210 research outputs found
Numerical approaches to the study of organic Rankine cycle systems for decentralized applications
No full textOrganic Rankine Cycle systems (ORCs) are a well-known technology to obtain useful work from energy sources whose temperature and thermal power are too low for being exploited with conventional steam Rankine cycles: this is possible because water is replaced by an organic fluid, which is characterized by a lower ebullition temperature, allowing its vaporization and consequent expansion for smaller thermal inputs. Because of this, ORCs make it possible to generate power from a broad series of heat sources, such as low-temperature, renewable energy ones (as in geothermal and solar fields), industrial processes in which hot streams are present and heat rejected by engines through their flue gases. ORCs can also be used for heat and power applications meaning that, in addition to the electrical energy, also the low-grade heat rejected by the cycle (e.g. at the condenser) is used, for example for district heating or just to warm a single flat or house. When the user requires a limited power output, or when the heat source thermal power is limited, micro-scale ORCs have to be used, which are characterized by an electrical power output in the order of 10 kWe and, with respect to the systems of greater size, pose additional issues in terms of choice of the cycle layout, of the components and of the working fluid since manufacturing and maintenance costs have to be kept the lowest possible to allow for an acceptable payback period. Given this, since a few components are specifically designed to operate in this power range, it is common to use off-the-shelf devices, like compressors used as expanders. Then, it would be useful to study the behavior of these single cycle components and their interaction when part of a micro-ORC system, especially when the thermal conditions vary during cycle operations, such as when the electrical load increases or the temperature of the heat source or the cold one decreases.
In this thesis, the study of the ORC technology has been conducted by focusing on those systems and their components which are to be used for power generation in the micro range. An approach based on numerical simulations of the main components of the cycle, as the expander and the heat exchangers, has been of great use to understand what are the main phenomena which affect the performance of an entire system, such as pressure pulsations of the working fluid or its leakages inside the expander. It has been possible to observe this latter issue by working on an experimental micro-ORC test stand which has been operated to test the performances of a prototypal scroll expander: the heat source of the cycle was a hot stream of air, simulating engine flue gases, and the working fluid was circulated in the system by means of a prototype scroll pump.
Before showing the results of the numerical analysis of the single devices, an innovative approach of modeling via Computational Fluid Dynamics (CFD) simulations the behavior of an entire system is reported, since it can provide useful information about how the system layout or the working conditions of a given component can affect the operations of the other devices in the cycle. At first, an idealized cycle has been simulated to study the feasibility of the solution and then a portion of an ORC system has been discretized and the flow field characteristics computed. In those cases in which great computational resources are not available, another possibility has been investigated. By connecting the simulations of the single devices by means of a Python script, it is shown the feasibility of an approach in which the different parts of the system are simulated by means of different 3D CFD tools, allowing for different grid and solver set-up for each of these devices, and letting the behavior of a given component of being conveniently reflected on the one operating downstream of it.I cicli Rankine a fluido organico (ORC) sono una tecnologia che viene notoriamente utilizzata per ottenere lavoro utile da quelle fonti energetiche le cui temperatura e potenza termica sono troppo basse per poterle sfruttare con i convenzionali cicli Rankine: questo è possibile sostituendo l’acqua con un fluido organico, caratterizzato da un’inferiore temperatura di ebollizione che quindi ne consente la vaporizzazione e la conseguente espansione per input termici inferiori. Grazie a ciò, tramite il loro utilizzo è possibile ottenere potenza utile da sorgenti termiche come quelle rinnovabili (ad esempio solare e geotermico), processi industriali in cui flussi termici a bassa temperatura sono presenti così come i gas di scarico dei motori a combustione interna. Inoltre, sistemi ORC possono essere utilizzati per applicazioni cogenerative, in modo da poter fornire all’utilizzatore, oltre all’energia elettrica, anche il calore a bassa temperatura scartato dal ciclo a scopo, ad esempio, di riscaldamento domestico o distrettuale. Quando la potenza richiesta o quella disponibile sono limitate, vengono utilizzati i cicli ORC di taglia micro, caratterizzati da una potenza generata nell’ordine dei 10 kWe i quali, rispetto ai sistemi di taglia maggiore, pongono ulteriori vincoli in termini di scelta del layout d’impianto, tipo di componenti e fluido di lavoro, in quanto i costi di produzione e manutenzione devono essere ridotti il più possibile per consentire all’utente di ammortare le spese sostenute pur con tali valori di potenza generata. Per questo motivo, in tali sistemi è solito l’impiego di componenti non specificatamente progettati per queste applicazioni, come ad esempio compressori volumetrici usati come espansori. È pertanto interessante studiare il comportamento di suddetti componenti per questo utilizzo in condizioni fuori progetto, soprattutto durante i transitori.
In questa tesi, lo studio dei sistemi ORC è stato condotto focalizzandosi proprio sugli apparati di taglia micro; un approccio basato sullo sviluppo di simulazioni numeriche dei componenti principali del sistema, come espansore e scambiatori di calore, è stato utile per comprendere quali siano i fenomeni principali che condizionano le prestazioni di un intero ciclo, come ad esempio le pulsazioni di pressione del fluido di lavoro o le sue fughe all’interno dell’espansore. È stato possibile osservare soprattutto quest’ultimo aspetto operando su un sistema prototipale ottimizzato per il recupero di energia dai gas di scarico di motori a combustione interna, adottante macchine di tipo scroll sia come espansore, sia come pompa.
Prima di mostrare i risultati numerici relativi all’analisi dei singoli componenti del ciclo, verrà riportato un approccio originale riguardante, tramite l’utilizzo dello strumento della fluidodinamica computazionale, la simulazione di un intero sistema. In questo modo, è possibile capire come il di questi layout o le condizioni operative di un certo componente influenzino il funzionamento degli altri componenti del ciclo. Per prima cosa, si è simulato un sistema idealizzato per verificare la fattibilità dell’approccio, poi una porzione di un sistema reale è stata discretizzata e di questa è stato determinato il campo di moto all’interno dei componenti. In quei casi in cui le risorse computazionali per svolgere questo tipo di simulazioni non siano disponibili, verrà proposto un ulteriore metodo d’analisi in cui le simulazioni fluidodinamiche dei singoli componenti sono state interfacciate fra loro tramite uno script Python, in modo tale da riflettere una variazione delle condizioni al contorno di un certo componente sul funzionamento di quello posto a monte o valle dello stesso
Experimental and Numerical Characterization of an Oil-Free Scroll Expander
No full textMicro-ORC systems are characterized by low efficiency values, but at the same time could be used as energy recovery systems in domestic applications for which reliability and low noise level represent the biggest challenges. In this paper, an integrated Reverse Engineering (RE)-Computational Fluid Dynamics (CFD) methodology is applied in order to study the adaptation of a commercial scroll compressor to be used as an expander in a micro-ORC system. The analyses reported in this paper consist of: (i) the acquisition of the 5-kW oil-free scroll expander through a RE procedure and its CAD reconstruction, (ii) the set-up of fully three-dimensional transient simulations with the Chimera strategy using the Siemens PLM software, (iii) the validation of the computational analysis by means of experimental tests and finally, (iv) the analysis of the geometry-flow features like flank and axial gaps, coupled with the analysis of the scroll volumetric efficiency and overall performance. Chimera strategy is able to move the computational grid at each time step in order to accommodate the shape and size changes of the gas pockets. The scroll characterization was carried out using both experimental and numerical tests. Six different rotational velocities in the range of (400 - 2400) rpm with a fixed pressure level (7.5 bar) were tested for validating the numerical model using air as a working fluid. The numerical model was then used to calculate the scroll expander performance operating in an existing ORC system with R134a as working fluid
Factors and associations for physical activity in severely obese adults during a two-year lifestyle intervention
No full text<p>First author: Randi Jepsen. </p
Must be treated with respect: evolving ethics and curation of Mesoamercian human remains
No full textThis paper explores the ethical protocols for the handling of human remains sourced in Central America and stored in academic collections within the United States. Although all such institutions profess a commitment that osteological remains “Must be treated with respect,” the definition of what constitutes “respect” is often subjective. My research and data collected will draw upon the international mandates that govern the exportation, storage, study, and conservation of human remains with attention to three aspects that contribute to the legal framework in which human remains fall: 1) The laws and where they originate; 2) The organizations that maintain these laws; and 3) The extent by which these laws are applied and enforced. I will compare varying internal policies directed towards the conservation and handling of human remains in four academic institutions. As these policies and practices are necessarily institution-specific, they will be compared to demonstrate areas of significant alignment and areas of contrast. The ultimate goal is to establish how following ethical guidelines can become a sustainable feature in archaeological practice by crafting a framework in which ethical principles are designed in such a way that they can have a positive impact on the quality of scientific data. This position is supported by a demonstration of how standardization in ethical issues has consequences for the standardization in the scientific method and long-term conservation of remains. Other improvements discussed include the possibility for enhanced international cultural diplomacy to impact the overall discipline of archaeology in the public perception of its role as a steward of important cultural heritage.M.A.Includes bibliographical referencesIncludes vitaby Randi Renee Ragsdal
The search for the chimera
No full textSession 1 Mr. Randi will give an update of his lecture to the American Physical Society on the occasion of his award of the 1989 Forum Prize. The citation said: "for his unique defense of Science and the scientific method in many disciplines, including physics, against pseudoscience, frauds and charlatans. His use of scientific techniques has contributed to refuting suspicious and fraudulent claims of paranormal results. He has contributed significantly to public understanding of important issues where science and society interact". He is a professional magician and author of many books. He worked with John Maddox, the Editor of Nature to investigate the claims of "water with memory"
Interplay between European regulation and national policies in biodiversity conflict reconciliation
No full textSuccessful public conservation policies at various governmental levels have increased some populations of protected species to the extent that they are causing damage to human activities. As a reaction public authorities are developing biodiversity reconciliation policies. Finland and Germany have both created reconciliation policies including a package of measures like management of population, support of technical measures and compensation for damage. All these measures are affected by European policy and law, though no special reconciliation policy has been adopted at European level. This article explores the options European legislation offers and the restrictions it imposes on member states. Based on experiences with German and Finnish biodiversity reconciliation policies, the interrelationship between European and national regulation is elaborated, leading to suggestions for better coordination of reconciliation policies between different governmental levels. --Biodiversity conflict reconciliation,European regulation,fisheries and aquaculture,local damage management,nature conservation,policy instruments
The perks of being bold: Overconfidence predicts persistence
No full textOverconfidence is a widely researched bias that most people exhibit across a broad range of domains. Most of the past research has focused on the negative, dangerous consequences of overconfidence. In the present studies, following recent work that has identified some advantages of overconfidence, we explored persistence as an additional advantage. In the present research, overconfidence is operationalized as the degree to which self-assessed performance exceeds actual performance. Performance on each task was incentivized. We examined overconfidence and persistence in three different domains: logical reasoning, creative thinking, and effort expenditure. Across two studies (Ns = 304 and 306), evidence showed that overconfidence in one’s performance predicted a greater willingness to invest time and effort in working on all three tasks. Moreover, we also explored several personality predictors of overconfidence. The results showed that narcissism, risk seeking, and pride predicted higher levels of overconfidence, though some variation existed across tasks. These results suggest that overconfidence is associated with positive gains like persistence, which is in turn associated with success and aids the acquisition of valuable resources.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2020-08-01The student, Randi Vogt, accepted the attached license on 2018-07-06 at 10:23.The student, Randi Vogt, submitted this Thesis for approval on 2018-07-06 at 10:53.This Thesis was approved for publication on 2018-07-06 at 11:05.DSpace SAF Submission Ingestion Package generated from Vireo submission #12754 on 2018-09-27 at 11:36:17Made available in DSpace on 2018-09-27T16:47:25Z (GMT). No. of bitstreams: 2
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Total Artificial Heart: A Retrospective Multiple-Case Analysis of Occupational Therapy in a Quaternary Hospital
No full textAbstract
Date Presented 3/31/2017
A retrospective multicase study of functional outcomes was done with patients with an implanted total artificial heart. Results show improved function with occupational therapy provided postoperatively. Knowledge and evidence can be used to develop and implement interventions for this population.
Primary Author and Speaker: Hannah Oldenburg
Additional Authors and Speakers: Jennifer Bergstrom, Gina Christensen
Contributing Authors: Caitlin Polley, Randi Privette, Maureen Musselmann, Mary Pyffereon, Charles Brannon</jats:p
Improving Traumatic Brain Injury Outcomes: Early Identification and Management of Paroxysmal Sympathetic Hyperactivity
No full textAbstract
Background: Paroxysmal sympathetic hyperactivity (PSH) can occur in patients with acutely acquired brain injury and is associated with mortality, poor clinical outcomes, prolonged hospitalizations, physical disability, and increased healthcare costs. The most common cause of PSH syndrome is traumatic brain injury (TBI). Symptoms consist of hyperthermia, diaphoresis, arterial hypertension, tachycardia, tachypnea, and extremity motor dystonic posturing, often in response to evoked stimuli and occurs in 8% to 33% of TBI patients. Critical care nurses are at the forefront of providing direct patient care to TBI patients and are often the first to identify PSH.
Purpose: The objective of this quality improvement project (QI) was to comprehensively evaluate the literature and provide evidence-based information regarding PSH to nurses, advanced practice providers, residents, and trauma/surgical critical care attendings who deliver care to TBI patients in a surgical trauma intensive care unit (ICU).
Methods: An integrative literature review was performed, PowerPoint was created to conduct seminars, and pre-and post-test analyses were obtained to evaluate knowledge attainment of the management of PSH. The overall goal of the educational seminars was to increase scores by \u3e20% for adequate knowledge attainment, which was obtained. Limitations: high acuity patients, staffing schedules, seminar timing, and lack of perceived educational need by providers.
Conclusion: This QI project identified a gap in clinical knowledge and practice surrounding PSH in TBIs. Continuous education on PSH is imperative to promote early identification and timely management for prevention of secondary brain injury and worsening healthcare outcomes in this complex patient population.
Author Contact Information
Randi Rockwell
[email protected]
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