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Fukushima: There Are Lessons to Be Learnt, on Both Sides
Enrico Sciubba
Energies , 2011, DOI: 10.3390/en4050818
Abstract: On Friday March 11, at 2.46pm (5.46am GMT), an earthquake of magnitude between 8.9 and 9.1 (Richter scale) hit the superficial submarine crust, about 10 km below sea level and about 120 km south-east of the east coast of Japan. Minutes later, a tsunami wave of up to 10 m reached the north-east coast of Japan. Less than two hours later, the Tokyo Electric Power Company (TEPCO) announced that over 4 million households were without power because of the quake-induced power generation and transmission failures. In particular, TEPCO stated that units 1, 2 and 3 at the Fukushima Daiichi nuclear plant and units 1 to 4 at Fukushima Daini stopped automatically because of the quake. This was the beginning of the worst nuclear accident of the last two decades (the Tschernobyl tragedy dates back to 1986).
Entropy Generation Minima in Different Configurations of the Branching of a Fluid-Carrying Pipe in Laminar Isothermal Flow
Enrico Sciubba
Entropy , 2010, DOI: 10.3390/e12081855
Abstract: The paper discusses a simple multi-variable optimization problem: the bifurcation of a branch of a pipe of circular cross-section with a given initial radius r0 and delivering a given mass flow rate m0.The optimization is performed using an objective function that prescribes the minimization of the entropy generation rate due — in this simple case — only to viscous flow effects within the tubes. Several fundamental simplifying assumptions are made to reduce the problem to a multi-variable optimization in three independent variables: the aspect ratio of the domain served by the flow, the diameter ratio of the primary and secondary branches, and the length of the secondary branch (the location of both the “source” of the fluid and the “sink”, i.e., the place of desired delivery of the fluid, being a datum).It is shown that the solution is strongly dependent both on the aspect ratio and on the diameter ratio, and that the "optimal" configurations display some resemblance to the branching patterns observed in natural structures. The study poses a challenge both to Designers and to Natural Scientists: are the optima suggested by the present procedure compatible with the structures currently used in heat exchangers and flow devices? Are they compatible with the structures observed in nature? No final answer is provided in this preliminary study, but a possible "falsification" procedure is outlined in the conclusions.
Energies—A Trans-Disciplinary Journal
Enrico Sciubba
Energies , 2009, DOI: 10.3390/en20401007
Abstract: It is customary for a new Editor to address the audience of the Journal he is called to contribute to, to define or redefine its aims and scope and to state or restate its scientific and strategic priorities. In my case, this task is made much easier by the excellent relationship that has been established, in the two months since my nomination, with the Editorial Staff and with the Editorial Board of Energies. [...]
A Thermodynamically Correct Treatment of Externalities with an Exergy-Based Numeraire
Enrico Sciubba
Sustainability , 2012, DOI: 10.3390/su4050933
Abstract: The concept of “sustainable development” implies that the environmental externalities unavoidably generated by human activities be reduced to a minimum: In fact, the very definition of “sustainability” leads—as it will be briefly discussed in the paper—to a physically measurable upper limit for untreated discharges. Since the current state of affairs on Earth is far from being sustainable, any proposal for a future scenario that is not substantiated by an accurate assessment of the effects of the environmental externalities is devoid of real sense and ought not to be pursued. The present paper illustrates the application of Extended Exergy Accounting (EEA) to the quantification of such externalities. The exergy flow diagrams of EEA include non-material and non-energetic production factors like labor, and capital and environmental remediation costs, providing a quantitative measure of the amount of primary resources that are cumulatively used in the production of a good or service, and it is shown to provide a wealth of quantitative information to energy managers and planners.
Flow Exergy as a Lagrangian for the Navier-Stokes Equations for Incompressible Flow
Enrico Sciubba
International Journal of Thermodynamics , 2004, DOI: 10.5541/ijot.132
Abstract: A novel variational derivation of the Navier-Stokes equations for incompressible flows is presented and discussed. The Lagrangian density is obtained from the exergy balance equation written for both the (Lagrangian) steady and quasi-stationary isothermal flows of an incompressible fluid. The exergy of a fluid mass (composed of a kinetic, a pressure-work, a diffusive, and a dissipative portion, the latter being the result of viscous irreversibility) is derived first, and it is then shown that a formal minimisation of the exergy variation (i.e. destruction) generates, without recurring to “local potentials”, the Navier-Stokes equations of motion under the given assumptions. The acceleration being held constant, the proposed variational method can be classified as a “restricted” principle. The problem is also briefly discussed both in its historical perspective and in its possible formal and practical implications.
Testimonial to Yehia El-Sayed
Enrico Sciubba
International Journal of Thermodynamics , 2012, DOI: 10.5541/ijot.465
Hybrid Semi-Quantitative Monitoring and Diagnostics of Energy Conversion Processes
Enrico Sciubba
International Journal of Thermodynamics , 2004, DOI: 10.5541/ijot.130
Abstract: This paper presents a novel development in the field of automatic, “intelligent” process monitoring. It is possible to show that some of the limitations of a totally qualitative approach may be overcome by judicious use of reconciled experimental data and/or of the results of numerical simulations. The major problem in basing the response of a monitoring & diagnostic system on a process simulator is that, to run efficiently in real time, the simulator must introduce some simplification in the process model, and therefore its reliability as a source of “process data” is negatively affected. The approach proposed in this paper consists of adopting a mix (thence the attribute “hybrid” in the title) between reconciled data and physical modeling, to extract a limited number of numerical coefficients that introduce a sufficient degree of “quantification” in a qualitative monitoring system. The result is a fast and reliable intelligent procedure that assists human operators by presenting them a preliminary fault analysis based on a limited set of relevant reconciled process variables. An application to a regenerated gas turbine expansion process is discussed in detail.
Entropy Generation Minimization as a Design Tool. Part 1: Analysis of Different Configurations of Branched and Non-branched Laminar Isothermal Flow Through a Circular Pipe
Enrico Sciubba
International Journal of Thermodynamics , 2011, DOI: 10.5541/ijot.293
LES of a Meso Combustion Chamber with a Detailed Chemistry Model: Comparison between the Flamelet and EDC Models
Angelo Minotti,Enrico Sciubba
Energies , 2010, DOI: 10.3390/en3121943
Abstract: The goal of this paper is to contribute to the design of high-performance mesocombustors, a field currently under rapid development, in particular for propulsion, e.g., for UAVs, and micro/meso-electrical power generators. This study is focused on a cylindrical combustor of 29?cm 3, fuelled by methane and air, which provides 2?kW of thermal power. The device was entirely designed and built at the Sapienza University of Rome and coupled with an ultra-micro turbine. Two 3D LES simulations with detailed chemistry are presented. They differ only for the combustion models, so that a model comparison can be carried out. The calculated maximum temperature inside the chamber, the gas exhaust temperature and the combustion efficiency are compared and discussed. The results, reported at two different physical times, show the effects of the different combustion models, which predict different temperature and species concentration maps, but similar values for the combustion efficiency. Thermal, chemical and kinematic maps show that the Eddy Dissipation Concept allows for a more accurate estimatation of the performance parameters for application to first-order design procedures.
Application of the EGM Method to a LED-Based Spotlight: A Constrained Pseudo-Optimization Design Process Based on the Analysis of the Local Entropy Generation Maps
Giorgio Giangaspero,Enrico Sciubba
Entropy , 2011, DOI: 10.3390/e13071212
Abstract: In this paper, the entropy generation minimization (EGM) method is applied to an industrial heat transfer problem: the forced convective cooling of a LED-based spotlight. The design specification calls for eighteen diodes arranged on a circular copper plate of 35 mm diameter. Every diode dissipates 3 W and the maximum allowedtemperature of the plate is 80 °C. The cooling relies on the forced convection driven by a jet of air impinging on the plate. An initial complex geometry of plate fins is presented and analyzed with a commercial CFD code that computes the entropy generation rate. A pseudo-optimization process is carried out via a successive series of design modifications based on a careful analysis of the entropy generation maps. One of the advantages of the EGM method is that the rationale behind each step of the design process can be justified on a physical basis. It is found that the best performance is attained when the fins are periodically spaced in the radial direction.
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