle-Tempo. A comparison is made with the results from the solid oxide fuel cell study.Economics of Technology and InnovationProcess and Energ
Quantifying time-dependent uncertainty in the BEAVRS benchmark using time series analysis
No full textThesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 85-87).Advances in computational capabilities have enabled the development of high-fidelity methods for large-scale modeling of nuclear reactors. However, such techniques require proper benchmarking and validation to ensure correct and consistent modeling of real problems. Thus, the BEAVRS benchmark was developed to legitimize the advancements of new 3-D full-core algorithms in the field of reactor physics. However, in order to address the issue of BEAVRS uncertainty quantification (UQ) of Uranium-235 fission reaction rate data, this thesis proposes a new method for measuring uncertainty that goes beyond merely conducting statistical analysis of multiple measurements at one given point in time. Instead, this work hinges on principles of time series analysis and develops a rigorous method for quantifying the uncertainty in using "tilt-corrected" data in an attempt to evaluate time-dependent uncertainty. Such efforts show consistent results across the four dierent methods and will ultimately assist in demonstrating that BEAVRS is a non-proprietary international benchmark for the validation of high-fidelity tools.by Shikhar Kumar.S.M
Nonlinear development of centrally ignited expanding flames in laminar and turbulent mediums
No full textEmbargo set by: Seth Robbins for item 115870
Lift date: 2022-08-27T00:51:40Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemAuthor requested closed access (OA after 2yrs) in Vireo ETD systemLimited"Large scale premixed flames are always susceptible to hydrodynamic instabilities. It is amongst one of the most prominent intrinsic flame instabilities. The presence of the hydrodynamic instability was originally discovered in the pioneering works of Darrieus and Landau more than eighty years ago, and the Darrieus-Landau (DL) instability was named in their honour. In both works, the flame treated as a surface of density discontinuity, segregating the burnt mixture from unburnt gases and propagating at a constant speed, the unstretched laminar flame speed, was used to demonstrate that planar deflagrations were unconditionally unstable. The DL instability has numerous implications in premixed combustion as it promotes the creation of corrugated flames with sharp cusps which enhance the flame surface area leading it to propagate at a speed larger than the laminar flame speed. Landau argued that the instability all by itself could lead to the emergence of turbulent motion and thus turbulent flame propagation at relatively low Reynolds numbers (based on the flame radius). Subsequent experiments have since verified that, in the absence of any significant external disturbances, obstacles or boundaries, expanding cylindrical and spherical flames originating from weak ignition sources are indeed unstable, will self-accelerate and eventually self turbulise albeit at far larger Reynolds numbers than originally postulated. Physically, this instability prevents a planar flame from becoming flat and an expanding flame from propagating smoothly.
In this work, the propagation of expanding flames is examined within the context of the hydrodynamic theory using an embedded manifold methodology, one capable of handling multi-valued and disjointed surfaces that often arise from flame-turbulence interactions. The asymptotic model was formally derived from first principles by exploiting the disparity in length scales between the flame thickness (characterised by a diffusion length scale) and the much larger local radius of curvature. While phenomologically similar to Darrieus-Landau's treatment of the premixed front, the flame speed incorporates a first order correction which depends upon the local geometrical properties of the flame and the underlying flow conditions, more succinctly referred to as flame-stretch. The dependence on the local stretching experienced by the flame is tempered by a coefficient on the order of flame thickness which mimics the effects of diffusion and chemical reactions occurring inside the flame zone. This parameter has since become known as the Markstein length.
A systematic study has been carried out examining the three regimes of flame propagation, which in increasing orders of complexity include: a) a smoothly expanding laminar flame; a regime devoid of flame instability, and more concisely referred to as the ``linear regime'', b) a ``nonlinear regime'' wherein disturbances on the flame surface grow and devolve into characteristic cusp-like structures that protrude into the burnt gas and punctuate the flame surface even under laminar flow conditions, a hallmark of the DL instability, and c) a turbulent regime where there is an interplay between the effects of a decaying isotropic turbulent flow-field and the DL instability itself.
Linear analysis conclusively demonstrates that for mixtures with Lewis numbers above criticality, thermo-diffusive effects have a stabilising influence at flame radii comparable to the flame thickness. The amplitude of any small amplitude disturbance will initially decay and only begin to grow once the flame becomes of a certain size; an observation consistent with experimental studies. Predictions of the critical flame radius marking the onset of instability are obtained as functions of the Markstein length and thermal expansion parameters. The numerical scheme proposed is able to replicate this behaviour and suitably capture the critical radius demarcating the onset of instability. There also exists a critical wavenumber disturbance that will be first mode to become excited. It is hypothesised that this wavenumber will dictate the cellular structure that will be observed as the long-time solution. Correspondingly, once the flame transitions to cellularity, the temporal variation in the propagation speed is seen to become non-monotonic. The investigation also examines the early response and long-time evolution of an initially laminar flame kernel subjected to the turbulent velocity fluctuations of an underlying flow field. In the wrinkled and corrugated flamelet regimes of turbulent combustion, distinct regimes of turbulent propagation exist, depending upon the influence that the DL instability exerts. Emphasis is placed on understanding the effect of differing turbulent flow characteristics (intensity and eddy size) on the burning rate and on isolating the role that the instability plays. Normalising the turbulent flame area with respect to the area of an unperturbed flame of equal mean radius reveals an asymptotic behaviour in time of the turbulent flame speed, allowing preliminary attempts to be made at computing a turbulent flame speed based on Damk\""{o}hler's first hypothesis for expanding flames in decaying turbulence."Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2022-05-01The student, Shikhar Mohan, accepted the attached license on 2020-04-19 at 10:30.The student, Shikhar Mohan, submitted this Dissertation for approval on 2020-04-19 at 10:40.This Dissertation was approved for publication on 2020-04-24 at 17:19.DSpace SAF Submission Ingestion Package generated from Vireo submission #15002 on 2020-08-25 at 17:40:24Made available in DSpace on 2020-08-27T00:49:57Z (GMT). No. of bitstreams: 3
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Previous issue date: 2020-04-24Embargo set by: Seth Robbins for item 115870
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MultiTune: Dynamic budget allocation for hyperparameter tuning
No full textHyperparameter optimization(HPO) forms a critical aspect for machine learning applications to attain superior performance. BOHB (Bayesian Optimization and HyperBand) is a state of the art HPO algorithm that approaches HPO in a multi-armed bandit strategy, augmented with Bayesian optimization to drive configuration sampling. However, BOHB requires predefined distribution of fidelities for each tuning task. The challenge in this is that it is impossible to define fidelities a priori, since each machine learning model is uniquely complex and requires different amount of compute resources for convergence. Furthermore, in our empirical analysis, we found that each HPO task rendered different performance trajectories on different fidelity (budget) types. Thus, the challenge of defining fidelities also extends to choosing an optimal budget type. To alleviate these challenges, we present MultiTune: a budget allocation scheme that builds on top of BOHB to dynamically define fidelities for optimization. MultiTune incorporates an algorithm to dynamically choose a preferred budget type for an HPO task, coupled with 2D gradient based budget constraint explorations to enable granular definition of fidelities. Through our empirical analysis, we show that MultiTune can consistently converge to a well performing configuration without significant computation overhead
DataSheet1_Exploring the Possibility of Using Molten Carbonate Fuel Cell for the Flexible Coproduction of Hydrogen and Power.PDF
No full textFuel cells are electrochemical devices that are conventionally used to convert the chemical energy of fuels into electricity while producing heat as a byproduct. High temperature fuel cells such as molten carbonate fuel cells and solid oxide fuel cells produce significant amounts of heat that can be used for internal reforming of fuels such as natural gas to produce gas mixtures which are rich in hydrogen, while also producing electricity. This opens up the possibility of using high temperature fuel cells in systems designed for flexible coproduction of hydrogen and power at very high system efficiency. In a previous study, the flowsheet software Cycle-Tempo has been used to determine the technical feasibility of a solid oxide fuel cell system for flexible coproduction of hydrogen and power by running the system at different fuel utilization factors (between 60 and 95%). Lower utilization factors correspond to higher hydrogen production while at a higher fuel utilization, standard fuel cell operation is achieved. This study uses the same basis to investigate how a system with molten carbonate fuel cells performs in identical conditions also using Cycle-Tempo. A comparison is made with the results from the solid oxide fuel cell study.</p
Effect of Row Ratio and Planting Methods on Growth, Yield Performance of Wheat (Triticum aestivum L.) and Mentha (Mentha arvensis L.)
No full textThis study was investigates the effects of row ratio and planting methods on the cultivation of wheat (Triticum aestivum L.) and mentha (Mentha arvensis L.). Mentha is also called Japanese mint, it is an important essential oil-bearing plant of the family Lamiaceae. Essential oil obtained from the leaves used in aromatherapy, flavour, and pharmaceutical industries. Hence, a field experiment was conducted during 2016-17 at the Soil Conservation and Water Management Farm to investigate the response of mentha when intercropped with wheat under various row ratios and planting methods. The trial was laid out in Randomized Block Design (RBD) with three replications keeping one variety of Mentha ‘Shivalik’& Wheat ‘Halna’. The experiment consisting of nine treatments are T1:Sole Mentha direct sowing (50 cm apart), T2:sole mentha transplanting (50 cm apart), T3:sole wheat (25 cm apart), T4:wheat+mentha (1:1), T5:wheat+mentha (1:1), T6:wheat+mentha (2:2), T7:wheat+mentha (2:2), T8:wheat paired+mentha (2:3), T9: wheat paired+mentha (2:3). The results showed that the highest number of leaves per plant (457 at maturity) and number of branches per plant (80.97 at 90 DAS) were observed in Wheat Paired+Mentha (T9). The sole wheat (T3) exhibited the maximum number of tillers per plant in wheat (6.20). wheat+mentha (T4) had the highest yield attributes for wheat. The higher herbage yield of mentha (177 q/ha) was found in wheat+mentha (T7). Sole Mentha direct sowing (T1) gave the highest oil content (0.85%) and oil yield (163.35 l/ha) of mentha. The wheat paired+mentha (T8) recorded the highest equivalent oil yield (189.97 l/ha) and land equivalent ratio (1.50). However, sole wheat (T3) yielded the maximum grain yield (39.80 q/ha), straw yield (74.52 q/ha), and harvesting index (38.95%)
Under Reporting Practices of Adverse Drug Reaction: An Observational Study Corresponding Author
No full textABSTRACT Objective: The present study was to estimate extend or percentage of Adverse Drug Reaction (ADR) reporting in Bhopal region at pilot level. Our main objective is not only to find out the reporting status but is to find out the possible causable reason behind the under-reporting of the suspected ADRs by the private practioners. Methods: A questionnaire based short intensive survey was conducted on the private practioners of the Bhopal region. The questionnaire consists of ten questions from which most of it was totally based and design so that we can get the much close and exact reason for the under-reporting practices. The survey was conducted by a random sample of approximate 150 private practioners of the Bhopal region. Results: The overall reporting percentage was only approximately 7% or the under-reporting percentage was approximately 93% that clearly indicates somewhat a considerable obstacle for the roadmap forecast by the CDSCO in collaboration with IPC. Conclusion: The under-reporting percentage was quite considerable (93%) so as to look after the issue to resolve or for improvement. As majority of population have their reliability and first exposure of treatment via private practices. So ADRs at this level if reported earlier in the phase of drug exposure could be better controlled as per quality concern and also its global exposure may be prevented
Life cycle sustainability assessment of crops in India
No full textIn India, the modernization in the agricultural sector is continuously growing to meet the food demand of rising population. However, along with addressing hunger, modern agriculture impacts the ecosystem, human health, and resources, due to huge consumption of agrochemicals, and emission-intensive farming hence urges sustainable assessment. Till now, no impact assessment is reported on world's second-largest agricultural country- India. This paper is the first of its kind in evaluating the impact of the cultivation of 21 commonly grown crops that possess high production and emissions in India. The results were discussed in the order of impact parameters in respective years with possible causes and remedial measures. The results showed that rice has topped in maximum indices followed by sugarcane, wheat, and banana. The study forecasted that coconut played a concentrated role in global warming, while potato and sugarcane have a higher impact on water and ozone depletion, respectively. The outcomes of this study suggested appropriate improvements in farming practices, which can bring the emissions down and make the system more sustainable. Besides, these 18 indices were individually assessed for their connection with the 17 sustainable development goals (SDGs) in the aspects of agricultural activities to select the appropriate indices to measure the agricultural sustainability along with the identification of gaps to upgrade the existing indices or formulate a new one. Subsequently, this helps in achieving the SDGs in India with the least impact on the environment without compromising the socio-economic aspects involved in crop production and agricultural systems. © 2021 The Author
Uncovering the knowledge flows and intellectual structures of research in technological forecasting and social change: A journey through history
No full textTechnological Forecasting and Social Change (TF&SC) celebrates its fiftieth anniversary this year. The anniversary represents an appropriate time for an introspective analysis of the journal's history and impact. This study presents a bibliometric analysis of TF&SC in terms of how often TF&SC is cited by other journals (citation outflow), how often other journals are cited by TF&SC (citation inflow), citations by Web of Science and SClmago disciplinary categories, most-cited articles in TF&SC, co-citation of journals, and co-occurrence of author keywords. Analysis is conducted by using the Web of Science (WOS) database and Visualization of Similarities (VOS) viewer software. The incoming versus outgoing citation patterns identified here suggest an asymmetry in the knowledge flows of TF&SC. Papers published in TF&SC have increasingly cited knowledge from journals in Technology and Innovation Management (TIM), Engineering, and Decision Sciences, but the journal impacts a different set of disciplinary categories such as Energy, Environmental Sciences, and Social Sciences. From 1969-2018, Innovation, Foresight and Forecasting feature as the most popular keywords. Focus on topics such as Patents/Patent Analysis, Climate Change, Sustainability, and Energy seems to have intensified in the last decade.
Findings suggest that focus on two countries of interest, India and China, is emerging in research published in TF&SC. Different regions of the world can be expected to place differential emphasis on various topics based on their socioeconomic-technological environments. The journal needs to be receptive to this diversity of perspectives from a growing community of scholars worldwide
