1,721,120 research outputs found
Domestic corpuscular inflaton
No full textThe aim of this paper is to provide a more precise description of the paradigm of corpuscular slow-roll inflation, which was previously introduced by Casadio et al. in [Corpuscular slow-roll inflation, Phys. Rev. D 97 (2018) 024041]. Specifically, we start by expanding the Starobinsky theory on a curved background and then infer the number and nature of the propagating degrees of freedom, both in the true inflationary phase and in a quasi-de Sitter approximation. We correctly find that the particle spectrum contains a transverse trace-free mode and a scalar one. The scalar mode displays a tachyonic nature during the slow-roll phase, due to the instability of the system, whereas it acquires the appropriate oscillatory behavior as the background approaches a critical value of the curvature. These results confirm the fact that the Einstein-Hilbert term acts as a perturbation to the quadratic one, and is responsible for driving the early Universe out of the inflationary phase, thus realizing the inflaton field in terms of pure (corpuscular) gravity
Robust design of a fuel cell - Turbocharger hybrid system
No full textPressurized solid oxide fuel cell systems are a particularly attractive conversion technology for their high electric efficiency, potential for cogeneration applications, low carbon emissions and high performance at part-load. In this work an innovative biofueled hybrid system is considered, where the fuel cell stack is pressurized with a turbocharger, resulting in a system with improved cost effectiveness than a microturbine-based one at small scales. In a previous work, a detailed steady state model of the system, featuring components validated with industrial data, was developed to simulate the system and analyze its behavior in different conditions. The results obtained from this model were used to create response surfaces capable of evaluating the impact of the main operating parameters (fuel cell area, stack current density and recuperator surface) on the performance and the profitability of the plant considering system uncertainties. In this paper, similar but extended response surfaces will be used to perform a multi-objective optimization of the system considering the capital costs of the plant and the net power produced as objectives (turbocharger is fixed in geometry). The impact of the energy market scenario on the optimal design of such a system will be investigated considering its installation in three different countries. Finally, the Pareto front produced by optimization will be used to evaluate the robustness of the top performance solutions
Robust Design of a Fuel Cell - Turbocharger Hybrid System
No full textPressurized solid oxide fuel cell (SOFC) systems are a particularly attractive conversion technology for their high electric efficiency, potential for cogeneration applications, low carbon emissions, and high performance at part-load. In this work, an innovative biofueled hybrid system is considered, where the fuel cell stack is pressurized with a turbocharger, resulting in a system with improved cost effectiveness than a microturbine-based one at small scales. In a previous work, a detailed steady-state model of the system, featuring components validated with industrial data, was developed to simulate the system and analyze its behavior in different conditions. The results obtained from this model were used to create response surfaces capable of evaluating the impact of the main operating parameters (fuel cell area, stack current density, and recuperator (REC) surface) on the performance and the profitability of the plant considering system uncertainties. In this paper, similar but extended response surfaces will be used to perform a multi-objective optimization of the system considering the capital costs of the plant and the net power produced as objectives (turbocharger is fixed in geometry). The impact of the energy market scenario on the optimal design of such a system will be investigated considering its installation in three different countries. Finally, the Pareto front produced by optimization will be used to evaluate the robustness of the top performance solutions
Integration of a flue gas condensing heat pump within a combined cycle: Thermodynamic, environmental and market assessment
No full textAlthough considered as the bridging technology to a decarbonized economy, in the current energy market scenario Combined Cycle Gas Turbine (CCGT) must deal with more demanding requirements of efficiency and flexibility, and often they are not profitable enough to avoid mothballing or closure. The purpose of this work is to propose an innovative solution to enhance the plant flexibility, integrating a combined heat and power CCGT with a flue gas condensing heat pump. The paper firstly evaluates the thermodynamic performances of two possible plant layouts coupled with a District Heating Network, illustrating the respective advantages and disadvantages under different operating conditions. Then, in order to assess the viability of the investment the best solution is selected and a thermoeconomic analysis is performed using as benchmark the same CCGT integrated with a natural gas fed Heat Only Boiler in, a cheaper state of art solution but with a higher carbon footprint. Different energy market scenarios are assessed, considering the effect of different parameters on the integrated CCGT's final profitability. On the environmental side, the heat pump allows reaching an higher global efficiency (average annual efficiency increase up to 5 percentage points), and reducing the annual CO2 emission (−13.9% in the best case). On the economic side, the higher heat pump capital expenditure, with respect to the heat only boiler limits the field of viability of the investment to high gas to electricity price ratios. In particular, the minimum ratio between the cost of natural gas and the average cost of electricity that make the solution viable was found to be between 0.7 and 0.8, a ratio envisaged in case of large RES production share in the grid network. The proposed layout can be of interest for already existing or new CCGT coupled with an heat demand in the temperature range (80–150 °C) as a power to heat solution able to increase the overall system efficiency
Emergency Surgery ina a patient with large spontaneous epidurl hematoma determinig exellent neurological recovery: review of the literature
No full textStudy Design: Case report
Objectives: we report a case of a 75-year-old woman suffering voluminous idiopathic spontaneous
spinal epidural hematomas (SSEH) that was rapidly diagnosed and successfully treated
Methods: Clinical presentation was characterized by sudden and intense back pain that rapidly
evolved into plegia of the right leg and severe paresis of the left leg. Hypoesthesia below T6 and
urinary retention were also present. The MRI showed a significant posterior spinal compression
from T6 through L3 caused by an epidural hematoma that involved 10 metameric levels, extending
for approximately 20 cm, with a maximum thickness of 1.6 cm from T12 to L1.
Results: Within 12 hours, emergency decompressive laminectomy from T10 to L1 was
performed, and evacuation of the hematoma was achieved. The post-operative course and
neurological recovery of the patient were optimal. After discharge, the patient continued the
rehabilitative treatment started during hospitalization, achieving an excellent functional outcome in
one month.
Conclusions: Spinal epidural hematomas SEH are rare clinical findings that can occur following
trauma or spontaneously (SSEH). We describe, to the best of our knowledge, the second most
extensive idiopathic SSEH and the longest with involvement of the dorso-lumbar spine that had a
excellent functional outcome due to emergency decompressive laminectomy which is emphasized in the treatment of these rare pathologies
Emergency surgery in a patient with large spontaneous spinal epidural hematoma determining excellent neurological recovery: Review of the literature
No full textStudy design: Case report. Objectives: We report a case of a 75-year-old woman suffering from voluminous idiopathic spontaneous spinal epidural hematoma (SSEH) that was rapidly diagnosed and successfully treated. Methods: Clinical presentation was characterized by sudden and intense back pain that rapidly evolved into plegia of the right leg and severe paresis of the left leg. Hypoesthesia below T6 and urinary retention were also present. Magnetic resonance imaging showed a significant posterior spinal compression from T6 through L3 caused by an epidural hematoma that involved 10 metameric levels, extending for ∼20 cm, with a maximum thickness of 1.6 cm from T12 to L1. Results: Within 12 h, emergency decompressive laminectomy from T10 to L1 was performed, and evacuation of the hematoma was achieved. The postoperative course and neurological recovery of the patient were optimal. After discharge, the patient continued the rehabilitative treatment started during hospitalization, achieving an excellent functional outcome in 1 month. Conclusions: Spinal epidural hematoma (SEH) is a rare clinical finding that can occur following trauma or spontaneously (SSEH). We describe, to the best of our knowledge, the second most extensive idiopathic SSEH and the longest with involvement of the dorsolumbar spine that had a excellent functional outcome due to emergency decompressive laminectomy, which is emphasized in the treatment of these rare pathologies
Uncertainty Quantification Analysis of a Pressurized Fuel Cell Hybrid System
No full textPressurized solid oxide fuel cell (SOFC) systems are a sustainable opportunity for improvement over conventional systems, featuring high electric efficiency, potential for cogeneration applications, and low carbon emissions. Such systems are usually analyzed in deterministic conditions. However, it is widely demonstrated that such systems are affected significantly by uncertainties, both in component performance and operating parameters. This paper aims to study the propagation of uncertainties related both to the fuel cell (ohmic losses, anode ejector diameter, and fuel gas composition) and the gas turbine cycle characteristics (compressor and turbine efficiencies, recuperator pressure losses). The analysis is carried out on an innovative hybrid system layout, where a turbocharger is used to pressurize the fuel cell, promising better cost effectiveness then a microturbine-based hybrid system, at small scales. Due to plant complexity and high computational effort required by uncertainty quantification methodologies, a response surface (RS) is created. To evaluate the impact of the aforementioned uncertainties on the relevant system outputs, such as overall efficiency and net electrical power, the Monte Carlo method is applied to the RS. Particular attention is focused on the impact of uncertainties on the opening of the turbocharger wastegate valve, which is aimed at satisfying the fuel cell constraints at each operating condition
Uncertainty quantification analysis of a pressurised fuel cell hybrid system
No full textPressurised solid oxide fuel cell (SOFC) systems are a sustainable opportunity for improvement over conventional systems, featuring high electric efficiency, potential for cogeneration applications and low carbon emissions. Such systems are usually analyzed in deterministic conditions. However, it is widely demonstrated that such systems are affected significantly by uncertainties, both in component performance and operating parameters. This paper aims to study the propagation of uncertainties related both to the fuel cell (ohmic losses, anode ejector diameter and fuel gas composition) and the gas turbine cycle characteristics (compressor and turbine efficiencies, recuperator pressure losses). The analysis is carried out on an innovative hybrid system layout, where a turbocharger is used to pressurise the fuel cell, promising better cost effectiveness then a microturbine-based hybrid system, at small scales. Due to plant complexity and high computational effort required by uncertainty quantification methodologies, a response surface is created. To evaluate the impact of the aforementioned uncertainties on the relevant system outputs, such as overall efficiency and net electrical power, the Monte Carlo method is applied to the response surface. Particular attention is focused on the impact of uncertainties on the opening of the turbocharger wastegate valve, which is aimed at satisfying the fuel cell constraints at each operating condition
Performance analysis of a fuel cell hybrid system subject to technological uncertainties
No full textNowadays research in energy field is focused on conversion technologies which could achieve higher efficiencies and lower environmental impact. In such a context, fuel cells in general and pressurized solid oxide fuel cell (SOFC) hybrid systems are attractive for their high electric efficiency, potential for cogeneration applications, low carbon emissions and high performance at part-load. The aim of this work is to perform the design under uncertainty of an innovative turbocharged hybrid system, where a turbocharger is used to pressurize the fuel cell, featuring better cost effectiveness than a microturbine-based hybrid system at small scales (<100kWe). In this study, a response surface of the plant steady-state performance is developed considering the main operating parameters (fuel cell area, stack current density and recuperator exchange surface) as factors to create the metamodel, taking into account the uncertainties related to the turbocharger efficiency and to the ohmic losses of the fuel cell stack. The optimal economic design of such a turbocharged hybrid system is then analysed at off-design conditions, to preliminary assess the operating costs and profitability within the Italian market scenario considering the variability of fuel and electricity prices. Finally, the impact of uncertainties both on plant performance and economics are discussed, showing that both payback period and internal rate of return present a significant variability, mostly due to the uncertainties related to the prices, showing that a proper evaluation of the evolution of the prices along the years should be performed for a proper economic feasibility analysis
Effects of market and climatic conditions over a gas turbine combined cycle integrated with a Heat Pump for inlet cooling
No full textThe growing need of dispatchable units, capable to balance the variable renewable energy electrical production leads to the development of strategies aimed at increasing power plants operational flexibility and global efficiency in part-load operation. A highly efficient heat pump (integrated in a conventional natural gas combined cycle is here proposed as a flexibility enhancement solution. Such concept, applied to power oriented combined cycle, allows to modify the compressor intake temperature with a consequent increase of the power production. While this operation for open cycle gas turbine is beneficial also to electric efficiency, combined cycles’ efficiency is less sensitive to the temperature variation and thus more influenced by the auxiliary consumption. The selection of the proper heat pump size for the proposed layout was based on an optimization process considering both combined cycle and heat pump off-design performance. After a statistical analysis of climatic data and their correlations with energy market condition for the six Italian price zones, the models developed were applied to assess the thermoeconomic potential of the proposed layout. This work highlights how a proper optimization process influences both revenues and size optimization and to highlight how such integrated system can be selected at its best considering typical market and climatic frames. The ratio between the air-cooled heat pump electrical consumption and the electrical combined cycle capacity that maximize power production increase was found to be 1/100. This finding can be extended to the others world Humid subtropical climate and Mediterranean hot summer climates zones. It is underlined how electrical market conditions could jeopardize the installation profits even under favourable climatic potential reducing the optimal economic heat pump size. Using off-design curves and optimization algorithm in performing coupling analysis appears to be more effective, with respect to simplified calculations under unfavourable economic and climate conditions
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