41 research outputs found
Thermodynamic optimization subsumed in stability phenomena
[EN]In the present paper the possibility of an energetic self-optimization as a consequence of
thermodynamic stability is addressed. This feature is analyzed in a low dissipation refrigerator
working in an optimized trade-off regime (the so-called Omega function). The relaxation after a
perturbation around the stable point indicates that stability is linked to trajectories in which the
thermodynamic performance is improved. Furthermore, a limited control over the system is analyzed
through consecutive external random perturbations. The statistics over many cycles corroborates the
preference for a better thermodynamic performance. Endoreversible and irreversible behaviors play
a relevant role in the relaxation trajectories (as well as in the statistical performance of many cycles
experiencing random perturbations). A multi-objective optimization reveals that the well-known
endoreversible limit works as an attractor of the system evolution coinciding with the Pareto front,
which represents the best energetic compromise among efficiency, entropy generation, cooling
power, input power and the Omega function. Meanwhile, near the stable state, performance and
stability are dominated by an irreversible behavior
Propagación del conocimiento: de la investigación a la docencia. Aplicación al concepto rendimiento en condiciones de máxima potencia
Memoria ID-003. Ayudas de la Universidad de Salamanca para la innovación docente, curso 2013-2014
Compartmental Learning versus Joint Learning in Engineering Education
[EN]Sophomore students from the Chemical Engineering undergraduate Degree at the University
of Salamanca are involved in a Mathematics course during the third semester and in an
Engineering Thermodynamics course during the fourth one. When they participate in the latter
they are already familiar with mathematical software and mathematical concepts about numerical
methods, including non-linear equations, interpolation or differential equations. We have focused
this study on the way engineering students learn Mathematics and Engineering Thermodynamics.
As students use to learn each matter separately and do not associate Mathematics and Physics, they
separate each matter into different and independent compartments. We have proposed an experience
to increase the interrelationship between different subjects, to promote transversal skills, and to
make the subjects closer to real work. The satisfactory results of the experience are exposed in this
work. Moreover, we have analyzed the results obtained in both courses during the academic year
2018–2019. We found that there is a relation between both courses and student’s final marks do not
depend on the course
Desarrollo e integración de la asignatura FÃsica de Convertidores Energéticos del nuevo grado de FÃsica en la plataforma Studium
Memoria ID12-0026. Ayudas de la Universidad de Salamanca para la innovación docente, curso 2012-2013
Optimization induced by stability and the role of limited control near a steady state
[EN]A relationship between stability and self-optimization is found for weakly dissipative heat devices. The effect of limited control on operation variables around an steady state is such that, after instabilities, the paths toward relaxation are given by trajectories stemming from restitution forces which improve the system thermodynamic performance (power output, efficiency, and entropy generation). Statistics over random trajectories for many cycles shows this behavior as well. Two types of dynamics are analyzed, one where an stability basin appears and another one where the system is globally stable. Under both dynamics there is an induced trend in the control variables space due to stability. In the energetic space this behavior translates into a preference for better thermodynamic states, and thus stability could favor self-optimization under limited control. This is analyzed from the multiobjective optimization perspective. As a result, the statistical behavior of the system is strongly influenced by the Pareto front (the set of points with the best compromise between several objective functions) and the stability basin. Additionally, endoreversible and irreversible behaviors appear as very relevant limits: The first one is an upper bound in energetic performance, connected with the Pareto front, and the second one represents an attractor for the stochastic trajectoriesJunta de Castilla y León, SA017P17 ; Universidad de Salamanca, 2017/X005/1 ; National Natural Science Foundation of China, 1140503
Energetic Self-Optimization Induced by Stability in Low-Dissipation Heat Engines
[EN]The local stability of a weakly dissipative heat engine is analyzed and linked to an energetic multiobjective
optimization perspective. This constitutes a novel issue in the unified study of cyclic energy
converters, opening the perspective to the possibility that stability favors self-optimization of thermodynamic
quantities including efficiency, power and entropy generation. To this end, a dynamics simulating the
restitution forces, which mimics a harmonic potential, bringing the system back to the steady state is
analyzed. It is shown that relaxation trajectories are not arbitrary but driven by the improvement of several
energetic functions. Insights provided by the statistical behavior of consecutive random perturbations show
that the irreversible behavior works as an attractor for the energetics of the system, while the endoreversible
limit acts as an upper bound and the Pareto front as a global attractor. Fluctuations around the operation
regime reveal a difference between the behavior coming from fast and slow relaxation trajectories: while
the former are associated to an energetic self-optimization evolution, the latter are ascribed to better
performances. The self-optimization induced by stability and the possible use of instabilities in the
operation regime to improve the energetic performance might usher into new useful perspectives in the
control of variables for real engines.University of Salamanca Contract No. 2017/X005/1 ; Junta de Castilla y León Project No. SA017P17 ;
National Natural Science Foundation of China (No. 11405032)
Plataforma social para el fomento de la empleabilidad y el emprendimiento en la Facultad de Ciencias
Memoria ID-0016. Ayudas de la Universidad de Salamanca para la innovación docente, curso 2017-2018
Continuous power output criteria and optimum operation strategies of an upgraded thermally regenerative electrochemical cycles system
[EN]In order to utilize the low-grade thermal energy efficiently, a more realistic model of thermally regenerative
electrochemical cycles system with continuous power output is proposed in which the heat transfer irreversibility,
external heat leakage and non-ideal regeneration losses are taken into account. Besides, the symmetry of
cells, which is necessary for a practical thermally regenerative electrochemical cycles system operated at steady
state, is considered. Analytic expressions for the efficiency and power output of the system are derived. The
design and operation criteria of the system for achieving continuous power output are obtained. The general
performance characteristics and the optimally operating regions of several parameters are reported. The influences
of the external heat leakage on the system performance and the upper and lower bounds of efficiency at maximum power output at different situations are evaluated and discussed.National Natural Science
Foundation of China (No. 11405032) and Junta de Castilla y Leon
under project SA017P17. Universidad de
Salamanca contract 2017/X005/1
The equivalent low-dissipation combined cycle system and optimal analyses of a class of thermally driven heat pumps
[EN]The performance characteristics, operation, and design strategies of a class of thermally driven heat pumps are
investigated due to their important roles in the efficient utilization of low-grade thermal energy. In order to
establish a more generic thermodynamic model of thermally driven heat pumps mainly including absorption,
adsorption, and ejector heat pumps, low-dissipation assumption is adopted. Accordingly, the associated dissipation
parameters accounting for the specific information on the irreversibilities in each heat-transfer process
are introduced rather than specifying heat-transfer law. Based on the proposed model, the theoretical results of
the coefficient of performance and heat load are derived with regard to two key parameters denoting the size
ratio of the two involved subsystems and the matching deviation from reversible limit. The performance
characteristics and the optimally operating regions of the whole system are determined and the differences
between thermally driven heat pump and refrigerator are highlighted. The proposed model and obtained results
further develop the low-dissipation mode
Towards a Sustainable Future through Renewable Energies at Secondary School: An Educational Proposal
[EN]A compilation of innovative educational activities to work on concepts related to the production of electrical energy is presented. To approach the real-life secondary education curriculum, they are grouped to be performed during a week denominated Renewable Energy Week: an educational proposal aimed to promote the respect for the environment through the insight on Sustainable Development Goals (SDG) and renewable energy sources. The students would build and perform low-cost experiments so as to deeply understand the essence of energetic transformations, as well as electricity generation. Learning by discovery, collaborative learning and experimentation, are the methodological pillars that characterize Renewable Energy Week, since they have been proven to be efficient methodologies to promote students’ learning. Innovative techniques for pupils evaluation are employed, including a rubric, Socrative application and a set of sheets regarding experiments. Through this educational proposal, the students are expected to achieve a deep understanding of some key concepts related to electricity and awaken their interest in scientific subjects, making them conscious of the transition to sustainable development that our planet urgently requires. At the same time, this project offers to teachers a series of experiments and innovative activities to work on the SDG in Physics, Chemistry and Technology subjects.University of Salamanca through Innovation and teaching
improvement project ID 2019/16